HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept
{
"count": 5068,
"next": "http://www.astro4edu.org/oae-api/glossary-terms/?format=api&page=2",
"previous": null,
"results": [
{
"term_name": "A-type Star",
"term_definition": "A star with spectral type \"A\". Astronomers identify A-type stars by the presence of strong absorption lines from hydrogen in their spectra. They have typical (effective) temperatures between around 7400 kelvins (K) and 10,000 K. Compared to other stars, they appear white or bluish white to human eyes unless affected by interstellar or atmospheric reddening. Sirius, the brightest star in the night sky, and Vega, the star against which all other stars' brightnesses are measured in the apparent magnitude scale, are A-type stars.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 1,
"term_in_english": "A-type star",
"based_on_current_english_version": null,
"linked_terms": [
15,
304,
325,
331,
396,
440,
515
],
"alternate_terms": [
"A Star",
"A-Star"
],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/1/"
},
{
"term_name": "Absolute Magnitude",
"term_definition": "Absolute magnitude is a measure with two different definitions. Both relate to how bright objects appear under a special set of conditions. This allows the intrinsic properties of objects at different distances to be compared. This is in contrast to apparent magnitude which is a measure of how bright an object appears from the location of the observer.\r\n\r\nFor objects outside the Solar System such as stars and galaxies, absolute magnitude is defined as the apparent magnitude an object would have when viewed from a standard distance of 10 parsecs, ignoring the effects of interstellar extinction. This standardized number allows different objects to be compared by how intrinsically bright they are. \r\n\r\nWithin the Solar System, absolute magnitude is defined as the apparent magnitude an object such as an asteroid would have if viewed at a distance of one astronomical unit from the observer, while the object is at a distance of one astronomical unit away from the Sun, and at opposition. Note that an object in the Solar System can never match these conditions when viewed from Earth but the definition removes factors that depend on the locations of the object and the observer to allow Solar System objects in different locations to be compared.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 2,
"term_in_english": "Absolute Magnitude",
"based_on_current_english_version": null,
"linked_terms": [
15,
45,
185,
238
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/2/"
},
{
"term_name": "Absolute Zero",
"term_definition": "Absolute zero is the zero point of the kelvin temperature scale, corresponding to -273.15 degrees on the Celsius scale and -459.67 degrees on the Fahrenheit scale. This choice of zero point is motivated by fundamental physics: for a classical system, the temperature of absolute zero would correspond to a state where all of the particles are at perfect rest, each with kinetic energy zero. In the real world, basic effects of quantum theory mean that this state of complete rest will never be reached.\r\n\r\nIn the language of thermodynamics, which describes general systems and their abilities to exchange heat and other forms of energy, an idealized system at temperature absolute zero would be a system from which no heat could be extracted at all. In practice, it is impossible to bring a system into that ideal state. This is codified by the so-called 3rd law of thermodynamics, also called Nernst's theorem: we can get arbitrarily close to absolute zero, but we can never reach it.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 3,
"term_in_english": "Absolute Zero",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/3/"
},
{
"term_name": "Accelerating Universe",
"term_definition": "In the late 1990s, measurements of the light emitted from Type Ia supernovae (a class of exploding star), located in very distant galaxies showed that they appeared fainter than expected for a universe with a constant rate (speed) of expansion. The measurements were consistent with the scenario for a universe where the rate of expansion was accelerating. The cause for the accelerated expansion is attributed to dark energy, the nature of which is still unknown and a topic of current research. The accelerated expansion is occurring on very large scales and has no significant effect in individual gravitationally bound galaxies.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 4,
"term_in_english": "Accelerating Universe",
"based_on_current_english_version": null,
"linked_terms": [
69,
72,
119,
349,
374
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/4/"
},
{
"term_name": "Active Galactic Nucleus",
"term_definition": "An active galactic nucleus (AGN) is a very luminous region at the center of a galaxy. It is thought to be powered by a supermassive black hole which accretes surrounding matter, forming an extremely hot accretion disk around it. AGNs have quite complex structures, with many different regions that emit light with different characteristics, and are often surrounded by a donut-shaped torus of dusty material. An AGN sometimes sends out jets of material in opposite directions. While many galaxies have a supermassive black hole in the center, not all are accreting matter and hence not all are AGN.\r\n\r\nAGN is a general term that includes objects such as quasars, blazars, Seyfert galaxies, and radio galaxies. The different observational properties of these types of objects are thought to result in part from AGNs being viewed from different angles.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 5,
"term_in_english": "Active Galactic Nucleus",
"based_on_current_english_version": null,
"linked_terms": [
81,
119,
268,
348,
426
],
"alternate_terms": [
"AGN"
],
"categories": [
"Galaxies"
],
"category_ids": [
8
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/5/"
},
{
"term_name": "Altitude",
"term_definition": "Altitude has two meanings: it denotes either a specific angle in a certain type of coordinate system (\"the altitude of a star\") or a vertical distance relative to a given reference level (\"5000 m above sea level\").\r\n\r\nIn astronomy (and surveying), altitude is an angle in so-called horizontal coordinate systems. That angle measures how high an object is above the horizon – if you point your finger at the object, and then move that finger straight down to the horizon, the direction of your arm will have changed by the angle that is the altitude. Altitude is measured either in degrees or in radians. An object on the horizon would have an altitude of 0°, and an object that is directly overhead, \"at the zenith,\" would have an altitude of 90°. Negative altitude values are assigned to objects that are currently below the horizon – there, the altitude angle measures how far the object is below the horizon. An object that is straight below your feet, \"at the nadir,\" would have an altitude of –90°. \r\n\r\nIn other contexts, such as aviation or atmospheric physics, the altitude is a measure of how high a place is above some given reference level. On Earth, altitude is often defined as the height above mean sea level. With this meaning, altitude is measured in a unit of length, such as meters.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 6,
"term_in_english": "Altitude",
"based_on_current_english_version": null,
"linked_terms": [
36,
145,
390,
460
],
"alternate_terms": [],
"categories": [
"Space Exploration"
],
"category_ids": [
10
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/6/"
},
{
"term_name": "Andromeda",
"term_definition": "Andromeda is a constellation and is best known as the location of the Andromeda galaxy. Its name comes from Greek mythology – Andromeda was the daughter of King Cepheus and Queen Cassiopeia and was offered as sacrifice to the sea monster Cetus. She was saved by the hero Perseus who then married her.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 7,
"term_in_english": "Andromeda",
"based_on_current_english_version": null,
"linked_terms": [
8,
66
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/7/"
},
{
"term_name": "Andromeda Galaxy",
"term_definition": "The Andromeda galaxy is a spiral galaxy like ours although twice as large. It is the only such galaxy visible to the naked eye from the northern hemisphere, although only from dark places away from city light. It is also known as M31 after the French astronomer Charles Messier, who created a catalog of 110 objects with Andromeda in position 31.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 8,
"term_in_english": "Andromeda Galaxy",
"based_on_current_english_version": null,
"linked_terms": [
7,
119,
194,
199,
330
],
"alternate_terms": [],
"categories": [
"Galaxies",
"Naked Eye Astronomy"
],
"category_ids": [
8,
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/8/"
},
{
"term_name": "Angular Diameter",
"term_definition": "The angular diameter of an object is its visible diameter from a specific location measured as an angle. The angular diameter is used in astronomy as one way to express the size of celestial objects on the sky. The angular diameter increases with increasing physical size of an object and decreases when an object is farther away. For example, the Moon and Sun both have angular diameters of about half a degree when viewed from Earth. The Moon is about 400 times smaller than the Sun but appears the same size (about half a degree across), as the Sun is about 400 times further away.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 9,
"term_in_english": "Angular Diameter",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/9/"
},
{
"term_name": "Annual Parallax",
"term_definition": "Over the course of a year, as the Earth and all astronomical observers on it travel around the Sun, the perspective of those observers changes. Compared with the backdrop of the most distant astronomical objects in the night sky, this change in perspective makes for a change in the apparent position of nearer astronomical objects in the night sky. It makes those objects appear to move on tiny ellipses in the night sky over the course of one year, an effect known as annual parallax. The major axis of that apparent-motion ellipse, expressed as an angle, corresponds to twice the object's so-called (annual) parallax angle. The parallax angle corresponds to a change in observer position by one astronomical unit (AU), that is, by the average Earth–Sun distance, or the Earth's displacement between two astronomical observations performed half a year apart. The distance unit \"parsec\", short for \"parallax second\", is defined so that for a star at a distance of one parsec from Earth, the annual parallax angle amounts to one arc second.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 10,
"term_in_english": "Annual Parallax",
"based_on_current_english_version": null,
"linked_terms": [
237
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/10/"
},
{
"term_name": "Annular Solar Eclipse",
"term_definition": "",
"term_approval_level": "N",
"language_code": "en",
"term_number": 11,
"term_in_english": "Annular Solar Eclipse",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"override_term_number": 310,
"categories": [],
"category_ids": [],
"override_url": "https://astro4edu.org/resources/glossary/term/310/",
"url": "https://astro4edu.org/resources/glossary/term/11/"
},
{
"term_name": "Antimatter",
"term_definition": "In the early 20th century, theoretical physicists realized that for every kind of particle there should be a corresponding kind of antiparticle – a particle with the same mass, but otherwise completely opposite properties, in particular opposite electric charge. A few years later, the antiparticle of the electron was discovered: The \"positron\" has the same mass as an electron, but opposite electric charge. For some neutral particles, like the photon, the antiparticle is the same as the particle. When particle and corresponding antiparticle meet, they can annihilate to form photons. Our Universe appears to be made mostly of matter, not of antimatter consisting of antiparticles. The details of how that came about are the subject of ongoing research.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 12,
"term_in_english": "Antimatter",
"based_on_current_english_version": null,
"linked_terms": [
191,
241,
242,
441
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/12/"
},
{
"term_name": "Aphelion",
"term_definition": "Aphelion is the point along an orbit around the Sun where the orbiting body is farthest from the Sun. Objects orbiting the Sun and not affected by any other object have orbits with an elliptical shape with the Sun at one of the foci of this ellipse. Mathematically, aphelion marks one end of the major axis of the ellipse. In this word \"ap\" denotes farthest point and \"helion\" denotes the Sun. Accordingly, this term may only be used when the central body is the Sun. When the central body is a star that is not the Sun, the term is either \"apastron\" or \"apoastron\"; when the central body being orbited is the Earth the term is \"apogee\". The general term regardless of the central body is \"apoapsis\".",
"term_approval_level": "A",
"language_code": "en",
"term_number": 13,
"term_in_english": "Aphelion",
"based_on_current_english_version": null,
"linked_terms": [
98,
232,
244,
314
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/13/"
},
{
"term_name": "Apollo",
"term_definition": "There are two meanings of the word Apollo in astronomy. The first refers to the Apollo program that put the first human beings on the surface of the Moon. These missions were mostly powered by the Saturn V rocket. In total there were fourteen numbered missions launched (Apollo 4–17); eleven missions were crewed with nine of these going to the Moon, of which six made lunar landings with the other three orbiting the Moon.\r\n\r\nOn the other hand, a group of near-Earth asteroids is also known as Apollo, named after the asteroid (1862) Apollo. This group of asteroids is characterized as having a semi-major axis greater than the Earth–Sun distance of one astronomical unit (AU) and with perihelion distances less than 1 AU. This means that during their orbits, Apollo asteroids move from inside the Earth's orbit to outside the Earth's orbit although these asteroids rarely come close to the Earth itself.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 14,
"term_in_english": "Apollo",
"based_on_current_english_version": null,
"linked_terms": [
26,
203,
207,
244,
288,
324,
393
],
"alternate_terms": [],
"categories": [
"Solar System",
"Space Exploration"
],
"category_ids": [
1,
10
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/14/"
},
{
"term_name": "Apparent Magnitude",
"term_definition": "Apparent magnitude is a measure of how bright a celestial body appears to an observer. For historical reasons, the magnitude scale assigns larger numbers to fainter objects. Magnitude is a logarithmic scale with a difference of five magnitudes corresponding to a factor of 100 in measured brightness. There are many magnitude scales because brightness can be measured at different wavelengths and with different techniques. The common \"visual magnitude\" scale is set so that the bright star Vega has an apparent magnitude of zero. On this scale, Sirius, the brightest star in the night sky, has magnitude -1.46, and the magnitudes of the Sun and the full Moon are -26.7 and -12.7, respectively. The negative numbers indicate that these objects appear brighter than Vega. In very dark conditions, people with excellent vision can see stars up to about visual magnitude 6. The Hubble Ultra Deep Field reaches a visual magnitude near 31. This is about 100 to the power five or 10,000,000,000 times fainter than magnitude 6.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 15,
"term_in_english": "Apparent Magnitude",
"based_on_current_english_version": null,
"linked_terms": [
2,
45,
185,
382
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/15/"
},
{
"term_name": "Aries",
"term_definition": "Aries is the smallest constellation in the Zodiac. The stars that make up this constellation are in the part of the sky that intersects with the ecliptic (the plane defined by the orbit of the Earth around the Sun). Hence, from Earth, we can regularly find the planets, and also the Sun, in the constellation Aries. In the case of the Sun this occurs from mid-April to mid-May (at that time, of course, we cannot see the constellation's stars). Aries is one of the 88 modern constellations defined by the International Astronomical Union, but goes back much further – it was already one of the 48 constellations named by the 2nd century astronomer Claudius Ptolemy.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 16,
"term_in_english": "Aries",
"based_on_current_english_version": null,
"linked_terms": [
92,
252,
351,
391
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/16/"
},
{
"term_name": "Asteroid",
"term_definition": "An asteroid is a small body that orbits around the Sun or another star or stellar remnant. Asteroids are solid bodies of various compositions: a number of them are rich in carbon, some contain more rocky material (silicates), and others are mainly composed of metals. \r\n\r\nMost asteroids are piles of rubble bound together by gravity, with bumpy, uneven shapes. Some asteroids have moons – other small asteroids which orbit them.\r\n\r\nAsteroids are smaller than dwarf planets (which have enough mass for gravity to pull them into a nearly round shape). They are larger than meteoroids; the lower size limit of an asteroid is commonly set at between one and 10 meters across. If heating by the Sun or star causes the small body to emit gas and dust, the body is a comet and not an asteroid (although the distinction is not always clear). \r\n\r\nHistorically, the name asteroid was given to any astronomical body that orbits the Sun that was too small to resolve with a telescope. As they appeared as star-like points through a telescope they were named asteroids after the Greek word for star-like.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 17,
"term_in_english": "Asteroid",
"based_on_current_english_version": null,
"linked_terms": [
18,
19,
61,
62,
64,
207,
314,
369,
513
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/17/"
},
{
"term_name": "Asteroid Belt",
"term_definition": "The asteroid belt is located in a region between the planets Mars and Jupiter; orbiting in this region are the dwarf planet Ceres and a huge number of mainly small asteroids that consist primarily of rocks and some minerals. The asteroid belt has been described as the main asteroid belt in order to distinguish it from other small bodies that are found in the Solar System, i.e. the near-Earth objects and the Trojan group.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 18,
"term_in_english": "Asteroid Belt",
"based_on_current_english_version": null,
"linked_terms": [
17,
169,
189,
207,
314,
369
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/18/"
},
{
"term_name": "Asteroid Family",
"term_definition": "A family of asteroids is a group of asteroids with the similar orbital elements: semi-major axis (the typical distance from the Sun), eccentricity (a parameter relating to the shape of the orbit), and orbital inclination. Members of an asteroid family may also share similar compositions, i.e. the amount of rocky material, different metals, or water they contain. It is thought that the members of these groups may be the remains of past collisions between larger asteroids.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 19,
"term_in_english": "Asteroid Family",
"based_on_current_english_version": null,
"linked_terms": [
17,
98,
232,
393,
395
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/19/"
},
{
"term_name": "Astrobiology",
"term_definition": "Astrobiology is a multidisciplinary field of investigation comprising knowledge from astronomy, biology, physics, geology, chemistry, and other science fields to study life from its origin, evolution, and distribution in the Universe, including Earth, currently the only place where life is known to exist.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 20,
"term_in_english": "Astrobiology",
"based_on_current_english_version": null,
"linked_terms": [
21,
108,
109
],
"alternate_terms": [],
"categories": [
"Chemistry",
"Exoplanets & Astrobiology",
"Space Exploration"
],
"category_ids": [
12,
6,
10
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/20/"
},
{
"term_name": "Astrochemistry",
"term_definition": "Astrochemistry is a branch of astronomy that combines chemistry, astronomy, and physics to explain the behavior of matter at the molecular level, under the various conditions prevailing in space. Extremes of, e.g. pressure, temperature, or radiation levels in extraterrestrial environments result in chemical elements combining and forming molecules in different ways. This diversity in harsh environments causes chemicals to behave in unexpected ways. Thus, astrochemists use electromagnetic radiation received from space to study atoms and molecules in the interstellar medium and stars (both in our Galaxy and other galaxies), and planets, and to analyze their behavior and explain their properties. As of late May 2022, more than 245 molecular compounds have been detected in the interstellar medium, circumstellar shells, and other astronomical objects.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 21,
"term_in_english": "Astrochemistry",
"based_on_current_english_version": null,
"linked_terms": [
20,
96,
253,
331,
450
],
"alternate_terms": [],
"categories": [
"Chemistry",
"Milky Way and Interstellar Medium",
"Stars"
],
"category_ids": [
12,
7,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/21/"
},
{
"term_name": "Astrology",
"term_definition": "Astrology refers to claims that the positions of celestial objects in the sky predict future events in any person's life. Astrological practices were part of most ancient cultures and are still present in modern societies. However, such practices do not have any scientific basis: there is no feasible causal agency, predictions cannot be rigorously tested, and interpretations are affected by confirmation bias.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 22,
"term_in_english": "Astrology",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/22/"
},
{
"term_name": "Astronaut",
"term_definition": "An astronaut is a person who is qualified to be part of a crew onboard a space flight. Astronauts are trained in the operation of rockets, space stations, and to solve specialized technical problems that are unique to trips outside Earth's atmosphere. They are often trained to carry out science experiments in space. A few astronauts have even walked on the Moon. Astronaut was originally used to refer to space crews from the United States of America but is now a general term used by many different countries. Russian space crew are called cosmonauts, Chinese space crew are often called taikonauts, and European space crew are called spationauts.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 23,
"term_in_english": "Astronaut",
"based_on_current_english_version": null,
"linked_terms": [
288,
321,
324
],
"alternate_terms": [
"cosmonaut",
"taikonaut",
"spationaut"
],
"categories": [
"Space Exploration"
],
"category_ids": [
10
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/23/"
},
{
"term_name": "Astronomer",
"term_definition": "An astronomer studies the objects that make up the Universe. Astronomers can be professionals or amateurs. Professional astronomers and some amateur astronomers analyze scientific data obtained through telescopes on Earth and in space to answer questions about the composition of objects in the cosmos, their distribution, evolution, and future. With this information astronomers formulate new theories that explain what we see in the Universe from the small to large scales. Some amateur astronomers observe the sky simply to admire the wonder of the Universe. In practice, there is no difference between a professional astronomer and an astrophysicist. In modern astronomy, professional observations are always linked with attempts to model the physical processes producing the phenomena that are being observed, and university-level training in astronomy includes the relevant physics knowledge as a matter of course.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 24,
"term_in_english": "Astronomer",
"based_on_current_english_version": null,
"linked_terms": [
27
],
"alternate_terms": [],
"categories": [
"Astronomy and Society"
],
"category_ids": [
11
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/24/"
},
{
"term_name": "Astronomical Observatory",
"term_definition": "An astronomical observatory is a place designed and built exclusively to facilitate the scientific observation of extraterrestrial objects. It has specialized instruments such as telescopes, CCD cameras with special filters, computer rooms, and appropriate tools to analyze images and other kinds of scientific data. It usually has domes or dome-shaped roofs designed to protect the telescopes and other instruments from the weather. These roofs open and move to allow the observation of a certain region of the sky. The observatory may have special temperature controls to keep their mirrors or lenses and other equipment in the best condition. It should be noted the space-based telescopes are often referred to as space-based observatories (e.g. Chandra X-ray Observatory; Solar and Heliospheric Observatory)",
"term_approval_level": "A",
"language_code": "en",
"term_number": 25,
"term_in_english": "Astronomical Observatory",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/25/"
},
{
"term_name": "Astronomical Unit",
"term_definition": "An astronomical unit (AU) is a convenient unit of distance equal to exactly 149,597,870.7 kilometers (km). This is approximately the average distance between the Earth and the Sun, which was a previous definition of the AU. The AU is often used to measure distances in the Solar System and in other planetary or stellar systems. For example, Neptune orbits about 30 AU from the Sun",
"term_approval_level": "A",
"language_code": "en",
"term_number": 26,
"term_in_english": "Astronomical Unit",
"based_on_current_english_version": null,
"linked_terms": [
178,
238,
393
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Solar System"
],
"category_ids": [
6,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/26/"
},
{
"term_name": "Astronomy",
"term_definition": "Astronomy is one of the ancient sciences and involves the study of celestial bodies in the sky such as stars, planets, galaxies, meteors, and meteorites. It also studies the atmosphere for the purposes of comparing planet Earth with neighboring planets. In the past, astronomy was concerned with tracking the positions of the Sun, Moon, and planets for calendar and navigational purposes. Modern astronomers now also study the physical phenomena that govern the formation and behavior of astronomical objects.\r\n\r\nIn ancient times astronomy was often closely related to the pseudoscience astrology and many people still do not know the difference between the two. \r\n\r\nAstronomy is one of the few sciences in which amateurs can play an important role, as amateur astronomers have contributed to many important discoveries.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 27,
"term_in_english": "Astronomy",
"based_on_current_english_version": null,
"linked_terms": [
24,
28,
47,
295
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Telescopes, Instruments and Observatories"
],
"category_ids": [
11,
3
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/27/"
},
{
"term_name": "Astrophysics",
"term_definition": "Astrophysics is a science that employs the principles of physics to study the nature of astronomical objects. In astrophysics, the radiation across the entire electromagnetic spectrum, together with non-electromagnetic signals, such as gravitational waves and neutrinos emitted by astronomical objects, are studied, alongside their properties in terms of brightness, density, and temperature. Astrophysics is a very broad science that includes branches of theoretical and observational physics.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 28,
"term_in_english": "Astrophysics",
"based_on_current_english_version": null,
"linked_terms": [
23,
295,
447,
461
],
"alternate_terms": [],
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/28/"
},
{
"term_name": "Atmosphere",
"term_definition": "Atmosphere is a layer of gas that surrounds a celestial body. It is maintained because of the gravitational pull of the celestial body and therefore it is densest at the surface and merges into interplanetary space at high altitudes. \r\n\r\nFor planets with solid or liquid surfaces the lower boundary of the atmosphere is clear. Stars have gaseous interiors so have no clear lower bound to their atmospheres. A stellar atmosphere normally refers to the outer gaseous layer of a star through which light from the interior travels out into space. \r\n\r\nA magnetic field of a planet can protect its atmosphere from rapidly dissipating in space because of solar or stellar wind. In Earth's case, it also protects all organisms from genetic damage due to harmful effects of the solar wind and cosmic rays.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 29,
"term_in_english": "Atmosphere",
"based_on_current_english_version": null,
"linked_terms": [
124,
135,
315,
455
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Naked Eye Astronomy",
"Solar System",
"Space Exploration"
],
"category_ids": [
6,
4,
1,
10
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/29/"
},
{
"term_name": "Atmospheric Extinction",
"term_definition": "Atmospheric extinction is the scattering or absorption of the light from celestial objects passing through the Earth's atmosphere. Atmospheric gases allow the entry of visible light and are transparent to radio and some infrared light, so these types of ground-based telescopes are widely used. To avoid this phenomenon and to observe light of other wavelengths, some telescopes are located beyond the atmosphere.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 30,
"term_in_english": "Atmospheric Extinction",
"based_on_current_english_version": null,
"linked_terms": [
29,
107,
156,
229,
272,
472
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/30/"
},
{
"term_name": "Atom",
"term_definition": "Atoms are the smallest building blocks of matter that constitute any given chemical element. For example, helium gas consists of a collection of many helium atoms, each such helium atom indistinguishable from the next; carbon in the form of, say, diamond, is a collection of carbon atoms. \r\n\r\nThe word \"atom\" goes back to Democritus, an Ancient Greek philosopher, who postulated that atoms are the indivisible fundamental components for all of matter. In contrast, atoms according to the modern definition are made up of electrons, protons, and neutrons. Protons and neutrons form the atomic nucleus. All atoms of a given chemical element have the same number of protons, uniquely characteristic for that element. The atomic nucleus is surrounded by electrons. As the term is commonly used, atoms are electrically neutral, with as many protons (each with unit positive electric charge) as electrons (each with unit negative charge). When electrons are taken away from, or added to, this neutral configuration, an atom becomes an ion.\r\n\r\nThe electron shell determines the chemical properties of an atom. The differences and similarities between the different kinds of atoms are organized and classified in the periodic table of chemical elements. The electron shell also determines how an atom interacts with radiation. The resulting features in the spectrum of light received from astronomical objects allow astronomers to identify the different kinds of atoms in space.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 31,
"term_in_english": "Atom",
"based_on_current_english_version": null,
"linked_terms": [
32,
160,
441,
514,
515,
516
],
"alternate_terms": [],
"categories": [
"Chemistry"
],
"category_ids": [
12
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/31/"
},
{
"term_name": "Atomic Structure",
"term_definition": "Atomic structure is the internal organization of the particles within an atom. It tells you how many neutrons and protons can be found in the nucleus of an atom and describes how each of these particles is made up of quarks. It also shows that the electrons are in permanent motion around this nucleus, at different levels according to their energy. Atoms are electrically neutral because they have the same number of electrons and protons. An atom can get charged by losing or absorbing an electron, in which case it becomes an ion.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 32,
"term_in_english": "Atomic Structure",
"based_on_current_english_version": null,
"linked_terms": [
31,
101,
160,
441
],
"alternate_terms": [],
"categories": [
"Chemistry"
],
"category_ids": [
12
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/32/"
},
{
"term_name": "Aurora",
"term_definition": "An aurora is a display of diffuse variable-color light in Earth's atmosphere, mainly in the polar regions. In the north it is known as the Northern Lights or aurora borealis, in the south, Southern Lights or aurora australis. The aurorae vary in color from blue and purple to greenish-white to red, mainly occur at altitudes of about 100 kilometers, and form around two irregular auroral ovals centered on Earth's magnetic poles. They occur when charged particles from the solar wind or coronal mass ejections (CMEs) are trapped in Earth's magnetosphere, concentrated by magnetic fields in the upper atmosphere, and spiral along Earth's magnetic field lines toward the poles. Their interactions with atmospheric atoms and molecules produce the auroral emissions. This effect is enhanced during times of high solar activity. Aurora have also been observed on other planets in the Solar System notably on Jupiter and Saturn.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 33,
"term_in_english": "Aurora",
"based_on_current_english_version": null,
"linked_terms": [
184,
308,
315,
323,
455
],
"alternate_terms": [
"Aurorae"
],
"categories": [
"Astronomy and Society",
"Exoplanets & Astrobiology",
"Naked Eye Astronomy"
],
"category_ids": [
11,
6,
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/33/"
},
{
"term_name": "Equinox",
"term_definition": "The equinox is the moment in time in which the Sun, in its annual journey through the ecliptic, crosses the celestial equator. The word is derived from the Latin aequinoctium with aequus (equal) and nox (genitive noctis) (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet, rather than just near to the equator. To an observer on Earth, the Sun rises exactly from the cardinal point east and moves, apparently, along the line of the celestial equator during that day, setting exactly in the west. There are two equinoxes per year, one around March 20 and one around September 23. When the equinox is in March, it indicates the apparent passage of the Sun towards the northern hemisphere; in the September equinox the apparent passage of the Sun is to the south.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 34,
"term_in_english": "Equinox",
"based_on_current_english_version": null,
"linked_terms": [
92,
300,
317
],
"alternate_terms": [],
"categories": [
"Astronomy and Society"
],
"category_ids": [
11
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/34/"
},
{
"term_name": "Axis",
"term_definition": "An axis is an imaginary line that can be used to define a coordinate system. An axis of rotation is an imaginary line around which something revolves. This could be the axis of rotation of a system such as a galaxy, or a solid body such as an asteroid.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 35,
"term_in_english": "Axis",
"based_on_current_english_version": null,
"linked_terms": [
439,
473,
498
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology"
],
"category_ids": [
6
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/35/"
},
{
"term_name": "Azimuth",
"term_definition": "In a horizontal coordinate system, azimuth refers to the direction (angle along the horizon) at which the object is found. It is measured in degrees starting from the north and towards the east. Azimuth values cover a full circle from 0 degrees to 360 degrees. In other words, if you draw an imaginary arc on the celestial sphere from the object to the horizon and perpendicular to the horizon, the azimuth will tell you the location of the point where this arc meets the horizon. An object located directly north would have 0 degrees azimuth, an object directly east would have 90 degrees azimuth and so on. In older textbooks used in multiple countries, the convention was to start measuring the azimuth from the south towards the west. Thus, azimuth values in those textbooks would be shifted by 180 degrees.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 36,
"term_in_english": "Azimuth",
"based_on_current_english_version": null,
"linked_terms": [
6,
145
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/36/"
},
{
"term_name": "B-type Star",
"term_definition": "A star with spectral type \"B\". Astronomers identify B-type stars by the presence of neutral helium lines along with hydrogen lines in their spectra. They have typical (effective) temperatures between around 10,000 kelvins (K) to 30,000 K. Compared to other stars, they appear bluish white to human eyes unless interstellar or atmospheric reddening is important. Examples of B-type stars include Regulus in Leo, Rigel in Orion, and Spica in Virgo.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 37,
"term_in_english": "B- type Star",
"based_on_current_english_version": null,
"linked_terms": [
325,
331,
396,
467,
514
],
"alternate_terms": [
"B star",
"B-star"
],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/37/"
},
{
"term_name": "Big Bang Theory",
"term_definition": "The Big Bang theory is the basic explanation for the evolutionary stages of the Universe. In its simplest form, this theory gives us an idea of the origin of the Universe from its hot, dense early phase, to its expansion over the next 13.8 billion years, to become the Universe we know today. We see evidence of this expansion today in the Hubble Diagram. \r\n\r\nBecause our current tools do not allow astronomers to look back directly to the beginning of the Universe, much of what we understand about the Big Bang theory comes to us from mathematical models and theories. However, astronomers can study the chemical elements produced during the hot few minutes after the Big Bang (known as Big Bang Nucleosynthesis). They can also study the afterglow left from the Big Bang, a phenomenon known as the cosmic microwave background.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 38,
"term_in_english": "Big Bang Theory",
"based_on_current_english_version": null,
"linked_terms": [
69,
72,
148,
374,
430
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/38/"
},
{
"term_name": "Big Dipper",
"term_definition": "The Big Dipper is a well-known star pattern (or asterism, to use the technical term) which is part of the constellation Ursa Major in the northern sky. It consists of eight stars: Alkaid, Mizar/Alcor, Alioth, Megrez, Phecda, Merak, and Dubhe (Mizar/Alcor is a double star). The end two stars in the bowl of the Dipper can be used to locate the North Star (Polaris). The fact that the eight stars are similar in brightness makes the Big Dipper especially notable (though Megrez and Alcor are slightly fainter than the others) and it has been known under various names in many cultures. The five middle stars are part of a group of stars moving through space together (the Ursa Majoris Moving Group). Dubhe is reddish; the other seven stars are white.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 39,
"term_in_english": "Big Dipper",
"based_on_current_english_version": null,
"linked_terms": [
66,
429
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Naked Eye Astronomy"
],
"category_ids": [
11,
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/39/"
},
{
"term_name": "Binary Star",
"term_definition": "A binary star is a system of two stars that orbit around their common center of mass as a result of being bound together by the force of gravity. Their orbits follow Kepler's laws of motion and are elliptical (shaped like a squashed circle) or circular in shape. \r\n\r\nMore than half of all stars in the Milky Way are in binary systems or part of systems with more than one companion star (known as higher order multiple-star systems). Due to their enormous distances from Earth, most binary stars and higher order multiple-star systems appear to the observer as a single star.\r\n\r\nBinaries can be classified into a number of categories according to the observational method by which they were found to be binary stars. They may simultaneously belong to more than one category:\r\n\r\nVisual binaries can be observed as two separate stars close together on the sky. Not all stars that appear close on the sky (double stars) are binaries bound by gravity, some may just be close on the sky by coincidence but not bound by gravity. Double stars that are not binary stars bound by gravity can be separated by hundreds of light years in distance.\r\n\r\nSpectroscopic binaries are found due to the Doppler shift of the lines in the stars' spectrum as the stars orbit their common center of mass. \r\n\r\nEclipsing binaries can be detected when one of the component stars passes between its companion star and an observer, blocking some of the light from the companion star and causing the combined light of the system to look briefly dimmer. \r\n\r\nAstrometric binaries are systems where only one stellar image is observed – either due to one of the stars being too faint to be observed or the two stars' images being blended together – but where the orbital motion of the stars in the binary system causes the brightest point of the stellar image to show a periodic change in position on the sky.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 40,
"term_in_english": "Binary Star",
"based_on_current_english_version": null,
"linked_terms": [
41,
84,
91,
169,
232,
328,
331
],
"alternate_terms": [],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/40/"
},
{
"term_name": "Binary System",
"term_definition": "A binary system is any configuration of two astronomical objects of comparable size that orbit each other under the influence of their own gravity. This could be a binary star, with two stars orbiting each other, or a binary black hole, where both objects are black holes, or a binary system consisting of a black hole and a neutron star. Objects in a binary system orbit around the system's center of mass. When one of the objects is much lighter than the other, as for a star and a planet, or a planet and a moon, it is still appropriate, but less common, to use the term binary system. ",
"term_approval_level": "A",
"language_code": "en",
"term_number": 41,
"term_in_english": "Binary System",
"based_on_current_english_version": null,
"linked_terms": [
40,
43,
135,
214,
232,
253,
331
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/41/"
},
{
"term_name": "Blackbody Radiation",
"term_definition": "Blackbody radiation is electromagnetic radiation from an idealized object (blackbody) that absorbs all radiation that falls on it and re-emits it at a rate that maintains a state of thermal equilibrium. The spectrum of blackbody radiation is completely specified by the body's temperature according to known laws. Most stars emit light similar to that of a blackbody at a temperature of several thousand kelvins. To be contrasted with synchrotron radiation and other forms of \"non-thermal\" radiation.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 42,
"term_in_english": "Black Body Radiation",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Stars"
],
"category_ids": [
6,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/42/"
},
{
"term_name": "Black Hole",
"term_definition": "A black hole is a region of space where the gravitational force is so large that nothing, not even light, can escape from it. \r\n\r\nMany galaxies, including the Milky Way, have a large black hole (known as a supermassive black hole) in their center.\r\n\r\nOne of the ways astronomers think smaller black holes form is when a massive star collapses at the end of its life. However astronomers do not yet know the origins of supermassive black holes.\r\n\r\nThe outer boundary of a black hole is known as the event horizon.\r\n\r\nNear black holes the physics are so extreme that time runs much slower (compared to an observer far away from the black hole) and, around smaller black holes, objects are stretched and torn to pieces. Matter falling towards a black hole forms an accretion disk. This can often be accompanied by jets of matter sent out from this disk. Black hole accretion disks are the source of power of quasars and other active galactic nuclei (AGN) as well as many other X-ray sources.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 43,
"term_in_english": "Black Hole",
"based_on_current_english_version": null,
"linked_terms": [
5,
268,
292,
426
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/43/"
},
{
"term_name": "Blackbody",
"term_definition": "A blackbody is defined as a body that absorbs radiation that falls on it without reflecting any of it. Therefore, it is a hypothetical object with perfect absorption and perfect reflection for all radiation and all wavelengths. The spectral distribution of thermal energy radiated by a blackbody (the pattern of intensity of blackbody radiation over a range of wavelengths and frequencies) depends only on its temperature. The radiation from stars, and their effective temperatures and colors, can be described by assuming that they are blackbodies.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 44,
"term_in_english": "Blackbody Radiation",
"based_on_current_english_version": null,
"linked_terms": [
96,
440
],
"alternate_terms": [],
"override_term_number": 42,
"categories": [],
"category_ids": [],
"override_url": "https://astro4edu.org/resources/glossary/term/42/",
"url": "https://astro4edu.org/resources/glossary/term/44/"
},
{
"term_name": "Brightness",
"term_definition": "In astronomy, brightness is the term for the amount of electromagnetic radiation an object emits, or the amount of light we receive from an object. \r\n\r\nIt is not a formal scientific term but is often used to mean electromagnetic flux received from an object (energy received per unit time per unit area of the receiver in W/m²). The term \"intrinsic brightness\" is often used to mean the luminosity of an object (in watts) and \"surface brightness\" is used for extended objects as a measure of the energy received from an object per unit time per unit area of the receiver per unit area on the sky of the object (W/m²/steradian² or W/m²/arcsecond²). These different measures of brightness can be defined over the whole spectrum the object emits in or in specific areas of the electromagnetic spectrum.\r\n\r\nFor historical reasons, astronomers describe the brightness of an object using the so-called magnitude system which is a logarithmic system and gives lower numbered values to brighter stars. \r\n\r\nChanges in brightness can allow us to reconstruct physical processes, e.g. when a star grows and becomes brighter, or a darker object passes in front of a brighter one.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 45,
"term_in_english": "Brightness",
"based_on_current_english_version": null,
"linked_terms": [
96,
180,
185
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/45/"
},
{
"term_name": "Brown Dwarf",
"term_definition": "A brown dwarf is an object too low in mass to be a star but too high in mass to be a planet. Stars are fueled by hydrogen fusion in their cores. Brown dwarfs have internal temperatures that are too low to sustain hydrogen fusion. However, early in their lifetime brown dwarfs are able to briefly fuse deuterium, a heavier form of hydrogen. This deuterium fusion is used to distinguish brown dwarfs from planets but is hard to observe. Brown dwarfs typically have masses between 1.2% and 8% of the mass of the Sun (around 12–80 times the mass of Jupiter) and are roughly the same physical size as Jupiter. Young brown dwarfs have similar temperatures in their outer regions (effective temperature) to low mass stars (red dwarfs) but lacking internal heat sources they cool as they age, with some cooling to a few hundred degrees Celsius.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 46,
"term_in_english": "Brown Dwarf",
"based_on_current_english_version": null,
"linked_terms": [
149,
150,
167,
190,
253,
276,
440,
479
],
"alternate_terms": [],
"categories": [
"Chemistry",
"Exoplanets & Astrobiology",
"Stars"
],
"category_ids": [
12,
6,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/46/"
},
{
"term_name": "Calendar",
"term_definition": "A calendar is a system to reckon time, in particular to identify seasons. Calendars are often laid out in terms of days, weeks, months, and years. It is an abstract system based on the periodic motion of celestial objects (Moon, Sun, stars). Calendars have been used since ancient times. The Moon and the Sun were two objects in the sky which had easily identifiable periodic motions that resulted in identifiable changes in the passing of days, weeks, months, and seasons. Calendars can be based on the monthly lunar cycle (lunar calendars), based on the solar year (solar calendars), or be lunar calendars with additional days added to match the solar year (lunisolar calendars). There are a wonderful variety of calendars throughout the world resulting from local astronomical heritage.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 47,
"term_in_english": "Calendar",
"based_on_current_english_version": null,
"linked_terms": [
182,
300,
389
],
"alternate_terms": [],
"categories": [
"Astronomy and Society"
],
"category_ids": [
11
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/47/"
},
{
"term_name": "Capricornus",
"term_definition": "Capricornus is the smallest constellation in the Zodiac. The stars that make up this constellation are in the part of the sky that intersects with the ecliptic (the plane defined by the Earth's path around the Sun). In fact, all the constellations that comprise the Zodiac intersect the ecliptic. From Earth, we can regularly find the planets, and also the Sun, in the constellation Capricornus. In the case of the Sun this occurs from late January to mid-February (at that time, of course, we cannot see the constellation's stars). Capricornus is one of the 88 modern constellations defined by the International Astronomical Union, but goes back much further – it was already one of the 48 constellations named by the 2nd century astronomer Claudius Ptolemy. The stars that make up the constellation Capricornus are relatively faint. With a telescope, you can find the globular cluster M30 in Capricornus.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 48,
"term_in_english": "Capricorn",
"based_on_current_english_version": null,
"linked_terms": [
92,
132,
158,
391,
483
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/48/"
},
{
"term_name": "Celestial Body",
"term_definition": "In astronomy, the terms celestial body, celestial object, astronomical body, and astronomical object are used almost interchangeably as common terms for all the physical bodies and objects out there in space that astronomers study, including stars, planets, galaxies, gas clouds, and so on. Some astronomers use celestial or astronomical body in a narrower sense, namely for objects that are clearly separated from their environment – in that sense, a planet would be a celestial body, a gas cloud would not be (but it would still be an astronomical object). On the smallest scales, the terms are not commonly used. A proton might reach us from outer space, but would not be commonly referred to as an astronomical object, or a celestial body.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 49,
"term_in_english": "Celestial Body",
"based_on_current_english_version": null,
"linked_terms": [
17,
62,
119,
253
],
"alternate_terms": [
"Celestial Object",
"Astronomical Body",
"Astronomical Object"
],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/49/"
},
{
"term_name": "Celestial Coordinates",
"term_definition": "From Earth, we perceive celestial objects as being located on a sphere, traditionally called the celestial sphere. We can describe any position on that sphere using two numbers. Every method for assigning two such numbers to a sky position is called a celestial coordinate system, and the numbers are called the object's (celestial) coordinates. \r\n\r\nOn Earth's surface, we use geographical latitude and longitude for the same purpose, and in fact one way of defining celestial coordinates is derived from that: those points in the sky that are directly above Earth's equator form the celestial equator, and the point directly above a certain location on Earth's globe is assigned numbers in a way similar to the latitude/longitude of the base point. \r\n\r\nAstronomers use different kinds of coordinate systems, including a number that takes into account Earth's daily rotation, so the coordinates are universal and are usable anywhere on Earth. This also ensures that the coordinates of, say, a star do not change significantly over timescales of days, months, or years.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 50,
"term_in_english": "Celestial Coordinates",
"based_on_current_english_version": null,
"linked_terms": [
52,
78,
90,
102,
171,
179,
286
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/50/"
},
{
"term_name": "Celestial Equator",
"term_definition": "The celestial equator is defined as the great circle of the celestial sphere, whose plane is perpendicular to the axis of rotation of the Earth. In essence, it is the projection of the Earth's equator onto the celestial sphere.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 51,
"term_in_english": "Celestial Equator",
"based_on_current_english_version": null,
"linked_terms": [
50,
53
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/51/"
},
{
"term_name": "Celestial Pole",
"term_definition": "The celestial North and South Poles correspond to the points where the celestial sphere intersects with the Earth's axis of rotation. \r\n\r\nAt the Earth's North Pole, the celestial North Pole is always directly overhead and at the Earth's South Pole, the celestial South Pole is always directly overhead. Due to the Earth's rotation, the sky in the northern hemisphere appears to rotate around the celestial North Pole and in the southern hemisphere the sky appears to rotate around the celestial South Pole. The celestial North Pole is at a declination of +90 degrees and the celestial South Pole is at a declination of -90 degrees.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 52,
"term_in_english": "Celestial Pole",
"based_on_current_english_version": null,
"linked_terms": [
50,
439,
498
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/52/"
},
{
"term_name": "Celestial Sphere",
"term_definition": "The celestial sphere is an imaginary, hollow sphere of indefinitely large radius, which can be centered on Earth, the center of the Sun, or any convenient place. Celestial objects appear to be attached to the inside of the celestial sphere, and the planets, Sun, and Moon appear to move slowly across it. It is used in spherical coordinate systems.\r\n\r\nThe celestial sphere appears to turn once a day due to Earth’s rotation.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 53,
"term_in_english": "Celestial Sphere",
"based_on_current_english_version": null,
"linked_terms": [
50,
52,
145,
390,
436
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/53/"
},
{
"term_name": "Cepheid Variable",
"term_definition": "Cepheids are pulsating variable stars whose variability is caused by periodic oscillation of the outer layers of the star. They are named after the prototype star, Delta Cephei. An important feature of Cepheids is that their period is closely related to their luminosity. This is the famous period–luminosity relationship revealed by Henrietta Leavitt in 1908. Using this relationship, the absolute brightness of a Cepheid can be calculated from the pulsation period. The difference between the easily observable apparent brightness and absolute brightness derived from the relationship is indicative of the distance of both the given Cepheid and the external galaxy hosting this variable star. Thus Cepheids are primary distance indicators in establishing the cosmic distance scale.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 54,
"term_in_english": "Cepheid Variable",
"based_on_current_english_version": null,
"linked_terms": [
437,
476,
485
],
"alternate_terms": [],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/54/"
},
{
"term_name": "Chromosphere",
"term_definition": "The chromosphere (or \"color sphere\") of the Sun or other sun-like star is the thin layer in the atmosphere directly above the photosphere, which is the denser layer from which the sunlight or starlight is emitted. During a total eclipse of the Sun, the chromosphere is visible as a faint ring of glowing gases, mostly hydrogen which glows with a red color, hence the name.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 55,
"term_in_english": "Chromosphere",
"based_on_current_english_version": null,
"linked_terms": [
68,
251,
338
],
"alternate_terms": [],
"categories": [
"Stars",
"The Sun"
],
"category_ids": [
2,
5
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/55/"
},
{
"term_name": "Circumpolar Stars",
"term_definition": "In most locations on Earth, either the celestial North Pole or the celestial South Pole is visible in the sky at some distance above the horizon. For an observer at such a location, the stars appear to rotate around the celestial pole as time passes: Each star traces a circle in the sky, with the circle centered on the celestial pole to which Earth's axis points. At the two points where a circle crosses the observer's horizon, one eastern and the other western, the star in question will rise and set, respectively. For stars that are close enough to the celestial pole, the traced-out circle will be completely above the horizon. Our observer will never see those stars either rise or set. Those never-setting stars are called circumpolar stars. \r\n\r\nWhich stars are circumpolar depends on the observer's geographic latitude and on the star's declination – the latter is the angle between the star's location and the celestial equator. In the northern hemisphere, a star is circumpolar if its declination is larger than 90° minus the observer's latitude. In the southern hemisphere, we need to take into account that both southern latitudes on Earth and southern declination values have a minus sign. Taking these signs into account, on the southern hemisphere, a star is circumpolar if its declination is smaller than –90° minus the observer's latitude.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 56,
"term_in_english": "Circumpolar Stars",
"based_on_current_english_version": null,
"linked_terms": [
78,
171,
439
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/56/"
},
{
"term_name": "Cluster",
"term_definition": "A cluster is a group of stars or galaxies which are gravitationally bound together.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 57,
"term_in_english": "Cluster",
"based_on_current_english_version": null,
"linked_terms": [
120,
332
],
"alternate_terms": [],
"categories": [
"Milky Way and Interstellar Medium",
"Naked Eye Astronomy"
],
"category_ids": [
7,
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/57/"
},
{
"term_name": "Cluster of Galaxies",
"term_definition": "",
"term_approval_level": "A",
"language_code": "en",
"term_number": 58,
"term_in_english": "Cluster of Galaxies",
"based_on_current_english_version": null,
"linked_terms": [
120
],
"alternate_terms": [],
"override_term_number": 120,
"categories": [
"Galaxies"
],
"category_ids": [
8
],
"override_url": "https://astro4edu.org/resources/glossary/term/120/",
"url": "https://astro4edu.org/resources/glossary/term/58/"
},
{
"term_name": "Color",
"term_definition": "The color of an astronomical object can carry important information about its physical properties. Even with the naked eye, a blueish star you see in the sky, such as Alkaid at the end of the \"handle\" of the Big Dipper, will be considerably hotter than a reddish star, such as Betelgeuse at the shoulder of Orion. In order to quantify color, astronomers typically determine a star's brightness when seen through one of several possible specialized blue filters and compare to the brightness through a red filter. Several distinct color definitions of this kind, comparing brightness in specific different filters, are in use. The results can be used in statistical analyzes. An example are color–magnitude diagrams, which plot object color against object brightness.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 59,
"term_in_english": "Color",
"based_on_current_english_version": null,
"linked_terms": [
39,
60,
467
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Stars"
],
"category_ids": [
4,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/59/"
},
{
"term_name": "Color Index",
"term_definition": "The color index of a star or other celestial object is the difference between its brightness or magnitude, as measured in two different color or wavelength bands, such as yellow and blue. The most common color index is (B-V), where B is the magnitude as measured through a standard blue filter, and V is the magnitude as measured through a standard yellow filter. The B filter is similar to the color sensitivity of old-fashioned photographic plates, and the V filter is similar to the color sensitivity of the human eye. For stars, (B-V) is a measure of the temperature, though it can also be affected by the reddening effect of dust between the stars.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 60,
"term_in_english": "Color Index",
"based_on_current_english_version": null,
"linked_terms": [
59,
396
],
"alternate_terms": [],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/60/"
},
{
"term_name": "Cometary Coma",
"term_definition": "As a comet approaches the Sun, part of the solid substances bound in the comet's icy nucleus turn into gas. This gas, which mostly consists of water but will also contain other chemicals such as carbon monoxide, carbon dioxide, ammonia, methane, and methanol, as well as dust particles, surrounds the nucleus like a fuzzy, spherical cloud, which is called the cometary atmosphere, or coma. As the comet gets closer to the Sun, more and more molecules get split up by the Sun's ultraviolet photons, heating the coma and making its outer regions expand. Eventually, the outer regions get ionized, forming the comet's ion tail. ",
"term_approval_level": "A",
"language_code": "en",
"term_number": 61,
"term_in_english": "Cometary Coma",
"based_on_current_english_version": null,
"linked_terms": [
62,
63,
64
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Solar System"
],
"category_ids": [
4,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/61/"
},
{
"term_name": "Comet",
"term_definition": "A comet is a small object in the Solar System consisting of a nucleus made up of a mixture of different types of ice and rocky, dusty material – a dirty snowball. Comet nuclei can range in size from a few hundred meters to tens of kilometers across. Most comets have highly elliptical orbits. When the comet approaches the Sun, some of the surface ice evaporates and is blown back by the solar wind to form the distinctive coma and tail features. We see comets due to the sunlight reflecting off the coma or tail or (for comets far from the Sun) the nucleus. Comets are classified as either \"periodic\" or \"short-period\" if their passage has been observed more than once, or their period is known to be less than 200 years, and \"non-periodic\" otherwise.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 62,
"term_in_english": "Comet",
"based_on_current_english_version": null,
"linked_terms": [
61,
63,
64,
513
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Chemistry",
"Naked Eye Astronomy",
"Solar System"
],
"category_ids": [
11,
12,
4,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/62/"
},
{
"term_name": "Comet Nucleus",
"term_definition": "A comet nucleus is the core of a comet. This is a solid object, similar to a dirty snowball, made with ice and rocky, dusty particles. Far from the Sun the nucleus is the sole component of the comet. Closer to the Sun a comet's nucleus is heated due to sunlight. This causes the surface ice to sublimate. The sublimated ice and the dust embedded in it are ejected and surround the nucleus as a coma with a tail pointing away from the Sun.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 63,
"term_in_english": "Comet Nucleus",
"based_on_current_english_version": null,
"linked_terms": [
61,
62,
64
],
"alternate_terms": [],
"categories": [
"Chemistry",
"Solar System"
],
"category_ids": [
12,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/63/"
},
{
"term_name": "Cometary Tail",
"term_definition": "When a comet is close to the Sun, the Sun's radiation heats up the comet's surface. Ice on the surface turns to gas (it \"sublimates\"), taking rocky, dusty material with it. The resulting mix forms a cloud around the nucleus of the comet, which is called the coma. In general, a comet will have two tails: The ejected dust particles form the comet's dust tail, which has a characteristically curved shape. It is made up of dust particles released from the surface, which follow the comet along its orbit around the Sun. Dust tails can be millions of kilometers or more in length. They reflect sunlight, and if the conditions are right, their whitish, diffuse shape accounts for most of what can be observed when a comet is visible to the naked eye.\r\n\r\nA substantial fraction of the gas is blown away and ionized by the solar wind – the electrically charged particles emitted by the Sun. Those ions form the comet's ion tail, which typically has a blueish color. The ion tail always points straight away from the Sun. If the comet itself is moving away from the Sun, the ion tail precedes the comet.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 64,
"term_in_english": "Cometary Tail",
"based_on_current_english_version": null,
"linked_terms": [
61,
62,
63
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Solar System"
],
"category_ids": [
4,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/64/"
},
{
"term_name": "Conjunction",
"term_definition": "From the perspective of an observer on Earth, when two astronomical objects appear to be in close proximity in the sky they are said to be in conjunction. The conjunction does not need to be actually visible – for instance, the Moon and the Sun are approximately lined up whenever there is a new Moon, but we cannot see the Moon under those conditions, unless there is a solar eclipse. In that case, and whenever a conjunction is so close that one object appears to cover the other, astronomers would describe it as a transit or eclipse.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 65,
"term_in_english": "Conjunction",
"based_on_current_english_version": null,
"linked_terms": [
91,
182,
228,
367
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Solar System"
],
"category_ids": [
4,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/65/"
},
{
"term_name": "Constellation",
"term_definition": "A constellation in modern technical terms is a polygonal segment of the celestial sphere. The International Astronomical Union has divided the entire celestial sphere into 88 regions – constellations. This is based on those used in Ancient Greece together with more recent additions, especially in the southern hemisphere. Each of the 88 constellations occupies a certain part of the sky, and therefore, each of the heavenly bodies, from stars to galaxies to nebulae, etc., can be associated with a constellation. The Zodiac are 13 constellations that overlap the ecliptic (the annual path traced by the Sun across the celestial sphere). The 13 constellations are: Ophiuchus, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, and Scorpius.\r\n\r\nConstellations contain grouping of stars (asterisms) suggesting a pattern as seen from Earth. These patterns are imaginatively described as representing humans, animals, or other recognizable objects.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 66,
"term_in_english": "Constellation",
"based_on_current_english_version": null,
"linked_terms": [
158,
429
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Naked Eye Astronomy",
"Stars"
],
"category_ids": [
11,
4,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/66/"
},
{
"term_name": "Copernican Revolution",
"term_definition": "The Copernican Revolution refers to the replacement of the geocentric (Earth-centered) model of visualizing the Solar System with a heliocentric (Sun-centered) model. The geocentric model was the consensus in European scientific views for close to two millennia, even though some believed in a heliocentric model. This shift provided a first step in the move towards a new model for the motions of planets, moons, stars, and other celestial objects in the sky that occurred over the following centuries. The geocentric model is still used for explaining concepts related to the celestial sphere. The Copernican Revolution is named after Nicolaus Copernicus, who in the 16th century described the heliocentric model in his seminal work De revolutionibus orbium coelestium. Although it is often claimed Immanuel Kant was the first to use the term Copernican Revolution, the accuracy of this claim is debated.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 67,
"term_in_english": "Copernican Revolution",
"based_on_current_english_version": null,
"linked_terms": [
53,
127,
141,
434
],
"alternate_terms": [],
"categories": [
"Astronomy and Society"
],
"category_ids": [
11
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/67/"
},
{
"term_name": "Corona",
"term_definition": "The corona of a star is a region of extremely hot, low-density plasma surrounding the star's atmosphere, which can stretch millions of kilometers into space. Every star with a reasonably strong magnetic field, produced by a dynamo effect as charged matter moves inside the star, is expected to have a corona. Naked-eye observation of our Sun's corona is possible during a total solar eclipse, when the solar corona becomes visible as a whitish, irregularly shaped area surrounding the hidden solar disk. More generally, the shape of a star's corona is determined by the star's magnetic fields and the outward pressure of gas in its upper regions. Stellar coronas have very high temperatures: At more than a million kelvins, the solar corona is much hotter than the Sun's surface. The mechanism for heating the corona to that temperature is the subject of ongoing research, but it seems clear that the magnetic fields threading the corona play a major role. The shape of the Sun's corona changes on timescales between seconds and months, mostly in response to solar activity, such as flares ejecting plasma into the corona, or coronal mass ejections releasing a considerable amount of charged particles. It also changes on a timescale of years with what is called the solar cycle – the periodic change in strength and orientation of the Sun's magnetic field, with a period of nearly eleven years. Changes of this kind are expected to occur in an analogous fashion in other stars' coronas, as well.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 68,
"term_in_english": "Corona",
"based_on_current_english_version": null,
"linked_terms": [
55,
311,
313,
315,
338
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Stars",
"The Sun"
],
"category_ids": [
4,
2,
5
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/68/"
},
{
"term_name": "Cosmic Microwave Background (CMB)",
"term_definition": "The cosmic microwave background (CMB) is the relic electromagnetic radiation from when the Universe was about 380,000 years old and became transparent to light. It provides information about the Universe’s composition, geometry (shape), evolution, and development of structure. The early dense Universe, consisted of a \"hot soup\" of free particles (protons, neutrons, electrons) and light (photons). Before the CMB was released, the interaction of photons with free electrons prevented light from traveling long distances. The expansion and cooling of the Universe allowed free electrons to combine with protons to form atomic hydrogen, and allowed light to travel through the Universe. The expansion has subsequently stretched the wavelength of these photons, making them detectable today in the microwave region of the electromagnetic spectrum.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 69,
"term_in_english": "Cosmic Microwave Background (CMB)",
"based_on_current_english_version": null,
"linked_terms": [
38,
72,
75,
198,
441
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/69/"
},
{
"term_name": "Cosmic Ray",
"term_definition": "Cosmic rays are energetic charged particles (e.g. protons, nuclei of heavy elements, and electrons) that move through the cosmos. \r\n\r\nCosmic rays can enter Earth's atmosphere. Primary cosmic rays could come from the Sun, Solar System, our Milky Way, or distant galaxies. They are composed of protons (about 90%), helium nuclei (about 9%), heavier atomic nuclei and electrons (about 1%), and a very small amount of antimatter. Light coming from the cosmos is not cosmic rays. \r\n\r\nIf an energetic primary cosmic ray enters the Earth's atmosphere it can interact with atmospheric particles and produce a large number of secondary charged particles, called secondary cosmic rays. The highest energy cosmic rays are nuclear particles that have kinetic energy equivalent to a tennis ball moving at about 150 kilometers per hour. However, such highest energy particles are rare and most have lower energies.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 70,
"term_in_english": "Cosmic Ray",
"based_on_current_english_version": null,
"linked_terms": [
241,
435,
441
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/70/"
},
{
"term_name": "Cosmological Principle",
"term_definition": "The cosmological principle is the basis for modern cosmology and is built on observations and a fundamental assumption. It states that spatially the Universe is isotropic and homogeneous on large scales (scales larger than a few hundred million light years). Observations on sufficiently large scales, show that the Universe appears to \"look\" the same in any direction; there is no preferred direction (isotropic). The fundamental assumption, based on the Copernican Principle (humans do not occupy a special location in the Universe), is that the Universe is the same everywhere (homogeneous); there appears to be no preferred location. The cosmological principle is accompanied by universality, where the laws of physics and the fundamental constants are the same everywhere in the Universe: here on Earth or in a distant galaxy.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 71,
"term_in_english": "Cosmological Principle",
"based_on_current_english_version": null,
"linked_terms": [
72,
434
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Cosmology"
],
"category_ids": [
11,
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/71/"
},
{
"term_name": "Cosmology",
"term_definition": "Cosmology is derived from the Greek words kosmos (harmony or order), and logos (thought or reason). Cosmology as a discipline has its roots in philosophy and religion; various cultures around the world have their own cosmologies that aim to interpret and make sense of the Universe. Over the years cosmology has evolved to be a precision observational science. This has been made possible through the development of advanced ground-based and space-based observatories, together with pioneering theoretical work and computer simulations. Cosmology as a scientific endeavor aims to understand the evolutionary history, formation, structure, and future evolution of the Universe as a whole on the largest scales, by understanding the fundamental physical mechanisms operating within the Universe.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 72,
"term_in_english": "Cosmology",
"based_on_current_english_version": null,
"linked_terms": [
4,
27,
28,
38,
54,
58,
71,
73,
75,
76,
225,
356,
374
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/72/"
},
{
"term_name": "Cosmos",
"term_definition": "The term cosmos captures the grandeur of everything and has deep philosophical roots. Although the term cosmos is used synonymously with Universe, they do have subtle differences. Cosmos comes from the Greek word kosmos, which roughly implies harmony or order, and is an all-encompassing term for the ordered arrangement of a system, of which the Universe is a part. Although, it could be argued that the Universe is itself an ordered system, and hence can be referred to as the cosmos. Because ordered systems can to a degree be described by physical laws, the word \"cosmos\" can be extended to capture the idea of a world that can be explained by physical laws.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 73,
"term_in_english": "Cosmos",
"based_on_current_english_version": null,
"linked_terms": [
72,
374
],
"alternate_terms": [],
"categories": [
"Astronomy and Society",
"Cosmology"
],
"category_ids": [
11,
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/73/"
},
{
"term_name": "Crater",
"term_definition": "A crater is a circular depression in the surface of a solid planet, moon, or other small object in space. Some craters are volcanic, especially on Earth and Venus, but most are impact craters, caused by the impact of a large space rock or comet nucleus. There are dozens of impact craters on the surface of Earth, and thousands on the Moon. The maria, the large, darker, circular features on the Moon are giant impact craters, formed billions of years ago, and then filled with lava, which has since solidified.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 74,
"term_in_english": "Crater",
"based_on_current_english_version": null,
"linked_terms": [
154,
203
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy",
"Solar System"
],
"category_ids": [
4,
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/74/"
},
{
"term_name": "Dark Energy",
"term_definition": "Dark energy is a proposed cause for the accelerated expansion of the Universe, which has been happening for the past six billion years on the largest scales. Dark energy is often described as exhibiting a \"force\" opposite to gravity. The effects of dark energy are inferred through indirect observations and measurements of Type Ia supernovae, the cosmic microwave background (CMB) radiation, clusters of galaxies, gravitational lensing, and baryon acoustic oscillations, which seem to indicate that dark energy makes up just over 70% of the Universe’s composition. Despite this, there is much research and debate about the nature of dark energy, whether there are different types of dark energy, whether dark energy changes over cosmic time, and alternatives to dark energy. ",
"term_approval_level": "A",
"language_code": "en",
"term_number": 75,
"term_in_english": "Dark Energy",
"based_on_current_english_version": null,
"linked_terms": [
69,
76,
120,
134,
349,
476
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/75/"
},
{
"term_name": "Dark Matter",
"term_definition": "Dark matter is a proposed form of matter that has mass, but is completely transparent and does not emit light. It has been postulated as a joint explanation for a variety of phenomena related to gravitational interactions. \r\n\r\nEarly evidence for the existence of dark matter came from galaxies in galaxy clusters, which were found to be moving at comparatively high speeds. Postulating additional mass served to explain why, in spite of their speeds, the galaxies in question were gravitationally bound to their cluster instead of escaping. Measurements by Vera Rubin and others of the speeds at which stars and gas orbit in disk galaxies led to a wider acceptance of the concept of dark matter: there, the usual laws of gravity require considerable mass in addition to the visible matter in order to explain the observed high rotation speeds. More recently, gravitational lensing observations have indicated considerable non-luminous mass in galaxy clusters.\r\n\r\nIn cosmology, the expansion history of the Universe points to there being more matter in the Universe than is accounted for in the form of luminous matter. The common explanation for the growth of structure in the early Universe also relies on the presence of dark matter. For these reasons, the standard cosmological models are referred to as \"Lambda CDM models\", where CDM stands for cold (slow-moving) dark matter.\r\n\r\nThe nature of dark matter is a topic of intense research and debate both in cosmology and particle physics. Evidence for dark matter remains indirect, relying on observations of the effects of dark matter's mass on luminous matter or light. Several proposals exist for species of as yet undetected elementary particles that could make up dark matter, but the experiments set up to find direct evidence for such candidate particles have not so far been successful. There are also alternative proposed explanations that claim to account for the relevant observations without the involvement of new particle species.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 76,
"term_in_english": "Dark Matter",
"based_on_current_english_version": null,
"linked_terms": [
72,
75,
119,
120,
134
],
"alternate_terms": [],
"categories": [
"Cosmology"
],
"category_ids": [
9
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/76/"
},
{
"term_name": "Dark Nebula",
"term_definition": "A dark nebula is a cool cloud of gas and dust in space which blocks much of the light from stars and bright nebulae behind it, and therefore appears dark. It is the dust which blocks the light from behind, even though dust makes up only 1% of the matter in the nebula. Dark nebulae block visible and ultraviolet light, but it is possible to see through them by looking in infrared light. The best-known example is the Horsehead Nebula in the constellation of Orion.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 77,
"term_in_english": "Dark Nebula",
"based_on_current_english_version": null,
"linked_terms": [
85,
155,
211,
371,
378,
467
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/77/"
},
{
"term_name": "Declination",
"term_definition": "In equatorial coordinate systems, declination is one of two coordinates used to specify an object's position in the sky. Specifically, declination is the angular distance of the object to the celestial equator, commonly measured in degrees: positive for objects in the northern hemisphere, with a minus sign for objects in the southern hemisphere. In this way, declination is analogous to geographic latitude on Earth's surface. The celestial equator roughly corresponds to the projection of Earth's equator onto the celestial sphere, but modern coordinate systems like the International Celestial Reference System (ICRS) instead define the celestial equator without reference to the Earth, using the positions of very distant celestial objects in the sky for reference.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 78,
"term_in_english": "Declination",
"based_on_current_english_version": null,
"linked_terms": [
50,
51,
102,
171,
286
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/78/"
},
{
"term_name": "Degree",
"term_definition": "In mathematics a degree (symbol °) is a measure of angle. One degree is 1/360th of a full circle. It can be expressed as a decimal number or it can be divided into arcminutes (symbol ′) where 60′ is 1°, and arcseconds (symbol ″) where 60″ is 1′. One arcsecond is 1/3600th of a degree, an extremely small angle.\r\n\r\nDegrees measure the apparent size of an object (see angular diameter) and its position on the celestial sphere. See also: declination, right ascension, altitude, and azimuth. On Earth: latitude and longitude. They are also used to measure angular distance between objects on the celestial sphere. The width of your fist at arm’s length is about 10°; from the horizon to the zenith is 90°. Depending on the scale, a telescope’s resolution and field-of-view can be expressed in degrees, arcminutes, or arcseconds.\r\n\r\nAlternate meaning: A unit in the measure of temperature, used with the Fahrenheit or Celsius scales. The Celsius scale is defined by the freezing point of water at sea level being 0°C and the boiling point of water being 100°C. A change of one degree Celsius is the same as a change of one kelvin but they have different zero points. The zero point of the kelvin scale is absolute zero, the lowest temperature, -273.15°C. In the older Fahrenheit system a change of one degree is the same as a change of 5/9ths of a degree Celsius or kelvin.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 79,
"term_in_english": "Degree",
"based_on_current_english_version": null,
"linked_terms": [
3,
6,
36,
50,
78,
145,
171,
179,
286,
390
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/79/"
},
{
"term_name": "Density",
"term_definition": "Density is a physical characteristic of a substance or object that expresses the relationship of its volume to its mass. The higher the density, the greater the mass per unit volume. The average density of an object is its total mass divided by its total volume. Its SI unit is kilograms per cubic meter (kg/m³). \r\n\r\nDensities in the region of the Milky Way around the Sun can range from about 10⁻²⁰ kg/m³ for interstellar gas to more than 10¹⁷ kg/m³ for the interiors of neutron stars. \r\n\r\nEveryday densities on Earth fall between those extremes, with iron at about 7800 kg/m³, water at around 1000 kg/m³ and the air that surrounds us at sea-level at a bit more than 1 kg/m³. \r\n\r\nThe Universe includes not just the stars, planets, and gas in galaxies, but also the relatively empty space between galaxies and between clusters of galaxies. This leads to an average density of matter in the Universe of the order of 10⁻²⁷ kg/m³.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 80,
"term_in_english": "Density",
"based_on_current_english_version": null,
"linked_terms": [
190,
214,
450
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/80/"
},
{
"term_name": "Disk",
"term_definition": "A disk is a flattened system of matter that is in circular coplanar motion about a common center. The material in a disk can be many different things such as gas, dust, or even stars. Examples include accretion disks around protostars, protoplanetary disks around young stellar objects, accretion disks around active galactic nuclei, and galactic disks.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 81,
"term_in_english": "Disk",
"based_on_current_english_version": null,
"linked_terms": [
5,
117,
254,
264,
426
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Milky Way and Interstellar Medium"
],
"category_ids": [
6,
7
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/81/"
},
{
"term_name": "Disk Galaxy",
"term_definition": "A disk galaxy is a type of galaxy that features a flat component of stars, gas, and dust, all of which are in circular coplanar motion around the galaxy's center. Spiral arms and associated star-forming activity are often present in these disks. In most galaxy classification schemes, disk galaxies are differentiated from elliptical, irregular, and dwarf galaxies. ",
"term_approval_level": "A",
"language_code": "en",
"term_number": 82,
"term_in_english": "Disk Galaxy",
"based_on_current_english_version": null,
"linked_terms": [
81,
99,
117,
164,
330
],
"alternate_terms": [],
"categories": [
"Galaxies",
"Milky Way and Interstellar Medium"
],
"category_ids": [
8,
7
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/82/"
},
{
"term_name": "Diurnal Motion",
"term_definition": "Diurnal refers to daily. On Earth it is the motion of the sky due to Earth’s daily rotation. Stars and other celestial bodies appear to move from east to west. The axis of this apparent motion coincides with Earth's axis of rotation. A diurnal circle is the path which a star takes as the celestial sphere carries it across the sky. These can be seen in long exposure photographs of the night sky as star trails, in the form of arcs or parts of circles, centered on the north and south celestial poles. An observer on another planet would see stars and other celestial bodies make different paths across the sky due to that planet's different rotation axis and period compared to Earth.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 83,
"term_in_english": "Diurnal Motion",
"based_on_current_english_version": null,
"linked_terms": [
53,
90,
343,
439,
462
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/83/"
},
{
"term_name": "Doppler Effect",
"term_definition": "The Doppler effect is the change in detected wavelength (or frequency) of sound or light waves caused by the relative motion of the source toward or away from the observer. This effect allows astronomers to study the motion of any body (stars, galaxies, gas, etc.) that emits waves (e.g. electromagnetic radiation). For example, in the case of radiation emitted from a star with spectral lines at specific wavelengths, the wavelengths of all the spectral lines will be shifted. For speeds significantly less than the speed of light, the Doppler shift in frequency (or wavelength) is proportional to the relative velocity of the source in the line of sight of the observer divided by the speed of light.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 84,
"term_in_english": "Doppler Effect",
"based_on_current_english_version": null,
"linked_terms": [
96,
112,
382,
431,
471
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Galaxies"
],
"category_ids": [
6,
8
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/84/"
},
{
"term_name": "Dust",
"term_definition": "Unlike on Earth, dust grains in deep space are very tiny, with most being smaller than a thousandth of a millimeter. They represent an important constituent of the medium between stars called the interstellar medium. They are formed in different environments such as the outer layers of certain cool giant stars or supernovae and are dispersed into space when these stars begin losing mass. They are mostly composed of silicates, carbon compounds, and trace amounts of other elements. These could be coated with ices in cold, dense regions of the interstellar medium. They are mostly responsible for the interstellar extinction of starlight reaching us.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 85,
"term_in_english": "Dust",
"based_on_current_english_version": null,
"linked_terms": [
107,
130,
349,
450,
472
],
"alternate_terms": [
"dust grains",
"cosmic dust"
],
"categories": [
"Chemistry",
"Exoplanets & Astrobiology",
"Milky Way and Interstellar Medium"
],
"category_ids": [
12,
6,
7
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/85/"
},
{
"term_name": "Dwarf Galaxy",
"term_definition": "A dwarf galaxy is a small galaxy that is unusually faint either because of its very small size, or its very low surface brightness, or both. Typically, dwarf galaxies are at most as luminous as a billion times the solar luminosity, corresponding to less than one percent of the luminosity of our own home galaxy, the Milky Way. There are numerous different types of dwarf galaxy including dwarf ellipticals, dwarf spheroidals, dwarf spirals, and dwarf irregular galaxies. One of the most important examples of dwarf galaxies is the Small Magellanic Cloud, which is a dwarf irregular satellite of our home galaxy, the Milky Way.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 86,
"term_in_english": "Dwarf Galaxy",
"based_on_current_english_version": null,
"linked_terms": [
119,
500
],
"alternate_terms": [],
"categories": [
"Galaxies"
],
"category_ids": [
8
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/86/"
},
{
"term_name": "Dwarf Planet",
"term_definition": "A dwarf planet is a celestial body with the following properties: It orbits around the Sun, has enough mass to obtain a nearly round shape, has not cleared its path along its orbit, and is not a moon. Dwarf planets tend to orbit in regions made up of similar bodies, as in the case of the asteroid belt and Kuiper belt. In general, dwarf planets are smaller than Mercury, with icy, rocky structures. The amount of ice relative to the rocks depends on their position in the Solar System. Pluto is the most famous dwarf planet. The term dwarf planet should not be confused with the obsolete term minor planet.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 87,
"term_in_english": "Dwarf Planet",
"based_on_current_english_version": null,
"linked_terms": [
17,
18,
170,
200,
259,
366,
513
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/87/"
},
{
"term_name": "Dwarf Star",
"term_definition": "\"Dwarf star\" is a synonym for a star on the so-called main sequence: Stars that fuse hydrogen to helium in their cores. Stars spend most of their \"lives\" as dwarf stars. Our Sun is a middle-aged dwarf. Typically, when astronomers refer to such main sequence stars, they include a reference to the color, such as \"red dwarf\" for the most common, low-mass dwarf stars, or \"yellow dwarf\" for stars like our Sun. \r\n\r\nCaution: In astronomy, there are cases where the designation \"dwarf\" refers to objects that are not dwarf stars by this definition! Brown dwarfs are objects that have masses less than 8% of that of the Sun, and never start steady hydrogen burning in their cores – a kind of intermediate class of \"substellar objects\" between the mass range of stars and that of planets. White dwarfs, also called white dwarf stars, are the compact remnants of low to medium mass stars that have exhausted their nuclear fuel. When our Sun has reached the end of its stellar life, it will become a white dwarf.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 88,
"term_in_english": "Dwarf Star",
"based_on_current_english_version": null,
"linked_terms": [
46,
276,
386
],
"alternate_terms": [],
"categories": [
"Stars"
],
"category_ids": [
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/88/"
},
{
"term_name": "Earth",
"term_definition": "Earth is the third planet from the Sun and is the fifth largest planet in the Solar System. It is a rocky, terrestrial planet with a radius of about 6400 kilometers (km). It has a mass of about six trillion, trillion kilograms.\r\n\r\nThe Earth's typical distance from the Sun is about 150 million kilometers. This is defined as one astronomical unit. The Earth takes 365.26 days to complete on orbit of the Sun. The Earth has one natural satellite known as the Moon.\r\n\r\nEarth is home to millions of species of living creatures, including humans; it is the only place to date known to have life in the Universe. It is believed to have formed about 4.54 billion years ago. Earth has an atmosphere and magnetosphere that work to block harmful radiation and hence allow the multiplication of living organisms. Earth also has extensive surface water (the only planet in the Solar System known to do so), giving it a blue color.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 89,
"term_in_english": "Earth",
"based_on_current_english_version": null,
"linked_terms": [
26,
203,
314,
354
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/89/"
},
{
"term_name": "Earth's Rotation",
"term_definition": "Earth has two simultaneous motions: a daily rotation around its axis and an annual revolution (orbit) around the Sun. The rotation of Earth around its axis results in the phenomena of day and night, as the location of a particular place relative to the Sun changes in a gradual and regular manner over a 24-hour cycle as Earth turns from west to east.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 90,
"term_in_english": "Earth's Rotation",
"based_on_current_english_version": null,
"linked_terms": [
35,
343,
462,
473
],
"alternate_terms": [],
"categories": [
"Naked Eye Astronomy"
],
"category_ids": [
4
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/90/"
},
{
"term_name": "Eclipse",
"term_definition": "An eclipse occurs when an astronomical object is temporarily obscured by either passing into the shadow of another body or when another body passes between the viewer and the object. Examples for eclipses are lunar eclipses when the Earth stands between the Sun and the Moon and the Moon moves into the Earth´s shadow, or solar eclipses, when the Moon moves between the Earth and the Sun and blocks part or all of the Sun´s light. If the obscuring body only obscures a small part of other body, this phenomenon is called a transit. If the obscuring body completely obscures the other body, this phenomenon is called an occultation",
"term_approval_level": "A",
"language_code": "en",
"term_number": 91,
"term_in_english": "Eclipse",
"based_on_current_english_version": null,
"linked_terms": [
181,
310,
367,
464,
475
],
"alternate_terms": [],
"categories": [
"Exoplanets & Astrobiology",
"Solar System",
"Stars"
],
"category_ids": [
6,
1,
2
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/91/"
},
{
"term_name": "Ecliptic",
"term_definition": "The ecliptic is the great circle on the celestial sphere formed by projecting the plane of the Earth’s orbit around the Sun onto the celestial sphere. Effectively, the ecliptic is the apparent path of the Sun amongst the stars during the year. All constellations of the Zodiac lie along the ecliptic, and eight major planets lie relatively close to the ecliptic as observed from the Earth.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 92,
"term_in_english": "Ecliptic",
"based_on_current_english_version": null,
"linked_terms": [
53,
300,
391
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/92/"
},
{
"term_name": "Electric Field",
"term_definition": "Electrically charged particles attract or repel each other via the electric force – like charges repel, opposite charges attract. In physics, it has proven practical to divide the action of one charge on others into two steps: Every particle that carries an electric charge is taken to produce a so-called electric field in the surrounding space. The force acting on a second particle is given directly by the direction and strength (\"field vector\") of the electric field at the location of that second particle: multiply the field with the value of the second particle's electric charge to obtain the force acting on that second particle. The force acting on the first particle is then of the same strength but in the opposite direction.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 93,
"term_in_english": "Electric Field",
"based_on_current_english_version": null,
"linked_terms": [
95
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/93/"
},
{
"term_name": "Electromagnetic Force",
"term_definition": "Following Faraday and Maxwell in the 19th century, physicists describe space as filled with electric and magnetic fields. Moving electric charges create such fields around them, and in turn the motion of an electric charge is influenced by the electric and magnetic fields at its position. A positive charge will be accelerated in the direction of the electric field, a negative charge in the opposite direction; a moving electric charge will be deflected perpendicular to its direction of motion by a magnetic field. The umbrella term for these two field influences on charges is electromagnetic forces. Astronomical objects such as stars, gas clouds, whole galaxies, or swirling accretion disks have large-scale magnetic fields, where such forces can become important.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 95,
"term_in_english": "Electromagnetic Force",
"based_on_current_english_version": null,
"linked_terms": [
93,
426,
455
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/95/"
},
{
"term_name": "Electromagnetic Radiation",
"term_definition": "When 19th century physicists described electric and magnetic phenomena, they found that there is a way for patterns of electric and magnetic fields to propagate together through space at the speed of light, even in situations where there are no electric charges nearby. These waves are known as electromagnetic waves, or electromagnetic radiation. Elementary electromagnetic waves can be classified according to their wavelengths, and the resulting electromagnetic spectrum includes, from shorter to longer wavelengths: gamma rays, X-rays, ultraviolet, visible light, infrared, submillimeter, and radio waves (including millimeter/microwaves). Electromagnetic radiation from distant astronomical objects is astronomers' most important source of information about such objects.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 96,
"term_in_english": "Electromagnetic Radiation",
"based_on_current_english_version": null,
"linked_terms": [
95,
123,
155,
175,
198,
371,
378,
482,
487
],
"alternate_terms": [
"electromagnetic spectrum"
],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/96/"
},
{
"term_name": "Ellipse",
"term_definition": "An ellipse is a two-dimensional shape that resembles a squashed or elongated circle. The widest distance across an ellipse is called the major axis and the shortest distance is called the minor axis. An ellipse has two foci (plural of focus) that lie along the major axis with both having the same distance from the widest points. At any point on the ellipse, the sum of the distances to the two foci is constant. The eccentricity, e, of an ellipse defines how squashed it is and lies within the range 0<e<1. A circle has zero eccentricity, and a very long, thin ellipse has eccentricity just smaller than one. \r\n\r\nA closed orbit such as the Earth's orbit around the Sun follows the shape of an ellipse. An orbit is characterized by the semi-major axis (half the size of the major axis) and eccentricity, but to fully describe an orbit the orientation of the ellipse also needs to be known. \r\n\r\nUnclosed orbits such as comets that make only one visit to the inner Solar System before being flung out into interstellar space follow parabolas (e=1) or hyperbolas (e>1).",
"term_approval_level": "A",
"language_code": "en",
"term_number": 98,
"term_in_english": "Ellipse",
"based_on_current_english_version": null,
"linked_terms": [
169,
232
],
"alternate_terms": [],
"categories": [
"Solar System"
],
"category_ids": [
1
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/98/"
},
{
"term_name": "Elliptical Galaxy",
"term_definition": "An elliptical galaxy is a type of galaxy that has a regular, elliptical appearance like a sphere squashed on one or two axes, in contrast to disk galaxies which appear pancake-shaped. It typically contains mostly old stars of yellow-red color. Elliptical galaxies typically have very little gas and very little ongoing star formation compared to spiral galaxies.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 99,
"term_in_english": "Elliptical Galaxy",
"based_on_current_english_version": null,
"linked_terms": [
82,
119
],
"alternate_terms": [],
"categories": [
"Galaxies"
],
"category_ids": [
8
],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/99/"
},
{
"term_name": "Energy",
"term_definition": "In very basic terms energy is defined as the capacity of a system to do some work. However, this definition does not capture the rich, multilayered aspect of energy, and its manifestation from the scale of fundamental particles to the entire Universe. One of the fundamental principles of physics is that total energy is always conserved. Energy takes various forms (e.g. kinetic, gravitational potential, thermal) depending on the context and can be converted from one form to another. Relativistic physics describes an innate connection between mass and energy. The unit of energy is the joule, and it quantifies the amount of work done on an object by a force of one newton moving it a distance of one meter. In particle physics, however, energy is expressed in electron volts.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 100,
"term_in_english": "Energy",
"based_on_current_english_version": null,
"linked_terms": [],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/100/"
},
{
"term_name": "Energy Level",
"term_definition": "An energy level is a discrete allowed quantum energy state within an atom or molecule. It is measured in electron volts (eV). When an electron in an atom or molecule moves from a level with higher energy to one with a lower energy this causes a photon to be emitted with an energy equal to the energy difference between the two levels. Similarly, a photon may be absorbed by an atom or molecule if its energy is the same as the energy difference between the present level and a higher level.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 101,
"term_in_english": "Energy Level",
"based_on_current_english_version": null,
"linked_terms": [
31,
201,
250,
441
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/101/"
},
{
"term_name": "Equator",
"term_definition": "The equator is an imaginary line running around Earth, equidistant from the North and South Poles and perpendicular to the Earth's rotation axis. The equator marks the line on the Earth's surface furthest from the rotation axis. At the poles the rotation axis intersects with the surface. In the latitude and longitude coordinate system on the Earth's surface, the equator is defined as having zero degrees latitude. The equator divides the Earth into a northern and a southern hemisphere. Places in the northern hemisphere have positive latitude; places in the southern hemisphere have negative latitude.",
"term_approval_level": "A",
"language_code": "en",
"term_number": 102,
"term_in_english": "Equator",
"based_on_current_english_version": null,
"linked_terms": [
35,
171,
179,
424,
436,
439,
462,
483,
496,
497
],
"alternate_terms": [],
"categories": [],
"category_ids": [],
"override_url": null,
"url": "https://astro4edu.org/resources/glossary/term/102/"
}
]
}