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"term_name": "Newton's Laws of Motion",
"term_definition": "Newton’s Laws of Motion are a set of models which explain how objects with mass change their motion due to interactions with other objects. These interactions are described as forces. Newton's Laws explain how forces affect the motion of objects. Newton developed three laws of motion and a law of gravitation. These laws can explain the motion of most objects in the Universe, with motions involving high velocities and/or very strong gravity requiring Einstein's theories of special and general relativity respectively.",
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"term_name": "North Celestial Pole (NCP)",
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"term_name": "Nova",
"term_definition": "A nova is a star that suddenly brightens, becoming many times brighter than before. The name derives from the Latin nova stella or new star, which was used in early-Modern Europe to describe bright stars that suddenly appeared in the sky. Novae have been observed as \"guest stars\" by many different cultures.\r\n\r\nNovae are caused by white dwarfs which accrete gas from a close binary star companion. This gas builds up in the white dwarf's atmosphere until it is hot enough to ignite through nuclear fusion. This nuclear fireball causes the white dwarf to brighten by several orders of magnitude. Unlike a Type Ia supernova, the white dwarf remains intact after this explosion. This means that the whole process can start again and the nova can recur.",
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"term_name": "Nuclear Fission",
"term_definition": "Nuclear fission is a process where the nucleus of a heavy element splits into two lighter nuclei. The mass of the remaining material is less than that of the original nucleus, while the deficit in mass is released as energy. \r\n\r\nThe two lighter nuclei produced by nuclear fission are often radioactive themselves and can release further energy through radioactive decay.",
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"term_name": "Nuclear Fusion",
"term_definition": "Nuclear fusion is the process where the atomic nuclei of lighter elements join together to form the nucleus of a heavier element. \r\n\r\nIn the Universe, nuclear fusion plays two important roles. For one, it provides the energy supply for the radiation emitted by stars like our Sun. When sufficiently light nuclei fuse, the total rest mass of the resulting nucleus is slightly smaller than the combined rest masses of the initial nuclei. This \"mass deficit\" corresponds to the energy released by the fusion reaction, via Einstein's famous formula E=mc², which links mass m, energy E, and the speed of light c. For example, in the core of the Sun, hydrogen nuclei fuse together to form helium and release energy in the form of radiation as well as neutrino particles. \r\n\r\nThe second role of nuclear fusion is that it is responsible for producing elements in the Universe that are more complex than hydrogen and helium. After the Big Bang, only hydrogen, helium, and trace amounts of lithium nuclei existed in the Universe. Fusion reactions in the cores of stars, in the course of supernova explosions, and from explosions caused by colliding neutron stars, are the source of (essentially) all the remaining heavier chemical elements in the Universe. The chemical elements that make up the greatest part of the human body by mass, notably oxygen and carbon, were formed by nuclear fusion in the core of stars or during supernova explosions, prompting the expression \"we are star dust\".",
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"term_name": "Nucleon",
"term_definition": "All the matter that we see around us is made up of atoms, and all atoms have the same basic structure: a tiny, dense nucleus that carries almost all of the atom's mass, surrounded by electrons. The main constituents of atomic nuclei are protons and neutrons, which are collectively called nucleons.",
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"term_name": "Nucleus",
"term_definition": "All the matter that we see around us consists of atoms, and each atom in turn consists of electrons surrounding a small, central nucleus. Atomic nuclei consist of protons, which are positively charged, and neutrons, which carry no electric charge. Although the protons repel each other due to their electric charge, there is an even stronger force, called the strong nuclear force or just the strong force, that holds the nucleus together. Nuclei with the same number of protons form atoms that belong to the same chemical element. \r\n\r\nNuclei are tiny, only about 1/100,000th of the size of an atom – so in a sense, most of the atom is empty space! The nucleus typically accounts for more than 99.9% of an atom's total mass. That mass at such tiny size makes nuclei very dense, with typical densities of a hundred million billion kilograms per cubic meter. \r\n\r\nNuclei are important in different areas of astrophysics. In the interior of stars, energy is set free as lighter nuclei (starting with hydrogen, whose nucleus is a single proton) fuse to form successively heavier nuclei – this is what makes stars shine. Nuclear fusion in stars can form heavy nuclei up to those of iron, with supernova explosions and the interior of certain cool stars able to form even heavier nuclei. Shortly after the Big Bang, a brief phase of \"Big Bang nucleosynthesis\" had hydrogen nuclei fusing to helium and traces of other elements. Neutron stars, as the remnants of the supernova explosions of massive stars, consist of mostly neutrons stacked to similar densities as those of nuclei. Certain types of atomic nuclei, stripped of their electrons, are emitted by stars as part of stellar winds, or travel the depths of space as cosmic rays.",
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"term_name": "Observable Universe",
"term_definition": "The observable universe refers to the patch of the Universe we can see, which is a sphere with us at the center. The radius of the observable universe is determined by how far light has been able to travel towards us since the beginning of the Universe. Regions at the boundary of the observable universe are so far away that their light has just had enough time to reach us over the past 14 billion years; in other words: over the age of the Universe. \r\n\r\nThe most distant regions of the Universe that we can see are now over 40 billion light years away. This is because the Universe has expanded a lot since the light reaching us from those regions was emitted. Light from objects outside the observable universe has not yet had enough time to reach us. \r\n\r\nThe longer we wait, the more time light has to reach us, and the larger the observable universe grows. Other observers in the cosmos have their own observable universes: a sphere with them at the center, its radius the greatest distance over which light from other regions has had time to reach them.",
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"term_name": "Observation",
"term_definition": "Astronomical observations involve collecting and/or measuring electromagnetic radiation, particles, or gravitational waves reaching us from an astronomical object. In the past, humans observed with their eyes, and from the early 1600s through telescopes. Now a variety of cameras, spectrometers, and other instruments can also be used. The information that is collected, such as a raw image we retrieve from a camera, is known as (observational) data.\r\n\r\nThis data contains information about the object and the intervening medium (e.g. the interstellar or intergalactic medium), but still depends on the specifics of the instrument, for instance if one part of the camera is more sensitive than another. The data also depends on contaminants; for example, when collecting light from an astronomical object, we will typically also collect foreground light scattered in Earth's atmosphere. Removing instrument-specific and contaminant portions as completely as possible is called data reduction. Typical end products of observations are images, spectra, and time series (repeated observations of the same object or objects, for instance, data from pulsars or variable stars). These can be used to measure various quantities such as the angle between two objects, the time an event was observed, or the apparent magnitude of an object.\r\n\r\nObservations differ from the experiments carried out in many scientific laboratories in that the observer cannot interact with the astronomical objects themselves in the same way as a chemist mixing two chemicals can. In some contexts, observations can sometimes be supplemented by experiments on the objects themselves such as the study of meteorites or by sending space probes to objects in the Solar System.",
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"term_name": "Observatory",
"term_definition": "An observatory is a site or building dedicated to astronomical observations. Optical and infrared observations are usually performed with telescopes placed in domes to protect them during bad weather. Radio telescopes, and some submillimeter telescopes are often placed outside. Modern, ground-based, optical, infrared, or submillimeter astronomical observatories are erected on mountaintops above as much of Earth's atmosphere as possible. These observatories have specialized instruments such as telescopes, cameras, and spectrographs. A high location is less necessary for radio and cosmic ray astronomical observatories. Other parts of the electromagnetic spectrum (gamma, X-ray, ultraviolet radiation, and longer wavelength infrared radiation) can be studied with specific space telescopes that are sometimes also referred to as observatories. Observations for radio telescopes at different sites can be combined together. These multiple sites are often referred to collectively as one observatory.",
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"term_name": "Opposition",
"term_definition": "When two astronomical objects appear to be lined up or nearly lined up with an observer, in opposite directions in the sky, they are said to be in opposition. It is not necessary for both objects to be actually visible for the observer. For instance, at a full moon, the Sun, observer on Earth, and Moon are lined up, so the visible part of the Moon's surface is fully lit up by the Sun – unless the alignment is perfect, in which case there is a lunar eclipse. When a planet, comet, or asteroid is said to be \"in opposition\", this commonly refers to the Sun and observers on Earth. When a planet is in opposition, it looks particularly bright, appears to move in a direction opposite than usual (\"retrograde motion\" as Earth moves faster on its inside track), and is particularly close to Earth.",
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"term_name": "Optical Astronomy",
"term_definition": "Optical astronomy is the practice of studying and observing the Universe (stars, planets, dwarf planets, asteroids, etc.) in the near-infrared, in visible light, and in ultraviolet light. The reason for lumping those three kinds of electromagnetic radiation together is that the optical telescopes, with glass lenses and/or metallic mirrors, that astronomers had originally constructed for observing visible light from celestial objects, are equally well-suited for observing near-infrared or ultraviolet light. In addition, the Earth's atmosphere is transparent not only for visible light, but for the directly adjacent infrared and ultraviolet regions, allowing all three kinds of observations from the ground. Last but not least, the camera chips astronomers use for visible-light observations can also detect near-infrared and ultraviolet light. Put all of this together, and the telescopes and instruments astronomers use to observe visible light work just as well for near-infrared and ultraviolet observations. In consequence, it makes sense for astronomers to collectively describe observations in that range of the electromagnetic spectrum with a single term, namely optical astronomy. The adjective \"optical\" is also used to describe the spectral range, as in \"the optical part of the spectrum.\" Observations in that range are \"optical observations\".",
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"term_name": "Optical Telescope",
"term_definition": "An optical telescope is an instrument that is used to observe and study astronomical objects in visible (optical) light. Optical telescopes use mirrors (a reflecting telescope) and/or lenses (a refracting telescope) to collect and focus light. Telescopes were originally developed to observe distant objects on Earth but were soon turned to astronomical use. Telescopes can range in size from a few centimeters across to diameters of over ten meters.",
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"term_name": "Optics",
"term_definition": "Optics is the science of light and its interactions with matter, and the art of constructing instruments that make use of the general principles of light–matter interactions. In astronomy, the \"optics\" of a telescope or instrument are those parts that guide light towards a detector, notably mirrors, lenses, masks, slits, or waveguides where visible light is concerned, as well as dispersive elements such as prisms and gratings that produce spectra. Active optics is the term for a mirror kept in the correct shape by active mechanical elements (\"actuators\"), while adaptive optics is a system whereby a mirror is quickly deformed in just the right way to counteract atmospheric disturbances (the \"twinkling\" of stars). The adjective \"optical\" is also used to refer to astronomy using visible light.",
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"term_name": "Orbit",
"term_definition": "An orbit is the path of a moving object in a system around the center of mass of that system, caused by the mutual gravitational force between the objects in the system. For systems such as the Solar System, where the central body is much more massive than the other bodies, this center of mass lies inside or close to the most massive object (in the case of the Solar System, the Sun). In a binary star system the center of mass the stars orbit often lies between the two stars.\r\n\r\nOrbits are typically elliptical in shape with the center of mass of the system lying at one focus of the ellipse. The size and shape of the orbit is defined by the semi-major axis and the eccentricity of the ellipse. More eccentric orbits have higher ellipticities. Most planets in the Solar System have orbital eccentricities very close to zero, for example, Venus (0.007) and Earth (0.017). The exceptions are Mercury (0.206) and the dwarf planet Pluto (0.244).",
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"term_name": "Orbital Period",
"term_definition": "The orbital period is the time it takes for an object to make one complete orbit of another object. Another way of stating this is that it is the time it takes for an object to arrive back to the same point in its orbit. This could be a planet going around a central star (for example, Earth orbiting the Sun); it could be a moon orbiting around a planet; it could be a star, group of stars, or nebulae going around the center of a galaxy; it could be two (binary) stars orbiting their common center of mass.",
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"term_name": "Outer Planets",
"term_definition": "In our Solar System, the outer planets are Jupiter, Saturn, Uranus, and Neptune. Their orbits are outside the asteroid belt, and all of those planets are so-called giant planets, with an extremely thick atmosphere made up mostly of hydrogen. This makes them physically distinct from the inner planets, each of which is a comparatively small rocky body with a comparatively thin atmosphere. \r\n\r\nPlanets around stars other than our Sun do not necessarily fall into inner and outer groups with similar characteristics – we know a number of stars with at least one gas giant, a \"hot Jupiter\", in close orbit.",
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"term_name": "Outer Space",
"term_definition": "Outer space, often shortened to \"space\", is the term for all regions within our Universe that lie beyond Earth's atmosphere. Spaceflight is the endeavor to fly suitable conveyances into and through outer space, and such conveyances are called spacecraft. Space sciences is an umbrella term for all branches of science that are concerned with space exploration, spaceflight, or astronomical bodies in outer space that may be reached by spacecraft, which includes astronomy and planetology.",
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"term_name": "Ozone",
"term_definition": "Ozone is a colorless or pale blue-colored gas in which each molecule consists of three oxygen atoms. It has the chemical formula O₃ and it is poisonous to humans. Its proportion in the atmosphere is small, and in some areas it may not exceed one part in a million. Depending on where the ozone is, it can protect or harm life on Earth. \r\n\r\nMost of the ozone is located in the stratosphere, where it acts as a shield that protects Earth's surface from ultraviolet radiation from the Sun. This armor has weakened due to human introduction of chlorofluorocarbons into the atmosphere, thus increasing the risk of skin cancer, cataracts, and weakened immune systems. In 1987, the Montreal Protocol banned use of these gases as refrigerants and aerosol spray propellants with the result that the stratospheric ozone layer has begun to recover.\r\n\r\nNear Earth's surface and within the troposphere, ozone is a very harmful pollutant and can cause damage to lung tissue and plants.",
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"term_name": "Parallax",
"term_definition": "Parallax is the apparent change in position of a celestial object on the sky due to a change in the observer’s point of view. The position change in the sky, expressed as an angle, is determined relative to the most distant objects we know – historically, distant stars; in modern astronomy, extremely distant objects called quasars, which determine what is called the International Celestial Reference Frame. The angle of apparent position change is inversely proportional to the object's distance from us, making parallax measurements a powerful tool for determining distances in our cosmic neighborhood (\"parallax method\"). For Solar System objects, simultaneous observations from different locations on Earth can yield useful parallax values. For stars, parallax angles are given for a standard shift of observer position by one astronomical unit (the average Earth–Sun distance) at right angles to the line of sight. Observer position shifts of that magnitude can be achieved by making observations several months apart, with Earth moving along its orbit around the Sun in between. By definition, an object whose parallax angle under those conditions is 1 arcsecond is at a distance of 1 parsec (3.26 light years) from Earth. Over one year, the apparent position of a star in the sky traces out an ellipse, whose semi-major axis is the parallax angle. The most accurate stellar parallaxes to date are supplied by ESA's Gaia mission, a space telescope specifically designed for that task.",
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"term_name": "Parsec",
"term_definition": "The parsec (pc) is a standard unit of distance measure in astronomy, defined as follows: Imagine a circle with a radius of one astronomical unit (which is the average Earth–Sun distance), which we are viewing face-on. From a distance of exactly one parsec, we will see the circle's radius subtend an angle of one arcsecond. This makes 1 pc equal to approximately 3.26 light years, and to as many astronomical units as there are arcseconds in one radian: 206,264.8 astronomical units. The practical importance of this definition is its relation to the parallax method of distance determination. For this method, one measures tiny position shifts of astronomical objects in the sky as the observer position changes by a given length. For an astronomical object at a distance of one parsec, a change in observer position by one astronomical unit (usually because the Earth has moved along its orbit between the two observations) corresponds to an apparent position shift, called the object's parallax (angle), of one arcsecond. This results in a simple relationship: The distance in parsecs is one divided by the parallax angle in arcseconds. Its direct geometrical meaning makes the parsec the professional astronomer's preferred measure of distance, more common in the literature than distances given in light years. Sirius is 2.7 pc distant from us, corresponding to a parallax of 1/2.7=0.37 arcseconds. Even Proxima Centauri, the closest star apart from our Sun, has a parallax of less than 1 arcsecond.",
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"term_name": "Partial Solar Eclipse",
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"term_name": "Particle",
"term_definition": "A small constituent of matter may be referred to as a particle. In classical physics, particles move through space, and at each given moment a particle has a definite location. In quantum physics, particle properties are different. Particles do not always have a definite location, and in some ways behave similar to waves.\r\n\r\nParticle physics is the study of the smallest constituents of matter, the so-called elementary particles. For astronomy, the most important matter particles are the electron as well as the quarks, up quark and down quark, that make up the composite particles proton and neutron. Atomic matter consists of protons and neutrons forming the atomic nucleus, surrounded by electrons.\r\n\r\nElectromagnetic radiation, as the main astronomical messenger, consists of quantum particles called photons. At lower photon energies, the wave properties of these quantum particles are most important. Radio astronomers, for instance, describe the electromagnetic radiation they receive not in terms of separate particles, but as electromagnetic waves, characterized by wavelength or frequency. On the other end of the electromagnetic spectrum, for the highest-energy photons, the particle properties are the most important. High-energy astronomers who observe using X-rays or gamma rays typically make their observations using particle detectors, and describe the properties of the radiation they receive in terms of particle energies.",
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"term_name": "Particle Physics",
"term_definition": "Particle physics is the branch of physics that studies the smallest constituents of matter, including the particles that atoms are made of (electrons, neutrons, and protons), as well as the particles that neutrons and protons are made of (so-called quarks). These and more exotic, short-lived particles can be produced in particle accelerators. There particles are collided at high energies, resulting in the production of various types of other particles. All known elementary particles and their interactions are described by the so-called standard model of particle physics. Some astrophysical objects, notably the jets of stellar-mass or supermassive black holes, or supernova explosions, are natural particle accelerators. Cosmic particles accelerated in that way reach us as cosmic rays.",
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"term_name": "Penumbra",
"term_definition": "The penumbra (Latin for \"almost shadow\") has two meanings. \r\n\r\nIn the first, penumbra refers to the outer, less dark, part of the shadow cast onto a body during an eclipse, in which the light is only partially blocked. For example, in a solar eclipse, observers in the penumbra region will see the Moon only partially cover the Sun and experience a partial eclipse only. \r\n\r\nIn the second, penumbra refers to the distinct outer and brighter part of a sunspot.",
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"term_name": "Perihelion",
"term_definition": "Most objects in the Solar System have elliptical orbits, with the Sun at one of the foci. Perihelion is the point along the orbit where the orbiting body is closest to the Sun. Mathematically, this point marks one end of the major axis of the ellipse. In this word \"peri\" denotes closest point and \"helion\" denotes the Sun. Accordingly, this word 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 \"periastron\"; when the central body being orbited is the Earth the term is \"perigee\". The general term regardless of the central body is \"periapsis\".",
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"term_name": "Period",
"term_definition": "Numerous processes in astronomy are cyclic: They repeat regularly. An example is the orbit of a planet around the Sun, with the planet orbiting the Sun along the same trajectory again and again. The time it takes between one repetition of such a cycle and the next is called the cycle's period. The orbital period of a planet, for instance, is the time it takes the planet to go once around the Sun. The repetition does not need to be perfect, and orbital periods can change slowly over time. For instance, the slight systematic decrease in the period of the first binary neutron star provided the first indirect evidence for the emission of gravitational waves.",
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"term_name": "Phase",
"term_definition": "In astronomy, phase refers to the state of partial illumination of a moon or planet with respect to a specific observer. A distant light source typically illuminates only half of a spherical body's surface; the rest remains dark. Similarly, only about half of a spherical body's surface is within a distant observer's sight. The phase specifies which fraction of the surface within the observer's sight is illuminated. It changes as the relative positions of the object, the observer, and the light source change.\r\n\r\nThe best-known examples are the phases of the Moon. The relative positions of the Moon, of the Earth as the location of the observer, and of the Sun as the light source, change as the Moon orbits the Earth over the course of about one month. Hence, over that time, an observer on Earth will see different phases of the Moon. The phase where all of the Moon's surface that is in the observer's sight is illuminated is called \"full Moon\"; when no illuminated surface regions are visible, we have \"new Moon\". The two half-illuminated phases are called \"first\" or \"second quarter\", respectively. Less-than-half illumination makes for a \"crescent (Moon)\".\r\n\r\nPhases are also seen in planets in the Solar System (particularly prominent for Mercury and Venus), and have been inferred for exoplanet systems. For the Moon, even non-illuminated regions are not completely dark: they reflect light reaching them from Earth, in a phenomenon known as Earthshine, first documented by Leonardo da Vinci.",
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"term_name": "Photoelectric Effect",
"term_definition": "When light or other electromagnetic radiation strikes a material, electrons can, depending on the material and frequency of the light, be emitted: This is the photoelectric effect. It can be explained by considering light as particles or packets of energy called photons. For materials, mostly metals, the frequency of light should be greater than a threshold frequency (characteristic of the material) for the emission of these photoelectrons to occur. Their maximum energy is determined by the frequency; increasing the frequency of the light brings about an increase in the maximum kinetic energy of the electrons. On increasing the intensity of monochromatic light, more electrons are released, but there is no change in their maximum kinetic energy. This is because the intensity of the light is directly proportional to the number of photons.",
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"term_name": "Photometry",
"term_definition": "The term photometry is derived from the Greek phōs meaning light, and metro meaning to measure. Although there are various types of photometry, the basic method involves measuring the intensity of the light (photons) radiated by various astronomical objects. The light from objects passes through specialized filters (known as passbands), and that light is captured on a digital device such as a camera CCD. Separate passbands cover ranges of wavelengths, that may include infrared, visible, and ultraviolet. Astronomical telescopes often have filter groups, which are called photometric systems. Some common systems include UBVRI, JHK, and ugriz. Photometry allows different physical characteristics of astronomical objects to be measured, for example, temperature, color, and change in brightness.",
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"term_name": "Photon",
"term_definition": "The term photon comes from the Greek phōs, which means light, and is therefore used synonymously and interchangeably with light. When astronomers refer to light, they are referring to all types of electromagnetic radiation from radio waves all the way to gamma rays. \r\n\r\nA photon is a fundamental particle, carrier for the electromagnetic force, and considered to be the smallest packet (quanta) of electromagnetic energy. The quanta of energy associated with a photon of given frequency is proportional to this frequency and inversely proportional to its wavelength. \r\n\r\nModern views consider a photon as being not only a particle but also a wave. In astronomy, photons are foundational to our ability to observe and measure various aspects of the Universe and the objects it contains.",
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{
"term_name": "Photosphere",
"term_definition": "The photosphere (\"light sphere\") is the layer of a star from which the light that we observe emerges. Light emitted from deeper, denser layers will be absorbed before it can escape from the star. Higher layers are less dense, and do not emit significant light.",
"term_approval_level": "A",
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"term_name": "Pisces",
"term_definition": "Pisces is a constellation in the Zodiac, i.e. the stars that make up this constellation are in the part of the sky that intersects with the ecliptic – with the plane defined by the Earth's orbit around the Sun. Hence, from our point of view here on Earth, we can regularly find the Sun, and also the other planets in the Solar System, in this constellation. In the case of the Sun this is from around mid-March to mid-April, which includes the time of the March equinox. (Of course if the Sun is there, we cannot see the constellation's stars.) Pisces is one of the 88 modern constellations defined by the International Astronomical Union, but it goes back much further – it was already one of the 48 constellations named by the 2nd century astronomer Claudius Ptolemy.",
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"term_name": "Planet",
"term_definition": "A planet is defined by the International Astronomical Union as a celestial body in orbit around a star or the remnant of a star, that is large enough to be nearly round in shape by its own gravitational force, but not massive enough for thermonuclear fusion to ever occur in its core. It must also be large enough for its gravity to remove other objects that pass close to its orbit around the star. Therefore, they are cold bodies (as compared to stars) that shine in the visible band only by the light reflected from their stars but they do emit light at infrared wavelengths. In our Solar System, eight planets orbit around the Sun. Planets may be basically rocky objects, such as the inner planets – Mercury, Venus, Earth, and Mars – or primarily liquid and gas with a small solid core like the outer planets – Jupiter, Saturn, Uranus, and Neptune. Planets outside the Solar System are called extrasolar planets or exoplanets for short.",
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"term_in_english": "Planet",
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"term_name": "Planet Formation",
"term_definition": "When a cosmic gas cloud collapses to form a star, that nascent star is surrounded by a swirling disk of gas and dust. This is a protoplanetary disk, where planets form: Ice-covered dust particles will stick to each other, forming slightly larger clumps, which will continue to grow. There are still open questions about how the next stages happen: What, for instance, is the role of turbulent gas motion in bringing those clumps closer together? Eventually, so-called planetesimals more than about a kilometer in size are formed. Some of those are pulled together by their own gravity to form larger planets, others remain behind as the first asteroids. Some protoplanets manage to draw large amounts of gas towards them to become gas giants. Some other protoplanets in cold regions far from the central star will accrete large amounts of frozen material along with gas, becoming ice giants. Others, with less gas, become terrestrial planets.",
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"term_name": "Planetarium",
"term_definition": "A planetarium is a theater with specialized equipment that can be used for visualizing astronomical phenomena. Most planetaria consist of specialized projection equipment and a hemispherical dome. When stars and planets are projected onto the dome, the audience is sitting under an artificial night sky. Traditional, opto-mechanical, projectors are built specifically for simulating the night sky. Digital planetariums instead use one or more \"specialized beamers\", which can project not only the night sky, but any kind of moving image. This allows for \"full dome movies\" not only on astronomy, but on other topics – the audience can travel in a virtual spaceship, but also explore the micro-world of human DNA, for example.",
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"term_number": 255,
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"term_name": "Planetary Nebula",
"term_definition": "A planetary nebula is a cloud of gas and dust, coming from the external layers of a dying star and expanding into the general interstellar medium. The gas, energized by ultraviolet light from the dying star, glows with an emission-line spectrum. Some planetary nebulae are approximately spherical, and may look like a planet in a small telescope but their nature is completely different. Other planetary nebulae are not spherical, due to the star's rotation, magnetic field, or binarity.",
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"term_name": "Planetary Science",
"term_definition": "Planetary science is the branch of science which deals with the nature, origin, and evolution of planets in our Solar System and beyond.",
"term_approval_level": "A",
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"term_number": 257,
"term_in_english": "Planetary Science",
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"term_name": "Plasma",
"term_definition": "Plasma is a quasi-neutral (i.e. charge balanced) gas where a significant fraction of the particles are positive ions and negative electrons, often mixed with molecules and neutral atoms. The properties of plasma are so different from those of ordinary neutral gases that plasma is considered a \"fourth state of matter\". The positive ions and negative electrons allow a plasma to conduct electricity. Plasma can form at high temperatures (as in stars) or by photoionization (as in interstellar gas). Plasma is found in stars, the interstellar medium, in the space between the planets in the Solar System in the form of the solar wind, within the planetary magnetosphere, and in the space between galaxies. It is estimated that more than 99% of the ordinary matter in the observable Universe (excluding dark matter and dark energy) is in the plasma state.",
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"term_name": "Pluto",
"term_definition": "Pluto is one of the celestial bodies in our Solar System. It is located in the Kuiper Belt, beyond the orbit of Neptune. It used to be known as the ninth Solar System planet, but in 2006 it was reclassified as a dwarf planet. It was discovered in 1930 by Clyde Tombaugh. Pluto's average distance from the Sun is 6 billion kilometers (km), and its radius is 1185 km (smaller than the Earth's moon). One year on Pluto is equivalent to 247.9 Earth years and its day is equivalent to 6.4 Earth days.\r\n\r\nNASA's New Horizon mission was the first spacecraft to fly by Pluto, in 2015, and provided the first ever detailed view of its surface and its atmosphere. The surface of Pluto is so cold that very little of the hydrogen can exist in gaseous form. What little atmosphere Pluto has is mainly nitrogen, and the surface has large plains of frozen nitrogen. Its atmosphere extends to a distance of 1600 km. Pluto is composed of rocks (70%) and ice (30%). It has five known moons: Charon, Styx, Nix, Kerberos, and Hydra.",
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"term_name": "Polar Axis",
"term_definition": "",
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"term_name": "Polaris",
"term_definition": "Polaris is the nearest bright star (within one degree) to the celestial North Pole. Its official designation is α Ursae Minoris, but it is commonly known as Polaris, the North Star, or the Pole Star. All the stars of the northern hemisphere appear to rotate around it, so it provides an excellent fixed point from which to perform measurements for navigation and astrometry. Its elevation above the horizon gives the approximate latitude of the observing site. However, its position on the celestial sphere is slowly changing due to the precession of the rotation axis of Earth, so in several centuries Polaris will not indicate the location of the celestial North Pole anymore.\r\n\r\nPolaris is a triple star system, composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab, a very close main sequence star; the pair has a wide companion, Polaris B, a main sequence star orbiting at a distance of 2400 astronomical units. Polaris B can be resolved with a modest telescope. The Hubble Space Telescope was able to resolve all three members of the Polaris ternary system. The apparent visual magnitude of Polaris fluctuates because Polaris Aa is a Cepheid variable. The Polaris system is about 447 light years from Earth.",
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"term_in_english": "Polaris",
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"term_name": "Proton",
"term_definition": "A proton is a subatomic particle with positive electric charge. Protons are one of the main constituents of atomic nuclei, alongside neutrons. The number of protons is the \"atomic number\" of a nucleus, and each atom with a specific atomic number corresponds to a specific chemical element. The atomic nucleus of hydrogen is a single proton, and the most elementary nuclear fusion reaction in a star is when two protons collide, one of them decays, and a deuteron is formed, consisting of one proton and one neutron. Protons can also be found in the high-energy cosmic rays reaching us from outer space.",
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