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{
"sub_idea_id": 1,
"sub_idea_of": 1,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "Understanding the sky and the movements of the Sun and planets was one of the first attempts to understand the natural world",
"language_code": "en",
"headline": "Understanding the sky and the movements of the Sun and planets was one of the first attempts to understand the natural world",
"text": "The first records of astronomical observations come from drawings and artefacts created by prehistoric people, documenting what they saw in the sky. In ancient cultures, Astronomy was related to religious and mythological beliefs. Astronomical phenomena were used to measure time and to create calendars, allowing such cultures to plan daily and seasonal events.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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{
"sub_idea_id": 2,
"sub_idea_of": 1,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "Earlier cultures imagined patterns connecting stars in the night sky",
"language_code": "en",
"headline": "Earlier cultures imagined patterns connecting stars in the night sky",
"text": "Patterns in the night sky formed by connecting stars using imaginary lines are called constellations. The earliest constellations were defined by early cultures. These recognisable groups of stars were often connected to cultural stories and mythology from cultures such as Greek, Mayan, Native American and Chinese. In modern Astronomy, constellations are well-defined regions of the sky, which combine both ancient constellations and those defined in the 15th, 16th, 17th and 18th centuries. Some cultures, such as the Indigenous Australians and the indigenous people of South America, also identified patterns using the dark silhouettes in the luminous band of the Milky Way.",
"number_substitute": null,
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{
"sub_idea_id": 3,
"sub_idea_of": 1,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "Astronomy has inspired and is represented in the art and culture of many civilisations",
"language_code": "en",
"headline": "Astronomy has inspired and is represented in the art and culture of many civilisations",
"text": "Over the centuries, artists, poets, writers, and many creative thinkers, have used the night sky either as inspiration and/or as subjects in their work. Astronomical themes can be seen represented, for example, in paintings, sculptures, music, movies and literature. These works have used the observable motifs seen in the night to directly, or indirectly, communicate the essence, beauty and mystery of the night sky. The universality of art and its intimate connection to culture, can thus be a powerful means to make people appreciate not only the innate beauty of celestial objects and phenomena, rather the knowledge we have acquired about them. This increases the worldwide interest in astronomy and promotes a cross cultural understanding encompassed by the notion of being under one sky.",
"number_substitute": null,
"categories": [
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"category_ids": [
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"sub_idea_id": 4,
"sub_idea_of": 1,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "Astronomy provided important timekeeping knowledge, essential for ancient agriculture",
"language_code": "en",
"headline": "Astronomy provided important timekeeping knowledge, essential for ancient agriculture",
"text": "In many ancient cultures, astronomy was developed to increase the accuracy of farming calendars. As an example, Egyptians developed a calendar based on their observations of the star Sirius, using it to determine the annual flooding of the river Nile.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
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},
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"sub_idea_id": 5,
"sub_idea_of": 1,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "Astronomy was important for navigators in the past",
"language_code": "en",
"headline": "Astronomy was important for navigators in the past",
"text": "Many civilisations used the position of the stars and other celestial objects to navigate the land, seas and oceans. Celestial navigation is still taught to this day.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
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"sub_idea_id": 6,
"sub_idea_of": 1,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "Astronomy, by using the scientific method, is different from astrology",
"language_code": "en",
"headline": "Astronomy, by using the scientific method, is different from astrology",
"text": "Until pre-modern times, the distinction between astronomy and astrology was vague. Today astronomy and astrology are clearly distinguished from each other. Astronomy is a science and astrology is not. Astrology uses positions of celestial objects to predict future events. However, extensive studies of astrology and its predictions show that astrology is not accurate in its predictions and is without any scientific foundation.",
"number_substitute": null,
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{
"sub_idea_id": 7,
"sub_idea_of": 1,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Earth was believed, by most earlier cultures, to be the centre of the Universe",
"language_code": "en",
"headline": "Earth was believed, by most earlier cultures, to be the centre of the Universe",
"text": "Most early cultures, with notable exceptions by some of the Greek astronomers active around 300 BCE, believed that Earth was the centre of the Universe. This Geocentric view lasted for over two millennia in European and Asian Cultures until the so-called Copernican Revolution in the XVI Century. Modern astronomers have found that the Universe appears to have no specific centre in space.",
"number_substitute": null,
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{
"sub_idea_id": 8,
"sub_idea_of": 1,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "The century-long Copernican revolution led to the Sun replacing Earth as the accepted centre of the Solar System",
"language_code": "en",
"headline": "The century-long Copernican revolution led to the Sun replacing Earth as the accepted centre of the Solar System",
"text": "In the 16th century, Copernicus proposed arguments for the Heliocentric theory in which the Sun was the centre of the Universe and Earth moved around it. Although we now know that the Sun is not the centre of the Universe, it is the centre of the Solar System and the Copernican Heliocentrism theory was revolutionary at that time, contributing to the development of modern Astronomy.",
"number_substitute": null,
"categories": [
"Solar System"
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{
"sub_idea_id": 9,
"sub_idea_of": 1,
"sub_idea_number": 9,
"version_number": 2,
"headline_in_english": "Over 400 years ago, astronomers undertook the first methodical observations within astronomy using a telescope",
"language_code": "en",
"headline": "Over 400 years ago, astronomers undertook the first methodical observations within astronomy using a telescope",
"text": "Although he did not invent the telescope, Galileo was the first to use it for scientific purposes. His improvements of the refracting telescope led him to discoveries such as the phases of Venus and the four largest moons of Jupiter, which are still referred to as Galilean moons. His discoveries provided compelling evidence that supported the Heliocentric view of the Universe.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
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"category_ids": [
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{
"sub_idea_id": 10,
"sub_idea_of": 1,
"sub_idea_number": 10,
"version_number": 2,
"headline_in_english": "Planet Earth is approximately spherical in shape, and this has been illustrated for centuries in many different ways",
"language_code": "en",
"headline": "Planet Earth is approximately spherical in shape, and this has been illustrated for centuries in many different ways",
"text": "Some early cultures in many areas of the world have described Earth as a flat plane or disk as part of their description of the Universe. The idea that Earth is a sphere has been around for a few millennia and has been a significant part of the worldviews of many cultures, becoming the dominant paradigm more than 1000 years ago. There are numerous empirical ways to test that Earth is approximately spherical in shape (it is technically referred to as an oblate spheroid). One of the earliest mathematical methods was by Eratosthenes, who measured the circumference of Earth by analysing the lengths of shadows cast by sticks at different locations in ancient Egypt (3rd century BCE).",
"number_substitute": null,
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{
"sub_idea_id": 11,
"sub_idea_of": 2,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "We experience day and night because of Earth’s rotation around its axis",
"language_code": "en",
"headline": "We experience day and night because of Earth’s rotation around its axis",
"text": "Earth’s side facing the Sun experiences daytime, while the opposite side experiences nighttime. The time that Earth takes to rotate around its axis such that the Sun returns to the same position in the sky defines the duration of the (solar) day, which on average is 24 hours.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
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{
"sub_idea_id": 12,
"sub_idea_of": 2,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "We experience seasons because of the tilt of Earth’s axis of rotation as Earth moves around the Sun in a year",
"language_code": "en",
"headline": "We experience seasons because of the tilt of Earth’s axis of rotation as Earth moves around the Sun in a year",
"text": "Earth’s axis of rotation is tilted by 23.4o relative to the line perpendicular to its orbital plane around the Sun. For this reason, during part of Earth’s orbit around the Sun, the Northern or Southern hemisphere is tilted towards the Sun while the other one is tilted away from it. The former experiences summer, as the sunlight falls more directly on its surface and the days are longer because the Sun reaches a higher altitude in the sky. On the other hand, the hemisphere tilted away from the Sun experiences winter because the sunlight falls at a highly inclined angle to Earth’s surface, causing it to spread over a larger area. The days become shorter because the Sun is at a lower altitude in the sky.",
"number_substitute": null,
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{
"sub_idea_id": 13,
"sub_idea_of": 2,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "We see different phases of the Moon throughout a Moon cycle",
"language_code": "en",
"headline": "We see different phases of the Moon throughout a Moon cycle",
"text": "As the Moon orbits Earth, its relative position with respect to the Sun and Earth changes. The region of the Moon’s surface which is lit by sunlight changes, producing the different phases we see from Earth — New Moon, Waxing Crescent, Full Moon and Waning Crescent taking 29.53 days from Full Moon to Full Moon. While the phases of the Moon are (more or less) the same for any observer on Earth, the orientation of the Moon will vary, depending on the observer’s hemisphere. For instance, some observers might see the crescent of the Moon open to the left while others, observing the same phase but from a different location, might see the crescent open to the right.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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{
"sub_idea_id": 14,
"sub_idea_of": 2,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "Eclipses occur due to special alignments of the Sun, Earth and Moon",
"language_code": "en",
"headline": "Eclipses occur due to special alignments of the Sun, Earth and Moon",
"text": "Occasionally, when the Moon passes exactly between the Sun and Earth, the Moon blocks the light from the Sun and casts a shadow on Earth, creating a solar eclipse. Occasionally, Earth can be directly between the Sun and the Moon. In that case, Earth casts a shadow on the Moon, obscuring its surface and creating a lunar eclipse. Eclipses can be partial, when just a fraction of the object is eclipsed, or total, when the whole object is eclipsed. A lunar eclipse occurs only at Full Moon and, consequently, can only be observed at night. At any given location on Earth, you are more likely to see a lunar eclipse than a solar eclipse. Lunar eclipses also last for longer periods of time than Solar eclipses.",
"number_substitute": null,
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},
{
"sub_idea_id": 15,
"sub_idea_of": 2,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "The tides on Earth are a result of the gravity of the Sun and Moon",
"language_code": "en",
"headline": "The tides on Earth are a result of the gravity of the Sun and Moon",
"text": "The Moon and, to a smaller degree, the Sun cause tides on Earth. Slight bulges on Earth, and especially its oceans, occur both on the side closest to the Moon and closest to the Sun, and away from them. As Earth rotates, these bulges reach the shorelines, causing the water level to increase there. When the Sun, Earth and Moon are almost in a straight line (at Full Moon and at New Moon), we experience higher “Spring tides”. In contrast, when the Sun and Moon are at right angles to each other relative to Earth (at First and Third Quarter Moon) we experience lower “Neap tides”.",
"number_substitute": null,
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"sub_idea_id": 16,
"sub_idea_of": 2,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "Light from the Sun is essential for most life forms on Earth",
"language_code": "en",
"headline": "Light from the Sun is essential for most life forms on Earth",
"text": "The Sun is the primary source of energy used by life forms on Earth. For instance, plants perform photosynthesis using sunlight, allowing their growth and, consequently, the production of molecular oxygen. That oxygen is used by animals for breathing. It is believed that the devastation of the global environment when an asteroid collided with Earth was the cause of the extinction of flightless dinosaurs and of the majority of species on Earth. The resulting explosion transported large amounts of dust into the atmosphere, blocking the Sun’s light and causing a long impact winter. Sunlight also affects our physical and mental health. When exposed to sunlight, our skin produces vitamin D, which plays an important role in our body’s biochemical processes. Some studies show a relation between human depression and the lack of exposure to sunlight.",
"number_substitute": null,
"categories": [
"The Sun"
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},
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"sub_idea_id": 17,
"sub_idea_of": 2,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Particles from the Sun travel to Earth and cause the aurora",
"language_code": "en",
"headline": "Particles from the Sun travel to Earth and cause the aurora",
"text": "During a solar eruption, charged particles (primarily electrons and protons) from the Sun traverse the 150 million kilometre journey toward Earth. They latch onto Earth’s magnetic field, flow towards the magnetic poles, and interact with particles in the atmosphere. The fastest of these particles can travel from the Sun to Earth in about half an hour; the slowest take about five days. Occasionally, these particle storms disturb the Earth’s magnetic field, damaging satellites and power grids. Often, particles from the Sun interact with oxygen and nitrogen in Earth’s atmosphere. This interaction gives rise to Aurorae – wonderful light shows that illuminate the night sky around the magnetic poles of the northern (Aurora Borealis) and southern (Aurora Australis) hemispheres.",
"number_substitute": null,
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"Naked Eye Astronomy",
"The Sun"
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"sub_idea_id": 18,
"sub_idea_of": 2,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "Technology developed for astronomical research is part of our daily life ",
"language_code": "en",
"headline": "Technology developed for astronomical research is part of our daily life ",
"text": "Analytical tools and methods used to study astronomical data have been applied to industry, medical sciences and technology we use everyday. Detectors originally developed for astronomical research are now also used in digital cameras, like the ones in our mobile phones. Special glass developed for astronomical telescopes is used in manufacturing LCD screens and computer chips, as well as in ceramic stovetops. The knowledge transfer between astronomy and medicine has contributed to the development of magnetic resonance imaging (MRI) and computerised tomography (CAT scanners), among other devices. ",
"number_substitute": "",
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{
"sub_idea_id": 19,
"sub_idea_of": 3,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "We can see several thousands of stars with our eyes on a clear and dark night",
"language_code": "en",
"headline": "We can see several thousands of stars with our eyes on a clear and dark night",
"text": "When we gaze up into the night sky, far away from the light pollution of cities and during a New Moon or when the Moon is not in the sky, we can see roughly 4000 stars with the naked eye. All the stars we see with the unaided eye belong to our galaxy. Although there are billions of stars in other galaxies and trillions of galaxies in the observable Universe, those stars are too far away and hence much too faint for our eyes to distinguish them as individual points of light. Depending on our location on Earth and on the time of observations, our Solar System’s five brightest planets, the band of the Milky Way, two satellite galaxies of the Milky Way (the Large and Small Magellanic Clouds), and the Andromeda Galaxy (a big spiral galaxy) are also visible to the naked eye.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
4
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},
{
"sub_idea_id": 20,
"sub_idea_of": 3,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "The night sky can help us to orient on Earth and navigate",
"language_code": "en",
"headline": "The night sky can help us to orient on Earth and navigate",
"text": "Looking up at the night sky allows us to find the cardinal directions. In the Northern Hemisphere, the easiest way to find North is to look for the star Polaris, also known as the North Star, which is very close to the celestial North pole. The easiest way of finding Polaris is through the constellations of Ursa Major and Ursa Minor. In the Southern Hemisphere, the star Sigma Octantis, which is the closest star to the celestial South Pole is not easily visible. However, one quick method to find South is to use the constellation Crux and the two brightest stars in the constellation Centaurus.",
"number_substitute": null,
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{
"sub_idea_id": 21,
"sub_idea_of": 3,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "The rotation axis of Earth wobbles (precesses) over thousands of years",
"language_code": "en",
"headline": "The rotation axis of Earth wobbles (precesses) over thousands of years",
"text": "As Earth rotates on its axis, it moves like a rotating spinning top. The direction of its axis of rotation changes in a slow precession with a period of about 26,000 years. This movement causes the axis to point in different directions over time and, as a consequence, the celestial North and South poles slowly change position over time. As an example, Polaris will eventually cease to indicate the North direction, although another star might, depending on the direction of Earth’s axis at the time. Although there is currently no bright star near the celestial South pole, in the future we will have a proper “South Star”!",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
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},
{
"sub_idea_id": 22,
"sub_idea_of": 3,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "Only a few celestial bodies are bright enough to be seen with the unaided eye when the Sun is above the horizon",
"language_code": "en",
"headline": "Only a few celestial bodies are bright enough to be seen with the unaided eye when the Sun is above the horizon",
"text": "Most of the objects in the night sky are too dim to be observed against the bright, sunlit sky. A similar effect happens at night in cities, where, due to light pollution, we can see only a small fraction of the stars due to the brightening of the sky by artificial lighting. Only a few celestial bodies are bright enough to be seen with the unaided eye when the Sun is above the horizon. Depending on its phase, it is possible to see the Moon during the day. At certain times, Venus can be observed in the morning (“Morning star”), in the evening (“Evening star”), and if you know where to look, Venus is also visible in the midday sky. Very rarely, a particularly bright comet might be visible during the daytime.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
4
]
},
{
"sub_idea_id": 23,
"sub_idea_of": 3,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "Celestial objects rise in the East and set in the West due to Earth’s rotation",
"language_code": "en",
"headline": "Celestial objects rise in the East and set in the West due to Earth’s rotation",
"text": "Due to Earth’s rotation around its axis from West to East, an observer on the surface sees the whole sky move in the opposite direction, from East to West, seemingly rotating around our planet. This apparent movement of the sky around Earth is called Diurnal movement. This is the reason why we see celestial bodies rise above the eastern half of the horizon, and set below the western half.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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4
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},
{
"sub_idea_id": 25,
"sub_idea_of": 3,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Millions of meteoroids enter Earth’s atmosphere daily",
"language_code": "en",
"headline": "Millions of meteoroids enter Earth’s atmosphere daily",
"text": "A meteoroid is a small rocky or metallic object ranging from the size of a grain of sand to one metre. When it enters Earth’s atmosphere it is heated by ram pressure, which creates a streak of light in the night sky. This phenomenon is called a meteor (or a shooting or falling star). When a meteoroid survives its passage through Earth’s atmosphere and lands on the surface, it is called a meteorite. Although millions of meteors occur in Earth’s atmosphere daily, most of the meteoroids that they originate from are burned to gas and dust before reaching the ground.",
"number_substitute": null,
"categories": [
"Naked Eye Astronomy"
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"category_ids": [
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},
{
"sub_idea_id": 26,
"sub_idea_of": 4,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "Light (otherwise known as electromagnetic radiation) is the main source of information for astronomical research",
"language_code": "en",
"headline": "Light (otherwise known as electromagnetic radiation) is the main source of information for astronomical research",
"text": "Since most celestial objects are too far away to travel to, we must rely on the electromagnetic radiation (light) of these objects to study them. Different wavelengths of the electromagnetic spectrum provide information about various mechanisms of astronomical phenomena and the nature of celestial objects. In modern astronomy, the study of the Universe is mainly conducted using the whole electromagnetic spectrum: radio, microwaves, infrared, visible, ultraviolet, X-rays and gamma-rays. Although in common parlance light only refers to visible light, in astronomy light can refer to the electromagnetic spectrum.",
"number_substitute": null,
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},
{
"sub_idea_id": 27,
"sub_idea_of": 4,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "On large scales, gravitation is the dominant interaction in the Universe",
"language_code": "en",
"headline": "On large scales, gravitation is the dominant interaction in the Universe",
"text": "On average, astronomical objects carry no net electric charge. The dominant way in which such objects interact over long distances is gravitation. Gravitation is what makes planets orbit the Sun, stars orbit galaxy centres, and keeps the hot plasma of stars together in spherical shape. Most astronomical phenomena can be described using the Newton’s law of gravitation, but in the most extreme situations Einstein’s general theory of relativity is required to provide an accurate description.",
"number_substitute": null,
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{
"sub_idea_id": 28,
"sub_idea_of": 4,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "Gravitational waves and subatomic particles provide new ways of studying the Universe",
"language_code": "en",
"headline": "Gravitational waves and subatomic particles provide new ways of studying the Universe",
"text": "The existence of gravitational waves — ripples in spacetime — was predicted by the general theory of relativity in the early 20th century. Their first confirmed direct detection was achieved in 2015, and scientists can now use them as a new window to study the Universe. Gravitational waves are generated by strong gravitational interactions, such as the merger of two massive black holes or neutron stars. Astronomers also detect various kinds of subatomic particles, such as neutrinos, electrons or protons to learn about the interior of our Sun and some of the most energetic processes in the Cosmos.",
"number_substitute": null,
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"sub_idea_id": 29,
"sub_idea_of": 4,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "Astronomy makes use of data obtained from observations and simulations to model astronomical phenomena in the framework of current theories",
"language_code": "en",
"headline": "Astronomy makes use of data obtained from observations and simulations to model astronomical phenomena in the framework of current theories",
"text": "Astronomers create mathematical models of astronomical objects, their associated phenomena and their evolution. The framework of these models is given by the fundamental theories in physics and chemistry. Some models consist of elementary mathematical relations, more complex models make use of numerical simulations. The most sophisticated simulations are run on some of the largest supercomputers in the world. Observational data from telescopes and detectors is used to test and refine models. The interaction between observational evidence and models is an important aspect of discovery.",
"number_substitute": null,
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"sub_idea_id": 30,
"sub_idea_of": 4,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "Astronomical research combines knowledge from different fields, such as physics, mathematics, chemistry, geology and biology",
"language_code": "en",
"headline": "Astronomical research combines knowledge from different fields, such as physics, mathematics, chemistry, geology and biology",
"text": "Professional astronomical research combines knowledge from mathematics, physics, chemistry, engineering, computer sciences, as well as other fields. This broad view has proven essential for revealing and modelling the nature of astronomical objects and phenomena. For example, to understand the nuclear reactions taking place inside stars, scientists need nuclear physics; in order to detect the resulting elements in the atmospheres of stars, they need chemistry. Engineering is essential for the manufacturing of telescopes and detectors, and the development of custom software is crucial for analysing the data provided by these instruments.",
"number_substitute": null,
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"sub_idea_id": 31,
"sub_idea_of": 4,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "Astronomy is divided into a number of specialties",
"language_code": "en",
"headline": "Astronomy is divided into a number of specialties",
"text": "Since a good description of astronomical objects and phenomena requires a good knowledge of other scientific fields, modern astronomy is commonly divided in specialties according to the main topics addressed. Some of these specialties include: astrobiology, cosmology, observational astronomy, astrochemistry and planetary science. Astronomers may also pick a specialty of studying one particular kind of object, such as white dwarf stars. Given the important role that physics plays within astronomy, the terms “astrophysics” and “astronomy” are used interchangeably.",
"number_substitute": null,
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"sub_idea_id": 32,
"sub_idea_of": 4,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Time and distance scales in astronomy are a lot larger than the ones we use in our daily life",
"language_code": "en",
"headline": "Time and distance scales in astronomy are a lot larger than the ones we use in our daily life",
"text": "The Moon is the closest celestial object to Earth at a distance of about 384,400 kilometres. Our Sun has a diameter of 1.39 million kilometres, a mass of about 1989 thousand trillion trillion kilograms, and it is the closest star to Earth at a distance of about 150 million kilometres (which defines the Astronomical Unit, au). The star closest to the Sun is Proxima Centauri which is about 4.25 light-years away. One light-year is the distance that light travels (in a vacuum) in one year, which is just over 9 trillion kilometres. Our galaxy is 100,000-120,000 light-years in diameter and other galaxies can be as far as billions of light-years away. The units in astronomy are a lot larger than we could imagine. Astronomical time scales are long and ages of millions or billions of years are typical.",
"number_substitute": null,
"categories": [],
"category_ids": []
},
{
"sub_idea_id": 33,
"sub_idea_of": 4,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "Spectroscopy is an important technique allowing us to probe the Universe from a distance",
"language_code": "en",
"headline": "Spectroscopy is an important technique allowing us to probe the Universe from a distance",
"text": "Several characteristics of astronomical objects can be revealed only by studying their spectrum — the rainbow-like decomposition of their light into myriads of different colours, each characterised by the light’s wavelength. By analysing the light collected from these objects, astronomers can determine details such as their elemental composition, temperature, pressure, magnetic field, among other characteristics.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
]
},
{
"sub_idea_id": 34,
"sub_idea_of": 5,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "Telescopes and detectors are crucial to the study of Astronomy",
"language_code": "en",
"headline": "Telescopes and detectors are crucial to the study of Astronomy",
"text": "Since electromagnetic waves are the main source of information in astronomy, telescopes and detectors play an important role when it comes to collecting and analysing these waves. Larger telescopes collect more light, allowing astronomers to identify and analyse very faint objects. Larger telescopes also have more resolving power, allowing astronomers to study their target objects in finer detail. While early astronomical observations were performed by looking directly through a telescope, detectors today allow astronomers to document their observations objectively, at many different wavelengths.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
]
},
{
"sub_idea_id": 35,
"sub_idea_of": 5,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "Some telescopes can be linked together to act as one big telescope",
"language_code": "en",
"headline": "Some telescopes can be linked together to act as one big telescope",
"text": "By linking together many telescopes, astronomers can make them work as a single big telescope using a technique called interferometry. The resolution of the combined instruments will be that of a single telescope with a diameter equal to the greatest distance between any two of the smaller linked telescopes. This allows astronomers to see smaller and finer details in astronomical objects as well as distinguish between separate objects, such as a star and its planetary system.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
]
},
{
"sub_idea_id": 36,
"sub_idea_of": 5,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "Astronomical observatories are located on Earth and in Space",
"language_code": "en",
"headline": "Astronomical observatories are located on Earth and in Space",
"text": "Earth’s atmosphere absorbs radiation from most of the electromagnetic spectrum. It is transparent to visible light, some ultraviolet and infrared, and shortwave radio, but otherwise mostly opaque. Most ultraviolet bands and large portions of infrared light, as well as X-rays, cannot penetrate the atmosphere. For this reason, most of the telescopes that collect light other than visible, radio and a smaller number of other wavelength bands, must be placed in space. Although visible light can be observed from the surface, the turbulence of Earth’s atmosphere affects the quality of the images, so some optical telescopes are also placed in space.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
]
},
{
"sub_idea_id": 37,
"sub_idea_of": 5,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "Earth-based astronomical observatories are often located in remote regions all around the world",
"language_code": "en",
"headline": "Earth-based astronomical observatories are often located in remote regions all around the world",
"text": "Few locations on Earth provide the pristine observing conditions associated with high altitudes, an absence of light pollution, and transparency of the atmosphere to certain wavelengths. These locations can often be hostile, hard to access, and are usually far removed from larger human settlements. Astronomers either travel to those locations for their observations, allow experienced local telescope operators to carry them out for them, or make use of robotic telescopes, which are operated remotely.",
"number_substitute": null,
"categories": [
"Telescopes, Instruments and Observatories"
],
"category_ids": [
3
]
},
{
"sub_idea_id": 38,
"sub_idea_of": 5,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "Astronomy today is part of “Big Science” and “Big Data”",
"language_code": "en",
"headline": "Astronomy today is part of “Big Science” and “Big Data”",
"text": "Astronomical surveys have started producing large amounts of data, and this will increase greatly in the coming years. This evolution is called “Big Data Astronomy”, where the focus is on finding novel ways to store, deliver and analyse these data. This has led to the development of various citizen science projects to tap into the acute pattern recognition ability of humans. On the other hand, modern telescopes and instruments are expensive, and their construction requires a variety of technical skills. In this era of “Big Science”, they are commonly constructed by international organisations or consortia involving numerous astronomical institutes from different countries. ",
"number_substitute": "",
"categories": [],
"category_ids": []
},
{
"sub_idea_id": 39,
"sub_idea_of": 5,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "Complex simulations and huge data in astronomy require the development of powerful supercomputers ",
"language_code": "en",
"headline": "Complex simulations and huge data in astronomy require the development of powerful supercomputers ",
"text": "The processing of vast amounts of data from both simulations and observations requires computers that are capable of performing complex simulations in a short amount of time. Current supercomputers can perform in the order of a couple of hundred quadrillion calculations every second. These supercomputers allow astronomers to create simulated Universes and compare them with observations from large-scale surveys. ",
"number_substitute": "",
"categories": [],
"category_ids": []
},
{
"sub_idea_id": 40,
"sub_idea_of": 5,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Astronomy is a global science, with international teams, and where data and publications are shared freely ",
"language_code": "en",
"headline": "Astronomy is a global science, with international teams, and where data and publications are shared freely ",
"text": "The data available from most professional observatories is publicly available. Over the course of their career, astronomers will typically work in different countries. Large astronomical projects, from the construction of telescopes and instruments to coordinated observing campaigns, are frequently undertaken in collaboration between researchers and institutes from different nations. Astronomy is global and international. We are all crew members of “Spaceship Earth”, under one sky, exploring the cosmos. ",
"number_substitute": "",
"categories": [],
"category_ids": []
},
{
"sub_idea_id": 41,
"sub_idea_of": 5,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "Numerous spacecrafts have been launched to space to study the Solar System",
"language_code": "en",
"headline": "Numerous spacecrafts have been launched to space to study the Solar System",
"text": "In order to explore and learn more about our place in the Universe, we have been sending robotic probes throughout the Solar System. Some of these probes orbit planets, moons, or even asteroids, while others have landed on such objects. Among some places in the Solar System that have been visited (landing, orbit or fly-by) by robotic probes are all the planets, the dwarf planets Pluto and Ceres, our Moon and other moons of Jupiter and Saturn, comets and asteroids.",
"number_substitute": null,
"categories": [
"Solar System",
"Space Exploration"
],
"category_ids": [
1,
10
]
},
{
"sub_idea_id": 42,
"sub_idea_of": 6,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "The Universe is over 13 billion years old",
"language_code": "en",
"headline": "The Universe is over 13 billion years old",
"text": "The estimated age of the Universe based on modern observations and on state-of-the-art cosmological models for its early evolution, is approximately 13.8 billion years. Cosmology is a research field which studies the evolution and the structure of the Universe.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 43,
"sub_idea_of": 6,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "The Universe is homogeneous and isotropic on the large scale",
"language_code": "en",
"headline": "The Universe is homogeneous and isotropic on the large scale",
"text": "At the largest scales (approximately greater than 300 million light-years), matter in the Universe appears to be uniformly distributed. Because of this nearly uniform density and structure, the Universe looks nearly the same at any location (homogeneous) and in every direction (isotropic).",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 44,
"sub_idea_of": 6,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "We always observe the past",
"language_code": "en",
"headline": "We always observe the past",
"text": "Due to the finite speed of light, we never see objects as they are now, but always as they were in the past. We can only see the Sun as it was about eight minutes ago, since light from the Sun takes about eight minutes to reach us. We see the Andromeda galaxy as it was about 2.5 million years ago, since it takes the galaxy’s light that long to arrive on Earth. In this way, astronomers always observe the past, even up to 13.8 billion years ago. Observing astronomical objects at various distances thus provides us with a cross-section of cosmic history. Since on average, the Universe has the same properties everywhere, this cross-section provides valuable clues as to our own history.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 45,
"sub_idea_of": 6,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "We can only directly observe a fraction of the total Universe",
"language_code": "en",
"headline": "We can only directly observe a fraction of the total Universe",
"text": "Since light travels in space at a finite speed, there are distant regions of the Universe we cannot yet observe. The reason for this is simply that light from those regions has not had enough time to reach our detectors on Earth. We can only see objects that lie inside a certain region that is called the “Observable Universe,” comprising all objects whose light has had the necessary time to reach us. Of particular interest are very distant objects near the border of that region. Those appear to us in the form they were when the Universe had just begun.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 46,
"sub_idea_of": 6,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "The Universe is mainly composed of Dark Energy and Dark Matter",
"language_code": "en",
"headline": "The Universe is mainly composed of Dark Energy and Dark Matter",
"text": "The stars, the air we breathe, our bodies and everything we see around us consist of atoms, which themselves are composed of protons, neutrons and electrons. This so-called baryonic matter, is what we interact with in our daily life. Observational evidence shows that it represents only about 5% of the total composition of the Universe. In fact, the Universe is mainly composed of an unknown form of energy referred to as Dark Energy (around 68%), and an unusual form of matter called Dark Matter (around 27%). The nature of the so-called Dark Energy and Dark Matter is an active area of research, especially through observations of their influence on the baryonic matter.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 47,
"sub_idea_of": 6,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "The Universe is expanding at an accelerated rate",
"language_code": "en",
"headline": "The Universe is expanding at an accelerated rate",
"text": "Observational evidence shows that the Universe is expanding at an accelerated rate, which is attributed to Dark Energy. As the Universe expands in a systematic way on large scales, clusters of galaxies move away from each other. In the modern models, all distances between galaxy clusters grow in proportion to the same universal scale factor. Observational data show that the more distant a galaxy is from us, the faster it moves away from us (Hubble-Lemaître Law). Hypothetical alien observers in other galaxies would find the same. Bound systems, such as clusters of galaxies, and groups of galaxies bound by their own gravity, or galaxies themselves, are not affected by cosmic expansion. Within galaxy clusters and groups, individual galaxies can be orbiting each other, or they can be on a collision course with each other. The latter is true for the Milky Way Galaxy and the Andromeda galaxy.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 48,
"sub_idea_of": 6,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "The expansion of space causes light from distant galaxies to be redshifted",
"language_code": "en",
"headline": "The expansion of space causes light from distant galaxies to be redshifted",
"text": "Cosmic expansion influences the properties of light in the Universe. Light reaching us from distant galaxies is increasingly redshifted with larger distances. This cosmological redshift can be understood directly in terms of wavelengths of light increasing (stretching to longer wavelengths) with the cosmic scale factor. That is why distant galaxies can only be observed in the infrared or radio bands, and why the Cosmic Microwave Radiation reaches us mostly in the microwave regime.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 49,
"sub_idea_of": 6,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "The natural laws (e.g. gravity) that we study on Earth appear to work the same way throughout the Universe",
"language_code": "en",
"headline": "The natural laws (e.g. gravity) that we study on Earth appear to work the same way throughout the Universe",
"text": "There have been many tests to see if the laws of physics, such as the laws governing gravity, thermodynamics and electromagnetism, are the same on Earth and in the distant Universe. So far, all such tests indicate that the fundamental laws of physics apply throughout the whole Universe.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 50,
"sub_idea_of": 6,
"sub_idea_number": 9,
"version_number": 2,
"headline_in_english": "The large-scale structure of the Universe is composed of filaments, sheets and voids",
"language_code": "en",
"headline": "The large-scale structure of the Universe is composed of filaments, sheets and voids",
"text": "Large redshift surveys of the Universe have revealed that on large scales in the order of a few hundred million light-years, the Universe resembles a three-dimensional, sponge-like web of filaments and voids, which astronomers call the “cosmic web”. Filaments and sheets contain millions of galaxies. These large-scale structures extend over hundreds of millions of light-years and are typically tens of millions of light-years thick. The filaments and sheets form boundaries around voids, which are in the order of hundred million light-years in diameter, and contain only very few galaxies.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 51,
"sub_idea_of": 6,
"sub_idea_number": 10,
"version_number": 2,
"headline_in_english": "The Cosmic Microwave Background allows us to explore the early Universe",
"language_code": "en",
"headline": "The Cosmic Microwave Background allows us to explore the early Universe",
"text": "The oldest electromagnetic radiation, emanating from the most distant regions in the Universe that we can observe, is the Cosmic Microwave Background radiation. It is the relic left over from the hot and dense early Universe, imprinted with information from a time when the Universe was about 380,000 years old. The Cosmic Microwave Background allows us to measure key characteristics of the Universe as a whole: the amount of Dark Matter, baryonic matter and Dark Energy it contains, the geometry of the Universe and its current expansion rate. The Cosmic Microwave Background shows that the Universe is nearly isotropic and thus also provides indirect evidence for homogeneity.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 52,
"sub_idea_of": 6,
"sub_idea_number": 11,
"version_number": 2,
"headline_in_english": "The evolution of the Universe can be explained by the Big Bang model",
"language_code": "en",
"headline": "The evolution of the Universe can be explained by the Big Bang model",
"text": "According to the best available evidence so far, all the matter and energy we see around us were contained in a volume smaller than an atom over 13 billion years ago. The Universe expanded from this very high density and temperature phase (Big Bang phase) into its present state. The models describing the expanding Universe are referred to as LambdaCDM (where Lambda stands for the Dark Energy component of the Universe, and CDM for Cold Dark Matter). The Big Bang phase, despite its name, wasn’t an explosion where matter is flung out into previously existing empty space. All the available space was filled with matter from the very beginning and, as the space increased, the average matter density has decreased ever since. Ever since galaxies formed, the average distances between them has been constantly increasing. The Big Bang model makes numerous testable predictions about our current Universe, most of which have been confirmed using observational data.",
"number_substitute": null,
"categories": [
"Cosmology"
],
"category_ids": [
9
]
},
{
"sub_idea_id": 53,
"sub_idea_of": 7,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "The Solar System was formed about 4.6 billion years ago",
"language_code": "en",
"headline": "The Solar System was formed about 4.6 billion years ago",
"text": "Radioactive dating of meteorites has allowed us to determine the age of the Solar System. This age is also consistent with the dating of lunar rock samples and oldest rocks found on Earth’s surface.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 54,
"sub_idea_of": 7,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "The Solar System is composed of the Sun, planets, dwarf planets, moons, comets, asteroids, and meteoroids",
"language_code": "en",
"headline": "The Solar System is composed of the Sun, planets, dwarf planets, moons, comets, asteroids, and meteoroids",
"text": "Our Solar System consists of a central star that we call the Sun and of every object in its orbit, under the influence of its gravity. These objects include planets and their natural satellites, dwarf planets, asteroids, meteoroids and comets. The Sun accounts for more than 99.87% of the Solar System’s total mass.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 55,
"sub_idea_of": 7,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "There are eight planets in the Solar System",
"language_code": "en",
"headline": "There are eight planets in the Solar System",
"text": "According to the 2006 International Astronomical Union resolution, in order for an object to be a planet it must fulfil three criteria. The first is that it must orbit the Sun. The second is that a planet must have enough mass for gravity to transform it into an approximate spherical shape, and finally, its gravitational influence must be sufficient so as to clear its orbital neighbourhood from other objects. Objects that are not moons and obey the first two rules, but not the third, are called dwarf planets. Counting from the Sun, the planets in our Solar System are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 56,
"sub_idea_of": 7,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "There are several dwarf planets in the Solar System",
"language_code": "en",
"headline": "There are several dwarf planets in the Solar System",
"text": "Dwarf planets are all smaller than Earth’s Moon, which has a diameter of about 3474 kilometres. Pluto is currently the largest of the dwarf planets, followed by Eris, Haumea, Makemake and Ceres. Each of these objects are solid, with icy surfaces, and have similar compositions. Ceres is located between the orbits of Mars and Jupiter, while the other four dwarf planets can be found beyond Neptune’s orbit, in the Edgeworth-Kuiper belt.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 57,
"sub_idea_of": 7,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "The planets are divided into terrestrial (rocky) planets and gas giants",
"language_code": "en",
"headline": "The planets are divided into terrestrial (rocky) planets and gas giants",
"text": "The four planets closest to the Sun are called terrestrial planets. All of these planets have a solid surface and are composed mostly of rock. Mercury has no atmosphere but compared to Earth, Venus has the densest atmosphere and Mars the thinnest atmosphere. In contrast with the small inner planets, the four outer planets, which are called gas giants, are much larger. These planets are mainly gaseous (hydrogen and helium) and their atmospheres are very dense. All the gas giants have rings around them. Saturn has by far the most impressive ring system, which is visible even through a fairly small telescope.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 58,
"sub_idea_of": 7,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "Some planets have dozens of natural satellites",
"language_code": "en",
"headline": "Some planets have dozens of natural satellites",
"text": "With the exception of Mercury and Venus, all planets have at least one natural satellite. Earth is the only planet in the Solar System which possesses only one moon, while Mars has two moons. Contrasting with the terrestrial planets, all the gas giants have a great number of objects orbiting them. With over 75 confirmed moons each, Jupiter and Saturn are the planets with the most natural satellites, followed by Uranus, and Neptune.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 59,
"sub_idea_of": 7,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "Earth is the third planet orbiting around the Sun, and has one natural satellite, the Moon",
"language_code": "en",
"headline": "Earth is the third planet orbiting around the Sun, and has one natural satellite, the Moon",
"text": "Our home planet is the third planet counting from the Sun and has an almost circular orbit. Earth’s atmosphere is mainly composed of nitrogen and oxygen and the average temperature at its surface, which is covered for over 70% by water, is about 15 degrees Celsius. The Moon is Earth’s only natural satellite and the only celestial object upon which humans have set foot.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 60,
"sub_idea_of": 7,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "There are millions of asteroids, which are remnants from the early formation of our Solar System",
"language_code": "en",
"headline": "There are millions of asteroids, which are remnants from the early formation of our Solar System",
"text": "Remnants from the early formation of the Solar System can be mainly found in the asteroid belt, located between the orbits of Mars and Jupiter, and the Edgeworth-Kuiper belt, located beyond Neptune’s orbit. These asteroids range in size from about 10 metres to 1000 kilometres and the combined mass of all the asteroids in the Solar System is less than the mass of Earth’s Moon.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 61,
"sub_idea_of": 7,
"sub_idea_number": 9,
"version_number": 2,
"headline_in_english": "A comet is an icy object that acquires a tail when it is heated by the Sun",
"language_code": "en",
"headline": "A comet is an icy object that acquires a tail when it is heated by the Sun",
"text": "Comets are mainly composed of ice, but they also contain dust and rocky material. The ice is volatile and evaporates when the comet approaches the Sun due to solar winds and radiation. This creates two tails – a dust tail that is slightly bent in the direction opposite to the comet’s movement, stretching for millions of kilometres, and a plasma tail which is straight and not often visible to the unaided eye. The comet’s tails always point in the opposite direction of the Sun, independently of the direction the comet is moving. Most comets are believed to come from two specific regions: the Edgeworth-Kuiper Belt, located beyond Neptune’s orbit, and the Oort Cloud, at the edges of the Solar System.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 62,
"sub_idea_of": 7,
"sub_idea_number": 10,
"version_number": 2,
"headline_in_english": "The boundary of the Solar System is called the Heliopause",
"language_code": "en",
"headline": "The boundary of the Solar System is called the Heliopause",
"text": "The magnetic field of the Sun stretches out far beyond its surface. This creates a bubble that encases the entire Solar System. The region where the magnetic field of the Sun interacts with the magnetic field of other stars is called the Heliosheath. The outer boundary of this roiling, turbulent region is called the Heliopause. Beyond the Heliopause lies interstellar space. In 2012, spacecraft Voyager 1 was the first human-made object to cross the Heliopause.",
"number_substitute": null,
"categories": [
"Solar System"
],
"category_ids": [
1
]
},
{
"sub_idea_id": 63,
"sub_idea_of": 8,
"sub_idea_number": 1,
"version_number": 2,
"headline_in_english": "A star is a self-luminous body generating its energy by internal nuclear reactions",
"language_code": "en",
"headline": "A star is a self-luminous body generating its energy by internal nuclear reactions",
"text": "Stars are composed of very hot plasma (a gas where the electrons and nuclei of atoms are largely separated) that is held together by its own gravity. The sustaining energy output of a star is generated by nuclear reactions taking place in its centre, which initially fuse hydrogen into helium, via the proton-proton chain (and for more massive stars via the carbon-nitrogen-oxygen CNO cycle) before moving onto fusing higher elements. Stars are stabilised by the pressure sustained via the energy set free during their central fusion processes, which counteracts the star’s urge to collapse under its own gravity. In this way, most stars of similar or less mass to our Sun remain stable for a few billions or even tens of billions of years.",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 64,
"sub_idea_of": 8,
"sub_idea_number": 2,
"version_number": 2,
"headline_in_english": "Stars form from massive clouds of dust and gas",
"language_code": "en",
"headline": "Stars form from massive clouds of dust and gas",
"text": "The gravitational collapse of giant cold molecular clouds gives birth to stars. As the cloud collapses, it fragments into cores whose central regions get ever denser and hotter. Beyond critical values for temperature and pressure, nuclear fusion ignites, and a star is born. This young star is initially surrounded by a protoplanetary disk of dust and gas. Over the course of millions of years, this disk differentiates into planets and smaller bodies.",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 65,
"sub_idea_of": 8,
"sub_idea_number": 3,
"version_number": 2,
"headline_in_english": "The closest star to Earth is the Sun",
"language_code": "en",
"headline": "The closest star to Earth is the Sun",
"text": "With an equatorial diameter of about 1.4 million kilometres, the Sun, the nearest star to Earth, is so big that we could fit roughly 1.3 million Earths inside. Even though our star is enormous compared to our planet, there are much bigger stars in the Universe. The supergiant VY Canis Majoris, with about 1400 times the diameter of the Sun, is the largest star known to date. If placed in the centre of the Solar System, the surface of VY Canis Majoris would extend beyond the orbit of Jupiter. There are also stars much smaller than the Sun. The closest star, Proxima Centauri, is a red dwarf with a diameter of about 200,000 kilometres, only 16 times the diameter of Earth.",
"number_substitute": null,
"categories": [
"The Sun"
],
"category_ids": [
5
]
},
{
"sub_idea_id": 66,
"sub_idea_of": 8,
"sub_idea_number": 4,
"version_number": 2,
"headline_in_english": "The Sun is a dynamic star",
"language_code": "en",
"headline": "The Sun is a dynamic star",
"text": "Although it seems uniform in appearance, the surface of the Sun can be mottled with dark spots. These sunspots, or regions of strong magnetic field, appear dark because they are cooler than the surrounding material. Every 11 years, the Sun cycles between producing many spots and producing a few spots. Sometimes, the Sun’s magnetic field gets twisted up, builds a lot of energy, and releases this energy in a burst of light and particles. These bursts are called flares or coronal mass ejections. But even when it is calm, the Sun constantly spews about 1.5 billion kilograms of hot, magnetized gas into space every second. This solar wind flows through the solar system and interacts with planets. Other stars also produce flares and winds.",
"number_substitute": null,
"categories": [
"The Sun"
],
"category_ids": [
5
]
},
{
"sub_idea_id": 67,
"sub_idea_of": 8,
"sub_idea_number": 5,
"version_number": 2,
"headline_in_english": "The colour of a star tells us its surface temperature",
"language_code": "en",
"headline": "The colour of a star tells us its surface temperature",
"text": "Stars can have surface temperatures between a few thousand degrees Celsius and fifty thousand degrees Celsius. Hot stars radiate away most of their energy in the blue and ultraviolet region of the electromagnetic spectrum (at short wavelengths), and thus look blueish to our eyes. Cooler stars look reddish, since they radiate away most of their energy in the red and infrared regions of the electromagnetic spectrum (at long wavelengths).",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 68,
"sub_idea_of": 8,
"sub_idea_number": 6,
"version_number": 2,
"headline_in_english": "The space between stars can be largely empty or it can contain clouds of gas, which can produce new stars",
"language_code": "en",
"headline": "The space between stars can be largely empty or it can contain clouds of gas, which can produce new stars",
"text": "The space between the stars contains minute traces of matter in the form of gas, dust and high energy particles (“cosmic rays”). This matter content is called the Interstellar Medium. It can be more or less dense in different parts of the galaxy. However, even the most dense regions of the Interstellar Medium are still one thousand times less dense than the best vacuum created in a laboratory.",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 69,
"sub_idea_of": 8,
"sub_idea_number": 7,
"version_number": 2,
"headline_in_english": "A star goes through a life cycle which is largely determined by its initial mass",
"language_code": "en",
"headline": "A star goes through a life cycle which is largely determined by its initial mass",
"text": "Computer simulations reveal that the first stars had life spans of some millions of years. In contrast, the average life expectancy of a star similar to the Sun is about 10 billion years. Low-mass red dwarf stars can live for trillions of years. A star with a mass similar to that of our Sun will eventually evolve into a red giant star and later on eject most of its mass to space, leaving behind a compact white dwarf star surrounded by what is called a planetary nebula. A star with at least eight solar masses will evolve into a red supergiant before exploding in an event called supernova, leaving behind a neutron star or a stellar black hole.",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 70,
"sub_idea_of": 8,
"sub_idea_number": 8,
"version_number": 2,
"headline_in_english": "Massive stars can end their life cycle as stellar black holes",
"language_code": "en",
"headline": "Massive stars can end their life cycle as stellar black holes",
"text": "A black hole is a region of space whose extreme gravitational field prevents anything, even light, from escaping once it has crossed the event horizon. The event horizon is a boundary surface surrounding a black hole, where the speed needed to escape its gravitational field is greater than the speed of light. Theoretical models predict that at the centre of a black hole is a singularity, where the density of matter and curvature of spacetime approaches infinity. Stellar mass black holes have masses in the order of a few tens of solar masses, in a region having a radius of some few kilometres to tens of kilometres (depending on the mass).",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 71,
"sub_idea_of": 8,
"sub_idea_number": 9,
"version_number": 2,
"headline_in_english": "New stars and their planetary systems are born from matter left behind by previous stars in that region",
"language_code": "en",
"headline": "New stars and their planetary systems are born from matter left behind by previous stars in that region",
"text": "Apart from hydrogen, most of the helium and a small amount of lithium, all elements in the present Universe have been produced inside stars by nuclear fusion. Low-mass stars, like the Sun, produce elements up to oxygen, while massive stars can create elements heavier than oxygen and up to iron. Elements heavier than iron, like gold and uranium, are created during high-energy supernova explosions and neutron star collisions. As they die, stars release most of their mass into the Interstellar Medium. From this matter, new stars form, in the cosmic version of a recycling process.",
"number_substitute": null,
"categories": [
"Stars"
],
"category_ids": [
2
]
},
{
"sub_idea_id": 72,
"sub_idea_of": 8,
"sub_idea_number": 10,
"version_number": 2,
"headline_in_english": "The human body consists of atoms that can be traced back to earlier stars",
"language_code": "en",
"headline": "The human body consists of atoms that can be traced back to earlier stars",
"text": "Elements other than hydrogen and helium and a small amount of lithium, were mainly created in the interior of stars, and released into space in th