Concept

Sun

Overview

The Sun is the star located at the centre of the Solar System. It is a massive sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies. It is the main source of energy for life on Earth. The Sun has been an object of veneration in many cultures and a central subject of astronomical research since antiquity.

The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years. Its mean distance from Earth is about 1.496×108 kilometres or about 8 light-minutes. The distance between the Sun and the Earth was used to define a unit of length called the astronomical unit (au), now defined to be 149.5978707×106 kilometres. It is the largest and most massive object in the Solar System; its diameter is about 1,391,400 km (864,600 mi), around 109 times that of Earth. The Sun's mass is around 330,000 times that of Earth, making up about 99.86% of the total mass of the Solar System. The mass of the Sun's surface layer, its photosphere, consists mostly of hydrogen (~73%) and helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.

The Sun formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the centre; the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is now classified as a G-type main-sequence star (G2V). Every second, the Sun's core fuses about 600 billion kilograms (kg) of hydrogen into helium and converts 4 billion kilograms of matter into energy.

About 4 to 7 billion years from now, when hydrogen fusion in the Sun's core diminishes to the point where the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature which will cause its outer layers to expand, eventually transforming the Sun into a red giant. After the red giant phase, models suggest the Sun will shed its outer layers and become a dense type of cooling star (a white dwarf), and no longer produce energy by fusion, but will still glow and give off heat from its previous fusion for perhaps trillions of years. After that, it is theorised to become an extremely dense black dwarf, giving off negligible energy.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

In the original texts

Passages from public-domain books where Sun is discussed.

Anaximander says, that the sun is a circle eight and twenty times bigger than the earth, and has a circumference very much like that of a chariot-wheel, which is hollow and full of fire; the fire of which appears to us through its mouth, as by an aperture in a pipe; and this is the sun. Xenophanes, that the sun is constituted of small bodies of fire compacted together and raised from a moist exhalation, which…
Plutarch, Complete Works of Plutarch — Volume 3
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The conception of the Sun's constitution thus set forth, is like that of M. Faye in so far as the successive changes, the resulting structures, and the ultimate state, are concerned; but unlike it in so far as the Sun is supposed to have reached a later stage of concentration. As I gather from your abstract of M.
Herbert Spencer, Essays
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At a temperature approaching a thousand times that of molten iron, which is the calculated temperature of the solar surface, very many, if not all, of the substances we know as solid, would become gaseous; and though the Sun's enormous attractive force must be a powerful check on this tendency to assume the form of vapour, yet it cannot be questioned that if the body of the Sun consists of molten substances, some of…
Herbert Spencer, Illustrations of Universal Progress
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6. The sixth is meridianal setting; when the star is found on the occidental horizon, while the Sun is on the meridian. Of this, one species is diurnal and invisible; when the star sets while the Sun is above the earth on the meridian: the other is nocturnal and visible; when the star sets while the Sun is on the meridian below the earth. 7. The seventh aspect is called vespertine subsolar; when the star is found on…
Ptolemy, Ptolemy's Tetrabiblos
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In the heavens, the Sun and Moon are, by interpreters of dreams, put for the persons of Kings and Queens; but in sacred Prophecy, which regards not single persons, the Sun is put for the whole species and race of Kings, in the kingdom or kingdoms of the world politic, shining with regal power and glory; the Moon for the body of the common people, considered as the King's wife; the Stars for subordinate Princes and…
Isaac Newton, Observations upon the Prophecies of Daniel, and the Apocalypse of St. John
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Sun

Overview

In the original texts

Philosophers who discussed Sun

Related ideas

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