Sun
The Sun is the central star of the Solar System.
The Sun is the star at the center of our Solar System. It is a vast sphere of intensely hot plasma, glowing because nuclear fusion reactions in its core generate energy that radiates from its surface mostly as visible light and infrared radiation, with about 10% in ultraviolet. This energy is the primary driver of life on Earth. Across history, many cultures have revered the Sun, and it has been a focus of astronomical study since ancient times.
The Sun orbits the center of the Milky Way Galaxy, lying between 24,000 and 28,000 light-years from that center. Its average distance from Earth is roughly 8 light-minutes, a span once used to define the astronomical unit (au). As the largest and most massive object in the Solar System, its diameter is about 109 times that of Earth, and its mass is around 330,000 times Earth’s, accounting for approximately 99.86% of all mass in the Solar System. The Sun’s visible surface, the photosphere, is composed mostly of hydrogen (about 73%) and helium (about 25%), with smaller amounts of heavier elements like oxygen, carbon, neon, and iron.
The Sun formed roughly 4.6 billion years ago when matter in a region of a large molecular cloud collapsed under gravity. Most material gathered at the center, while the rest flattened into a rotating disk that became the Solar System. The central mass grew so hot and dense that nuclear fusion ignited in its core. Today, the Sun is classified as a G-type main-sequence star (G2V). Every second, its core fuses about 600 billion kilograms of hydrogen into helium, converting four billion kilograms of matter into energy.
In about four to seven billion years, when hydrogen fusion in the core slows enough to break hydrostatic equilibrium, the core will become denser and hotter, causing the outer layers to expand and turn the Sun into a red giant. After that phase, models suggest the Sun will shed its outer layers, leaving behind a dense, cooling white dwarf that no longer produces energy through fusion but will continue to glow and radiate heat from past fusion for perhaps trillions of years. Eventually, it is theorized to become a black dwarf, emitting negligible energy.
The English word "sun" comes from Old English, with cognates across Germanic languages such as West Frisian, Dutch, Low German, Standard German, Bavarian, Old Norse, and Gothic, all tracing back to Proto-Germanic.
Quick Facts
- Type
- G-type main-sequence star (G2V)
- Mass
- About 330,000 times that of Earth, making up about 99.86% of the total mass of the Solar System
- Distance from earth
- About 8 light-minutes (1 astronomical unit)
- Surface composition (photosphere)
- Hydrogen ~73%
- helium ~25%
- with smaller quantities of heavier elements
- Age
- Formed approximately 4.6 billion years ago
- Rotation period (equator)
- Approximately 25.6 days as seen from the stars
Facts from the source article.
Lore & Background
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 of hydrogen into helium and converts four billion kilograms of matter into energy.
The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years. It does not have a definite boundary; its radius is considered to be the distance from its centre to the edge of the photosphere. The Sun is the natural object closest to a perfect sphere ever observed, with an oblateness of about 8 parts per million. The Sun rotates faster at its equator than at its poles, with a rotational period of approximately 25.6 days at the equator and 33.5 days at the poles.
About four to seven billion years from now, when hydrogen fusion in the Sun's core diminishes, its core will undergo a marked increase in density and temperature, causing its outer layers to expand and transforming the Sun into a red giant. After that phase, models suggest the Sun will shed its outer layers and become a white dwarf, no longer producing energy by fusion but still glowing and giving off heat for perhaps trillions of years. It is then theorised to become an extremely dense black dwarf.
Reader's Guide
The Sun is the largest and most massive object in the Solar System, making up about 99.86% of its total mass. Its mean distance from Earth defines the astronomical unit. The Sun is a Population I, or heavy-element-rich, star, and its formation may have been triggered by shockwaves from one or more nearby supernovae. The English word 'sun' developed from Old English and has cognates across Germanic and other Indo-European languages; the principal adjectives are 'solar' (from Latin) and 'heliac' (from Greek). The astronomical symbol for the Sun is a circle with a central dot (☉), used for units such as solar mass (M☉), solar radius (R☉), and solar luminosity (L☉). The scientific study of the Sun is called heliology. The Sun's photosphere consists mainly of hydrogen and helium, with heavier elements accounting for less than 2% of the mass. The interior composition is not known, with estimates based on models of stellar nuclear reactions differing from those based on observations of solar seismology. The Sun's original chemical composition was inherited from the interstellar medium, originally about 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements.
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