The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radiation, and is the most important source of energy for life on Earth.

The Sun's radius is about 695,000 kilometers (432,000 miles), or 109 times that of Earth. Its mass is about 330,000 times that of Earth, comprising about 99.86% of the total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.

The Sun is a G-type main-sequence star (G2V). As such, it is informally, and not completely accurately, referred to as a yellow dwarf (its light is actually white). It 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 center, whereas 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 thought that almost all stars form by this process.

Every second, the Sun's core fuses about 600 million tons of hydrogen into helium, and in the process converts 4 million tons of matter into energy. This energy, which can take between 10,000 and 170,000 years to escape the core, is the source of the Sun's light and heat. When hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand, eventually transforming the Sun into a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable – but not for about five billion years. After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, and no longer produce energy by fusion, but still glow and give off heat from its previous fusion.

History

Ancient cultures often modified natural rock formations or built stone monuments to mark the motions of the sun and moon, charting the seasons, creating calendars and monitoring eclipses. Many believed the sun revolved around the Earth, with the ancient Greek scholar Ptolemy formalizing this "geocentric" model in 150 B.C. Then, in 1543, Nicolaus Copernicus(opens in new tab) described a heliocentric (sun-centered) model of the solar system, and in 1610, Galileo Galilei(opens in new tab)'s discovery of Jupiter's moons confirmed that not all heavenly bodies circled Earth.

To learn more about how the sun and other stars work, after early observations using rockets, scientists began studying the sun from Earth orbit. NASA launched a series of eight orbiting observatories known as the Orbiting Solar Observatory (opens in new tab)between 1962 and 1971. Seven of them were successful, and analyzed the sun at ultraviolet and X-ray wavelengths and photographed the super-hot corona, among other achievements.

In 1990, NASA and the European Space Agency launched the Ulysses (opens in new tab)probe to make the first observations of its polar regions. In 2004, NASA's Genesis spacecraft returned samples of the solar wind(opens in new tab) to Earth for study. In 2007, NASA's double-spacecraft Solar Terrestrial Relations Observatory(opens in new tab) (STEREO) mission returned the first three-dimensional images of the sun. NASA lost contact with STEREO-B in 2014, which remained out of contact except for a brief period in 2016. STEREO-A remains fully functional.

The Solar and Heliospheric Observatory(opens in new tab) (SOHO), which last year celebrated 25 years in space, has been one of the most important solar missions to date. Designed to study the solar wind, as well as the sun's outer layers and interior structure, it has imaged the structure of sunspots below the surface, measured the acceleration of the solar wind, discovered coronal waves and solar tornadoes, found more than 1,000 comets, and revolutionized our ability to forecast space weather.

Megathreads and spaces to hang out:

reminders:

  • 💚 You nerds can join specific comms to see posts about all sorts of topics
  • 💙 Hexbear’s algorithm prioritizes struggle sessions over upbears
  • 💜 Sorting by new you nerd
  • 🌈 If you ever want to make your own megathread, you can go here nerd
  • 🐶 Join the unofficial Hexbear-adjacent Mastodon instance toots.matapacos.dog

Links To Resources (Aid and Theory):

Aid:

Theory:

Remember nerds, no current struggle session discussion here to the general megathread, i will ban you from the comm and remove your comment, have a good day/night :meow-coffee: