Mini intermediate:Sun

The Sun, and the Solar System.

The Sun is the star at the center of our Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions occurring in its core. This process radiates energy from its surface primarily as visible light and infrared radiation, with about 10% emitted as ultraviolet energy. The Sun is the most important source of energy for life on Earth and has been revered in many cultures throughout history. It has also been a central focus of astronomical research since ancient times.

The Sun orbits the Galactic Center at a distance of approximately 24,000 to 28,000 light-years. Its distance from Earth defines the astronomical unit, which is about 93 million miles or roughly 8 light-minutes. The Sun's diameter is about 864,000 miles, making it about 109 times wider than Earth. In terms of mass, the Sun is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. Approximately three-quarters of the Sun's mass is hydrogen (around 73%), while the rest is mostly helium (about 25%), along with trace amounts of heavier elements such as oxygen, carbon, neon, and iron.

The Sun is classified as a G-type main-sequence star (G2V), commonly referred to as a yellow dwarf, although its light is actually white. It formed around 4.6 billion years ago from the gravitational collapse of matter within a large molecular cloud. Most of this matter accumulated in the center, while the remaining material flattened into an orbiting disk that eventually became the Solar System. The central mass became so hot and dense that it initiated nuclear fusion in its core. Every second, the Sun fuses about 600 billion kilograms of hydrogen into helium and converts 4 billion kilograms of matter into energy.

In about 4 to 7 billion years, when hydrogen fusion in the Sun's core decreases significantly, the Sun will no longer be in hydrostatic equilibrium. This will lead to an increase in density and temperature in its core, causing its outer layers to expand and transforming the Sun into a red giant. After this red giant phase, models suggest that the Sun will shed its outer layers and become a dense, cooling star known as a white dwarf. Although it will no longer produce energy through fusion, it will continue to glow and emit heat from its previous fusion for potentially trillions of years. Eventually, it is theorized that the Sun will become a super dense black dwarf, giving off negligible energy.

The Sun is a fascinating and vital part of our universe, playing a crucial role in the existence of life on Earth.