Mini advanced:Sun

Graphical representation of the deflection by the Sun's gravitational field of a radio wave sent by the Cassini probe.

The Sun, by the Atmospheric imagery.

The Sun is the predominant star at the center of our Solar System, characterized as a massive, nearly perfect sphere of hot plasma. Its energy is generated through nuclear fusion reactions occurring in its core, where hydrogen nuclei combine to form helium, releasing vast amounts of energy in the process. This energy radiates from the Sun's surface primarily as visible light and infrared radiation, with approximately 10% emitted as ultraviolet radiation. The Sun serves as the essential energy source for life on Earth and has been a significant object of veneration and study across various cultures and scientific disciplines throughout history.

The Sun orbits the Galactic Center at a distance ranging from approximately 24,000 to 28,000 light-years. Its distance from Earth defines the astronomical unit (AU), which is about 93 million miles or roughly 8 light-minutes. The Sun's diameter is approximately 1.39 million kilometers (about 864,000 miles), making it roughly 109 times the diameter of Earth. In terms of mass, the Sun is about 330,000 times that of Earth, constituting approximately 99.86% of the total mass of the Solar System. The composition of the Sun is predominantly hydrogen (around 73%), followed by helium (approximately 25%), with trace amounts of heavier elements such as oxygen, carbon, neon, and iron.

Classified as a G-type main-sequence star (G2V), the Sun is often referred to as a yellow dwarf, although its emitted light is actually white. The formation of the Sun occurred approximately 4.6 billion years ago through the gravitational collapse of matter within a large molecular cloud. Most of this material coalesced at the center, while the remaining matter formed an orbiting protoplanetary disk that eventually gave rise to the Solar System. As the central mass became increasingly hot and dense, it initiated nuclear fusion in its core, a process that fuses about 600 billion kilograms of hydrogen into helium every second, converting approximately 4 billion kilograms of matter into energy.

In an estimated 4 to 7 billion years, as hydrogen fusion in the Sun's core diminishes, the Sun will no longer maintain hydrostatic equilibrium. This will result in a significant increase in core density and temperature, leading to the expansion of its outer layers and the transformation of the Sun into a red giant. Following this red giant phase, theoretical models suggest that the Sun will expel its outer layers, ultimately becoming a dense, cooling remnant known as a white dwarf. Although it will cease to produce energy through fusion, the white dwarf will continue to emit residual heat and light for potentially trillions of years. Eventually, it is hypothesized that the Sun will evolve into a super dense black dwarf, emitting negligible energy.

The Sun is a remarkable and vital component of our universe, playing an indispensable role in the sustenance of life on Earth and serving as a focal point for astronomical research and understanding of stellar evolution.