Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma intervoven with magnetic fields. It has a diameter of about 1,392,684 km (865,374 mi), around 109 times that of Earth, and its mass accounts about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen, while the rest is mosly helium.

The sun formed about 4.567 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, while the rest flattened into an orbiting disk that would become the Solar System. The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all stars form by this process. In the spectral class label, G2 indicates its surface temperature, of approximately 5778 L (5505 ºC, 9941 ºF).

Once regarded by astronomers as a small and relatively insignificant star, the Sun is now though to be brighter than about 85% of the stars in the Milky Way. The Sun is by far the brightest object in the Earth's sky with the apparent magnitude of -26.74. This is about 13 billion times brighter than the next brightest star, Sirius, with an apprent magnitude of -1.46.

The mean distance of the Sun from the Earth is approximately 1 astronomical unit (about 150,000,000 km; 93,000,000 mi) though the distance varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from Sun to Earth in about 8 minutes and 19 seconds.