The Sun

The Sun

Our star, the Sun, makes up 99% of all the mass in the Solar System. Its core is so dense and hot that normally repellent nuclei fuse together in nuclear reactions that produce vast amounts of energy.

The Sun is mostly hydrogen (its main fuel) and helium, and radiates charged particles called solar wind across the Solar System. Phenomena such as solar flares and sunspots are evidence of the Sun's strong magnetic field, which changes on a roughly 11-year cycle.

Read about eye safety during solar eclipses on the NASA website.

Photo: The Sun taken by the SOHO probe (ESA/NASA)

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The Sun

About Sun

The Sun's core powers the Solar System.

About Sun

The Sun[a] is the star at the center of the Solar System. It is by far the most important source of energy for life on Earth. The Sun is a nearly perfect spherical ball of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. The diameter of the Sun is about 109 times that of Earth, and it has a mass about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. Chemically, about three quarters of the Sun's mass consists of hydrogen, whereas the rest is mostly helium, and much smaller quantities of heavier elements, including oxygen, carbon, neon and iron.

The Sun is a G-type main-sequence star (G2V) based on spectral class and it is informally designated as a yellow dwarf. It formed approximately 4.567 billion[b] 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 increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all stars form by this process. The Sun is roughly middle age and has not changed dramatically for four billion[b] years, and will remain fairly stable for four billion more. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes and become a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury, Venus, and possibly Earth.

The enormous effect of the Sun on the Earth has been recognized since prehistoric times, and the Sun has been regarded by some cultures as a deity. Earth's movement around the Sun is the basis of the solar calendar, which is the predominant calendar in use today.

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