The Sun

The Sun is the star at the centre of the solar system and the source of nearly all the energy that sustains life on Earth. It is an enormous ball of hot, glowing gas, mostly hydrogen and helium, far larger than any planet; it contains the great majority of the solar system's mass, and its gravity holds the planets in their orbits. By cosmic standards it is an ordinary middle-aged star, one of an immense number in the Milky Way galaxy.

The Sun's energy comes from nuclear fusion in its core, where extreme heat and pressure fuse hydrogen nuclei into helium and release vast amounts of energy. This energy slowly works its way outward and finally escapes from the visible surface, the photosphere, as light and heat that cross space to reach the planets. Above the photosphere lie the thin outer layers, including the faint corona that becomes visible during a total solar eclipse when the Moon blocks the bright disc.

The Sun's surface is not uniform. Sunspots are cooler, darker regions linked to its magnetic field, and their numbers rise and fall over a cycle of roughly eleven years. Magnetic activity also drives solar flares and large eruptions of charged particles, which can reach Earth and produce auroras and occasional disturbances to communications and power systems. Because of its brightness, the Sun must never be viewed directly without proper protection, as its light can permanently damage the eyes.

Frequently asked questions

How does the Sun produce its energy?

By nuclear fusion in its core, where hydrogen nuclei combine to form helium under intense heat and pressure, releasing energy that radiates outward as light and heat.

What are sunspots?

Cooler, darker patches on the Sun's surface caused by its magnetic field. Their numbers vary over a cycle of about eleven years.

Why is it dangerous to look directly at the Sun?

Its light is intense enough to permanently injure the eyes. Safe viewing requires proper filters or indirect projection methods.