An image of the sun with arcs of light leaping from its surface.

Eclipse of the Sun by the Earth. Image courtesy of Flowers Gallery. © NASA SDO/GSFC/Michael Benson, Kinetikon Pictures

Factfile: the Sun

The last 100 years have transformed our understanding of the Sun, but our star's inner workings are yet to be fully understood.

The Sun is a 4.6-billion-year-old ball of raging plasma constituting 99.86 per cent of the total mass of our solar system. All of the other bodies in our solar system, from planets to asteroids, are remnants of the disc-shaped nebula that collapsed to form our star.

It wasn't until 1920 that nuclear fusion was proposed as the source of the Sun's heat. Around 70 per cent of the sun is made up of hydrogen, which is gradually converted to helium in a nuclear fusion process that releases extraordinary quantities of energy.

Coronal loops

This image of the Sun, one of 77 photographs appearing in Otherworlds: Visions of our Solar System, shows our star partly eclipsed by a silhouette of Earth.

The bright arcs shown erupting from the surface of the sun are coronal loops: arcs of plasma that follow the curvature of the Sun's magnetic field, like iron filings around a magnet.

The star's powerful magnetic field is generated by physical processes known as the solar dynamo. It is thought that electric currents generated by flows of ionised plasma within the Sun help produce the magnetic field, but the exact mechanisms of the solar dynamo are yet to be fully understood.

Audio commentary extract

Dr Emma Humphreys-Williams, an analytical chemist at the Museum, discusses how she uses plasma from a 'mini sun' in her daily research. 

Extraterrestrial materials

Explore the Museum's research on the moon, sun, Mars, comets and asteroids.