The Sun
Star · Yellow dwarf
The Sun is a star – a giant ball of hot gas. In its core, hydrogen atoms smash together to make helium, releasing the energy that lights and warms our planet. It holds about 99.8% of all the mass in the Solar System.
- 1.39 million kmAbout 109 Earths would fit side by side across it.
- ~5,500 °CSurface
- ~15 million °CCore
Take a closer look
Not a campfire
The Sun isn’t burning like a fire – there is no oxygen to burn. It is made of about three-quarters hydrogen and one-quarter helium, so hot that the gas becomes glowing plasma. Every second, its core turns about 4 million tonnes of matter into pure energy, and it has enough fuel left for billions of years.
Spots and storms
Sunspots are darker patches where tangled magnetic fields hold back the heat, and many are bigger than Earth. Their numbers rise and fall in a cycle of about 11 years. Near the busy peak, the Sun hurls out flares and giant clouds of gas that can light up auroras on Earth.
A wind from the Sun
The Sun constantly blows a stream of charged particles into space called the solar wind, racing outward at over a million kilometres per hour. It inflates an enormous bubble around all the planets, called the heliosphere. Voyager 1, launched in 1977, crossed its edge in 2012 and entered interstellar space.
Size it up
About 109 Earths would fit side by side across it. Both are drawn to the same scale.
How we found out
- 1543
Copernicus puts the Sun at the centre of the Solar System.
- 1610s
Galileo and others observe sunspots, showing the Sun changes and rotates.
- 1868
Astronomers discover a new element in sunlight and name it helium, after Helios, the Greek Sun god. It is found on Earth only in 1895.
- 1939
Hans Bethe explains how fusion powers the stars.
- 2024
NASA’s Parker Solar Probe flies just 6.1 million km from the Sun’s surface – the closest any human-made object has ever been.
What will happen when the Sun runs out of fuel?
In about 5 billion years it will swell into a red giant, then puff off its outer layers and shrink into a white dwarf about the size of Earth.
See it yourself
⚠️ NEVER look directly at the Sun, and never through binoculars or a telescope – it can blind you instantly. Use certified eclipse glasses or a pinhole projector.
From the encyclopedia
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