The Sun

Our own star. Never look straight at it. You could pour more than a million Earths inside the Sun — and still have room! Line up 109 Earths in a row and they would just stretch across it.

What it is

Our star — almost all the material in the whole solar system, mostly hydrogen and helium.

Star: A ball of gas with enough mass to fuse hydrogen in its core. Every kind of thing there is →

How to find the Sun

What you will really see

Worth knowing about the Sun

About 109 Earth diameters across — line up 109 Earths side by side and they'd just span the Sun. Out of every 1,000 parts of the solar system, the Sun is 998 of them. Everything else — every planet, moon, asteroid and comet put together — shares the last 2. All that material means the Sun's gravity overwhelms everything else's, which is exactly why everything circles the Sun and not the other way round.

What it is made of

For every 100 kilograms of the Sun, about 73 are hydrogen and 25 are helium, leaving barely 2 for everything else. Down in the core it is hot and squeezed enough that hydrogen fuses into more helium, and that is where our daylight comes from.

How we know: Nobody has ever gone near the Sun's core — scientists split sunlight into a rainbow spectrum and read the dark lines different elements leave behind, like a chemical fingerprint. The core temperature comes from physics models of nuclear fusion, checked against real vibrations on the Sun's surface called 'sunquakes'.

Its weather

Yes, the Sun has weather! Giant magnetic storms called solar flares and eruptions called coronal mass ejections blast material into space and can cause auroras on Earth. Dark 'sunspots' come and go in an 11-year cycle.

Rotation

Unlike Earth, the Sun isn't solid, so it doesn't spin around all in one piece. Its middle (the equator) spins all the way around in about 27 days, but its top and bottom (the poles) lag behind, taking closer to 36 days — only a giant ball of gas could get away with that.

How we know: Tracked by watching sunspots and other surface features drift at different speeds depending on latitude, and confirmed by Doppler-shift measurements of the surface plasma itself.

What makes it worth knowing

Never look at it directly without a proper solar filter.

Seen next to things you know

How anyone knows this

Nobody flew a tape measure out there. Every number on this page was worked out from the ground:

• How far away is the Sun?
• How a star is born, and how it ends

What it belongs to

Then go outside

Clear tonight? The Planetarium will show you what is worth a look. Then just go out.