Halley's Comet

Halley's comet comes back every 75 years or so, which means most people see it once if they are lucky — next time is 2061! People have been writing down its visits for more than two thousand years.

Also called: Halleys Comet.

What it is

Famous short-period comet, returns every 76 years, next in 2061.

Comet: A dirty snowball that grows a tail near the Sun. Every kind of thing there is →

How to find Halley's Comet

What you will really see

Worth knowing about Halley's Comet

Halley's Comet is about as long as 150 football pitches end to end — a three-hour walk. Made of ice, dust and rock: a 'dirty snowball'. If Earth were a fully loaded container ship, Halley's Comet would be a single coin lying on the deck. Sunlight takes 2.5 hours to reach Halley's Comet — on average, because that distance changes as it goes round. Its day: complex, tumbling rotation — no single simple 'day length'.

Its weather

As it nears the Sun, its ice turns straight to gas, creating the glowing coma and long tail that always points away from the Sun.

How it moves

You might get to see it twice in your lifetime if you're lucky — it returns every 76 years.

How we know: Astronomer Edmond Halley realized in 1705 that comets seen in 1531, 1607, and 1682 all had nearly identical paths — using Newton's new laws of gravity, he figured out they were the same comet and correctly predicted its return in 1758 (he didn't live to see it, but it showed up right on schedule).

The machines we sent

The Giotto spacecraft flew past its nucleus in 1986, the first close-up comet pictures.

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:

• Eclipses, conjunctions and other sky events

What it belongs to

Then go outside

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