Alpha Centauri A & B

The nearest stars to us look like one bright star, but there are two of them going round each other — and both are rather like our Sun! Even so, the fastest spacecraft we have would take tens of thousands of years.

Also called: the nearest star system.

🕒 When can I see it?🚀 Travel there

Alpha Centauri A & B — Drawn, not photographed.

What it is

Bright binary of two Sun-like stars, appears as one bright naked-eye 'star', splits in any small telescope.

Binary star system: Two stars orbiting each other. Most stars are in pairs. Every kind of thing there is →

How to find Alpha Centauri A & B

Look in the constellation Centaurus.

Too far south to rise for most of the Northern Hemisphere.

Finding it: One of the bright 'Pointer' stars beside the Southern Cross.

The Planetarium works out where it actually is from your own place and the date — including whether it is above the horizon at all tonight.

Show me Alpha Centauri A & B in tonight's sky

What you will really see

With your own eyes

A bright point of light — even big telescopes can't show a star as a disc. Some doubles split into two points!

🔭 See it drawn as it looks through a telescope

🖨️ A sheet to print for this

🖨️ Print a sheet and go and look

🖨️ Sheet to take outside →

Worth knowing about Alpha Centauri A & B

In weight, a has a bit more mass than the Sun, B a bit less. On the 100-meter-track scale model of the Milky Way, Alpha Centauri would be about 4 millimetres from the Sun — roughly the length of a grain of rice. Light takes 4.4 Earth years to get here from Alpha Centauri A & B, so what you are looking at is Alpha Centauri A & B as it was 4.4 Earth years ago.

How bright it is: A shines a bit brighter than the Sun, B noticeably dimmer.
What it is made of: Two Sun-like stars (one slightly bigger/hotter, one slightly smaller/cooler) locked in a close orbit, forming one bright naked-eye 'star'.
How it moves: Orbit each other over roughly 80 years.; How we know: Astronomers tracked the two stars' positions for over a century, confirmed with Kepler's and Newton's laws. Rung 5 of the cosmic ladder — the distance to the stars
What makes it worth knowing: More than half of Sun-like stars in the galaxy have a companion star like this.