The nearest stars

The Sun is a star, and the other stars are suns. They look like tiny points only because they are so far away.

The nearest one is called Proxima Centauri. Its light takes four and a quarter years to get here, so we say it is 4.25 light years away. Sunlight reaches the Earth in about eight minutes.

You might expect the nearest star to be a bright one. It is not. Proxima is a red dwarf, a small, cool star so dim that you need a telescope to see it at all.

Most of the Sun’s neighbours are like that. In the list of stars this site draws, there are 108 within 20 light years, and 85 of them are far too faint to see by eye. Only six give out more light than the Sun.

So the night sky gives the wrong idea. The stars you can see are the rare, powerful ones that show up from a long way off. The ordinary stars, the small red ones, are all around us and invisible.

In the 3D view every dot is a real star, placed where a catalogue of measured positions puts it.

The space round the Sun is the one part of the galaxy where we can count nearly every star, including the faint ones. That makes it the fairest sample we have of what stars are really like.

The nearest. These are the named stars within 10 light years in the catalogue this site draws. The distances are the catalogue’s, rounded, except Alpha Centauri’s 4.4, which comes from a newer measurement (1.338 parsecs) than the catalogue holds. Brightness is visible light only, compared with the Sun.

Star	Distance	Visible light, Sun = 1
Proxima Centauri	4.2 light years	About 1/17,000
Alpha Centauri A (Rigil Kentaurus)	4.4	1.5
Alpha Centauri B (Toliman)	4.4	0.4
Barnard’s Star	5.9	About 1/2,300
Wolf 359	7.8	About 1/50,000
Lalande 21185	8.3	About 1/180
Sirius	8.6	22
Ross 154	9.7	About 1/1,900

Two of the eight outshine the Sun. Five are red dwarfs, hundreds or thousands of times fainter. The column counts visible light only. Cool stars also give out infrared, which the eye cannot see and this column leaves out.

How the distances are known. As the Earth goes round the Sun, a nearby star seems to shift a little against the distant ones. The size of the shift gives the distance directly, with no guesswork about the star itself. This is parallax. Proxima’s shift is 0.768 arcseconds, the largest of any star, and even that is tiny. The Gaia spacecraft has measured such shifts for well over a billion stars.

The nearest system is three stars. Alpha Centauri A and B are a close pair, and A gives out about one and a half times the Sun’s visible light. Proxima goes round the two of them a long way out, about once in 550,000 years. More than half of all stars have at least one partner, so a single star like the Sun is not the rule.

A planet next door. Proxima has a planet of about the mass of the Earth. It goes round every 11.2 days, at a distance where water could be liquid. Whether it has air or water is not known.

Why the sky misleads. A star’s brightness in the sky depends on two things: how much light it gives out and how far away it is. Sirius is the brightest star in the night sky mostly because it is close. Rigel, in Orion, gives out about 2,000 times more light from a hundred times further off. Meanwhile most of the stars within 20 light years cannot be seen at all. Count the stars you can see and you would think most stars are giants. Count the stars that are really there and the typical star is small, red and dim.

How far that is. Voyager 1, launched in 1977, is the most distant thing people have made. After nearly fifty years it is about one light day from the Sun. Proxima is 1,550 times further.

Small and long-lived. Red dwarfs are the smallest stars that shine by fusion, a fraction of the Sun’s size and mass. They use their fuel so slowly, and stir it so thoroughly, that they can last for trillions of years. Some are expected to live longer than the universe has existed so far.