Where is Proxima Centauri?

Editor’s Note: Proxima Centauri is the nearest star to Earth. It’s part of the triple Alpha Centauri star system, visible as a single star from very southerly latitudes in the Northern Hemisphere and best seen from the Southern Hemisphere. Generally speaking, the three stars in the Alpha Centauri system are 4.4 light-years away. Proxima is the closest of the three at 4.2 light-years. But where is Proxima Centauri?

Where is Proxima Centauri?

The diagram above shows you where Alpha Centauri is with respect to other nearby stars. Included are stars within 12 light-years from the sun. The glows of light representing the stars are millions of times larger than the stars themselves, which would be microscopically small on this scale.

The grid serves to show Earth’s equatorial plane – the plane of our celestial equator – and also the scale. Note that the lines are four light-years apart. The slightly thicker line is the vernal equinox direction (the Earth-sun direction in space, around every March 20).

Imaginary stalks from the equatorial plane to the stars show how far north or south they are. I’ve cropped the picture so that some of the stars are off the top or bottom. But they are obscure stars you might not have heard of, with designations such as Lalande 21185, Luyten 726-8 and DX Cancri. Most stars, including most of those near to us, are smaller than our sun: red dwarfs.

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Proxima, in context

The exceptions near to us are Sirius, Procyon and Alpha Centauri.

The Alpha Centauri system – which includes the star Proxima – is the 3rd-brightest star in our sky. That is, it’s 3rd-brightest as seen from our place in space, and not counting our sun. Like the 1st- and 2nd-brightest stars – Sirius and Canopus – it is a southern star. Indeed it’s much farther south on our sky’s dome than either of those, which is why it has no traditional name in our culture (except a rather faux-traditional one, Rigil Kentaurus).

Notice the stalk to Alpha Centauri on the space diagram above. It shows it at a steep southward angle from our sun. This angle (its declination -61°) means it doesn’t peep above the horizon until you go down to the latitude of northern Florida.

To see it properly, you might go south of Earth’s equator.

Want to know more about Proxima? Check out the video below:

More about Alpha Centauri

In a telescope, Alpha Centauri appears as a double star. Yes, it’s really triple, but Proxima is tiny and not easy to see. The other two stars in the Alpha Centauri system comprise one of the widest and easiest to “split” double stars in our sky. Here is part of my diagram of the pair with which I used to fill a space in Astronomical Calendar 2016:

Again, the symbols for the stars are vastly larger than the bodies of the stars would be. It isn’t really that the B star revolves around the A one: they both revolve around their common center of gravity.

You can see that this year of the diagram, 2016, is the year when B appeared closest to A, though in the true (untilted) orbit it will reach periastron in 2035. The blue lines are one second of arc apart; that’s the apparent size of a tennis ball 10 miles away.

Alpha Centauri A is a star much like the sun, slightly larger and of about the same 4.6-billion-year age or slightly older. Alpha Centauri B is slightly smaller and cooler. In their elliptical orbits around their common center of gravity, they range from about 11 astronomical units (sun-Earth distances) apart when closest, to 36 when farthest apart. In other words, they range from something like the sun-Saturn to something like the sun-Pluto distance.

Proxima Centauri again

And the distance of the Alpha Centauri system from us is only 4.4 light-years: nearer than all other stars … except for one, Proxima, discovered in 1915 (by Robert Jones in South Africa).

Proxima is one of those numerous dwarfs whose surfaces are reddish, meaning cooler and dimmer. Only about 1/7 as wide as the sun, and at a magnitude (brightness) of 11, it is about 100 times too dim to be seen with the unaided eye. Proxima is more than two degrees away from the Alpha Centauri pair; on observatory photographs, there are thousands of background stars in between.

Yet studies of it found that it is only 4.24 light-years away from us, closer than the other two stars in the Alpha Centauri system.

Hence it is dubbed Proxima Centauri, with the word Proxima having the same root as the word proximity, meaning near.

The nearest stars not only have the largest parallax (apparent angular shift as we go around the sun) but are liable to have large proper motion (travel across the starry background from year to year). Proxima is found to be still coming gradually toward us; it will be nearest, at only about three light-years, about 27,000 years into the future. And it is probably, though not quite certainly, gravitationally bound to the Alpha Centauri pair 0.2 light-year away from it, in an enormous, slow orbit of something like 500,000 years. So it can be called Alpha Centauri C.

Humbling distances

Yes, these are humiliating numbers, and I hesitate to crush you further with the reminder that a light-year is nearly 6,000,000,000,000 miles, and the distance across the Milky Way galaxy is something like 30,000 times greater than the distance to these our nearest neighbors in it.

Thus, even if there is a Proximan with a telephone, and one day you receive a call from her asking:

What is your name, how many legs do you have, and how many sexes are there in your world?

… It will be more than four years before she receives your reply and more than eight before you know what she thinks of it.

Bottom line: Diagram and explanation from astronomer Guy Ottewell, showing the location in space of the Alpha Centauri system and, in particular, the star Proxima Centauri, the nearest star to Earth.

Read more: Proxima Centauri, the closest star to our sun