Our Closest Star

Proxima Centauri 300s exposure 2020-08-25 Copyright Roger Powell

Proxima Centauri

Designations:     V645 Centauri, HIP70890.
Magnitude: +11.
Diameter:8.48% of the Sun.
Distance:4.24 light years.
Image date and exposure:25th August 2020. 10 x 30 sec.
Field of View:47.8 x 31.7 arcmin; up is 174° E of N.

Triple Star System

Proxima Centauri is understood to be in a wide orbit around the binary system, Alpha Centauri A and Alpha Centauri B, two Sun-like stars which orbit each other.

It’s hard to grasp that it is currently more than 2° 11′ from Alpha Centauri.

Proxima lies about 15,000 Astronomical Units (0.2 light years) from the much tighter orbits of the binary pair and if its membership of the Alpha Centauri System is verified, it’s orbital period would be about a million years.


The Alpha Centauri system is the closest star system to our Solar System and of its three stars, Proxima is currently the closest – a mere 4.24 light years away from us. It only looks bright in the image because it is much closer than the other more remote stars.

Despite it’s proximity to us, Proxima is a very tiny faint type M star, a red dwarf, located in a star-rich region of the Milky Way – and it moves. So it is difficult to pin down.

Tracking it Down

During the execution of the imaging, I could not be certain which of the many stars on my monitor represented the target. It was fun tracking it down with a spot of research the next day.

The best planetarium software I have (Sky Safari Pro v6) only displays about half of the stars shown in my image. At least it does show Proxima and after an hour of comparing the star patterns around Proxima in Sky Safari with the many stars in my image, I tracked down the exact spot where it was supposed to be.

There was nothing there! 😨

Proper Motion

Proxima has an apparent motion of nearly four arc-seconds per year, which is a lot, so I checked the settings in Sky Safari and sure enough, whilst it was correctly displaying Epoch J2000.0, the “Proper Motion” box was not selected. As soon as I ticked it, Proxima disappeared and reappeared about 77 arc-seconds away.

Back to my image and “bingo”, there it was!

Never before have I had to worry about a star’s proper motion. So, based on a reverse image of my photo, here is the motion of Proxima from 1980 to 2020:

Proxima’s motion over forty years reminded me of the motion I “discovered” when I imaged dwarf planet Pluto twice in eight days – but Pluto was only 30 AU from the Sun. For context, Proxima is about 266,840 AU from the Sun.

Interesting facts

  1. According to Wolfram Alpha, whilst light from Proxima takes 4.2 years to reach us, it would take 6.3 years if travelling that distance by optical fibre. The things you learn!

2. Proxima is also a UV Ceti flare type variable star, so don’t pin your SETI hopes on finding any alien civilisations living there.

I hope you enjoyed reading about our nearest neighbouring star.

That’s it. Thanks for reading.

Telescope Details
SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Field flattener; No filter; 2x Powermate
SkyWatcher EQ6-R Pro mount; ZWO ASI120 guide camera.
Camera: ZWO ASI 071 MC Pro (CMOS 28.4mm 16 Mpx).
Software: PHD2; SharpCap, Gimp, EQMOD with Carte du Ciel.
Observatory latitude: 34° South.

See annotated image at Astrometry.net


    1. We’ve been having lots of haze from fires in the western states. It is drifting over the central US. I’m sure you know how that makes the sky look after your recent fires.

      Liked by 1 person

      1. Thanks.

        Yes, I’ve just been reading about the fires in California. It’s a terrible time over there – again. I heard that some of our fire-fighters are heading over there soon.

        Our bushfire season “officially” begins in about five weeks but we’ve had some rain, so maybe it will hold off a bit longer.

        Meanwhile, we are prisoners in our own home.


        1. The air has cleared here the past two days. The winds are carrying smoke elsewhere. And, yes we are prisoners, too. The university semester started last Monday. Thousands of students are in town and hitting the bars. Our case numbers in town are rising very rapidly. Residents are being asked to be extra vigilant about exposure. Public schools are trying to start their year now. It isn’t going well for those doing face-to-face classes.


          1. Pubs, clubs & restaurants, are big spreaders here – I don’t understand why anyone would want to go there.
            Workplaces, churches & schools too – but aged care facilities are the worst affected.

            It looks like we’re controlling the second wave now but we are not going out.


  1. Hi Roger, I was so pleased to read about and see your research. I have special interest in Alpha Centauri that is very dear to my heart., Thank you.
    Hope all goes well for you.

    Liked by 1 person

  2. I thought the Sun was the closest star . . .

    Nice research and hard to imagine a 1M years orbital period . . . and it dosn’t get any easier if I try to imagine four 250K years orbital periods.

    Liked by 1 person

    1. Astronomers believe Proxima to be in orbit around Alpha Centauri but there is still a degree of uncertainty. It will probably be confirmed in a few thousand years….. 😑

      Part of the joy of astronomy is to be boggled by the incomprehensibly extreme numbers involved. I’m glad it worked for you.

      By the way, it always makes me smile when I hear people refer to large numbers as being of “biblical proportions”, which to me translates as: “exaggerated but easily comprehended numbers which are most likely fictional”.

      Liked by 1 person

      1. Biblical numbers are pretty small, really . . . 6 days to make everything, 800 years lifespans (OK, that’s a bit long), and the universe only 6,000 years old, a dearth of first-born. Twelve apostles, and only one savior, and he didn’t even hang around for the post-interview after his gig. Three days, and see ya!

        . . . although, some say he visited North America before leaving.

        Liked by 1 person

        1. Well, sticking to an astronomy theme, they say there are billions of Earth-like planets out there. If his Dad makes him “die” on a cross each time a semi-advanced civilisation arises somewhere in the Universe, he might be about half-way through them by now – and getting a bit sick of doing it.

          Liked by 1 person

  3. Great stuff! That is real astronomy and astrometry you’re doing there! Clyde Tombaugh would be proud. He lived right here in my hometown and taught physics and astronomy at New Mexico State for awhile.

    Liked by 1 person

  4. Love this real time (sorta) tracking down of Proxima Centauri, and the ensuing comments. Related, I’ve come across a few additional notes about my search for Pluto many years ago, in as much …a little bit similar to your insanely impressive tracking of Proxima, and will post a note about that shortly. As you know we are now under that forest fire pale, as one tv newscaster sail last night, it would not be a good time for star gazing! M 🙂

    Liked by 2 people

    1. It was an interesting exercise and it taught me the importance of ensuring the star chart is adjusted to the current year.

      I look forward to your notes. Doing it through the eyepiece by star hopping to a mag 14 object is much more impressive than my photographic method. I’d like to know more about how you did it.



  5. Hi Roger,
    You’ve done it again. Your extraordinary research and photos are so appreciated. Thank you.


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