Pluto wanders into a Messier situation

By Phil Plait | September 20, 2010 7:00 am

When Pluto was discovered 80 years ago, it happened to be moving through Gemini, a part of the sky that had a lot of stars. Clyde Tombaugh did an amazing job finding it, since it was almost lost among those stars.

I wonder if he could’ve found it had he been looking earlier this year? "Amateur" astronomer Anthony Ayiomamitis sent me this image he took of Pluto as was in Sagittarius, the most densely-packed area of the sky!


[Click to undwarfplanetate.]

Hard to spot, isn’t it? Pluto is unresolved in the picture, so it looks like just another star. And there are a lot of stars here; this region of sky is actually a cluster called Messier 24 (or just M24, and it’s pronounced "MEZ-ee-ay", since Charles Messier was French); the two dark splotches are thick dust clouds called Barnard 92 and 93. Finding Pluto in this ain’t easy.

… or is it? When I first looked over the picture, I found Pluto almost immediately, and then laughed, because I know a secret. First, take a look… can you find it?

ayiomamitis_pluto2OK, here’s the secret: this is a color picture, which means Anthony had to take four images, one each through a red, green, and blue filter, and one unfiltered. The stars all look good because they don’t move, but by the time he took the red image Pluto had moved a bit compared to the stars’ positions. So when my eye happened to catch a bright red spot in the image, I knew right away I was seeing Pluto. The picture here has Pluto’s position marked; click it to see the full sized version.

In modern terms, Pluto is pretty bright; I’ve never seen it with my own eyes through a telescope, but using a small ‘scope equipped with a digital camera I’ve gotten decent images of it in under a minute! But Tombaugh didn’t have that, nor did he have a computer to tell him where it was. He had to take picture after picture, night after night, guiding the telescope, developing the glass plates, then comparing each picture one after another. That’s why it took him months to find Pluto!

And remember, he didn’t even know if it existed!

Astronomy is not for the faint of heart. But for those of us who love it, it truly is something we do from the heart.

Related posts featuring Anthony’s imagery:

Does this perigee make my Moon look fat?
Runaway star
Actually, if you’re a comet, it *is* easy being green
Amazing shot of the ISS and Jupiter… during daytime!

CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

Comments (36)

  1. I guess my question would be why the green, blue, and unfiltered images don’t show a shift in Pluto. How much time was there between the first three, and why was there a long delay before taking the red one? (And how long was that delay?) Or did he do that on purpose, hoping to find Pluto that way?

    On the other hand… “cool”.

    And “undwarfplanetate”? I think you’re stretching things here. :-)

  2. Very cool trick to spot a planet! I never would have thought of that, although I’m not immediately familiar with the procedure of capturing colour photos of the cosmos.


  3. I saw the title, and I thought Messier Tidier Upper was going to get a tip or credit for this one. :)

  4. Jean H

    It is Mess-ee-ay, not Mez-ee-ay (contrary to popular opinion, not all “s” are pronounced “z” in French).

    Thank you for the trick, too. :)

  5. Fred Eliot

    New meaning to red shift.

  6. Wayne on the Plains

    @3 Larian,

    Yeah, I hope he at least says something clever in the comments…

  7. @5Wayne,

    FSM knows I won’t!

  8. @Ken-
    I’ll jump in on this one.
    (I just embiggened the image and saw that each color exposure was 5×6 minutes (30 min)… so he must have had a time lag between the red and green blue, maybe to take the unfiltered image but I’ll leave my other explanation up!)

    Usually when taking 3 different images in different filters you usually change the exposure times.
    It often depends on the spectrum of the source to determine how long one wants to expose.
    For example, I used to work on young stars which are very red. The IR exposures were short because the spectrum peaked there, our blue exposures were the longest because there is so few photons coming from that area of the spectrum.

  9. @ Ken B (#1), actually if you look really close in the largest image, you can see the green, blue and white (luminance) resolved. My guess behind the prominence of the red subframe is that 1.) blue & green are too faint to be seen next to the bright luminance 2.) the final stack gives different weights to the R,G,B channels to bring up features.

    You can actually see a similar effect on the Sloan Digital Sky Survey (SDSS) used by Galaxy Zoo – here’s a blog post about that.

  10. @Spacemom (#7), actually if you look at the image info, all color subframes are 6 mins exposure. But I’ll point out that a lot (if not all) commercial CCD camares are most sensitive around the red part of the spectrum.

  11. Kullat Nunu

    To be precise, Messier 24 is not a cluster, just a bright patch of the Milky Way visible to us. Actual star clusters consists of stars gravitationally bounded to each other.

  12. @Scibuff-

    Yes, I forget that commerical CCDs are most sensitive around the red part. (and yes, I think most are in general- I’ve been working with X-ray CCDs for a while, so I forgot that part of optical CCDs). (open mouth…insert foot!) :)
    I couldn’t find the other colors in the image, except that Pluto was not quite a point source, but slightly elongated.

    It is also true, as you said, that the final image depends on the weighting of the colors. The person making the image can weight the frame that they wish to bring out whatever details they want.

  13. Thanks, Spacemom and scibuff. I still only see a crescent red to the left of the almost-white almost-circle to its right. Maybe it’s my aging eyes? I saw the info on the multiple exposures for each color.

    I suppose that, if all the reds were taken at the end, along with your explanations on CCDs and weighting, that might account for it. I’m not a professional (or even “good amateur”, as the ones the BA posts obviously are) sky-photographer(*), but I would think that one might rotate filters, rather than “a bunch of luminescence”, “a bunch of green”, “a bunch of blue”, and finally “a bunch of red” exposures.

    (*) Truth be told, I’ve only done a few shots of the Moon, and some dismal attempts at stars and planets, with my hand-held digital camera.

  14. Michael Swanson

    To the left of Pluto, and directly under the large, bright yellow object is another faint but distinctly red object.

    So what’s that one, mister smarty-astronomer?! :)

  15. Brian Schlosser

    “That’s why it took him months to find Pluto!

    And remember, he didn’t even know if it existed!”

    Even more incredible is that the reason he was even LOOKING for it, the gravitational pertubations of Uranus’s orbit, never actually existed. He was looking for a much bigger planet (that also never existed), and it was only by coincidence and pure luck* that he found anything at all.

    * for “luck” read “totally random chance” if you prefer

  16. MadScientist

    Didn’t Tombaugh have a blink comparator at that stage? It’s trivial to find differences in a blink comparator – for example, take the separate photos in that composite image and run them through a blink comparator. The hardest part is setting up the two images to coincide. The reason it took so long to find Pluto is that no one knew it existed or where to look – even surveying a few degrees above and below the ecliptic plane would take a phenomenal effort, even with a comparator. CCDs + computers offer a phenomenal advantage over the old methods (not to mention a CCD is trivial to calibrate for light intensity and spectral response in comparison to photographic plates).

  17. @Michael (#14) alright lets see:

    Using d=160mm and f/7.5, the focal length is 1200mm and using my calculator selecting ST-10XME, I get the FoV 42.3′ x 28.5′.

    Going to putting Date = 2010 07 06, Time = 21 00 00 UT (because the time was UT+3), Ra = 18 15 32, Dec = -18 10 48, Lim Mag = 20, Prob 68, Fov RA 2520″ (=42′) and Dec 1710″ (=28.5′)

    all other known objects (with the exception of 10696) are too faint to be shown. Also they all have much higher apparent motion than pluto, and in 6 minutes would trail through several arcseconds (pixels) thus reducing the SNR. I doubt you could find 10696 in the image above manually (but should be possible with a reduction software).

  18. Yes, Tombaugh did use a blink comparator, which was considered state of the art technology at the time.

  19. John Sandlin

    @Michael Swanson: I haven’t found what you’re looking at. Does it exhibit the color shifting like Pluto or is it just red?

  20. Yeah, it’s a double “s”, so it doesn’t transform into a “z” sound when pronounced, it stays an “s”.

  21. Michael Swanson

    I think it’s just red. You have to follow the link that Phil posted ( to really embiggen the photo; clicking on the photo itself from the blog doesn’t make the photo very much larger. Up and to the left of Pluto are two very bright blue stars, and then up above them is a very bright yellow star. Directly below the yellow star and then almost directly to the left of Pluto (just slightly above) is small, faint red smudge.

    I’m sure it’s nothing more than Planet X, hurtling directly toward the Earth at terrifying speed.

  22. Doug

    You know, a blink comparator is basically the same technique as what the BA used, just with a different way of showing the shift in time (superimposing the images rather than blinking between them).

  23. #16 MadScientist:
    Spotting an object as faint as Pluto was far from trivial, even with a blink comparator. At Lowell Observatory, Tombaugh’s actual comparator is preserved as a museum piece, and is set up for public viewing, with the actual pair of plates on which he first spotted Pluto. It’s such a tiny dot, that it’s not easy to see, even when you know what you’re looking for.
    And Tombaugh had to blink thousands of pairs of plates before he found it. He deserves great respect for his perseverance.

  24. Andy Beaton

    Spotting Pluto visually was one of the hardest observations I’ve made, and one of the most satisfying. It’s too bad it’s moving into the Milky Way, it makes me wonder if I will ever see it again.

  25. JoeSmithCA

    Just more proof that science is cool. =)

  26. TRL

    Here is an interesting problem for you, Phil. New Horizons, now on the way to Pluto is also intended to explore a yet to be discovered KBO that would be along it’s post-Plutonian trajectory. Statistically, there should be many good candidates. You just have to find them in the image that you showed (or one like it – I don’t know the true area needed on the sky, except that it’s also in Sagitattarius). This is an exceptionally hard problem that must be solved in the next few years. I have spent much time talking to the person who has been tasked to do it…

  27. Tribeca Mike

    Very nice work, Mr. Ayiomamitis. Reminds me of push pin art, a prime example of which is the spooky opening sequence of Orson Welles’ “The Trial” (1962), each image of which took hours to compose. It can be seen here…

  28. Gents,

    My thanks to Phil for using this result and for the various comments thereafter. Some comments from my end follow:

    (1) Since M24 is quite low for me, I must resort to good technique to get as much SNR as possible which is normally mitigated at these low altitudes due to atmospheric extinction and poor(er) seeing. To this end, Red has the least atmospheric extinction relative to green and blue and is also the least affected (relatively speaking) with respect to seeing. As a result, it is best to shoot the Red exposures when the target is lowest during the imaging session and which explains why the RED extended dot for Pluto appears first. I am almost certain that Green was shot next, followed by Blue at the maximum altitude for the M24 star cloud since it is the most sensitive to seeing (and also atmospheric extinction) and then followed by Luminance as Pluto was just passed the southern meridian (we want a very good Luminance since the detail for an LRGB image really comes from the Luminance channel)

    (2) I used equal length exposures and in spite of the fact the CCD camera and filters have differential transmissions as a combo. This is no big deal since a G2V calibration will reveal the necessary weights to use to get the necessary balance thereafter and which is applied when combining the individual master RGB channels to produce a colour result. Alternatively and as suggested, one can play with the length of exposure between R, G and B to accomplish the same.

    (3) On a similar note, it was asked why not take the RGB (or LRGB) images in sequence rather all the reds, all the greens etc. This gets back to (2) above where I want to minimize the affects of atmospheric extinction and poor seeing at less than 30 deg altitude. If I shoot my exposutes as LRGB-LRGB-LRGB-LRGB-etc, I will be mixing bad exposures with relatively better exposures for Blue which is much worse than shooting all of the blue exposures when the target is around the meridian (ie. highest point in the sky for my location and the best possible seeing and lowest possible atmospheric extinction for Blue). Similar argument applies for Green and also for the very important Luminance channel.

    (4) A comment was made that CCD cameras are most sensitive in the Red. Actually CCD cameras are most sensitive in the Green (!) and this is where the QE peaks. Depending on the chip, we then have enhanced sensitivity in the Red or Blue. For this exercise, I used an ST-10XME which is known for having very good response in the Red. My other camera (ST-2000XM) is known for having very good response in the Blue and UV and for being very poor in the Red.

    I hope the above comments answer some of the concerns and ambiguities raised above.


  29. Folks,

    I went back to my original master LRGB image and cropped the area around Pluto and then proceeded to oversample the result to 4x the original size …. I think you will be happy with the result: ….


  30. Tribeca Mike

    Thanks very much for the technical info and the lovely photo, Mr. Ayiomamitis.

    “The artist is the medium between his fantasies and the rest of the world.” — Federico Fellini

    Not to imply that you are in any way a fantasist, but your image is the work of an artist.

  31. Messier Tidy Upper

    Great image, neat trick! :-)

    Thankyou Anthony Ayiomamitis awesome work. :-)

    So when my eye happened to catch a bright red spot in the image, I knew right away I was seeing Pluto.

    Although, OTOH, it could’ve been a *really* red carbon star couldn’t it? 😉

    ..the two dark splotches are thick dust clouds called Barnard 92 and 93.

    Which is which btw? Is that Barnard 92 left and B 93 right or vice-versa?

    This is one of my favourite images seen here yet for combing three of my fave objects – the ice dwarf planet Pluto, the Messier objects (M24) and E. E. Barnard’s dark nebulae. :-)

  32. Messier Tidy Upper

    @3. Larian LeQuella Says:

    I saw the title, and I thought Messier Tidier Upper was going to get a tip or credit for this one.

    I wish! 😉

    First time I’ve seen this pic – but I absolutely *love* <3 the BA's headline for it. 😀

    Of course, its a situation that will be tidied up over years as Pluto wanders across the star cloud and out of Saggitarius .. making it easier to find without the red dot trick.

    BTW. Wonder how much more powerful equipment you'd need to have to get to spot Charon in such an image. For the other Plutonian moons Nix and Hydra you'd need something like the Hubble Telescope natch!

    Also wonder if the folks running the New Horizons are watching & taking similar images.. and where Pluto will have drifted along to when it arrives in 2015.

    @ 6. Wayne on the Plains Says:

    @3 Larian, Yeah, I hope he at least says something clever in the comments…

    I’m trying – some would say very trying! 😉

  33. Messier Tidy Upper

    For more on Messier 24 – the only star cloud to feature on Charles Messier’s list of “not-comet” heavenly objects see :

    For more on the remarkable and inspiring Edward Emerson Barnard – one of my astronomical heroes who has a truly moving life story – see :

    And for more on another astronomical hero of mine (& pretty much everybodies) Clyde Tombaugh – see :


    “…Marc Buie can very easily imagine what it must be like to walk around on Pluto: with less than 1% of your weight on Earth because of the low gravity, at temperatures of 230 degrees below zero, in the twilight because the Sun is nothing more than a dazzling star in the black sky, across snowfields of methane ice and transparent crystals of frozen nitrogen and with a gigantic moon hanging overhead – at least if you are on the right side of the planet.”
    – Page 61, ‘The Hunt For Planet X’, Govert Schilling, Copernicus Books, 2009.

    “During its summer, the frozen nitrogen on Pluto evapourates to
    create a temporary atmosphere. With the onset of winter the nitrogen
    turns to frost and falls back to the surface. On Pluto the winter
    weather doesn’t merely deteriorate – it completely disappears.”
    – Page 19, ‘The Planets’, McNab & Younger, BBC Worldwide Ltd., 1999.

    “The Ramans do everything in threes.”
    – Arthur C. Clarke, ‘Rendezvous with Rama’, Final page (252), Pan
    Books Ltd, 1973.

  34. @Michael Swanson:

    Pretty sure it’s just an artifact. Look above where Pluto is and you’ll see a whole bunch of little blue dots and another red smudge.

  35. Gamercow

    I’m sure Phil’s been plenty of times, but if any other of you are in Flagstaff, Arizona, you owe it to yourself to go to the Lowell Observatory. Its a wonderful place, with great, informative staff.

  36. Kevin/Michael,

    I am afraid I cannot identify the artifact which are referring to. Anyway, please note that my southern sky and below 30 degrees altitude is rather horrific due to light pollution as well as poor seeing and atmospheric extinction due to the low altitude itself. As a result, the background sky in any of my images in this area of the sky is certainly not the best and at times I must also use gradient removal software to identify and correct for light gradients.

    To this end, if you see something which seems to be an artifact, I would not be surprised in the slightest.

    Many times I must pursue an object five to six times before I can get a result which is half decent due to the aforementioned factors. This opportunity involving Pluto was basically a one-time event with no possibility of a repeat attempt if I wanted Pluto in the dark nebula itself.



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