Very Large Moonset… but not why you think

By Phil Plait | June 7, 2010 11:45 am

The European Southern Observatory just posted this lovely picture of the moon setting behind the Very Large Telescope observatory in Chile:


[Click to embiggen.]

Photographer Gordon Gillet was 14 km (8.5 miles) away from the observatory when he caught the full Moon behind it. The sky is pink because behind him, the Sun was rising — as it must be when the full Moon is setting.

But I had to chuckle when I read the description:

Contrary to what one may think, this picture is no montage. The Moon appears large because it is seen close to the horizon and our perception is deceived by the proximity of references on the ground. In order to get this spectacular close view, a 500-mm lens was necessary. The very long focal length reduces the depth of field making the objects in focus appear as if they were at the same distance. This effect, combined with the extraordinary quality of this picture, gives the impression that the Moon lies on the VLT platform, just behind the telescopes, even though it is in fact about 30 000 times further away.

The part about the long lens collapsing the perspective is absolutely correct. That effect has been used for decades in the film industry to make far away things look as close as things much nearer (like, say, people running along train tracks to escape an oncoming train).

When I first read the description, though, I thought they were referencing the Moon Illusion, where the Moon looks huge on the horizon. Reading it again, I see they aren’t (though it would be easy to think they are). And that’s good, because the Moon Illusion isn’t playing into this at all. I explain how it works in more detail elsewhere; it’s an illusion caused by the shape of the sky and the way our brains perceive it. Also, the Moon Illusion is an effect that only happens when we can see large parts of the sky and get a sense of perspective on it; so it can’t be photographed (or at least I’ve never seen it done, and don’t see how it could be). In the case of this picture, it’s all due to the magnification of the lens used.

And it’s a beautiful shot. If you’re on Twitter, you can follow the ESO and get notified when they post another gorgeous image like this one. This is part of their Image of the Week series, which is updated every Monday.

Image credit: G.Gillet/ESO

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: ESO, Moon, Moon Illusion, VLT

Comments (39)

  1. Oh, you silly tool.

    Obviously the ESO is using gravity waves focused by the Very Large Telescope to bring the moon closer to Earth so NASA can hop up there on the last space shuttle flight and tear down all those alien structures they found when they didn’t go to the moon in the first place.


  2. It looks like something in a Science Fiction movie. The telescopes are so distinctively futuristic looking, the starkness of the surrounding landscape, the huge moon, the coloring.

    AND when you add Kuhniggets explanation….I mean its got the makings of a cool movie.

  3. Like always Phil, great taste in cool pictures! (As well as great explanations.)

  4. dcsohl

    Very nice picture! I saw an APOD like this a while back… let’s see, here it is, showing Lick Observatory silhouetted by the moon. This, though, I have to say, is a better picture, mostly for the increase in color depth; the Lick photo is almost entirely red. Nicely done, Gordon Gillet!

    EDIT: In looking through the APOD archives, I came across this one. Looks suspiciously familiar… Hard to tell if it’s the same image as above or not. Same photo session, undoubtedly. I think.

  5. dcsohl (#4): Nice catch! You’re right, it’s the same shot. There’s no indication on the ESO page that this pic is from 2004, but that’s OK. It’s still pretty. :)

  6. Wayne on the plains

    I normally can’t improve on your explanations of things, but I was bothered in this post by the emphasis on the magnification and perspective rather than the distance involved (14 km). Being that far away from the VLT makes it’s apparent size shrink greatly, while being 14 km further away from the Moon is insignificant as a percentage of the total distance, making them appear closer to the same size on the horizon. The optics used, of course, is just what makes the image so large and clear considering the distance to the VLT.

  7. I remember being impressed by the effect when director Rob Reiner discussed it in the commentary track on STAND BY ME, which features a scene exactly like you describe (did you have this particular scene in mind?), Phil–a character running directly towards the camera, away from an oncoming train. Onscreen, it looks like the train is just a few feet behind him, but Reiner reveals that the train was actually very far away, and they just made it look close by putting the camera far away and zooming in a lot.

    Ever since learning how that shot was achieved, I’ve had a much better appreciation for how scale can be tricky to judge in photos.

  8. @ Carl:

    Ever since learning how that shot was achieved, I’ve had a much better appreciation for how scale can be tricky to judge in photos.

    Tell that to the UFO nuts who continually try to pass off models hanging in front of a camera as interstellar spacecraft. (I’m thinking of you, Mikey!)

  9. CW

    Yeah, Neil DeGrasse Tyson said that if you bend over and look through your legs, then the moon “illusion” is negated (or something to that effect). It sounded like a set-up, until I googled and found your blog post on it – and the comments verified this to be true.

  10. Ray

    Does anyone else find naming a very large telescope “Very Large Telescope” rather uncreative? Astronomers have been naming stars Betelgeuse, Orion, etc for centuries but suddenly all they can call a very large telescope is “Very Large Telescope”. Really? Come on.

  11. You’re all wrong. It’s morning right? They ordered up a HUGE orange and they’re going to make one heck of a tall glass of juice. Now there’s some sunshine in a cup for you!

    Oh, wait, we have to obey laws of physics? Drat! That’s a snazzy pic then! :)

  12. DrFlimmer

    @ Ray

    Then, what do you say about the next European extremely large telescope (diameter of primary mirror: 42m!!) that is supposed to be built on Cerro Amazones (Gee, on that hill is the location of a small telescope that is built by the Astronomical Institute of my university: )? What do you think does the abbreviation E-ELT mean?

    Yes, you’re right. Not very creative, either, is it?


    Btw: The picture of this post was once used as a “Merry Christmas” message from ESO; I have it somewhere on my computer.

  13. Carl (#7): Yup. :) We watched it a couple of weeks ago, and I was impressed with that scene.

  14. Madness. Next you’ll be telling us that in baseball the pitcher is 60.5 feet from the batter, and not right on top of him as it appears on TV! Flying frogs, indeed…

  15. bouch

    Just out of curiosity, anyone know how to find this location on google earth? If the buildings are large enough to look like that from 14km away (even with telephoto lens), it looks like an interesting place to see from the air…

  16. Mark

    I think this picture would look better if atop the hill I could see Luke Skywalker, scanning the horizon for an errant R2 unit.

  17. It’s impressive! Just type in “Observatorio cerro Paranal” in the “Fly To” on Google Earth.. Coordinates are 24 degrees 37 minutes 40.03 seconds South, 70 degrees 24 minutes 12.54 seconds West.

    …or, even easier, just Fly To “Very Large Telescope”!

  18. In fact Carl(#7), the kid running in front of the train is Phil’s favorite Mancrush, Wil Wheaton!

    Love that movie.

  19. Paul Hannah

    Agreed the lens size is responsible, but it alone is next to meaningless unless you know the film (or digital equivalent size) If the shot is done on a Hassleblad like the ones used on the moon, then 500mm is only about half as powerful as if it were shot on a Nikon or equivalent 35mm.

  20. Simon T. Digger

    Well, that’s a relief… I thought the Anti-Spirals were back.

  21. Graham Douglas

    Umm… The focal length of a lens has no effect on perspective. Perspective is _only_ dependent on the distances of the observer from the subjects. The picture looks unusual because the perspective comes from being 14 km away from the VLT. What a long lens does is to magnify a small portion of the view, resulting in a perspective that we’re not used to seeing, since our eyes have pretty much fixed ‘focal length’ (about a tenth of the focal length used): take the same picture with a shorter lens, then crop and magnify the central area to the same size as the original and the perspective would look the same as the one taken with a long lens. Also, depth of field is not relevant – it’s purely perspective, coupled with the small *field of view* of the long lens.

    Sorry, as a photographer-in-training, I get a bit pedantic about this.

  22. @Ray: VLT is the name for all four of them. The individual ones have names, in a local ancient language: Antu, Kueyen, Melipal, and Yepun.

    @DrFlimmer: Indeed, though I hope it”l be renamed before it is going into operation. Btw., that shot was taken from the very spot you’re talking about, the Cerro Armazones.

  23. Jon Hanford

    10. Ray Says:

    “Does anyone else find naming a very large telescope ‚ÄúVery Large Telescope‚ÄĚ rather uncreative?”

    Actually, the four 8.2m instruments are individually named. From the APOD caption:

    “Most prominent from left to right are the four enclosures of the 8.2 meter very large telescopes christened Antu, Kueyen, and Yepun almost hiding Melipal.”

    “Antu, Kueyen, Yepun, and Melipal are names taken from the Mapuche language. Fittingly they translate to Sun, Moon, Evening Star, and Southern Cross. ”

    Dr. Flimmer mentions the lameness of the E-ELT monniker. I would also nominate the Thirty Meter Telescope (TMT) and the MMT (used to stand for the Multi Mirror Telescope. With the transition to the monolithic 6.5m mirror, “MMT” is [officially] a meaningless acronym.)

  24. Chris Winter

    Ray wrote (#10): “Does anyone else find naming a very large telescope ‚ÄúVery Large Telescope‚ÄĚ rather uncreative?”

    Personally, I don’t. Presumably they didn’t have a single benefactor along the lines of Lick, Keck, or Allen from whom to derive a name.

    Anyway, there’s a lot of precedent in astronomy (the VLA), in physics (SLAC, LHC) or in computers (RAID, TWAIN.)

  25. Robin S

    @ Graham Douglas (21): Perspective is also dependent on FOV, with FOV being a focal length dependent quantity.

  26. But I do find the name of the 100m concept ‘scope rather compelling – THE OVERWHELMINGLY LARGE TELESCOPE

  27. Robert

    @Chris: Well, I’ll agree with RAID, as slightly more interesting than it’s successor, JBOD (Just a Bunch of Disks!), but TWAIN is actually quite literary. It is not “Toolkit Without An Interesting Name”, which is a silly backronym. It comes from Kipling’s “The Ballad of East and West” – “East is East and West is West, and never the twain shall meet”. The reference was to the struggle to get hardware manufacturers and software creators to cooperate.

  28. @dcsohl and @Phil Plait
    It certainly looks like the same image when you overlay them in Photoshop. The APOD one is a fraction smaller but you can scale it carefully so it’s the same size and switch between the two images.
    The ‘scope domes don’t move and there are no differences in the ground or the features of the Moon. I was trying to look for libration before I realised the telescope domes hadn’t budged an inch.
    The atmospheric distortion of the edge of the Moon is exactly the same and so is the graduation of the colours in the sky, change for change even though there’s an offset with the APOD image because the colours have not been adjusted. It might be the other way around of course but I can’t think why you’d take a great pic and make it less intense and more dull and then publish it as the APOD.
    The ESO version has also had some sensor dust removed from it and the colours improved.
    The APOD is a crop of the ESO image before it was adjusted I’m sure.

  29. Graham Douglas

    @Robin S (25). No – it’s the mismatch between the FOV of the lens and the FOV subtended by the physical size of the image on your retina causing a misinterpretation by the brain. The true perspective doesn’t alter unless the photographer physically moves. The angle subtended by the buildings and by the moon at the observer position does not change, regardless of the lens used. When you look at that picture, your brain sees a particular FOV (say, for the sake of argument, it’s 20 degrees), and it interprets the image using that FOV, since the brain has evolved to interpret depth information based on lens with a fixed focal length. Now, if the actual image has a FOV of, say, 5 degrees, then your brain is going to interpret it with a ‘squashed’ perspective because of the mismatch. Reduce the size of the image (or view it from further away), so that it now physically subtends the same FOV on your eye as that of the lens, and will look perfectly natural – no squashing going on at all.

    I know it’s a bit of a pedantic point, and you could argue that the word ‘perspective’ could be used to mean ‘apparent perspective as interpreted by the brain’s visual system’, but then you’d also have to include degree of enlargement and viewing distance in the calculation, as well as observer/subject distance and FoV of the lens.

    But it’s still nothing to do with depth of field…

  30. Al Johnston

    What Graham said.

    Although the effect/illusion is usually known as “telephoto compression”

  31. Tim H

    Just here to second Graham Douglas — most importantly on the point that even mentioning “depth of field” in this case is entirely erroneous, and really inexcusable.

  32. Dunc

    The sky is pink because behind him, the Sun was rising ‚ÄĒ as it must be when the full Moon is setting.

    I’m not entirely sure that’s correct, unless the full Moon happens to fall on one of the equinoxes… Although it’s probably close enough provided you’re not too far from the equator. Up here at 55 degrees North and nearly at midsummer, on the other hand… Not even close.

  33. Schwarzwald

    This reminds me of the first time I saw the moon on vacation in South Africa and noticed that it was “upside-down” (Mare Crisium in lower left instead of upper right) compared to how it looks here in Germany. Beautiful picture.

  34. Tom K

    That’s no moon. It’s a Space Needle.

  35. Messier Tidy Upper
  36. Robin S

    Re: perspective (29, 30). Please define what you “intend” by “perspective.” There are a host of definitions for the word. Note that physical properties of an image are a function of focal length (longitudinal and transverse magnification, depth of focus and depth of field, FOV,…).

  37. Renee Marie Jones

    Beautiful photo.

    Funny thing is that I look at the moon on the horizon and think that it looks about the same as when it is straight up. So I just smile and silently agree when someone says the moon looks “so big” when it’s on the horizon. Personally, I don’t understand it. :-)

  38. Brian Too

    I fully expect to hear, in not too many years, a proposal for the Very Extremely Overwhelmingly Large Embiggened Telescope (VEOLET)!

  39. I looked it up (url). The Moon -is- large. About 2000 miles wide, in Bad Astronomer units.

    (I didn’t read all the comments in the Ten Commandments article, but… you’re still getting the ol’ math wrong, I see. Well, so did God. Thirty cubits around, nuts.)


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