Dot Physics

How tall is that UFO?

You know I wander around the intertubes, right? Who doesn’t? Anyway, I saw this collection of strange google Earth images. Yeah, it is kind of dumb, but this one made me think:


That article said the image was from TechEBlog, so there is that.

I have no idea what this thing is, but it is clearly tall. How tall? Instead of searching online for info about this structure (that wouldn’t be any fun), I figured I could do a quick analysis of the shadow. Here we go. First, I need to make some measurements. It turns out that Tracker Video tool for analysis is also quite excellent to use for image analysis.

Before I look at the image, let me draw a diagram of two objects with shadows.


Both of these objects cast shadows. But, there are two important ideas. First, the Sun is so far away that the shadows cast from the objects are at the same angle ( θ ). These shadows make triangle shapes with the ground. Both objects are vertical which means that the triangles are right-triangles. Since they have two of the same angles, the triangles are similar. The ratio of height to length of the shadow is the same for both objects.


The plan is to measure the lengths of the two shadows and estimate the height of the building. This way I can solve for the height of the unknown object as:


And here are my measurements – note that I don’t really need to set a scale for the picture. The key is that I need the ratio of the lengths of shadows. Here is the building – I am setting the length of its shadow as 1 unit.


This gives a shadow length ratio of about 10 to 1. The UFO thingy is 10 times taller than the house structure. I am guessing that is some type of single story structure (just a guess) with a height of around 10 feet. This would make the UFO 100 feet tall.


  1. #1 dean
    August 25, 2010

    Neat little demonstration – nice and straightforward. I do have to admit that speaking about how “tall” the “UFO” is sounds odd.

  2. #2 Blaise Pascal
    August 25, 2010

    Since the UFO has a round shadow, I suspect it is a water tower, many of which consist of a ball-shaped tank on top of a narrow column.

  3. #3 NoAstronomer
    August 25, 2010

    “I have no idea what this thing is.”

    It’s clearly a water tower. Taken from almost directly overhead. Here’s a water tower in NJ not directly from above…,-74.262007&spn=0.001145,0.001588&t=h&z=19

  4. #4 Eric Lund
    August 25, 2010

    The links don’t give any information as to where this UFO is, but I can narrow it down a bit:

    (1) To get that sun angle, you have to be within 30 degrees of the equator.
    (2) It’s not in the US, because the center line on that road is white, not yellow. (The TechE blog shows a little more than Rhett; in particular, the road widens to four lanes a bit to the right of the edge of what Rhett shows.)
    (3) It’s surrounded by a substantial parcel of farmland, but trees line both sides of the side road as well as the buildings, so we are in flat, non-desert terrain with a low population density.

    At this resolution, I’m not sure whether the vehicle on the road is a truck headed down in the right-hand lane or a car headed up in the left-hand lane. The former would suggest a location in Latin America (perhaps Brazil), while the latter would imply Australia or southern Africa.

    And wow, that thing is big. Assuming the road width (including shoulders) is about 8 m (consistent with 11 ft lanes and 2 ft shoulders) and the altitude from which this perspective is taken is much larger than the height of the UFO, I come up with a 25 m diameter for that disk. It might be a water tower, as commenter #2 suggests, though it would be a relatively large one. It’s definitely too big to be a cell phone tower, but about the right size (though an unusual shape) to be a shortwave transmitter (25 m is the length of a 12 MHz wave).

  5. #5 Art
    August 25, 2010

    Looks like someone stobbed a Dremel tool cutoff wheel and arbor into a Google maps screen capture printout. The blurring disguises the slot in the screw, the round object in the middle of the disk.

    The difference in the color of the shadows, deep black for the houses, and more gray for the ‘UFO’ shadow had me wondering and then it dawned on me that I’ve seen that object before.

    But assuming it represented actuality the analysis is good on height.

  6. #6 Flavin
    August 25, 2010

    I think this calculation might benefit from some error bars. The ratio of the uncertainty in l_1 to its value looks like it could be pretty high, maybe around 1/3 or 1/2.

    I might invest some more time on this after dinner, unless someone else jumps in before me.

  7. #7 6EQUJ5
    August 25, 2010

    That may be a deep-space antenna (a ‘big dish’) parked at the stow position (aimed toward zenith). Seen from directly above, it will not be obvious that the surface is parabolic in cross-section. The small central circle would be the subreflector, which you can see is casting a shadow on the main reflector. The shadow of the main reflector does not seem to be fully black like the other shadows. Such antennas have panels with pinholes in them to drain off water (which would otherwise cause phase noise in transmission and reception) and they happen to let light through. (Think of the holes in the screens inside your microwave oven: these let air and light through, but the holes are invisible to S-band beams.)

  8. #8 Badger3k
    August 25, 2010

    I was going to say a silo or tower, but I’d agree that a water tower makes more sense.

    Either that, or the lizard-people-aliens are getting really, really lazy.

  9. #9 stephenk
    August 25, 2010

    I’m curious what it is.
    Don’t know much about water towers (though I have seen some in Thailand that were inverted conical from memory) the object looks flat on top not spherical.
    Compare to NoAstronomer’s photo and you can see the gradiation in shade (barely) from sunward to back side. The round object colouration in this pic looks really consistent across the top, hence flat.
    Also curious on the perimeter from about 3 to 5 oclock appears to be something sticking just slightly out (advertising hoarding pointing at the road?)
    I think it’s cylindrical, are US watertanks that shape too?

  10. #10 Rob (no, the other Rob)
    August 26, 2010


    It couldn’t be a cylinder and cast such a shadow, the vertical sides of would cast a straight line.

  11. #11 stephenk
    August 26, 2010

    shallow cylinder (like a puck) on top of a stick,
    Sorry I wasn’t clearer

  12. #12 stephenk
    August 26, 2010

    Got ‘im…
    55°44’5.92″N 9°33’48.98″E

    Inverted shallow conical water tower (Denmark)

    There about 3 Panoramio pix of it too.

    Also measured off Google Earth says it’s 34m across

  13. #13 Ashley Moore
    August 26, 2010

    It’s obviously a base from the arcade game Xevious.

  14. #14 Rhett Allain
    August 26, 2010


    Good job with the detective work. I am impressed. Most impressed.

  15. #15 Thomas
    August 26, 2010

    stephenk, can you explain how you found that location? Are there special tools or did you find the source for the original image?

  16. #16 Robert LaRue
    August 26, 2010

    @10 Rob gets it totally correct. Round objects cast straight sided shadows. Also, the round shadow is offset to the left slightly, while the shadows of the two buildings are not offset at all. If the sun is the light source, this is not possible. Length of the shadow from the round object is totally impossible. The proportion of the height of objects to the length of their shadows should be the same… shouldn’t they? Isn’t that the basis of the math above? The round shadow extends way beyond the object, unlike the shadows of what are assumed to be buildings. What am I missing here?

  17. #17 Sam
    August 26, 2010

    A water tower with a cylinder-shaped tank that has a flat top and flat bottom and a diameter that is grotesquely wide compared to its height? (And by “height” I mean the cylinder tank itself, not its elevation)

    I mean, I haven’t done the calcs but I would imagine that the same types of analyses that show that this thing is 100 feet up could also be used to figure its shape, and would presumably show that the object casting the shadow is flat on the top and bottom and is quite thin (or, if it’s an elevated cylinder, “short”?) in proportion to its diameter. I say this because the shadow appears to be nearly a perfect circle despite the fact that the sun is hardly directly overhead. At that angle, one would expect more distortion in the shadow if it were rounded on the top +/or bottom, or if the cylinder were significantly deep — no? And if the top is not flat, wouldn’t there be a ladder to climb to the center/top?

    Also, the diameter of this water tower seems exceptionally gigantic compared to the area of the other structures and the roadway.


  18. #18 stephenk
    August 26, 2010

    no special tools, just a bit of clue following.
    I did start off trying to find the original image source (but couldn’t). However, did find a reference to the town. Searched around on Google earth (it only took a couple of minutes) assuming that the image hadn’t been reoriented and I was looking for a paddock just to the west of an almost north/south road and also it wouldn’t be too far away from a population centre to use it.

  19. #19 Ricardo Sgrillo
    August 26, 2010

    These are the coordinates of the UFO:

    lat 55.735057
    lon 9.563656

    It is a place near Vejle in Denmark


  20. #20 stephen
    August 26, 2010


    Coming from a place with not that much water, water towers are not that common where I live although there are some they tend to be small. That’s what spiked my interest.
    Anyway, this one is not exceptionally gigantic. In my following of links for water towers trying to track this one down there seem to be plenty around. There is one in Finland 75m diameter.
    The shape of towers varies widely. Like I said, The ones I saw in Thailand were inverted cones and were metal (I think) the sphere on a stick shape seems to be a US common arrangement. The UK seems to prefer a comparatively deep and narrow cylinder (much like the old abandoned railway ones I remember here in Australia, that probably isn’t a coincidence). Europe seems to have the big concrete ones like in this article. But these are generalisations, lots of variation too.

  21. #21 Steve
    August 27, 2010

    Way to go, Ricardo. A view from the side is available on Google Street View if you go to those coordinates.

    View Larger Map

  22. hello,

    Tank you for righting this great’s great info to those people that never knowing about that kind..

  23. #23 mynet
    August 28, 2010

    I recommend a nice alternative for Sifterapp – I suggest a great and powerful tool with screen capturing application called

  24. #24 LUS
    August 28, 2010

    this picture just doesn’t look real…
    but it is, and that’s why is owesome

  25. #25 upgradeto3d
    August 29, 2010

    There always seems to be a logical explanation for most strange sightings but wouldn`t it be boring if we didn`t have them to try and debunk.This water tower one was a good find.

  26. #26 Bret Jones
    August 29, 2010

    I was going to say that the object was from the game Xevious, but someone beat me to it! Nice write up and what a fun bit of harmless speculation.

  27. #27 FreeSex
    August 29, 2010

    It couldn’t be a cylinder and cast such a shadow, the vertical sides of would cast a straight line.

  28. #28 Albert Tarpey
    August 29, 2010

    I also think that straight shadows can be seen from those objects that are rounded. .The light is comming from the sun, so is it still a possibility? From the look of this and the shadow length, I doubt it. It’s too tall. The shadow of the circle is far to wide, while the other shadow in the picture seem about right.

  29. #29 LordSwarovski
    August 29, 2010

    Could you give us a location of this object? I am interesting in viewing it.

    Beside that, interesting article and cleaver way of using math/computer, quite inspiring. But how accurate can this way of calculating can be?

  30. #30 Samuel
    August 29, 2010

    At first it really scared me!! lol.! Good post.

  31. #31 Rabbit Forum
    August 29, 2010

    Looks more like an angle grinder bit!!

    Is this not some sort of water tower as opposed to a UFO especially given its proximity to what looks like some outbuildings next to the road?

  32. #32 Arapça müzikler
    August 29, 2010

    Neat little demonstration – nice and straightforward. I do have to admit that speaking about how “tall” the “UFO” is sounds odd.

  33. #33 Eva
    August 29, 2010

    Is it a real UFO picture? yep , it’s about 100 feet tall. I agree 🙂

  34. #34 aflam online
    August 29, 2010

    i think UFO is a fake and the arrivals made it.

  35. #35 Simon Birch
    August 29, 2010

    I must agree with this statement

    “I have no idea what this thing is.”

    It’s clearly a water tower. Taken from almost directly overhead. Here’s a water tower in NJ not directly from above…,-74.262007&spn=0.001145,0.001588&t=h&z=19

    apart from that must be fake

  36. #36 ps3magic
    August 29, 2010

    It looks like a water tower to me, since the place looks like a farm. And another thing if it was a real UFO, it wouldn’t b flying a such low height.

  37. #37 Casey Pearson
    August 29, 2010

    This has a conspicuous resemblace to community thrashing devices used in Indian farms in remote villages. Those are also popularly known as ‘mini-twisters’ there.

  38. #38 Cristiano Ronaldo
    August 29, 2010

    Well done Rhett! Remind me of the good ol geometry class days. I agree with the guy above who said its a water tower. But what do I know?

  39. #39 Jimmy Alfaro
    August 30, 2010

    We cannot say that UFO are real, but think the whole outer space are so big and there’s a lot of galaxies anyways this post reminds me what I saw on youtube yesterday about UFO.

  40. #40 Phoenix Psychiatrist
    August 30, 2010

    Good work on the mathematics. I love looking at the strange google earth images, you always find crazy stuff. There is no denying this UFO has raised some eyebrows

  41. #41 Jerry
    August 30, 2010

    Awesome stuff! I’m currently teaching my children how to calculate the height of a tower without going to the tower to measure how far away they are. The estimating is a good technique! It’s amazing how different things look from straight up. This is a link to the picture of the tower from the street:

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