I've had this poster on my wall for years. Today I noticed that the shadows on the lower ring of the space station don't seem to be consistent with the shadow on the Moon. The shadow at the base of the lower left spoke seems particularly problematic.

It seems that Robert McCall was careful in his work; I would assume that he took the position of the Sun into account.

From the Moon it appears the Sun should be off to the upper right of the poster. Can the shadows on the lower ring be reconciled with this?

enter image description here

  • could not the earth be causing the shadow on the moon? Given the distance between the station and the moon, I wouldn't over think it lol (such a great poster in any case)
    – NKCampbell
    Jul 28 '17 at 2:45
  • OK, you’re going to have to help me out here as I can’t see a shadow on the moon. The dark patches are one of the moon’s “seas” aren’t they? That said, the shadows on the station itself seem inconsistent, I agree.
    – Darren
    Jul 28 '17 at 6:28
  • The un-illuminated half of the moon is in shadow. Jul 28 '17 at 11:15
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    @NKCampbell: It's not impossible that we're seeing the Earth's shadow, but that doesn't solve the problem. Look at the shadow directly right of the bay that the ship flies out of. It points down, thus suggesting that the sun is up. But that means that the Earth is not directly between the moon and the sun, thus it cannot be the Earth's shadow.
    – Flater
    Jul 28 '17 at 12:21
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    @OrganicMarble D'Oh, I was looking at this on my phone earlier and didn't notice what is actually the Moon in the picture, I was looking at what is presumably Earth thinking that was the Moon. Ignore me.
    – Darren
    Jul 28 '17 at 13:05

You are correct, this seems to be an error in the poster.

Look at the shadow directly to the right of the bay (that the ship flies out of). It points downwards, thus proving that the sun must be upwards from our perspective.
That clashes with the moon's shadow.

But what if the shadow on the moon is being cast by the Earth?

Though not impossible (the shape of the shadow on the moon is plausible if it were cast by Earth), that still doesn't solve the problem.

The ship's shadow clearly shows that the sun must be upwards, which means that it's impossible for the Earth to then be directly between the sun and the moon.
If they were directly in line with eachother, you should be able to draw a straight line between the three points (regardless of perspective, this remains true as long as there is no lensing or warping). However, that is clearly not the case.

So it's completely impossible?

Well... no.

When we look at the shadows on the ship, we can only conclude that there is a bright light upwards (from our perspective), causing the shadow to be cast downwards.
We assume that it is the sun, but that is not definitively proven.

If there is another bright light (brighter than the Sun, in regards to the space ship), then the shadows can be different without the composite image being wrong.

  • i'm no astronomer - wouldn't you get some reflection / light source from earth?
    – NKCampbell
    Jul 28 '17 at 14:08
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    @NKCampbell: What part of my answer are you referring to? I'm not sure. If you mean the local light source which casts a shadow on the ship, that seems incredibly unlikely as the light projected onto the ship is very bright. It also creates a sharp shadow, whereas light that bounces off (and goes through the atmosphere) diffuses, which would make for blurred shadow edges (in a gradient).
    – Flater
    Jul 28 '17 at 14:19
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    @NKCampbell: In the interest of being complete: reference image. If the light was bouncing off the Earth, you would expect a soft shadow like the one on the right. However, the shadow is clearly closer to that on the right, which is an indication that the shadow is being cast by direct light, rather than reflected light. Also, the angle of reflection would not make sense, the Earth is left, the light source is up.
    – Flater
    Jul 28 '17 at 14:34
  • @NKCampbell: I should learn how to proofread. The left image is what we actually see, the right image is what you'd expect to see from a diffused light source (as is the case for light bouncing off the Earth).
    – Flater
    Jul 28 '17 at 20:45

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