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On planet Tatooine which has two (main-sequence I guess) suns people still have one shadow only. Tatooine's suns seem quite close to each other, so it may actually be the case that the two shadows are so close that it almost looks like a single shadow, or not? And what if the two suns were far from each other on the day sky? I think this wouldn't look like two shadows from two lamps either, instead they would look equally dark (assuming both suns have about the same apparent brightness) as the region where the shadows meet, or would there be any noticeable difference between the darkness of the shadows and the darkness of both shadows upon each other?

What would a human's shadow(s) look like on a planet that has two suns close to each other (like Tatooine), and on a planet whose suns are far from each other on the sky?

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  • $\begingroup$ The movies didn't depict the shadows correctly, and it probably wouldhave been very expensive to do the special effects. I suppose at the present time it would not be that expensive to make multiple shadows. $\endgroup$
    – M. A. Golding
    Jun 14, 2021 at 17:22
  • $\begingroup$ @M.A.Golding We see in Attack of the Clones (2002) very well how those on Tatooine have one shadow only. But that's nothing weird for Hollywood movies as Hollywood rarely cares about science. For the Apollo 18 film which is portrayed like an actually found footage they didn't even bother to learn that the Moon's south pole is on the far side so in the film you can see the Earth from the south pole, just awkward! $\endgroup$
    – John
    Jun 15, 2021 at 4:59
  • $\begingroup$ Hank Marvin's never been to Tatooine, so we just don't know. $\endgroup$
    – ProfRob
    Jun 15, 2021 at 7:08
  • $\begingroup$ @ProfRob Who is Hank Marvin? $\endgroup$
    – John
    Jun 15, 2021 at 8:30
  • $\begingroup$ @John en.wikipedia.org/wiki/The_Shadows $\endgroup$
    – ProfRob
    Jun 15, 2021 at 8:53

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You will have two half-shadows, and maybe an overlapping part where no direct light reaches the ground. Thus there will be a shadow where light of neither reaches the space. There will be a partial shadow where only light from one star reaches the space. And then there is of course the space which is illuminated by both.

You totally right: one can try out the result at home in the evening or night hours: use two direct light sources, like spot lights at different angles, dim them to their relative brightness as desired. Don't use ambient light which illuminate walls, ceiling etc. Then place an object such that those two light sources illuminate the object and observe the shadows. You can observe a similar effect at night when you walk or cycle a street illuminated by spaced-out street lights: you will see shadows of yourself in two different directions.

The closer together the two stars are in the sky the more the two shadows will overlap and the more the shadows will look like you know it from Earth. The more apart they are, the different the directions of the shadow will be.

The difference in relative brightness (or shadow-ness) depends directly on the relative brightness of the stars. Of course the indirect light from the atmosphere, thus the scattering behaviour of the atmosphere influences the difference between complete shadow (only indirect light) and illuminated area (indirect light + direct light), too. That might vary a bit from planet to planet, too. On Earth the difference of the brightness of shadowed area compared to directly illuminated area (according to wikipedia) is of the order of 20000 lux vs. 120000 lux (thus illuminated area is about 6x brighter than shadows), but less contrast when the sun approaches horizon or worse atmospheric conditions.

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  • $\begingroup$ So obviously the makers were wrong, as Tatooine should have had a bit of distinction between each solar shadow. $\endgroup$
    – John
    Jun 14, 2021 at 10:05
  • $\begingroup$ Yes, as the suns clearly have different colour, I expect the hue of the shadows to be slightly different $\endgroup$
    – planetmaker
    Jun 14, 2021 at 11:55

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