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How much shadow would a floating continent the size of Australia cast if the bottom most point of the continent rested at about a mile above Mount Everest’s peak?

EDIT 07/12/2021 I’m still trying to find the best altitude for it… so bear with me…I am not wanting to overtly change the sustainability of living on the ground…I want to find an altitude that causes more of a cloud like effect but with a solid mass. As for how fast it’s going I kinda want it to “orbit” counter to the spin of the earth…also I don’t think I want there to be too much of an impact on the weather below…. Also, it has it’s own atmosphere…so high altitudes won’t be a problem…neither will high winds like the Gulf Stream.

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  • $\begingroup$ Welcome to Worldbuilding sophia, please take our tour and refer to the help center as and when you have time for guidance as to how we work, enjoy the site. $\endgroup$ Jul 6 at 8:23
  • $\begingroup$ How fast (if at all) does this continent drift about? It is interesting to ponder the potential weather impacts at various distances from the edge. $\endgroup$
    – JonSG
    Jul 6 at 18:14
  • $\begingroup$ I’m still trying to find the best altitude for it… so bear with me…I am not wanting to overtly change the sustainability of living on the ground…I want to find an altitude that causes more of a cloud like effect but with a solid mass… $\endgroup$ Jul 13 at 0:45
  • $\begingroup$ The object is sizeof the moon, a little bit bigger, so when it blocks sunligthand at distance of the moon effects close, but not exactly, to ones we see at total eclipse. This answer may be helpfull to evalute situation a little bit astronomy.stackexchange.com/a/35650/11784 . In general, if the thing orbits the earth then eclipse events will be rare(at most orbits) and won't last long. $\endgroup$
    – MolbOrg
    Jul 13 at 5:47
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You don't need to make sophisticated calculations to get the size of the shadow in this configuration.

Australia is about 4500 km across from East to West and 3700 km from North to South. As compared to the 9 km on top of the Everest, the border effect can be neglected, and the size of the shadow is practically the size of the object producing it.

For a reference with something we have experience in our daily life, imagine the shadow cast by a board 4 by 5 meters, placed flat at 1 cm from the ground.

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    $\begingroup$ Agreed, in relative terms the shadow is basically exactly the same as the thing causing it. The OP might be more interested in the effects at the very edge, e.g. how big an area gets sun/shadow only part of the time. That gets more interesting as it will still be quite a large area in human terms. But they haven't said that for sure $\endgroup$
    – Mr. Boy
    Jul 6 at 20:54
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Same as normal shadows

Shadows are created by blocking of light. If an object is bigger than the light source, the closer it'll get the more of the light source it'll block. Further away this effect becomes smaller until it nearly just creates a shadow as big as itself.

If an object is smaller than the light source, it is the reverse. The closer it gets to the light source, the smaller the shadow it casts. The further away, the closer it gets to it's own size.

But this isn't all. The shadow cast assumes a straight plane. 8f you make it crooked, you'll get a bigger shadow. You cast bigger shadows at sunrise and sundown.

For ease, lets grab the continent and assume the sun is directly 'above' it. The sun is bigger than our object, but it's very far away. So far away that the sunrays are nearly parallel. So much so we can treat them as parallel. If an object is caught in parallel light beams, it'll make a shadow exactly it's size. A floating continent will make a shadow as big as itself.

To determine the size of a shadow on a certain point of day, we need to use shadow trigonometry. It is too complex for me to write out now, but it's safe to say you can just use real mountains to get your answer. If you raise a mountain up into the air, it'll cast the same shadow. Just keep in mind that the mountain also cast a shadow under itself when it was standing on the ground, so it'll seem a bit bigger.

So because of parallel beams you get a shadow identical to the object. As the sun is moving, you can use shadow trigonometry to determine the shape. It'll look nearly identical to the shadows cast by real mountains, hills and plains.

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