I know shadows in the ground prove how the Earth is positioned close the Sun and how the light reflects off the moon and something to do with the curvature of space and/or roundness of Earth but can someone give me a quick overview? Something to do with the roundness of Earth creates shadows.
Also, for the stupid Flat Earthers, I know flat land or flat surfaces don’t experience as many shadows or very rarely, but yeah can someone explain?
Thanks for helping the random thought.
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One of the first pieces of evidence was observed by Pythagoras. He noticed that during a lunar eclipse, the shadow cast by the Earth on the Moon was _always_ round – no matter what part of the Earth was observing the eclipse or where the Moon was possiitoned in the sky. This could only reasonably happen if the Earth was a sphere.
There are other experiments you can do using shadows as well, observing how those shadows change in different places over the course of a day. [Wikihow](https://www.wikihow.com/Prove-the-Earth-Is-Round#:~:text=One%20way%20to%20prove%20the%20earth,because%20of%20your%20higher%20vantage%20point.&text=One%20way%20to%20prove,your%20higher%20vantage%20point.&text=to%20prove%20the%20earth,because%20of%20your%20higher) has a few great examples you can do yourself.
Is there a way to report a question for making too many false assumptions:
– the Earth is not that close to the Sun
– the moon CAN cast shadows, but it’s primarily the Sun
– this has nothing to do with “the curvature of space”
– Flat land experiences shadows all the time
Carl Sagan gave a good easy-to-understand explanation on his show Cosmos: https://www.youtube.com/watch?v=G8cbIWMv0rI&ab_channel=carlsagandotcom
Basically, a Greek guy noticed that if you have the sun directly overhead from you (your shadow stays right under you), then a stick pointing straight up from another location on Earth has its shadow pointing off to the side instead of right under it. This only makes sense if we are on a round object, so things pointing “up” are really pointing “out” from the center in different directions. If you know how far it is between yourself and the stick, and you can measure the angle the stick’s shadow makes, you can figure out about how big the earth has to be in order for the shadow to make that angle. He got a number within a few percent of the real value thousands of years ago.
The ancients had to hire someone to pace out vast distances and report on their findings. This experiment is much easier today.
Purpose: Measure the length of shadows simultaneously cast by identical objects at different lattitudes to discern whether Earth’s surface is curved or flat.
Hypothesis: If Earth’s surface is flat, simultaneous shadows cast by objects of identical height separated by any distance will be identical. If Earth’s surface is curved, the difference in shadow length will correspond to the distance between objects and the degree of surface curvature.
Method: Find a friend who lives several hundred miles north or south of you, preferably at the same longitude as you. Both you and your friend acquire identical standup carboard cutouts of Danny Devito. Verify each cutout is identical in height. Stand up each cutout in direct sunlight. At precisely noon, each person measures the length between the base of the cutout and the furthest extent of the cast shadow. Any difference in length implies Earth’s surface curvature. Use spherical trigonometry to calculate from this difference the degree of curvature, and the diameter of a sphere with such curvature. Compare your calculated diameter to other estimations of Earth’s curvature. Celebtate yet another example science’s triumph over stupidity.
So many questions at once… I think I’ll have to oversimplify a bit.
About the roundness of the earth with shadows: When measuring the length of a shadow, you are also measuring the angle between the ground and a line towards the light source. If you do this in multiple places, you get multiple lines towards that light source and can calculate how far away they intersect.
But there is one assumption you have to make, and that is that the ground at those different locations is in one plane. If you do this with the sun and two measurements, you get something in the “a couple thousand miles” range. But if you then measure how parallel the run’s rays are at one point, you won’t get the result you’d expect if the sun was that close. And if you do the shadow angle measurements at more than two points, the lines won’t intersect at one point anymore.
But if you change your assumption of a level ground to be part of the surface of a sphere, et voila, all the measurements suddenly line up perfectly.
Moon is reflective: There’s not much to measure here, this one is just an observation. Once you have a telescope that is good enough to see that the dark part of the moon is still there (and doesn’t get eaten by some sky snake), you can figure out that it’d be very unlikely for the moon’s surface to light up and go dark in such a weird way. And once your telescope gets even better, you will notice that the bright side of the moon isn’t uniformly lit. There are shadows up there, and they move around—just like shadows from a moving light source. And they point away from where we just calculated the sun should be.
In addition, when looking at how the lengths of shadows change over time at different locations on the moon, we can see that it cannot be flat either. Otherwise, those shadows would get longer and shorter by the same amounts. But they don’t. The closer they are to the dark side, the longer they are. And when the dark side is the other side (i.e. 14 days later), they point in the opposite direction. When there’s a full moon, the mountains in the centre have no shadow at all, but those at all sides have very long ones. etc.
Earth’s shadow: Someone else already answered that.
Curvature of space: You mean how heavy objects bend the space around them? The moon is a bit light to see that, but with modern telescopes, we can watch plenty of really heavy objects. And there we see this lensing effect. Around those objects is a ring where the stars are very dense, i.e. where what’s behind the object is visible around the object, all smooshed together. In some cases, it’s so extreme that we can see the same star at multiple locations, once directly and once where the light from it into another direction got bent towards us. However, the step from “light is attracted by gravity” to “mass bends spacetime” is quite big and complicated. Too big and complicated for me to explain it here.
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