A problem with astronomical observations is that celestial bodies don't like to stay at the same place in the sky. You set your telescope, find the object, adjust the focus, and it's there. Then you call a friend to show them the object, but when you return to the telescope the object is gone and you have to find it again.
Equatorial mounts were created to mitigate this problem by simplifying the process of re-centering the telescope in the object by just slightly turning a single rotating handle. So why does this work and how does this relate to the shape of the earth?
Long-story short, by assuming the earth is round and rotating, the mount head is set so it has one axis (called the polar axis) of rotation parallel to Earth's axis of rotation. This way, once you find a celestial object, you just need to rotate the polar axis in the oposite direction to the rotation of the Earth when the object is about exist your field of view to re-center it. Additionally, by setting a motorized mount to rotate the polar axis at a constant speed, the telescope will stay fixed in the objet the whole night.
Now, how do you set the mount? There's a number of steps to follow (In the northern hemisphere):
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Point the mount head towards true north.
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Make sure the mount base is level (i.e. a radius of the Earth is normal to the mount base) with a spirit level.
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Set the inclination of the base as the same as the latitude you're in (once the base is level, the inclination needed to be parallel to the rotation axis is equal to the latitude you're in).
A rule of thumb for setting up the mount is putting the telescope in "zeroes" and treat the mount base as an altazimuth mount and fix it on Polaris.
The above steps are only true in the northern hemisphere, as the setup is different in the southern hemisphere. The only differences are that you need to point to true south instead of north, and that there's no Polaris.
To demonstrate why this works, the angle of elevation requires high-school level math to verify, and the rest is explained by the fact that when the earth rotates a degree, you rotate the axis a degree in the opposite direction and you return to the starting point. Granted, due to earth's rotation and translation, there's a parallax component, but typically stellar objects are far enough that this is negligible.
Now, the question is, how would this work in a flat Earth? It is a fact that equatorial mounts work with the described setup. I'm curious to know how this fact works in a flat Earth, specially with the mount requiring to point South in the Southern Hemisphere.
“https://reddit.com/r/FlatEarthIsReal/comments/1elrre8/how_would_equatorial_mounts_work_in_a_flat_earth/”>View Reddit by tjkun – View Source
