Why is the earth flat?

Here's how I know it's not

Star constellations vary throughout the night/year

That's not a good reason.

FE here think it's not a valid reason

idk what will actually collapse FE

They wouldn't do that on a flat earth.

The stars could just be moving on the firmament.

what's the one subject that will collapse FE

If you want to disprove FE with constellations, compare them from different parts of the world.

Stars, which are lightyears away, do not move perceptibly

It's us moving

How do you know?

Look, you can tell easily on your own. With a telescope. Or schedule a visit at a high powered telescope

It's not hard

Didn’t you know it’s a true fact the Earth is round.

The stars move through the sky, sure. How do you know it's caused by our movement and not theirs?

Because I just do ok.

I didn't say they don't move

I said the distance makes it imperceptible to the human eye

Hence, they do not move perceptibly

Everything is in constant motion. Has been since the conception of the universe

So the earth is round

I don't think you get the gist of the question.

How do you know why the stars seem to move?

Because it's observable and mathematically verifiable

What is "it"?

The stars move and the earth spins around DUHHHH!

Here's an excerpt that gets the point I'm trying to make across much more effectively

There was no straightforward demonstration of Earth's motion until 1725 when James Bradley discovered stellar aberration. This is (apparent) yearly change in positions of all stars in the sky due to Earth's own motion. Aberration arises due to adding up of the speed of light coming from the star and Earth's own speed. This is a very complex phenomenon and its description requires some math.
Another, much simpler, consequence of Earth's motion is stellar parallax. If Earth changes its position relative to the stars, then the stars should appear to change position in the course of the year.
A common experiment illustrating parallax is just looking at a close object (a finger, a pencil etc) with one eye at the time. When you switch from one to the other eye, the object will appear to move against the background. Closer the object is to your eyes, more pronounced the effect is.
Parallax should not be confused with aberration: parallax arises from the change of Earth's position and depends on the distance to the star, while aberration is caused by Earth's great speed and does not depend on how far the star is.
Parallax of a star was first measured by Bessel in 1838. It was not measured before because this change of star's apparent position is very small (the stars are very far from us). This was a very important discovery because Aristotle himself mentioned the lack of observable stellar parallax as the proof that the Earth is not moving (he didn't have a telescope and didn't know that the stars are so distant).

Do you mean me

A third discovery demonstrating Earth's motion was that of Doppler effect. The wavelength of the light that we receive from objects moving relative to us becomes a little shorter (i.e. bluer) when we approach the source and becomes longer (i.e. redder) when we move away from the source. When Earth moves toward a star, the star will appear slightly bluer (only high-tech instruments can measure this) while it will appear redder when Earth is on the other side of the orbit and moves in the opposite direction. This effect demonstrates that Earth has a velocity relative to the stars, similar to aberration.

What is this about

Do you have an image of said parallax?

Nah

The parallax isn't something you can take an image of

Here's a graph that shows what the parallax would have to look like in order to be properly imaged.

Sure you can. Just take two photos months apart.

Wtf is a parallax

It has to be taken from an outside perspective or measured and graphed seperately

I'll put it in a very simple way