https://files.catbox.moe/dipkpn.png![]()
Parallax comes down to an equation with an observer and two objects. Take the distance between the observer and object A. Now multiply that number by two and place object B at that distance.
A quick example would look like this.
A @ 10ft or 500ly
B @ 20ft or 1000ly
It does not matter if it's 20 ft or 1,000 light years. The parallax effect is dictated by these two different numbers and can scale to any number.
So if we were to say that object A is a star at 500ly away. We can still take a timelapse photo of it and see the star trail which is just a recording of its apparent movement relative to our position on the moving Earth. We can print out that timelapse photo and measure how long of a star trail object A made. Let's say in the photo object A made a star trail that was 1" long. If object B is another star at 1000ly away, You would take the apparent distance that object A traveled on your photo and divide it by two. Now you should be able to measure the star trail that object B made. It should be 1/2". If it's not, then at least one of the numbers for distance is incorrect. If the stars show no movement at all relative to each other, then it means those stars are at the same exact distance from the observer. So basic observation and by the laws of perception, the stars in the night sky are a blanket.
Here's a post I made not only debunking the ridiculous claim that Eratosthenes proved the earth was round in 240 BC but I also proved the earth is flat.
https://www.upgoat.net/viewpost?postid=65f2576a41573 
chrimony 4 points 1.3 years ago
First, link to previous discussion that spawned this post: https://www.upgoat.net/viewpost?postid=65f056a78bf19#comment_65f07f6a4cc45
No, flattard, you only need a single object and an observer. Start with a candle on a dark night 1 foot away. Point your camera so that the candle is in the center, and take a picture. Now move 1 foot horizontally to your left and take another picture, without rotating the camera. The candle will have moved away from the center, to the right. How much it apparently moves is the parallax, and depends on distance to the camera and how much you moved.
Now do the same experiment, but place the candle two feet away instead. Can you tell if the candle changed positions? Of course, though it would be 1/2 less.
Now do the same experiment, but use a candle a MILE away instead. Can you perceive with your eyes if the candle moved? Probably not. Now use a candle TWO miles away. Can you visually tell if the candle moved? If you were unable to tell for one mile, then you won't be able to tell for two miles.
Now place stars light years away in all directions. Then spin the Earth. Can you visually tell if they changed positions? No. Whether it is one light year away or two, the difference is too small.
To measure parallax, you need precise instruments, and we don't use the diameter of a spinning Earth, we use the diameter of the Earth's orbit around the sun, and even then the measurements have to be very precise, and they are too hard to measure past a certain distance.