I posted this in another thread (well, most of it), but I wanted to make a new topic about it. Here is a picture I made (in paint) that shows the positions of the sun and Polaris (the north star, for those who don't know). During an equinox, the sun is directly overhead at the equator, shown here:
As you can see in the picture showing the position of the sun, it makes perfect sense that the Earth is round. The position (in degrees) of the sun in the sky during an equinox is equal to 90-your latitude. On the round earth, all the arrows pointing to where the sun should be point in the same direction. That means that the sun is extremely far away in the direction. But look at the flat earth. The angles the sun is at (compared to the ground) are the same as on the round earth. But look at where they point. With those 5 latitude positions, there are 10 places that the sun is at once, 4 of them being on the ground. How is that possible? Answer: It isn't.
Now look at the position of Polaris. As most of you (hopefully) know, Polaris hardly moves in the sky (.7 degrees off of the center of the earths axis according to Wikipedia). Its altitude (in degrees) in the sky at all times is equal to the latitude that you are at. So near the equator (0 degrees latitude) it is near the ground. At the north pole (90 degrees latitude) it is directly overhead. On the round earth, the arrows point in the same direction. That means that Polaris is extremely far away from us in that direction. Now look at the flat earth picture. Hmm... It seems that Polaris is at the north pole. How is that possible? Answer: Again, it isn't.
So there's proof that the earth must be round. I have even checked to see that my latitude (about 42 degrees north) is equal to the altitude of Polaris, and it is. You would be stupid to think that my information is wrong, because most likely millions of people have figured out the position of the sun during an equinox and the position of Polaris (and don't say that they are all in on the 'conspiracy', because that's impossible).
Still don't believe me? Here's another picture I made. It shows the distance from the sun to the earth if the earth was flat. As you can clearly see, the distance from the sun to the equator during an equinox is different depending on your latitude. Again, I ask: How is this possible? Again I answer: It isn't.