How is parallax used to find distances to stars?
In space, it is often useful to describe thing’s sizes or motion in angles. We can say the moon subtends 1 degree in the sky, which means if we were to draw an isosceles triangle where the side that isnt the same length is the thing in space, the angle is between the two longer sides. Namely the moon would be some distance away and the angle it subtends is one degree (which is about the same angle as your finger if you held it up at arms length). The actual size of the object depends on how far away it is, but if we know the angular size and how far away it is we can find the actual size. The same thing works with motion. Something can move a certain number of degrees in the sky, and if we know how far away it is we can know how far its moved. The parallax is referred to as the angle by which it moves. Now this method can work in the opposite way too. Because the stars are so incredibly far away, any motion is very small and for most cases we can consider them completely still. So then
