How Many Light Years Wide is the Sky?
Question:
If a person looks up at the sky, how many light years wide is their field of view?
Answer:
In order to determine how many light years across a given angle is on the sky, you need to know how far away the objects you are looking at are from you. Let’s say you are looking at stars on the edge of our Galaxy, which is about 7 kilo-parsecs, or about 23000 light years. Let’s further assume that we have an unblocked horizon, so that the angle on the sky that we can see is 180 degrees. Since an angle of 180 degrees would correspond to half of the circumference of a circle, or pi*R, on the sky, the distance across the sky while looking at stars on the edge of our galaxy would be pi*23000 light years, or about 72000 light years. If you are looking at objects that are further away than the edge of our galaxy, the size of field of view scales linearly with this increase in distance.