How do we measure things in the sky?
Throughout the descriptions of astro-happenings here on Darker View, I use the terms degrees, arc-minutes, and arc-seconds. This is how astronomers measure size and separation of objects in the sky.
The degrees used by astronomers are the same as those you learned in high school geometry, the same as marked on that old school protractor forgotten in the back of the desk drawer. 360 degrees mark a circle, 360 degrees reach once around the sky.
Degrees measure rotation, and just about everything in astronomy rotates… As the Earth rotates on is axis, the sky goes wheeling overhead. When we move a telescope from one point in the sky to another we rotate the telescope about its axis. How far does it rotate? That is measured in degrees.