Transcript: Angular measurement is an important part of astronomy. When you want to quote the position of an object on the sky you give it in terms of two different angles. The basic unit of angular measurement is a degree. There are 90 degrees in a right angle and 360 degrees in a circle. The system of angular measurement dates back to Babylonians over 5 thousand years ago. On smaller scales then a degree we divide the degree into 60 units called “minutes of arc” and the minute is divided into 60 further units called “seconds of arc”. One arcsecond is therefore 1/3600 of a degree, a very small angle indeed. It corresponds roughly to the angular resolution of a telescope on the ground. One arcsecond is a very small angle. It’s the angle subtended by the two sides of a quarter seen at a distance of about two miles.