How to measure angles in night sky?
Astronomers use the concept of ‘degrees’. ‘arc minutes’ and ‘arc seconds’ to measure angles in the night sky. Though a little unnerving they can be understood simply step by step.
Degrees: Angular separation of objects is measured in degrees. There are 360 degrees in a circle and it is considered that any point on the horizon or overhead is 90 degrees, whereas halfway from the overhead point to horizon is 45 degree.
To measure smaller angles, the astronomers use the hand and fingers as a measuring tool where stretch between thumb and little finger= 25 degree, index and little finger= 15 degree, on clenching the fist with its back to you= 10 degree, three middle fingers together are equivalent to 5 degree and lastly the width of the little finger at arm’s length is 1 degree.
Since view by a telescope only covers less than 1 degree, the astronomers measure it in arc minutes. There are 60 arc minutes in a degree and 60 arc seconds in 1 arc minute respectively.