Angles in Astronomy
The Moon
We can measure both the size of an object in the sky and mark its position using angles.
However, sometimes the angles are very small - much less than a degree. Therefore, astronomers often use things called arcminutes and arcseconds.
An arcminute is 1/60th of a degree (remember that there are 360 degrees in a circle).
An Arcsecond
An arcsecond is 1/60th of an arcminute. Therefore, there are 1,296,000 arcseconds in a circle! (1,296,000 = 360 degrees X 60 arcminutes X 60 arcseconds).
That means that a five-pence coin would seem to be 1 arcsecond across when it was 3 kilometres away! (This is the distance to Liverpool Cathedral in the picture).
