Angles are used a lot in astronomy. We can measure both the size of an object in the sky and mark its position by using angles.
However, sometimes the angles are very small - much less than a degree. Therefore, astronomers often use things called arcminutes and arcseconds.
• there are 360 degrees in a circle.
• an arcminute is 1/60th of a degree.
• an arcsecond is 1/60th of an arcminute.
Therefore, there are :
360 degrees × 60 arcminutes × 60 arcseconds = 1,296,000 arcseconds in a circle
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).