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Angles in Astronomy

An arcsecond is a very small angle

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).


Please note that over the weekend of the 26-29th May 2017 we will be switching over to our brand new website - during this time there may be periods where the site is difficult to access, and users will be unable to request observations from the telescope. Please bear with us during this time. All should be back up and running by the 30th May 2017.