In astronomy we use angles to measure the 'distance' between objects as seen from Earth, either with the naked eye, or with the aid of a telescope.
It is important to emphasize that the word, 'distance', in this context means the apparent size of an object or the apparent separation between two objects, and not the actual physical linear distance between them. An example is shown in the picture on the right. The full moon, as seen from earth, has an angular diameter of about one half of a degree, while its actual physical diameter is 3476 km.
There are 360° in a circle, 60 arc-minutes in a degree, and 60 arc-seconds in an arc-minute.
This article is a work in progress. Should you wish to be notified when this article is updated, please subscribe to the Skywatch Newsletter. Alternatively, you may subscribe to the RSS feed at the top of the General Background page.
General Background
