Indoor1

Indoor 1

Introduction to Angles

Introduction What is the simplest observation of the sky we can make? Although we might want to figure out how far away the stars are, how bright they are, or even what color they are, that is not so easy. The most basic observations we can make are things like how far apart do the stars appear or how big does the moon appear? This apparent distance is called the angular separation (or angular size), and is normally measured in degrees (or radians). We can make this measurement fairly easily by using something called a cross-staff. Of course, it is very important to remember that this measurement is an apparent measurement; if we were closer or further away, this apparent distance would change. We are very familiar with this concept, because large far away objects such as mountains can look smaller than closer, smaller objects like buildings.

We can determine the relationship between measured angles and absolute distances in astronomy by considering an angle as representing some fraction of a circle. Consider figure 1 below.