ABSTRACT
This chapter introduces an important application of spherical geometry and trigonometry in astronomy. It describes how to calculate the time of rise or set for an object in the sky such as the sun or a star, as well as the location of the object when it rises. The chapter shows how to determine the location of an object at other times of the day. To spot the object in the sky, the altitude-azimuth coordinates would be useful. This might be accomplished by using the time to determine the hour angle, and then switch from declination-hour angle to altitude-azimuth coordinates. The proper measurement of time requires one to find a unit of time. One way of doing this is to find an event that occurs with precise regularity. The chapter illustrates how to calculate the equation of time by using the Kepler equations for the elliptical orbit of a planet around a star.
