Mean Solar Time is defined as time based on a fictitious sun moving at a constant rate around the Earth. What is the angular rate of this fictitious sun?

• A. 15 degrees per hour
• B. 360 degrees per day
• C. 1 degree per hour
• D. 24 hours per day

Answer: (A)

The fictitious sun completes a full 360-degree circuit in one mean solar day (24 hours). So its angular rate is 360 degrees / 24 hours = 15 degrees per hour. Expressing the rate as 15 degrees per hour is the standard way to quantify angular velocity. (360 degrees per day expresses the same rate in a different unit, but the angular rate is conventionally given per hour.)