Which statement about the Mean Sun is accurate?

• A. It moves along the equator and its right ascension increases uniformly
• B. It moves along the equator and its right ascension decreases uniformly
• C. It moves along the ecliptic and its right ascension increases uniformly
• D. It moves along the ecliptic and its right ascension remains constant

Answer: (A)

Right ascension is the angular coordinate measured along the celestial equator. The mean Sun is a hypothetical point that is defined to move with a constant angular speed, and it is taken to travel along the celestial equator. Because it stays on that circle, its longitude on the equator increases at a steady rate, which means its right ascension increases uniformly over time. This makes the statement that the mean Sun moves along the equator and its right ascension grows uniformly the accurate description. In reality, the true Sun follows the ecliptic, and its right ascension does not increase at a perfectly constant rate due to the tilt between the ecliptic and the equator.