What is the angular distance measured along the hour circle from the celestial equator to the celestial body?

• A. Declination
• B. Right Ascension
• C. Polar Distance
• D. Zenith Distance

Answer: (A)

Declination is the angular distance north or south of the celestial equator, measured along the hour circle that passes through the celestial body. This is exactly how far the object sits from the celestial equator on its vertical circle, with north being positive and south negative. Right ascension, on the other hand, is measured along the celestial equator from the vernal equinox to the object’s hour-angle crossing, not from the equator to the body along the hour circle. Polar distance is the angle from the celestial pole to the object (related by p = 90° − declination), and zenith distance is the angle from the observer’s zenith to the object (dependent on latitude and altitude). So the described angular distance corresponds to declination.