The zero-point for ______ is the vernal equinox.

• A. Left Ascension
• B. Declination
• C. Altitude
• D. Right Ascension

Answer: (D)

Right ascension uses the vernal equinox as its starting reference point. Imagine the sky with the celestial equator projected like a big circle around Earth; you measure how far along that circle a star is, starting from the vernal equinox point and moving eastward. This mirrors how longitude is measured from a fixed zero on Earth, just aligned to the sky, and the units are hours, minutes, and seconds because a full 360-degree circle corresponds to 24 hours of time. Declination, on the other hand, is measured north or south of the celestial equator, so its zero is the equator itself, not the vernal equinox. Altitude is the angle above the local horizon, which changes with your location and time, not a fixed celestial reference point. Left ascension isn’t a standard term in this context.