The half-circle that defines the starting point for designating longitude on the celestial sphere is called the
A) vernal equinox.
B) ecliptic.
C) celestial prime meridian.
D) Greenwich meridian.

Question

Quizplus · Accepted Answer

The celestial prime meridian is the half-circle that extends from the celestial north pole to the celestial south pole, passing through the point in the sky directly above the Earth's prime meridian in Greenwich, England. It is used as the starting point for measuring celestial longitude.

The Half-Circle That Defines the Starting Point for Designating Longitude