The equinox is one of the two points of intersection of the __________ and the celestial equator occupied by the sun when its declination is 0º.

• A. Celestial equator
• B. Ecliptic plane
• C. Horizon
• D. Ecliptic

Answer: (D)

Equinoxes happen where the Sun’s apparent path through the sky, the ecliptic, crosses the celestial equator. At those two crossing points the Sun’s declination is zero degrees, meaning it lies on the celestial equator. The ecliptic is the projection of Earth’s orbital plane onto the sky, so its intersection with the celestial equator defines the two equinoxes. Hence the term that fits is ecliptic. The other options don’t describe the Sun’s path that creates the equinox.