Vernal and autumnal equinoxes occur when the North Pole is at a right angle to the Earth–Sun line and the hemispheres experience equal day and night. On which dates do these occur?

Vernal and autumnal equinoxes occur when the North Pole is at a right angle to the Earth–Sun line and the hemispheres experience equal day and night. On which dates do these occur?

• A. Around March 21 and September 23
• B. Around June 21 and December 21
• C. Around January 1 and July 1
• D. Around February 14 and August 14

Answer: (A)

Equinoxes happen when the Sun is directly above the Earth’s equator, so neither hemisphere is tilted toward or away from the Sun and day and night are nearly equal in length. In the Northern Hemisphere, this occurs in spring and autumn, around March 21 and September 23. Those dates reflect the Sun crossing the celestial equator and producing roughly equal daylight. The other dates correspond to solstices or are unrelated to this solar geometry, which is why they don’t fit the definition of equinoxes.

Equinoxes happen when the Sun is directly above the Earth’s equator, so neither hemisphere is tilted toward or away from the Sun and day and night are nearly equal in length. In the Northern Hemisphere, this occurs in spring and autumn, around March 21 and September 23. Those dates reflect the Sun crossing the celestial equator and producing roughly equal daylight.

The other dates correspond to solstices or are unrelated to this solar geometry, which is why they don’t fit the definition of equinoxes.