8th The Sun-Earth-Moon System (C20) Practice Test

The spring equinox happens when the Sun crosses the celestial equator moving north, so day and night are about equal in length. This occurs around March 20 or 21 in most years, which is why that date range is the correct pick. The other dates correspond to different seasonal events: late September is the autumnal equinox, while late December and late June are the winter and summer solstices, respectively. The exact date can shift by a day due to Earth's orbit and time zones, but spring equinox is typically around March 20–21.