Equinoxes

The seasons are a cycle. Winter will transition into spring as the Earth moves along its orbit around the Sun. During the transition times, the day and night are the same length when the Sun is directly over the equator. That means there are exactly 12 hours of daytime and 12 hours of nighttime. These are called equinoxes.

When the day and night are the same length at the beginning of the spring, you experience the vernal equinox, or the first day of spring. Spring fades to summer as Earth cruises around its orbit only to eventually cool off into autumn. When the day and night are the same length at the beginning of the fall, you experience the autumnal equinox, or the first day of fall. Then it is back to winter again.