What Is Spring Equinox 2024. The vernal equinox marks the beginning of astronomical spring, while. An equinox is one of two days in the year when the sun crosses the equator and day and night become equal in length.

It is also the point in the calendar where the day length is more or less equal to the length of the night. An equinox is one of two days in the year when the sun crosses the equator and day and night become equal in length.