September Equinox (Beginning of Autumn)

September Equinox in Boston, Massachusetts

There are two equinoxes each year: one in September and one in March.

In September, the Sun crosses the equator from north to south.

The March and September equinoxes mark the beginning of the spring and autumn seasons on Earth, according to one definition. The equinox in September is the start of fall in the Northern Hemisphere and the beginning of spring south of the equator. Learn more here.