It's the first day of Fall.

It's the first day of Fall.

The autumnal equinox, also called the September equinox or fall equinox, arrives Thursday night at 6:04 p.m.

It marks the start of fall in the Northern Hemisphere and spring in the Southern Hemisphere.

After the autumnal equinox, days become shorter than nights as the Sun continues to rise later and nightfall arrives earlier. This ends with the winter solstice, after which days start to grow longer once again.

The word “equinox” comes from Latin aequus, meaning “equal,” and nox, ”night.” On the equinox, day and night are roughly equal in length.