Welcome, fall! Send in those foliage pics

JACKSON, Wyo. — Goodbye, summer! It was fun while it lasted.

The autumnal equinox occurred in the early hours of Sunday, Sept. 22, marking the first astronomical day of fall in the northern hemisphere and the first day of spring in the southern hemisphere.

According to the Old Farmer's Almanac, an equinox describes the moment the sun's center crosses the celestial equator — earth's imaginary extension of the equator line into space. When the sun crosses the equator going from north to south, this marks the autumnal equinox in the northern hemisphere; when it crosses from south to north, this marks the vernal equinox.

Across the world, this happens at the exact same time but the hour and day differ depending on the time zone, so the equinox falls on Sept. 22 or Sept. 23.

What this all means is that after the equinox, days become shorter than nights because the sun continues to rise later and nightfall arrives earlier, until the winter solstice . The arc of the sun will slowly creep south, the leaves will begin to change and the temperatures will begin to dip.