The first day of autumn is Monday. Fall arrives when the high noon sun crosses the earth’s equator at precisely 10:29 p.m., Eastern Standard Time. The precise moment can be calculated and forecasted years ahead. But try and observe it, and things get incredibly difficult.

In the southern hemisphere, they are thinking first day of spring.

Day and night are about equal around the globe. According to our own tables for sunrise and sunset, the actual day when daylight and night time are equal is Sept. 26, when sunrise is at 6:32 a.m., and sunset is 6:32 p.m. The reason for the four day difference has to do with our atmosphere bending the light of the sun on the horizon at sunrise and sunset.

But the first day of autumn isn't a moment on a clock, it's a sense of a change. Poison ivy on the side of a wooded path has turned red. Bittersweet leaves are yellow. The stars overhead at night say autumn. And the dew in the morning says it too.

For early risers, Saturday morning a thin crescent moon appears close to the bright planet Jupiter. Look more than hour before sunrise for the two in the eastern sky.