On the East Coast – and that includes Maine, of course – fall arrived at 10:21 this morning, marking the second time this year the Earth is nor tilted toward or away from the sun.  This gives the entire planet roughly 12 hours of daylight and 12 hours of darkness on this one day.

There are two equinoxes occurring each year, one in the spring and the one marking the arrival of autumn. The length of day, position of the sun and strength of the sun are approximately the same for each equinox. Of course the difference between the spring equinox and today’s is now we are losing daylight, whereas in March we are rapidly gaining it.

Because of the way sunrise and sunset are calculated a 12-hour day usually occurs just before or just after the equinox. The equilux in Portland occurs on Sunday this year when the sun will rise and set at 6:32.

Did you know meteorologists and climatologists don’t consider fall as beginning on the same day? Those of us in the weather community look to the first day of autumn to be Sept. 1, the first day of winter Dec. 1, the first day of spring March 1 and the first day of summer June 1. This is when the meteorological seasons begin and are based on seasonal temperatures, not the position of the sun. Astronomical seasons are different and based on where the Earth is during its orbit around the sun.

The time of the equinoxes as well as the first day of summer and winter move around the calendar by about a day.  However, in the past and future, the first day of fall can come as early as the Sept. 21 or as late as Sept. 24,  which it did back in 1931 and won’t again until 2303.  Interestingly, in 2092 and 2096 the autumnal equinox will occur on Sept. 21.

In the Southern Hemisphere, today marks the start of spring.  Daylight will continue to increase there for another three months and peak just as we are beginning winter.

The sun will rise due east and set due west tomorrow, the first full day of autumn.  After that, the sun will continue to rise and set farther and farther south of this direction.  The sun’s shortest path across the sky will occur on the first day of winter.

One myth you might hear about the equinox is you can balance an egg or a broom on this day.  This isn’t true: If you could do that today or on the first day of spring, you could do that any other time of the year.

Lastly, Portland and the surrounding area will lose about 3 hours of daylight between now and the end of autumn.  If that depresses you, it’s only 12 more weeks until the days start getting longer again!