Fall officially arrives Monday, Sept. 22 at 2:19 p.m. Astronomically speaking, this is the date and time of the autumnal equinox, the precise moment when the sun is seen directly overhead at noon at the Earth’s equator.
Both the northern and southern hemispheres will have almost equal amounts of daylight and night as the sun rises due east and sets due west everywhere on the planet — except for the poles.
Seen from space, the Earth is equally illuminated by the sun. All of this is repeated during the vernal equinox which marks the arrival of spring in the northern hemisphere around March 21.
The Earth’s seasons — fall, winter, spring and summer — are caused by the Earth’s orbit around the sun and the 23.5 degree tilt of our planet’s axis. This causes the amount of sunlight falling on the northern and southern hemispheres to constantly change.
The two hemispheres are always opposite in their seasons — our fall is their spring, while our summer is their winter.
Take note of where the sun rises — that is due east. Every morning at sunrise after the autumnal (fall) equinox, you will notice that the sun is moving a little bit to the right, or toward the south at sunrise.
This will continue until the sun reaches a point on the horizon that marks its farthest point south — which marks the first day of winter and the shortest amount of daylight for the year: the winter solstice.
The sun will start to move to the left, or north on the horizon, and the amount of sunlight will increase until around June 21, the summer solstice — which offers the greatest amount of daylight for the year. Then the season cycle begins anew, with the sun heading south on the horizon.
If you plan on going out to see the sunrise, do so while conditions are still somewhat dark to see beautiful and bright Venus in the east.
In the southeast, mighty Orion the Hunter and other winter constellations are easily visible.
Also visible now, in the hours before sunrise in the east is the zodiacal light. You will need a dark sky site, such as Shenandoah National Park, and the moon out of view in order to see the alluring zodiacal light
If you plan on going to Shenandoah National Park, you can get updates on the fall colors using the park’s website.
The arrival of fall means that the sun is getting lower in the sky each day at noon and the nights are growing longer and cooler. Trees across the D.C. region are taking on the beautiful colors of fall and the air will have that wonderful “earthy” smell that can only happen at this time of year.
The longer nights allow us to better enjoy the night sky too. Be sure to use WTOP’s monthly What’s Up in the Sky, published on the first of each month, to see the month’s sky sights.
Enjoy the clean, crisp air of fall and the lengthening nights. Breathe deep while you gaze skyward to see the stars — you’ll be glad you did.
Follow Greg Redfern on his daily blog to keep up with the latest news in astronomy and space exploration.
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