Fall “Begins” Tomorrow, Harvest Moon on October 6
Full Harvest moon, 2007. Full resolution image, courtesy the author. 15 cm F/4 Newtonian astrograph.
The Autumnal Equinox
The Vernal and Autumnal Equinoxes are two days during the year with 12 equal hours of daylight and darkness. The Vernal Equinox heralds the beginning of Spring and the Autumnal Equinox, Autumn.
The Autumnal Equinox for this year occurs Monday, September 22, 2025, 18:19 UTC (Monday, September 22, 2025, at 2:19 PM EDT). Many astronomical dates throughout the year can be found here.
What does the ‘Beginning of Spring’ or the ‘Beginning of Fall’ actually mean, and what’s so special about these dates?
The changes we normally associate with the start of a new season are climactic, such as changes in temperature or weather. So, what does the ‘Beginning of Spring’ or ‘Beginning of Autumn’ actually mean? To answer that, we’ll have to consider the astronomical year in its totality and the other two significant dates during the year, the Summer and Winter solstices. Those events represent the points during the year when the sun is at its highest and lowest points on the sky respectively.
The sun, at its highest point during the third week in June (June 20-22) in the Northern Hemisphere, represents the ‘beginning of summer’. Likewise, the sun is at its lowest point during the third week in December (December 20-22) in the Northern Hemisphere, represents the ‘beginning of winter’. The two Equinoxes occur when the sun crosses the Celestial Equator at the midpoint between these highest and lowest points (see the view above). The Celestial Equator represents the projection of the Earth’s equator on the sky.
It should be noted that the Southern Hemisphere experiences the same seasons but at opposite times during the year. Summer in Australia occurs during December and January, while Winter occurs during June and July.
The Astronomical Beginning of Spring or Autumn are conventions, marking the first and second point respectively since the beginning of the year when the sun crosses the Celestial Equator.
The Vernal Equinox in March marks the first time there are 12 equal hours of daylight and darkness. Similarly, the Autumnal Equinox, occurring during the third week of September, marks the 2nd and final time during the year when there are equal hours of daylight and darkness.
What Happens During the Equinoxes?
12 equal hours of daylight and darkness.
The opposite seasons begin for our friends in the Southern Hemisphere.
The sun rises due east and sets due west at any point on the planet.
The sun’s elevation above the nearest horizon (southern horizon for Northern Hemisphere observers and northern horizon for Southern Hemisphere observers) is exactly equal to the compliment of their latitude; for example, if your latitude is +40 (40 degrees north latitude), the elevation of the sun would be 50 degrees above the southern horizon.
For those interested in the Lore and Lure of the moon and the naming traditions, the full moon nearest to the Autumnal Equinox is known as the “Harvest Moon”.
2025 Harvest Moon
We’ve written extensively about the lore of the moon’s names, most of which honor native traditions or coincide with seasonal events. This is especially relevant for hunter-gatherer or agrarian communities who depended on a plentiful harvest or hunt to survive.
For those interested in the Lore and Lure of the moon and the naming traditions, the full moon nearest the Autumnal Equinox is known as the “Harvest Moon”. Before the invention of the electric light, the light of the full moon gave aid to the farmers of old, extending the time during which they could harvest their crops.
This year’s Harvest Moon occurs on Monday, October 6th and, since the October 2025 full Moon is closer to the Autumnal equinox than September’s full moon, it takes the name Harvest Moon, while this year’s September full moon (already past 2 weeks ago) is the “Full Corn Moon”. Rarely does the Harvest Moon occur during October, but when it does, the September full Moon corresponds with the corn harvest.
September’s New Moon
Occurs tonight, September 21, 2025.
With the new moon occurring tonight, one of the last opportunities to view the summer Milky Way under a dark, moonless sky, will be tonight through next weekend.
In this view to the south, today during late evening twilight tonight, September 21, we see Saturn, low in the east at its rising with ruddy-red Mars low in the west and setting. Due south, we see the favorites of Summer, the “Teapot” of Sagittarius and the summer scorpion, Scorpius, the later stretched out along the horizon with the red giant star, Antares, its heart, about to set.
Since fall is upon us tomorrow, these summer favorites will soon be invisible and won’t be favorably placed for at least 6 months and then, only during the wee dawn hours before sunrise.
Featured Image
If you could turn off all the lights of civilization and remove the atmosphere, the following is the sky you would see tonight at 8:40 PM, EDT.
Saturn is high in the southeast, Mars has set, and the teapot of Sagittarius is just east of the Milky Way’s galactic center. Scorpius is stretched out along the horizon with its heart, the red giant star Antares, about to set.
“If the stars should appear one night in a thousand years, how would men believe and adore; and preserve for many generations the remembrance of the city of God which had been shown!
But every night come out these envoys of beauty, and light the universe with their admonishing smile.”
Ralph Waldo Emerson: excerpts from “Nature” (1836)
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