Next Thursday, Sept. 22, autumn arrives at 7:05 p.m. MDT. This is the moment of the Autumnal Equinox. The equinoxes (vernal and autumnal) are the two points in time and location where the sun appears to be roughly at the halfway point between the extremes of its annual south-north and north-south journeys through the sky. The equinoxes also mark the two times of the year when the temporal division of daylight and darkness are most nearly equal, at about 12 hours each.
The “ends” of the sun’s annual journey through the sky are the solstices. The farthest south point and shortest day happen with the winter solstice, just before Christmas on the first day of winter. When the sun reaches its most northerly point on or about June 20, the summer solstice is the first day of summer. Halfway between winter and summer, the vernal equinox marks the first day of spring and another roughly equal distribution of daylight and darkness.
Of course, the sun doesn’t really move through our sky. The Earth travels around the sun in an elliptical orbit, which takes 365 and a quarter day to complete. As Earth zips around the sun, it rotates once every not-quite 24 hours, and our planet rotates around a vertical axis which is tilted about 23 degrees from straight “up and down” (as defined by the plane of the ecliptic, or the plane where on average all of the planets orbit the sun).
The combination of our orbit about the sun and the tilt of our rotating planet is what makes the sun appear to move from south to north and then from north to south each year.
This is stuff we all know, but it’s worth revisiting and thinking about periodically.
So then, at 7:05 p.m. MDT this coming Thursday our Spaceship Earth will arrive at that point in its orbit called the Autumnal Equinox. From the Latin autumnale, ‘of autumn’, and aequinoctium, ‘the time of equal days and nights’.
While the Autumnal Equinox marks the end of summer and the beginning of fall, the shift in regional weather conditions is considerably more gradual. Most of us have already noticed that the days are getting shorter and the nights longer. Despite the recent heat wave, many of us have also noticed that the longer nights provide more cooling, while the shorter days provide less heating. Therefore, even though we’ll still see plenty of very warm days through September and well into October, the ongoing trend is one of cooling.
This cooling will continue for about three months, or until just before Christmas. Then, on Wednesday, Dec. 21, at 2:47 p.m. MST, winter will arrive with the Winter Solstice. At that moment the sun will stop moving south and begin moving north. It will be the shortest day of the year at 9 hours, 21 minutes and 22 seconds, followed by the longest night of the year at 14 hours, 38 minutes and 38 seconds. Then it will really get cold!
As summer fades and fall begins the annual cycle of life is winding down. Part of me looks at this with regret. The little kid in me wants summer to go on forever, these long days of hard work an easy livin.’ But the grownup in me understands that without autumnal senescence and the killing cold of winter there can be no spring rebirth followed by summer. I’ve been doing this long enough to know one of the delightful secrets of livin’ in this part of the world; that the moment of darkest winter is also the moment of annual rebirth. We won’t really notice it at first, but the sun will be moving northward day by day, and each day will be a little bit longer, each night a little bit shorter.
All of that is yet to come. In six months-time, it will be March 20 and spring will arrive with the Vernal Equinox. Six months seems a long time, but the days pass one by one, and knowing that spring will come is a comforting feeling.
In the meantime, while summer is still hanging on and autumn is yet to begin, it’s a good time for me to remember Henry David Thoreau’s admonition regarding livin’ through the seasons.
“Live each season as it passes; breathe the air, drink the drink, taste the fruit, and resign yourself to the influences of each.”
Be well and embrace the blessings of liberty.