The first trees are fired up in reds and oranges, and the tomato vines have withered to brown. I like that the sun sets so much earlier and rises fashionably late. Darkness has nibbled more than 4 hours from the day since the first day of summer, and it won’t stop noshing till the winter solstice. Longer and earlier dark hours mean easier access to the sky with the welcome option of going to bed on time.
Fall, the midway oasis between the two extreme seasons, begins Wednesday morning, September 23 at 3:21 a.m. CDT (4:21 a.m. EDT, 2:21 a.m. MDT and 1:21 a.m. PDT). At this instant of time, the sun will cross the celestial equator traveling south. You’ve already noticed it’s been dropping lower since summer. In September, the sun’s always in my eyes during an afternoon drive, while in June, it sits higher overhead and stays out of my windows.
Our star’s southward journey across the celestial equator — an extension of Earth’s equator projected onto the sky — is little more than an illusion. The sun’s not moving at all. No, no, no. It stays put during a year’s time, moving but the tiniest fraction of a degree in its orbit around the center of the Milky Way galaxy. It’s the Earth doing the moving, cruising along its orbit at 18.5 miles per second (30 km/sec) and causing the sun to appear to describe a giant circle around the whole sky during the year.
And the up and down stuff – the sun dropping into the southern sky during the winter months and blazing from near the zenith in the summer? That’s fake, too. Again, the sun essentially stays put. It’s the tilt of the Earth’s axis that causes the flip-flop of high sun-low sun across the seasons.
We’re tipped off to this by a simple fact: the sun never gets higher than 23.5° above the celestial equator and never gets lower than 23.5° below the equator. I’m sure you recognize that number — it’s the inclination of our planet’s axis. As we orbit the sun during the year the orientation of the axis (not the tilt) changes with respect to the sun, and these changes are reflected in the seasonal “ups and downs” of our star.
Fall’s entry also comes with a special bonus, days and nights that are equal or nearly equal in length. 12 hours of sunshine followed by 12 hours of moonshine. (Don’t take that the wrong way). The word “equinox” originates from the Latin for “equal” and “night”.
The sun’s slow dip southward means it rises later and sets earlier, spending less time in the sky. You can’t change one thing in nature without changing another. Shorten daylight and the temperature drops, rain becomes snow, chlorophyll in leaves breaks down to expose otherwise hidden red pigments, and we start taking that jacket with us to work and school in the morning.
Happy equinox and I hope you find fall as wonderful a season as I do.