Well, I don’t know about you, but I’ve had just about as much of the summer of 2020 as I can take. I’ve lived in the desert for a quarter-century, and while I enjoy the hot, dry summers, three consecutive months is plenty, thank you.
Couple the searing heat with smoke from all the Western wildfires and wearing face masks outdoors, and, well, you can see why I’ll be overjoyed to welcome autumn to our part of planet Earth next week. I can only hope that, within a few weeks, our high temperatures will drop back to consistently double-digit numbers and the smoke will finally clear out.
This whole business of the seasons comes about because the Earth’s rotational axis is tipped 23.4 degrees to our planet’s orbit around the sun. This causes sunlight to shine more in one hemisphere than in the other at different times of the year.
The moment during the Earth’s revolution around the sun when our star seems to cross our planet’s equator on its journey from north to south — in other words, the time when both hemispheres are equally illuminated — marks the autumnal equinox in the Northern Hemisphere (spring equinox in the Southern Hemisphere). This year, it occurs at 6:31 a.m. Tuesday, Sept. 22.
For a few days around this date, the sun will lie directly over the Earth’s equator and will appear to rise due east and set due west. It is also around this time of year that our days and nights are of nearly equal length, and it is from this phenomenon that we get the term “equinox,” which derives from Latin and means “equal nights.”
Over the billions of years of our planet’s history, life around the world has become accustomed to local seasonal changes that occur throughout the year. But did you ever wonder what conditions might be like if the Earth’s axis were not tilted and we had no seasons? How would things be different?
With no tilt, the Earth would experience a more moderate and stable climate. Flora and fauna would be forced to become quite specialized; creatures of different sizes and types would likely intermingle more; and the ecology of our world would be quite different than it is today.
And if our planet’s axis were tilted even more? Seasonal changes would be more extreme. Winds would blow more strongly; storms would be more powerful and prevalent; and local temperatures would vary dramatically throughout the year.
The areas where land-based life could evolve would shrink. Less of our planet’s surface would remain for long periods at a temperature conducive to life, and even less would have seasonal variations moderate enough for life to evolve successfully.
Any life that did manage to evolve on land would need to be quite mobile to cope with these stark seasonal changes. The migration ranges of animals would be huge, and most animals would be susceptible to extinction if geological changes such as earthquakes, volcanoes or avalanches were to prevent their migration to warmer climates.
Now, as I watch the temperature climb higher, I’m reminded just how thankful I am for the changing seasons!
— Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at dennis@mammana.com and connect with him on Facebook: @dennismammana. Click here to read previous columns. The opinions expressed are his own.