Week of Sept. 16-22, 2018

Around this time of year, I've had just about enough of summertime. Granted, the deserts of Southern California I call home didn't become as brutally hot as I remember in previous years, but still — enough is enough. So, when I realize that autumn is approaching, well, that's just fine and dandy with me!

This year, autumn officially arrives to the Earth's Northern Hemisphere — and spring to the Southern Hemisphere — at 9:54 p.m. EDT (6:54 p.m. PDT) on Saturday, Sept. 22. Astronomers know this exact moment as the equinox.

For those experiencing the onset of autumn, this is the autumnal equinox; for those entering spring months, it's known as the vernal equinox. Astronomically, this marks the moment when the sun crosses the celestial equator in the sky on its way southward. For a few days around this time, days and nights are of nearly equal length, giving rise to the term "equinox," which means "equal nights."

Many folks know that around the first day of autumn (and, of course, spring) the sun rises due east and sets due west. At these times, it's wise for people who drive those directions around dawn and dusk to be extra careful, since the rising and setting sun can make it difficult to see oncoming traffic and pedestrians along east-west roadways.

This whole change-of-seasons business comes about not because of our varying distance from the sun but because our Earth's axis is tilted relative to its orbit around the sun.

Over billions of years, life on our planet has become accustomed to local seasonal changes that occur during the year. But did you ever wonder what conditions might be like if the Earth's axis were not tilted and we were to have no seasons? How would things be different?

With no tilt, our planet 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 Earth's axis were tilted even more? Seasonal changes would be more extreme; winds would blow more strongly; storms would be more powerful and common; and local temperatures would vary dramatically throughout the year.

The landmass where 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 manages 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 like earthquakes, volcanoes or avalanches were to prevent their migration to warmer climates.

So, while it might seem sad to bid adieu to another wonderful summer, we must remind ourselves to enjoy the changes that are coming our way. We owe to them our very existence.

And as our desert temperatures gradually become more pleasant once again, I'm reminded how thankful I am for our changing seasons.

dem091318adAP.jpg (END IMAGE) (SET CAPTION) Watch a change of seasons after dark this week. (END CAPTION)