Photo taken by the author in Baja California, July 11, 1991.
I’m going to veer off the normal engineering focus of this column for a month to dabble in a scientific field that’s close to my heart: astronomy. We’re a month out from this year’s big heavenly spectacle in the U.S., the total solar eclipse on April 8th. This eclipse will sweep across the country from Texas to Maine, giving people close to the centerline almost four minutes of totality.
First attracted to astronomy in the mid-1980s with the passing of Halley’s Comet, I was soon swept up in the excitement leading up to a total solar eclipse in Baja California in July 1991. I saved up enough money in college to travel to see that eclipse and was awestruck. I’ve seen two more since, but I have been waiting for most of my life for the 2024 eclipse to come to me, and my hometown of Cleveland.
You may recall the “Great American” eclipse in August 2017, which swept across the nation from Oregon to South Carolina, affording so many people the opportunity to see this incredible event. My family drove to Tennessee to see it. But afterward, I was crestfallen to hear reports from so many friends that they saw it, too — “It was more than 97% here” or “We were right near the center, it was more than 90% covered at maximum for us … pretty cool.”
The key to total solar eclipses is the total part. One of the strangest coincidences about life here on Earth is that our Moon is 400 times closer to us (on average) than the Sun, but the Sun is 400 times larger. Thus, the two objects have about the same apparent size in our sky. There’s no law of physics that says this must be so. In fact, in a few billion years, the Moon will be noticeably smaller when viewed from the Earth’s surface. But this coincidence of apparent sizes today means that the geometry of the moon basely covering the sun is somewhat rare and provides an incredible spectacle when it happens.
Totality, when 100% of the sun is covered, is the magic part. You no longer need to use the darkened glasses (as long as you know how much time is left before the sun peeks out again), and you can see fiery red solar flares; the sun’s outer atmosphere, the corona; and brighter stars and planets. The leadup to this 100% coverup can include a drop in temperature, windy conditions, strange moving light bands on the ground, and animals behaving strangely. You’ve spent your entire life observing (actively or passively) sunsets and twilight — and having that 45-minute process compressed into a minute or so is mind-bending and astounding.
But again, if you aren’t in the narrow, hundred-mile-wide band of totality, you’ll miss all that. The difference between 99% and 100% is everything. In the years since the 2017 eclipse, I’ve finally found the words to explain this to friends who missed totality back then:
“If you drove 99% of the way to your favorite restaurant and then turned around and came home — and I asked you how the meal was — would you reconsider your choice?”
I hope you all are able to make your way into the shadow of the moon on April 8th, and let’s all cross our fingers for clear skies that day!
Filed Under: Commentaries • insights • Technical thinking
