On Monday, April 8th, 2024, a 300-mile-wide circular shadow, moving at a speed of around 1,500 miles per hour, will carve its way across North America. This solar eclipse will be visible “in totality” (when the Moon completely obscures the Sun) across a strip of North America, racing through areas such as Mexico, Texas, Arkansas, Illinois, Indiana, Ohio, New York, Vermont, and Maine before it veers out into the Atlantic Ocean, disappearing about two-thirds of the way to Europe.
According to the research group Great American Eclipse, an estimated 4 million people will travel to position themselves somewhere along this path of totality, some coming from as far as Norway. Upwards of 1 million of those people are expected in Texas, where I currently find myself visiting family. At least one county here, Kaufmann County, issued a disaster declaration, as they expect their population could double due to the influx of intrepid eclipse viewers. All of this begs the question: what is it about a solar eclipse that captivates us so deeply?
For many people, the answer to this question is the presumed rarity of a total solar eclipse; the temptation to see a “once in a lifetime” event is simply too strong to pass up. Amusingly, however, solar eclipses on Earth are not at all rare; some type of solar eclipse occurs on Earth roughly 237 times per century.
Many of these are partial eclipses or annular eclipses, where the Moon passes in front of the Sun, but its apparent size does not fully obscure the Sun, leaving a small ring, or annulus, of the Sun still visible. But roughly one-third of the solar eclipses on Earth are total, where the Moon covers up the entire surface of the Sun. That’s approximately one total solar eclipse every 18 months.
So, while it is much less common that a total solar eclipse appears in the same spot on Earth (once every 350-400 years or so), a total eclipse occurs somewhere on Earth about 50 times in a human lifespan. Clearly, this isn’t exactly a once-in-a-lifetime event. Something else must be going on.
Being able to predict where and when a total solar eclipse will occur is a relatively new accomplishment for humanity. Up until the fourth century CE or so, solar eclipses were unexpected and generally terrifying.
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In ancient China, it was believed that a solar eclipse was a dragon attempting to consume the Sun and needed to be warded off by ceremonial drumming. The ancient Assyrians believed that eclipses portended imminent danger for their rulers. However, eclipses also had some positive effects for our distant ancestors. In the sixth century BCE, for example, a solar eclipse presumably appeared during the Battle of Halys. The awe of this astronomical occurrence led both sides of the conflict to lay down their arms and declare a truce.
Even today, a solar eclipse is a truly awesome event to witness. During a total solar eclipse, as the Moon slowly passes in front of the Sun, daylight begins to wane and the temperature drops. If you happen to be viewing a solar eclipse while sporting those super stylish, cardboard eclipse glasses, you can actually see the outline of the Moon against the backdrop of the Sun.
At the point of total occlusion, when those fashionable spectacles can finally be removed, a legitimately alien object floats: a pitch-black, circular void surrounded by a halo of sparking streams of light. One could be forgiven for thinking that someone took a giant pencil and poked a hole through the sky, or that a dragon was devouring the Sun.
As awe-inspiring as a solar eclipse is to see, what is equally, if not more fascinating is that it occurs at all. For perspective, the diameter of the Sun is roughly 400 times larger than the diameter of the Moon. It just so happens that the Sun is so far away that its apparent size in the sky is nearly exactly the same as the Moon. What are the chances that we live on this rocky sphere in the universe, with a lone Moon whose orbit is at just the right distance to block out the Sun? If the Moon was slightly larger, or a bit closer to Earth, a solar eclipse would lack that beautiful crystalline ring of light. Smaller or further away, and a total solar eclipse would not be possible.
In a poetic twist, scientists have determined that the Moon is slowly moving away from the Earth (at a rate of about 1 inch per year). This means that there will come a time in the distant future when total solar eclipses can no longer occur on Earth. Ever.
Thus, a solar eclipse not only reminds us that we live in an immensely special place in the universe, but we also live at an immensely special time. A time when people can (and will) travel hundreds, even thousands, of miles across the globe, simply to stand in a shadow.