The 2024 North American Eclipse
Everyone has their story about where they were and what they were doing when the 2024 solar eclipse happened in North America in 2024. This is mine.
The wonderful thing about celestial mechanics is that they’re mathematically precise; there’s no doubt as to when things are going to happen. Heavenly events can’t be stopped or delayed by events on Earth, bad weather, or a collective lack of interest. They’re coming whether you’re ready or not. I first became aware of an impending solar eclipse several months before it happened from people who pay closer attention to these things than I do. Eclipses happen all the time around the world, but this one would be different: it would take place in my backyard. Not only would there be an eclipse in a place easily accessible to me, but it would also be a total eclipse, the most spectacular sky show of all.
Upstate New York gets its Moment in the (non) Sun
I’m fortunate to have a home in upstate New York, smack dab in the projected path of totality, the swath of land from which observers could experience a complete blotting out of the sun from the sky. In totality — those few minutes in which the moon completely obscures the sun — the sky darkens, temperatures fall, birds stop singing, and sunset-like conditions appear on the horizon, no matter which direction you look. Pretty spectacular.
My friend Will was able to make the trek upstate…and he was a great friend to have for this event because he’s an astronomy enthusiast who’s entertained our group of pals many times by bringing his serious telescope gear for nighttime stargazing. He prepared in advance by purchasing new hardware that would allow for direct observations of the sun which could be output to a laptop for digital image and video captures. We were going to collect some amazing pictures. Only one natural force had to cooperate. The weather.
Praying to the Weather App
The weather in upstate New York in April is notoriously overcast. As another friend said, “who’s bright idea was it to schedule this thing in April?!” Smartphones make it possible to obsessively watch developing weather conditions, and boy, did we ever. Starting 10 days out, until the day before the scheduled April 8 eclipse date, we reviewed the data hundreds of times. Not once in that lead-up period did the forecast look favorable. Of course, we held out hope.
Checking weather forecast on the morning of Eclipse Day, it looked like our home base was going to be socked in; we’d see nothing. Time for a new plan. Using a handy eclipse phone app, we looked for a location with a better forecast, somewhere that would be reachable within a two-hour drive. That location turned out to be Old Forge, NY, a tiny resort town in the Adirondack Mountains.
During the drive northeast, the conditions continued to look favorable: high, wispy clouds that were too thin to obscure the sun. Those conditions persisted as we pulled into one of the few parking lots that weren’t charging people for the privilege. Hopes soared as Will configured his gear — an hour-long process involving wires, screws, latches, and power cords running from his electric vehicle’s output port.
As the eclipse began, clouds began to move in from the east. Over the next hour and handful of minutes leading up to totality, things got steadily worse. By the time the Big Moment arrived, the clouds were pretty thick…but not thick enough to completely obscure the sun. It remained visible, though weak, during the period of totality.
A Shared Experience
One of the benefits of living in the 21st century is the ability to experience things communally, in real-time, no matter how distant others may be. Two other friends were able to share their experiences with us as the eclipse unfolded, one viewing from Dallas, another from western Pennsylvania. (A third friend had the misfortune to be watching from Buffalo, NY which was socked in with heavy cloud cover.) I’ve stitched all of these vantage points together in the following video.
Overall, we felt lucky to have experienced what we did. Had we stayed at the home base, we would have seen nothing. Not only did we see a clear partial eclipse on the going-in side, we were able to experience some of the dazzling effects of totality. It’s easy to see how some people become eclipse followers, traveling the world in search of another hit of celestial wonder.
Eclipse Mechanics
Having experienced this event of natural wonder, I wanted to know more about the mechanics of eclipses. It’s nice to trust the experts, but I wanted to know more about the math of accurately predicting them, and why we observe variations in eclipse types. Here’s how it works.
The first condition necessary for an eclipse is obviously for the moon to be between the Earth and the sun. We all understand that part.
Credit for this and all subsequent eclipse diagrams: Welsh Labs, https://www.youtube.com/watch?v=0fgbMTC30F8
The moon orbits the Earth with a period of roughly 29 days and so appears from the following view to be in position to produce a solar eclipse once a month.
But this doesn’t happen because of the third dimension not implied by the direct overhead view above. The moon’s orbital plane is at an angle to the Earth’s orbital plane around the sun, so during most of the times that the moon is between the Earth and the sun, it’s too high or too low with respect to the Earth’s orbital plane to result in the moon casting a shadow that intersects with the Earth. In the illustration below, the moon is between the Earth and sun, but its shadow is projected out into empty space. No eclipse occurs.
The moon is only in a position to cast a shadow on the Earth when it lies in the Earth’s orbital plane. That occurs twice during the moon’s orbit of the Earth. These points are known as lunar nodes.
Two times during every orbit of the sun, roughly 173 days apart, the moon hits one of its nodes while being directly between the Earth and the sun. These are potential eclipse points.
There’s another variable to consider when plotting out when a total solar eclipse will occur: the eccentricity of the moon’s orbit about the Earth. That is, the center of the moon’s orbit is not the Earth; the moon’s orbit takes it to a range of distances from the Earth. The point of closest approach is called the perigee, the furthest, the apogee. And to make things even more complicated, this orbital path slowly rotates about the Earth as both bodies travel through space.
So, even if the moon is in position at a lunar node while being directly between the Earth and sun, the moon may be too far away to completely obscure the sun. This results in an annular eclipse, instead of a total eclipse.
There are three orbital motions that must align in order for a total eclipse to happen. Each motion has a name associated with the length of time required for one cycle of that motion.
A synotic month is the time between two occurrences of the moon passing between the sun and the Earth. This is the familiar 29.5-day orbit of the moon that we associate with the phases of the moon.
A draconic month is the time it takes for the moon to move from its first node, through the second, and back to the first again, or roughly 27.4 days.
An anomalistic month is the average time the moon takes to go from perigee to perigee in its orbit about the Earth. It corresponds to about 27.6 days.
A total solar eclipse requires the alignment of all three cycles. This alignment occurs approximately every 18 years, 11 days, a period known as a saros. During a saros, eclipses repeat with similar characteristics, making it a valuable cycle for predicting future eclipses.