A solar eclipse isn’t all that rare. The moon is always revolving around the Earth, while the Earth revolves around the sun. Usually the moon appears slightly higher or lower than the sunlight hits the Earth. But twice a year, it’s right smack in front of it, and the moon blocks out the sun during the daytime, and that’s at least a partial solar eclipse.
When a total eclipse occurs, the shadow falls on just a tiny part of the Earth, about 60 to 100 miles wide, and then moves about a thousand miles over the course of a few hours. Because so much of the Earth is water, this almost always happens over an ocean.
The last total solar eclipse visible from the continental United States was in 1979, and it was only over a corner of the Pacific Northwest.
Something like this summer’s event, where so many people on land can see a total solar eclipse, is exceptionally rare — although the United States actually will experience another one, crossing an opposite diagonal swath of the country, in 2024.
This August, the “path of totality” cuts across the entire country, and every single spot in the continental United States will see an eclipse up to 60 percent.
That means that anyone in the country can step outside and see some darkness on that Monday in August. But eclipse-watchers — including Jay M. Pasachoff, a Williams College astronomer who has traveled around the world to witness an astonishing 65 eclipses — say that one truly has to see totality to really grasp the awe-inspiring nature of an eclipse. Even 99 percent, Pasachoff said, is nowhere near as dramatic as the moment it totally goes dark, which will last for up to two minutes and 40 seconds.
“You have to be in totality to do it. Basically the universe gets a million times darker,” Pasachoff said. “It is absolutely necessary to be in the path of totality. It’s a poor second to be off to the side.”
The population living in that long path of totality, from Oregon to the Carolinas, is about 12 million people, by the count of Angela Speck, co-chair of the American Astronomical Society’s task force on the 2017 eclipse. Speck says another 12 million or many more could easily visit for the eclipse date. Nearly everyone in the continental United States lives within one day’s drive of the eclipse path — so if 4 percent of the country decided they wanted to drive to the right spot that day and see the sun go dark, 12 million would turn to 24 million overnight.
There’s precedent: In 1991, Speck said, so many people tried to enter Mexico to see a total eclipse that the country closed parts of its borders.
Speck and others involved in this year’s eclipse preparation are concerned that rural communities on the eclipse path won’t be prepared for the massive traffic jams, the food and water needs of the hordes of visitors, or the safety glasses that every eclipse-watcher should have.
University of Redlands astronomer Tyler Nordgren, who is advising the National Park Service on handling this eclipse, looked at prior events. Just a partial eclipse, not a total one, set visitor records in 2012 when it crossed through National Park Service sites in the Southwest. For this summer, he told the Park Service, “Imagine the biggest event you’ve ever had, and double it.”
So come August, even nonbelievers looking out at the crowds on the eclipse path may find themselves comparing it to an apocalyptic event. For one Eastern Oregon park, Nordgren predicts 25,000 to 50,000 sky-watchers. The park has one toilet.
» Interactive Google Map: Solar Eclipse 2017