The total eclipse that will cross America — an event that last happened 99 years ago — will be an important moment for scientific observers and a massive nationwide spectator event. It will also, for many people of faith, be evidence of God’s majesty — and even, to a few, a harbinger of the coming end of the world.

“I don’t think it’s an accident that God put us human beings here on Earth where we can actually see total solar eclipses. I think God wants us to make these discoveries,” said Hugh Ross, who is both an astronomer and a minister. “I would argue that God on purpose made the universe beautiful, and one of the beauties is a solar eclipse.”

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Ross is leading a trip to watch the eclipse for about 80 people interested in finding spirituality in science. They’re preparing Monday to travel down a dirt road into a field in Eastern Oregon, where they will wait for the sun to be blotted out. Across the country, other church groups are preparing to do the same.

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.

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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.

The “path of totality” for the 2017 eclipse 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. 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.

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“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.”

For Ross and other clergy planning to showcase the eclipse as both a scientific and a religious event, that stunning experience of seeing totality is an opportunity for discussing God’s handiwork. When Ross was a researcher at the California Institute of Technology, he would take his fellow scientists on hiking trips in the Sierra Nevada, he said.

“When they would say, ‘Yeah, it’s gorgeous,’ I would say, ‘Why is it so beautiful?’ It would always lead to a discussion about the Christian faith,” he said. For that reason — the opportunity to use natural beauty as a tool for evangelism — this eclipse will be a popular Christian event. “A lot of leaders of churches are going to be encouraging people,” he said, to go see the eclipse.

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It’s certainly not just church leaders who have that idea. Visitors from as far as Europe and Asia started booking hotel rooms months ago in sleepy little corners of Wyoming and Idaho where they will be able to see the eclipse.

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.

In certain religious communities, the talk surrounding the eclipse has to do with a different sort of preparation. Gary Ray isn’t worried about just travel plans and adequate eye protection. He’s focused on the Rapture.

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Ray, a writer for the evangelical Christian publication Unsealed, views this eclipse as one of several astronomical signs that the day when Christians will be whisked away from the Earth is fast approaching.

“The Bible says a number of times that there’s going to be signs in the heavens before Jesus Christ returns to Earth. We see this as possibly one of those,” Ray said about the eclipse.

He is even more interested in another astronomical event that will occur 33 days after the eclipse, on Sept. 23, 2017.

The Book of Revelation, which is full of extraordinary imagery, describes a woman “clothed with the sun, with the moon under her feet and a crown of twelve stars on her head” who gives birth to a boy who will “rule all the nations with an iron scepter” while she is threatened by a red, seven-headed dragon. The woman then grows the wings of an eagle and is swallowed up by the earth.

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Ray says that image will be created in the sky on Sept. 23. The constellation Virgo — representing the woman — will be clothed in sunlight, in a position that is over the moon and under nine stars and three planets. The planet Jupiter, which will have been inside Virgo — in her womb, in Ray’s interpretation — will move out of Virgo, as if she is giving birth.

Astronomers don’t see this as a particularly unusual event. But to Ray and others, it could be the sign that the Rapture is ready to happen: “We think it’s God signaling to us that he’s about to make his next move.”

And Ray thinks the two eclipses that are slated to travel across the United States in 2017 and 2024, together marking an X across the nation, could be the starting and ending signs bookmarking a seven-year period of awful tribulations that Revelations says waits in store for nonbelievers who are left behind on Earth when the Rapture occurs.

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“That time frame is speculative, 2017 to 2024. But it makes a lot of sense. There are a lot of things that really point us to that,” he said.

Therefore, the eclipse preparation that Ray recommends is a bit different from the scientists’ association’s advice.

“My number one encouragement to people would be to just trust God. More importantly, to trust the right God,” he said, warning that those who do not believe when the day of the Rapture comes will be left behind to face the tribulations. “If people want to be ready, the one thing you can do is accept what He has offered, which is the gift of grace and forgiveness. That’s all we have to do to be ready.”

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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.”

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So come Monday, 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.

This story was originally published in March and has been updated.