If you are one of these millions, prepare to feel changed forever. So say the eclipse chasers who venture great distances and go to extreme lengths to witness the ethereal occurrence.

“This is the most awesome astronomical event there is, period,” said Mike Kentrianakis, a veteran eclipse chaser. “You’ll never ever forget it.”

Mr. Kentrianakis has spent his life in pursuit of totality, the fleeting moment when the moon aligns perfectly with the sun and throws everything into darkness.

His obsession has led him to a jungle in Mikongo, Gabon, the top of a mountain in Tianhuangping, China, and to the frigid wilderness of Svalbard, Norway (that last one in a wheelchair, no less).

He was so excited about the Great American Eclipse that he hit the road in 2015, traveling the 3,000-mile path of the coming eclipse as part of his work with the American Astronomical Society.

The purpose of his trip was as much to inspire people as it was to warn them of the inevitable and overwhelming crowds that would flood their towns, as he has seen happen numerous times before.

“This is two years out. They didn’t know what was coming,” Mr. Kentrianakis said. “We knew. No one can predict the future, except for an eclipse chaser.”

Here’s what he and his fellow eclipse aficionados say we should expect.

That First Eclipse

Wherever they come from, eclipse chasers often share a similar origin story that involves the first time they witnessed totality.

Kate Russo, a clinical psychologist and eclipse chaser who lives in Northern Ireland, saw her first eclipse on the coast of France in 1999.

“I thought this was my chance to see a total solar eclipse and take it off my bucket list,” she said. “How wrong I was.”

The totality viewed during an eclipse in Gabon by Mike Kentrianakis in 2013. Credit Allen Davis and Mike Kentrianakis

She has since written three books on eclipses, but the roller coaster of emotions she experienced the first time is still with her.

“Everyone sensed something was coming,” she said. “The world held its breath. It was eerie and quite frightening and so dramatic, and then suddenly you’re plunged into darkness.”

She was hooked, and in 2001 she traveled to Madagascar to catch her next total solar eclipse.

“That’s when I thought, ‘I’m an eclipse chaser,’” Dr. Russo said. “That’s when I discovered a map that had the paths of totality for all future eclipses. I saw that map and I thought: ‘This is the structure of my life for the next 20 years. This is where I’m going to be.’”

The chase led her to South Australia in 2002, on a Galápagos Islands cruise in 2005, Turkey in 2006, Mongolia in 2008, China in 2009, Australia again in 2012, the Faroe Islands in 2015 and Indonesia last year.

For all those eclipses and all that travel, she has spent just 22 minutes in all beneath totality.

“The endorphins kick in,” she said. “There’s an element to it that’s addictive.”

For Mr. Kentrianakis, the opportunity to see his first total solar eclipse was pure chance.

One day in 1978, when he was 14 and living on Long Island, he came across an article in his local paper about researchers preparing an expedition to Manitoba, Canada, to observe an eclipse on Feb. 26, 1979. The last line in the article announced that the team had one seat available.

Mike Kentrianakis, left, and fellow eclipse-chasers in Manitoba, Canada, to observe an eclipse on Feb. 26, 1979. Credit via Mike Kentrianakis

His parents let him call the researchers, who invited him to join the expedition. That February they arrived in Lundar, Manitoba, and trekked through 18 inches of snow to the field where they would observe the event.

On the day of the eclipse, one of the researchers, Fred Hess, shouted the countdown to totality. He announced every minute until the sun disappeared and a shining diamond ring appeared.

“He’s reading it out and he’s losing control,” Mr. Kentrianakis said. “He goes, ‘Look! Look! Look! Look!’”

Mr. Kentrianakis was overwhelmed by the sight, too, and for two minutes and 47 seconds he witnessed totality. (In a recording, you can hear him and the group shouting.)

“I’m looking at this corona in the sky and thinking, ‘Wow, this is really strange and beautiful,’” he said.

Get to Totality

One of Mr. Kentrianakis’s mentors, Jay Pasachoff, has experienced 65 solar eclipses. But he prefers not to be called an eclipse chaser.

“I’m an eclipse preceder,” he said. “We get there before the eclipse.”

Jay Pasachoff, an astronomer at Williams College, with a refractor dating back to 1851. He is a veteran of 33 total solar eclipses.

Credit Nathaniel Brooks for The New York Times

Dr. Pasachoff is an astronomer at Williams College who has used totality as an opportunity to probe the mysteries of the sun. He has set foot on every continent except Antarctica in pursuit of the phenomenon (though he has watched it in a plane above Antarctica).

He and his wife, Naomi, who has seen 39 eclipses, even witnessed a total solar eclipse on their honeymoon in 1974.

“I think there’s a primal feeling of excitement to see the universe darken at a time when it’s not usually supposed to,” he said.

Dr. Pasachoff advises that first-timers try to get within the middle of the path of totality rather than on the edges, just to make sure they see it. And he encourages them to make it a family event.

“Take a kid to the eclipse,” he said. “It can be inspirational to a new generation of students.”

He added that people shouldn’t worry about snapping the perfect picture with their phones.

“If it’s your first eclipse, don’t try to take any pictures,” he said. “Just enjoy yourself. Just watch all of the phenomenon and relax about it.”

Most important, leave early for it, he advised, to avoid being stuck in a traffic jam outside the path. Try to get into totality the night before.

That advice is echoed by Hakeem Oluseyi, an astrophysicist at Florida Institute of Technology who has chased eclipses in Ghana, Australia and the island of Mangaia in the South Pacific. His journey to Cairns, Australia, in 2012 was featured in the documentary “Black Suns: An Astrophysics Adventure.”

“The difference between being off the line of totality and on it is like the difference between seeing a lightning bug and lightning,” Dr. Oluseyi said.

For solar researchers like Dr. Pasachoff and Dr. Oluseyi, the eclipses are times for serious scientific work. But the weather can be a roulette-wheel spin. Sometimes it’s clear blue skies. Other times, it’s overcast.

“In the South Pacific, clouds had completely covered two minutes before totality and uncovered three minutes after,” Dr. Oluseyi said. “That was like a cruel joke.”

Mr. Kentrianakis has also found clouds to be a recurring adversary in his adventures, spoiling or nearly spoiling some eclipse trips. In 1998 he traveled to Aruba for his second total solar eclipse, but it was overcast on his part of the tiny tropical island.

“I thought, ‘How often does it rain in Aruba?’” he said.

When possible, he suggested, it’s a good idea to stay mobile on eclipse day in case the thick clouds move in and you need to relocate. That’s what he did in Aruba, getting into his car and racing to the other side of the island.

He made it just in time to see the blue and violet sky turn black.

But he advised that people not obsess over weather forecasts in the weeks and days leading up to an eclipse, saying that the stress isn’t worth it. Now, his most sacred rule is that he does not talk about weather in the days leading up to an eclipse.

‘Questions and Curiosities’

One way eclipse chasers ensure that the weather doesn’t dampen their plans is to get above the clouds.

In 2016, Mr. Kentrianakis joined other eclipse chasers aboard an Alaska Airlines plane as it journeyed from Anchorage to Honolulu. The plane altered its flight plan to cross the path of totality.

His excitement, which is practically contagious, was captured on video that went viral online.

“Oh my God! Corona, there it is!” he shouted. “Baily’s beads! Diamond ring! Look at that! Corona! Totality! Totality!”

But whether you end up tens of thousands of feet in the air or standing on the ground, eclipse chasers want you to know that the journey you take to see the total solar eclipse will be well worth your time and effort.

“I think every single person I’ve ever interviewed about their first eclipse experience says the same thing: ‘Why didn’t you tell me it would be so good?’” Dr. Russo said. “People don’t get it until after they experience it.”

To Dr. Oluseyi, the eclipse has the potential to affect the nation in the same way that these cosmic spectacles have had an impact on him.

“There are all these questions and curiosities that are inspired by these experiences,” he said. “Perhaps new eclipse chasers will be born out of this event.”

Source: The New York Times