“It’ll be kind of an orange ball. You’ll see some things that look like flames around the outside edge,” he says. “Those are prominences, and those will be, if you put them to scale for the Earth, maybe one to three times the size of the Earth. So they’re really, really, really huge.”

More About The Transit Of Venus

As Venus Transits The Face Of The Sun, Here’s How To Safely Watch

Do not stare at the sun! But there are ways to watch without hurting your eyes.

Look Up, Stargazers: June 5 Is The Transit Of Venus

The rare astronomical event won’t happen again until 2117.

But Small says if you want to see any of this, you’ll have to be careful.

“Especially don’t point any kind of astronomical or optical device like a binocular or telescope toward the sun unless you know specifically what you’re doing with that, because you can destroy your vision instantly in most cases,” he says.

This is your last chance to see a transit of Venus — it won’t happen again until 2117. University of Missouri-St. Louis astrophysicist Erika Gibb says even though Venus passes between Earth and the sun every year and a half or so, its orbit is tilted relative to ours, making a perfect alignment rare.

“Most of the time it misses — it either passes above the sun or below the sun,” she says.

In the 17th and 18th centuries, the transit played a key role in the history of astronomy. Gibb says scientists used it to figure out the size of the solar system. Astronomers had people in different parts of the world time when the transit began and ended.

“Then they could use triangulation techniques to figure out what the actual distance between Earth and the sun, and Earth and Venus were,” Gibb says.

This transit of Venus will be visible from all over the U.S. in the hours before sunset.