A total solar eclipse hits Mexico as it sweeps across North America

North America won't have another solar eclipse for 20 years.

A total solar eclipse is passing over North America on April 8, creating a path of totality that will leave parts of Mexico, the United States and Canada in darkness.

About 31 million people live along the path of totality and will be able to see the total eclipse, but most Americans will be able to see at least a partial eclipse. Cities across Mexico, including Matajalan, experienced North America's first total solar eclipse.

The lunar eclipse begins in Fort Worth, Texas

A partial eclipse is visible in Fort Worth, Texas on Monday as the moon partially blocks the sun. The city will experience totality at approximately 1:40 pm local time. How some schools prepare for the eclipse

As millions of Americans gather to watch the eclipse, science teachers are preparing their students for the historic event.

Latoya Padilla, an earth science teacher at the School of the Arts in the Rochester City School District in New York, said she has been talking to her students about the eclipse since October of last year. Rochester is on track for totality.

"We talked about how this was a once-in-a-lifetime experience, we talked about how the last eclipse was 99 years ago in Rochester, and how it can be a whole [other] lifetime before you see another eclipse because you're chasing them, which some people do," he told ABC News.

How some schools prepared students for the total solar eclipse

Padilla said he taught his students the difference between a partial solar eclipse, which is when the moon only partially covers the sun, and a total solar eclipse when the moon — for a short time — completely blocks the sun.

He also explained the proper eye protection to wear and how when the moon covers the sun, observers will be able to see the planets, including Venus and Jupiter, in the sky.

"I think it's very important because you don't want [students] to wait until they realize they missed this opportunity," Padilla said. "Even if they don't fully understand what a unique experience it is, talking to them about it now and convincing them that it's unique, and you may never experience it again."