Cities across Mexico, including Mazatlán, were the first in North America to experience the total solar eclipse.

A partial eclipse is viewable in Fort Worth, Texas on Monday as the moon partially blocks the sun. The city will experience totality at approximately 1:40 p.m., local time.

The eclipse has begun to cross North America with the first photos showing the partial solar eclipse in Mazatlán, Mexico.

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

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

"We talked about how it's kind of a once-in-a lifetime experience, we talked about how the last eclipse in Rochester was 99 years ago, and how it might be a whole [other] lifetime before you get to see another eclipse unless you go chasing them, which some people do," she told ABC News.

Padilla said she taught her 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 period -- completely blocks the sun.

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

"I feel like it’s very important because you don't want [students] to wait until they're older to realize that missed out on this opportunity," Padilla said. "Even though they might not fully understand what a unique experience it is, talking to them now about it and getting them to understand that it is unique, and you may never experience this again.”