A total solar eclipse is set to cross North America on Monday, providing a rare opportunity for millions to witness the afternoon skies darken as the moon blocks the sun. The eclipse’s path will traverse Mexico, 15 U.S. states, and a small part of eastern Canada, offering a partial solar eclipse in the rest of the continental U.S. Here’s your last-minute guide to this rare celestial event.

What is a solar eclipse?

Solar eclipses occur when the sun, moon, and Earth align, with the moon passing between Earth and the sun, temporarily blocking the sun’s light and casting a shadow on Earth. A total solar eclipse fully obscures the sun, while a partial solar eclipse blocks only a portion of the sun’s face.

Where and when will the eclipse be visible?

This year’s eclipse will cover a slightly wider path over more populated areas of the continental U.S. than previous total solar eclipses. NASA estimates that 31.6 million people over 15 U.S. states will be able to see the total eclipse, while the rest of the continental U.S. will witness a partial solar eclipse.

How to view the eclipse safely

It’s crucial to view the eclipse safely to avoid damage to your eyes. Special solar viewing glasses or handheld solar viewers are recommended for direct viewing of the eclipse. Additionally, homemade filters using aluminized Mylar are also considered safe for indirect viewing of the sun.

Fun milestones to look out for

If you’re lucky enough to be in the path of totality, keep an eye out for several exciting milestones. These include the appearance of the diamond ring effect, where a bright spot of sunlight creates the illusion of a sparkling diamond, and the emergence of the sun’s corona, the outermost atmosphere of the sun, visible only during a total solar eclipse.

So, mark your calendars and get ready to witness this extraordinary celestial event on Monday!