People who live in the 70-mile-wide path of totality that spans 14 states only have to put on eclipse-viewing glasses and step outside to watch the moon block out the sun.

Fred Espenak is the type of person who doesn't wait for a total eclipse to come to him.

For nearly 50 years, he's traveled to every continent -- even Antarctica -- to witness the natural wonder he rates "1 million" on a scale of 1 to 10.

NASA research scientist Lika Guhathakurta, who's known Espenak for nearly 25 years and worked alongside him, calls his contributions "monumental."

This time, he'll likely watch the eclipse in Casper, Wyoming, where he's speaking at an astronomy convention the previous week.

I talked with Espenak about the big event dubbed the Great American Eclipse, how a partial eclipse in no way prepares you for a total eclipse, and why you'd better not skip this one.

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