Story highlights A total solar eclipse will cross the US on August 21

It's the first eclipse to cross from the Pacific to the Atlantic in 99 years

For complete coverage of the Eclipse of the Century go to cnn.com/eclipse. Watch live, in virtual reality, as the eclipse moves coast to coast on August 21st.

(CNN) On August 21, the sun will disappear for a short time.

For a swath of the country from Portland, Oregon, to Charleston, South Carolina, it will feel like someone just turned off the sun in the middle of the day.

Even if you live elsewhere in the US, a portion of the sun will partially disappear.

It is being called the " Great American Eclipse ." And you can mark it on your calendar down to the millisecond.

The path of the "Great American Eclipse."

It's been 99 years since a total solar eclipse crossed the country from the Pacific to the Atlantic. The total solar eclipse on June 8, 1918, crossed the States from Washington to Florida.

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