This animation closely follows the Moon's umbra shadow as it passes over the United States during the August 21, 2017 total solar eclipse. Through the use of a number of NASA datasets, notably the global elevation maps from Lunar Reconnaissance Orbiter, the shape and location of the shadow is depicted with unprecedented accuracy.
During the August 21, 2017 total solar eclipse, the Moon's umbral shadow will fly across the United States, from Oregon to South Carolina, in a little over 90 minutes. The path of this shadow, the path of totality, is where observers will see the Moon completely cover the Sun for about two and a half minutes.
People traveling to see totality, likely numbering in the millions for this eclipse, will rely on maps that show the predicted location of this path. The math used to make eclipse maps was worked out by Friedrich Wilhelm Bessel and William Chauvenet in the 19th century, long before computers and the precise astronomical data gathered during the Space Age.
In keeping with their paper and pencil origins, traditional eclipse calculations pretend that all observers are at sea level and that the Moon is a smooth sphere centered on its center of mass. Reasonably accurate maps, including this one, are drawn based on those simplifying assumptions. Those who want greater accuracy are usually referred to elevation tables and plots of the lunar limb.
This animation shows the umbra and its path in a new way. Elevations on the Earth's surface and the irregular lunar limb (the silhouette edge of the Moon's disk) are both fully accounted for, and they both have dramatic and surprising effects on the shape of the umbra and the location of the path. To read more about these effects, go here.
The animation provides an overhead view of the umbra and runs at a rate of 30× real time — every minute of the eclipse takes two seconds in the animation. For an oblique view that emphasizes the terrain of the path, go here.
This animation of the August, 2017 umbra path begins at 2:45 p.m. EDT, when the umbra is about to leave land and travel into the Atlantic Ocean, and it ends at 4:02 p.m. EDT as the umbra is about to leave the Earth's surface.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 184.108.40.206.0