Combining elevation data gathered by the Lunar Reconnaissance Orbiter (LRO) with Earth topography data, NASA researchers have produced the most accurate map ever created for the path of totality of the total solar eclipse that will be seen across a large swath of the United States on Monday, August 21 this year.
NASA visualizer Ernie Wright, working at the Goddard Space Flight Center in Maryland, put together a new and more accurate representation of both the map of the eclipse path and the shape of the shadow (known as the umbra) cast by the Moon on the Earth during its encounter with the Sun.
By using the LRO lunar surface data (particularly that which shows the outline of the moon with the utmost precision), Wright was able to provide a continuously varying lunar silhouette of the moon as it transits over the United States. This is particularly important to know for observers, as ridges and valleys on the perimeter of the Moon can affect the shadow cast and, therefore, the time and length of the total eclipse by a matter of several seconds.
As for the accuracy of the eclipse path itself, Wright incorporated a range of NASA data sets in his elevation map renderings of the Earth to accurately reflect the path in relation to observer locations at their true altitude. This is a much more accurate way of providing observational certainty than the traditional methods of eclipse calculations that assumed all observers were at sea level and that the Moon was a perfectly smooth, symmetrical sphere rotating unerringly around its center of mass.
As a result of these improvements, the visualization maps now illustrate an exceptionally accurate, time-changing shape of the Moon's shadow that shows the effects of both a super-accurate lunar outline and the Earth's changing terrain which, according to the researchers, have never been observed before.
"We couldn't have done visualizations like this even 10 years ago," said Wright. "This is a confluence of increasing computing power and new datasets from remote sensing platforms like LRO and the Shuttle Radar Topography Mission."
With the new information applied to the shape of the Moon's umbra, the silhouette can be seen to look more like an irregular polygon with edges that are somewhat curved. These edges are valleys and peaks on the edge lunar limb and, as these shadows travel over mountain ranges on Earth, they are each altered by the landscape on which they are projected. This will be particularly noticeable as the umbra crosses the Cascades, the Rockies and the Appalachian mountain during the eclipse, and the new NASA maps will help observers account for these variations.
"We've known for a while now about the effects of the lunar limb and the elevation of observers on the Earth, but this is the first time we've really seen it in this way," said Wright. "I think it'll change how people think about mapping eclipses."
For the United States, the total solar eclipse will start in Oregon and finish in South Carolina, on Monday, Aug. 21, 2017, almost one hundred years since the last US total solar eclipse of 1918, when the path of totality started on the southwest corner of Washington, then traveled over Denver, Colorado, Jackson, and Mississippi before finally passing over Orlando and leaving via the Atlantic coast of Florida.
The video below shows a visualization created by NASA for the upcoming event.