Total Solar Eclipse in August 2017—New Data Shows Accurate Path of Moon’s Shadow

Avid sky-watchers, mark the date: August 21, 2017. A total solar eclipse will be happening on that day.

The most accurate map of the shadow of the moon during a total solar eclipse. Photo Credits: NASA/Goddard/SVS/Ernie Wright.

We had our fair share of eclipses and super moon events last year. 2017 promises not to disappoint either, and we even have a more accurate map this time, thanks to the Lunar Reconnaissance Orbiter’s (LRO) elevation data of the moon, and NASA’s topography data of the planet. The LRO and NASA have, thus, been able to design the most reliable maps depicting the path of totality of all known eclipses.

The August 2017 total solar eclipse will be visible in the US— as denoted by the updated map shedding light on the path of totality of eclipses, a term used to define the moon’s shadow on the sun completely covering the star. The eclipse will be spanning over the US, starting in Oregon to end in South Carolina. The last total solar eclipse of this nature happened in the US back in 1918, beginning from the state of Washington and finishing in Florida.

“Solar and lunar eclipses provide an excellent opportunity to talk about the moon, since without the moon there would be no eclipses,” says LRO’s deputy project scientist, Noah Petro. “Because we know the shape of the moon better than any other planetary body, thanks to LRO, we can now accurately predict the shape of the shadow as it falls on the face of the Earth. In this way, LRO data sheds new light on our predictions for the upcoming eclipse.”

Eclipse maps are not new to science. The concept was put together by astronomers and mathematicians Friedrich Wilhelm Bessel and William Chauvenet back in the 19th century—their work is still being used to plot the expected paths of the moon’s shadow. The conventional methods, however, do not fully take into consideration the reality of the situation: the varying elevations on Earth, and the uneven surface of the moon are not completely accounted for, when making eclipse calculations. This is where the new LRO and NASA data comes into play.

Mountains and valleys on the moon can influence the timing and duration of totality, and knowledge pertaining to this brings in more accuracy, hence the relevance of the new topography data assisting scientists to make better calculations. The researchers behind the recent improvement have used LRO elevation maps to draw a dynamic lunar limb profile (that provides information about the edge of the moon’s surface that is visible from our planet) during the anticipated passing of the shadow of the moon over the US. One of the scientists, NASA visualizer Ernie Wright, has been able to cater for an elevation map of the Earth to show eclipse observer locations at their real altitude.

“We couldn’t have done visualizations like this even 10 years ago,” says Wright. “This is a confluence of increasing computing power and new datasets from remote sensing platforms like LRO and the Shuttle Radar Topography Mission.”

The resulting maps are unprecedented: we can now visualise the varying shape of the shadow of the moon together with the changing effects of an accurate lunar limb, and the Earth’s topography.

“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,” explains Wright. “I think it’ll change how people think about mapping eclipses.”

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