NASA Develops Process to Create Highly Accurate Eclipse Maps

New NASA research reveals a method for generating highly accurate eclipse maps that plot the predicted path of the Moon’s shadow as it crosses Earth’s surface. Traditionally, eclipse calculations assume that all observers are at sea level on Earth and that the Moon is a smooth sphere perfectly symmetrical about its center of mass. As a result, these calculations do not take into account the Moon’s varying altitudes on Earth or its irregular, cratered surface.

To obtain slightly more precise maps, one can use elevation tables and plots of the lunar limb, that is, the edge of the visible surface of the Moon as seen from Earth. However, eclipse calculations have now become more precise thanks to the integration of lunar topographic data from observations by NASA’s Lunar Reconnaissance Orbiter (LRO).

Using elevation maps from LRO, NASA viewer Ernie Wright at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, created a profile of the lunar edge that changes constantly as the moon’s shadow passes over Earth. Mountains and valleys along the edge of the lunar disk affect the timing and duration of totality by several seconds. Wright also used several NASA data sets to provide an elevation map of Earth so that eclipse observers’ locations are represented at their true elevations.

The resulting visualizations show something never seen before: the true time-varying shape of the moon’s shadow, with the effects of both a precise lunar limb and Earth’s terrain.

“Since the 2017 total solar eclipse, we have been publishing eclipse maps and movies that show the true shape of the Moon’s central shadow, the umbra,” Wright said.

“And people wonder why it looks like a potato rather than a smooth oval? The short answer is that the Moon is not a perfectly smooth sphere.”

The mountains and valleys surrounding the Moon alter the shape of the shadow. The valleys are also responsible for Baily’s beads and the diamond ring, the last fragments of the Sun visible just before and the first just after totality.

Wright is the lead author of a paper published in The Astronomical Journal This study reveals for the first time exactly how the Moon’s relief creates the shape of the shadow. Valleys at the edge of the Moon act like pinholes projecting images of the Sun onto the Earth’s surface.

The shadow is the little hole in the middle of these projected solar images, the place where none of the solar images reach.

The edges of the shadow are made up of small arcs coming from the edges of the projected solar images.

This is just one of many surprising results from the new eclipse mapping method described in the paper. Unlike the traditional method invented 200 years ago, the new method renders eclipse maps pixel by pixel, much in the same way that 3D animation software creates images.

It’s also similar to how other complex phenomena, like weather, are modeled on computers by breaking the problem down into millions of tiny pieces, something computers do very well and which was inconceivable 200 years ago.