Tracing the 2017 Solar Eclipse

This visualization closely follows the Moon's umbra shadow as it passes over the United States during the August 21, 2017 total solar eclipse. It covers the one hour and 40 minutes between 10:12 am PDT and 2:52 pm EDT. 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. 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. 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.Earth radius6378.137 kmEllipsoidWGS84GeoidEGM96Moon radius1737.4 kmSun radius696,000 km (959.645 arcsec at 1 AU)EphemerisDE 421Earth orientationearth_070425_370426_predict.bpc (ΔT corrected)Delta UTC69.184 seconds (TT – TAI + 37 leap seconds)ΔT68.917 seconds For More InformationSee [http://eclipse2017.nasa.gov](http://eclipse2017.nasa.gov) Related pages

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 runs at a rate of 30× real time — every minute of the eclipse takes two seconds in the animation. The oblique view emphasizes the terrain of the umbral path. For an overhead view, go here.Earth radius6378.137 kmEllipsoidWGS84GeoidEGM96Moon radius1737.4 kmSun radius696,000 km (959.645 arcsec at 1 AU)EphemerisDE 421Earth orientationearth_070425_370426_predict.bpc (ΔT corrected)Delta UTC69.184 seconds (TT – TAI + 37 leap seconds)ΔT68.917 seconds For More InformationSee [http://eclipse2017.nasa.gov](http://eclipse2017.nasa.gov) Related pages

This animation shows the shape of the Moon's umbral shadow during the August 21, 2017 total solar eclipse, calculated at three different levels of detail. The dark gray is the closest to the true shape. Mountains and valleys near the south pole of the Moon are visible in this image of a partial solar eclipse taken from space by the Solar Dynamics Observatory spacecraft on October 7, 2010. The lunar limb as it changes during the two-month period centered on the 2017 eclipse. Orange lines mark the equator and meridian. The blue outline is the limb, exaggerated by a factor of 18. Higher elevations can lift the observer into or out of the shadow cone. For centuries, eclipse maps have depicted the shape of the Moon's umbra on the ground as a smooth ellipse. But as this visualization shows — in a way never seen before — the shape is dramatically altered by both the rugged lunar terrain and the elevations of observers on the Earth.The lunar umbra is the part of the Moon's shadow where the entire Sun is blocked by the Moon. In space, it's a cone extending some 400,000 kilometers behind the Moon. When the small end of this cone hits the Earth, we experience a total solar eclipse. The umbra shape discussed here is the intersection of the umbra cone with the surface of the Earth. On an eclipse map, this tells you where to stand in order to experience totality.The true shape of the umbra is more like an irregular polygon with slightly curved edges. Each edge corresponds to a single valley on the lunar limb, the last (or first) spot on the limb that lets sunlight through. This is the location of the diamond part of the diamond ring effect visible in the seconds just before or just after totality. An observer standing at the cusp where two edges meet will be treated to a double diamond ring.As these edges pass over mountain ranges (for the 2017 eclipse, the Cascades, Rockies, and Appalachians), they are scalloped by the peaks and valleys of the landscape. The higher elevations in the western states in 2017 also shift the umbra toward the southeast (in the direction of the Sun's azimuth) by as much as 3 kilometers.In the animation, the red ellipse is the shape that results from assuming that the Moon and the Earth are both smooth. This is the shape most commonly seen on eclipse maps. The white shape shows the effect of the mountains and valleys along the silhouette edge of the Moon (the lunar limb). The dark gray shape adds the effect of elevations on the Earth's surface.Details The math used currently to predict and map eclipses was first described by Friedrich Wilhelm Bessel in 1829 and was expressed in its modern form by William Chauvenet in 1863. Bessel's method uses a coordinate system based on a plane, called the fundamental plane, passing through the center of the Earth and perpendicular to the Sun-Moon line. This greatly simplifies the calculations. The intersection of the Moon's shadow with the plane is always a circle, for example, and its size depends only on the Moon's z-coordinate.Using this coordinate system, it's possible to calculate just a handful of numbers, called Besselian elements, that can be plugged into various equations to predict almost anything you'd want to know about an eclipse. This was especially important in the 19th and early 20th centuries, when the math had to be done by hand. Even now, the simplicity of this approach allows us to compare hundreds or even thousands of eclipses far into the past and the future, using a reasonable amount of computer time. Bessel's method for predicting eclipses pretends that the Moon is a smooth sphere, when in fact its terrain is more rugged and extreme than the Earth's. The valleys along the silhouette edge, or limb, of the Moon affect the timing and duration of an eclipse by allowing sunlight to sneak through in places where a smooth Moon would block it. Eclipse calculations can correct for this by using a limb profile, a description of the surface elevations around the disk of the Moon.Until quite recently, everyone used the limb profiles published in 1963 by Chester Burleigh Watts. To produce his profiles, Watts designed a machine that traced some 700 photographs of the Moon covering the full range of angles, or librations, visible from Earth, an effort that spanned 17 years. Eclipse calculations are now moving to much more accurate limb profiles based on data from NASA's Lunar Reconnaissance Orbiter (LRO) and the Japan Space Agency's Kaguya spacecraft. The lunar limb in the present work is based on LRO laser altimetry and on a hybrid LRO/Kaguya dataset called SLDEM2015. To create a limb profile, each point in an elevation map is transformed into 3D cartesian coordinates in a Moon body-fixed frame. At each time step in the eclipse calculation, the point cloud is rotated into fundamental plane coordinates. The limb profile then comprises the set of points lying farthest from the shadow axis. The animation above shows how this profile changes as the Moon librates.Observer elevations are taken from SRTM, a digital elevation map of the Earth based on radar data collected during the February, 2000 flight of the Space Shuttle Endeavor. As illustrated by the following cartoon, higher elevations can lift the observer either into or out of the umbra cone. The overall effect is to shift the umbra toward the Sun. For More InformationSee [http://eclipse2017.nasa.gov](http://eclipse2017.nasa.gov) Related pages

A map of the United States showing the path of totality for the August 21, 2017 total solar eclipse. This is version 2 of the map, available at both 5400 × 2700 and 10,800 × 5400. A global map of the path of totality for the August 21, 2017 total solar eclipse. A map of the United States showing the path of totality for the August 21, 2017 total solar eclipse. The shapes of the umbra and penumbra, provided in ESRI shapefile format suitable for use in GIS software. The umbra, path, and center line in shapefile format for use in GIS software. This shapefile set is intended for larger scale (higher resolution) mapping. The preview image shows the umbra at 90-second intervals as it passes through Nebraska. Map of the 1918 total solar eclipse, from the American Ephemeris and Nautical Almanac for the Year 1918. This is a scan from the copy of the almanac held by the NASA Goddard library. Map of the 1979 total solar eclipse, from the American Ephemeris and Nautical Almanac. This is a scan from Ernie Wright's personal copy of U.S. Naval Observatory Circular No. 157. This map of the United States shows the path of the Moon's umbral shadow — the path of totality — during the total solar eclipse on August 21, 2017, as well as the obscuration (the fraction of the Sun's area covered by the Moon) in places outside the umbral path. Features include state boundaries, major highways, and 833 place names. At 18" × 9" (45 × 22.5 cm), the scale of the map is approximately 1:10,000,000.The umbra is shown at 10-minute intervals. Umbra shapes within U.S. time zones are labeled in local time. To read about the reason the shapes aren't smooth ovals, go here.The map uses a number of NASA data products. The land color is based on Blue Marble Next Generation, a global mosaic of MODIS images assembled by NASA's Earth Observatory. Elevations are from SRTM, a radar instrument flown on Space Shuttle Endeavour during the STS-99 mission. Lunar topography, used for precise shadow calculations, is from NASA LRO laser altimetry and JAXA Kaguya stereo imaging. Planetary positions are from the JPL DE421 ephemeris. The lunar limb profile and eclipse calculations are by the visualizer. ShapefilesThe map was rendered in animation software, but maps are more typically created using GIS tools and vector datasets. A set of shapefiles describing the umbra and penumbra extents is provided below in two Zip archives, one for global, U.S., and statewide maps and the other for county and city scale mapping. eclipse2017_shapefiles.zip contains the following nine shapefiles:penum17 contains the contours for maximum obscuration at 90%, 75%, 50%, 25% and the penumbra edge at 0%.penum17_1m contains a time sequence of penumbra outlines at 1-minute intervals from 17:00 to 19:15 UTC, for 95% to 75% obscuration in 5% steps.upath17 and w_upath17 contain the path of totality. The w_ version is the complete (world) path, at somewhat reduced resolution, while the other is a high-resolution version of the path limited to the 96 degrees of longitude centered on the U.S.umbra17 and w_umbra17 contain umbra shapes spaced at 10-minute intervals, again at U.S. and world (w_) scales.w_umbra17_1m contains umbra shapes at 1-minute intervals from 16:49 to 20:02 UTC, covering the complete timespan of totality.center17 and w_center17 contain the center line.The projection for all of these shapefiles is WGS84, latitude-longitude, in degrees. A minimal .PRJ file reflecting this projection is included for each shape. eclipse2017_shapefiles_1s.zip is intended for larger-scale (higher resolution) mapping. It contains the following shapefiles:umbra17_1s contains 6000 umbra shapes at one-second intervals from 17:12 to 18:52 UTC. These are high-resolution shapes with roughly 100-meter precision. The attributes for each shape include both a string representation of the UTC time and an integer containing the number of seconds past midnight of eclipse day.upath17_1s contains the path of totality, limited to the extent of the 6000 umbra shapes, roughly the 54 degrees of longitude between 130°W and 76°W. The shape was calculated at a precision of 250 meters.ucenter17_1s contains the center line as a polyline with points at one-second intervals.durations17_1s contains shapefiles for duration of totality at 30-second intervals. As with the path, these shapes are truncated and invalid at the ends.Past Eclipses The last time a total solar eclipse spanned the contiguous United States was in 1918. The path of totality entered the U.S. through the southwest corner of Washington state and passed over Denver, Jackson (Mississippi) and Orlando before exiting the country at the Atlantic coast of Florida. Prior to 2017, the most recent total solar eclipse in the Lower 48 was in 1979. Totality was visible in Washington, Oregon, Idaho, Montana, and North Dakota, as well as parts of Canada and Greenland. The author saw this eclipse in Winnipeg, Manitoba. For More InformationSee [http://eclipse2017.nasa.gov](http://eclipse2017.nasa.gov) Related pages

See the most accurate map for Aug 21, 2017's total solar eclipse. Data visualizer Ernie Wright explains how he put together a more accurate eclipse path. The path of totality across the United States. The jagged profile of the moon as measured by NASA's Lunar Reconnaissance Orbiter. An illustration of the Lunar Reconnaissance Orbiter at the moon. Related pages