Solar Eclipse Shadow Shape Explained
Valleys around the lunar limb act like pinholes projecting images of the Sun onto the surface of the Earth during the August 21, 2017 total solar eclipse. This visualization shows the projected Sun images forming a flower-like pattern with a gap in the center, where the eclipse is total.
Traditional solar eclipse maps depict the shape of the Moon's umbra shadow as a smooth oval, but more detailed calculations that account for the Moon's terrain have revealed that the shape is a many-sided polygon. A 2024 paper published in the Astronomical Journal explains how the mountains and valleys around the limb (silhouette edge) of the Moon create this complex shape.
During a total solar eclipse, the valleys act like pinholes projecting images of the Sun onto the Earth's surface. The projected Sun images form a flower-like pattern with a hole in the middle where none of the images reach. That hole is the umbra, and its edges are made up of arcs from the edges of some of the Sun images.
During the August 21, 2017, total solar eclipse, only 49 valleys made significant contributions to the umbra shape. The new eclipse calculation method makes it possible to identify these valleys and match them to each polygon edge of the umbra.
The same idea can also explain the shape of the antumbra, the central shadow cast by an annular eclipse, although with two important differences. The focal points of the Sun projections are mountains instead of valleys, and the shape comprises the intersection of the projected Suns rather than a central hole. Note also that for both eclipse types, the outer edges of the Sun images define the edge of the penumbra.
Each edge of the umbra corresponds to a specific lunar valley on the limb. The umbra edges and their partner lunar valleys are indicated in matching colors. The ring around the Moon image on the right is an exaggerated graph of the lunar terrain on the limb.
This still image is a conceptual visualization of the geometry of a total solar eclipse. Viewed from beyond the night side of the Earth, the Moon casts its umbra and penumbra shadows onto the Earth's during the August 21, 2017 eclipse. The geometry is to scale. The position and focal length of the virtual camera were carefully chosen to capture all three solar system bodies in the frame.
This still image illustrates pinhole projection images of the Sun originating at lunar valleys along the edge of the Moon, shown conceptually as cones spreading from the Moon toward the Earth.
This still image shows the cones of pinhole projected Sun images arriving at the Earth and forming a flower-like pattern.
This still image is a closer view of the projected Sun images reaching the Earth as seen from behind the Moon. The black dot in the center of the image cones is the umbra. The outer edges of the Sun images mark the edge of the penumbra, drawn here in purple.
This still image zooms in on the umbra centered near Grand Island, Nebraska at 1 PM Central Time. The yellow arcs are the edges of Sun images projected from valleys on the edge of the Moon. They outline the umbra.
This still image illustrates the direct correspondence of each edge of the umbra shape with specific lunar valleys along the limb of the Moon.
Credits
Please give credit for this item to:
NASA's Scientific Visualization Studio
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Visualizer
- Ernie Wright (USRA)
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Technical support
- Laurence Schuler (ADNET Systems, Inc.)
- Ian Jones (ADNET Systems, Inc.)
Release date
This page was originally published on Thursday, September 19, 2024.
This page was last updated on Tuesday, September 17, 2024 at 4:29 PM EDT.
Related papers
Datasets used
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DEM (Digital Elevation Map) [LRO: LOLA]
ID: 653 -
DE421 (JPL DE421)
ID: 752Planetary ephemerides
This dataset can be found at: http://ssd.jpl.nasa.gov/?ephemerides#planets
See all pages that use this dataset -
SLDEM2015 (DIgital Elevation Model) [LRO/SELENE: LOLA/TC]
ID: 948A digital elevation model of the Moon derived from the Lunar Orbiter Laser Altimeter and the SELENE Terrain Camera. See the description in Icarus. The data is here.
See all pages that use this dataset
Note: While we identify the data sets used on this page, we do not store any further details, nor the data sets themselves on our site.