Basic Geometry of Solar Eclipse

Fred Espenak

Eclipses of the Sun can only occur during the New Moon phase. It is then possible for the Moon's penumbral, umbral or antumbral shadows to sweep across Earth's surface thereby producing an eclipse. There are four types of solar eclipses:

1. Partial - Moon's penumbral shadow traverses Earth (umbral and antumbral shadows completely miss Earth)
2. Annular - Moon's antumbral shadow traverses Earth (Moon is too far from Earth to completely cover the Sun)
3. Total - Moon's umbral shadow traverses Earth (Moon is close enough to Earth to completely cover the Sun)
4. Hybrid - Moon's umbral and antumbral shadows traverse Earth (eclipse appears annular and total along different sections of its path). Hybrid eclipses are also known as annular-total eclipses. See Five Millennium Catalog of Hybrid Solar Eclipses.

Annular eclipses are visible from within the Moon’s antumbral shadow while total eclipses are seen within the umbral shadow . These eclipses can be further classified as:

1. Central (two limits) - The central axis of the Moon’s shadow cone traverses Earth thereby producing a central line in the eclipse track. The umbra or antumbra falls entirely upon Earth so the ground track has both a northern and southern limit.
2. Central (one limit) - The central axis of the Moon’s shadow cone traverses Earth. However, a portion of the umbra or antumbra misses Earth throughout the eclipse and the resulting ground track has just one limit.
3. Non-Central (one limit) - The central axis of the Moon’s shadow cone misses Earth. However, one edge of the umbra or antumbra grazes Earth thereby producing a ground track with one limit and no central line.

The Five Millennium Canon of Solar Eclipses: -1999 to +3000 contains maps for all solar eclipses over a 5000 year period. The Five Millennium Catalog of Solar Eclipses contains tables listing information for each eclipse. Finally, the World Atlas Solar Eclipse Paths contains maps for the paths of all annular, total and hybrid solar eclipses.

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Acknowledgments

Permission is freely granted to reproduce this data when accompanied by an acknowledgment:

"Eclipse Predictions by Fred Espenak (NASA's GSFC)"