What is a hybrid solar eclipse?

A hybrid eclipse is a unique type of central eclipse where parts of the path are annular while other parts are total. This duality comes about when the vertex of the Moon's umbral shadow pierces Earth's surface at some points, but falls short of the planet along other portions of the eclipse path.

The curvature of Earth's surface brings some geographic locations along the path into the umbra while other positions are more distant and enter the antumbral rather than umbral shadow. In most cases, the hybrid eclipse begins annular, changes to total for the central portion of the path, and then converts back to annular towards the end of the path. However, some hybrid eclipses may be annular only at the beginning or at the end of the path.

A spectacular geocentric celestial event of 2005 was a rare hybrid eclipse of the Sun - a total or an annular eclipse could be seen depending on the observer's location. For Fred Espenak, aboard a gently swaying ship within the middle of the Moon's shadow track about 2,200 kilometers west of the Galapagos, the eclipse was total, the lunar silhouette exactly covering the bright solar disk for a few brief moments. His camera captured a picture of totality revealing the extensive solar corona and prominences rising above the Sun's edge.

But for Stephan Heinsius, near the end of the shadow track at Penonome Airfield, Panama, the Moon's apparent size had shrunk enough to create an annular eclipse, showing a complete annulus of the Sun's bright disk as a dramatic ring of fire. Pictures from the two locations are compared below.

How rare is such a hybrid eclipse? Calculations show that during the 21st century just 3.1% (7 out of 224) of solar eclipses are hybrid while hybrids comprise about 5% of all solar eclipses over the period 2000 BC to AD 3000. Today's hybrid solar eclipse is most widely visible beyond the central shadow track as a brief partial eclipse from northeastern Americas through Africa, and along the track in an annular phase for only the first 15 seconds.

Image & info via APOD
Image Credit & Copyright: Left: Fred Espenak - Right: Stephan Heinsiushttp://apod.nasa.gov/apod/ap131103.html