Date:08/04/2005 URL: http://www.thehindu.com/2005/04/08/stories/2005040802490700.htm

National

Hybrid solar eclipse

By Our Staff Reporter

CHENNAI, APRIL 7. On Friday April 9 (soon after midnight of April 8), the first solar eclipse of 2005 — a rare celestial event — a hybrid solar eclipse will occur. This 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 the Earth's surface at some points, but falls short of the planet along other portions of the eclipse path.

The orbit of the moon is an ellipse. Hence, the distance of the moon from the Earth will keep on varying. When the Moon is farther from the Earth it appears slightly smaller. During this time, the apparent disk of the moon is smaller than that of the Sun. A thin ring of the Sun will be visible at the eclipse maximum. The eclipse is called annular eclipse. If the distance to the Moon is smaller, during the eclipse, the Moon can cover the Sun entirely. This is known as total eclipse.

If the Moon can cover the Sun entirely, this is total eclipse. If the eclipse is total at some places and annular at some other place then it is known as total-annular eclipse or hybrid eclipse. The hybrid nature of this eclipse is caused by the curvature of the Earth's surface. Points on the Earth's surface near the start and end of the eclipse than at mid-eclipse.

This reduction in the size of the moon makes it appear slightly smaller than the Sun at the beginning and end of the eclipse resulting in an annular eclipse. In the central part of the eclipse, the slightly larger moon is sufficient to entirely cover the Sun, resulting in a total eclipse.

The curvature of the Earth's surface brings some places along the path into the umbra while other positions are more distant and enter the penumbral shadow.

At its greatest, the eclipse will last no more than 42 seconds. As it crosses the Pacific, the eclipse becomes total.

Further east, as the eclipse approaches Central America it reverts to an annular eclipse.

As such it crosses part of Costa Rica, sweeps through Panama and Colombia to terminate at sunset in Venezuela. On April 9, the eclipse begins at 0023 hrs (IST). Between 2000 AD and 2100 AD, there will be only seven such hybrid eclipses

This is the 51st eclipse of Saros series 129. The periodicity and recurrence of solar (and lunar) eclipses is governed by the Saros cycle, a period of approximately 6,585.3 days (18 years, 11 days and 8 hours). The eclipse is not visible in India.