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July 22 2009: Longest Total Solar Eclipse of the 21st Century!


The total solar eclipse of July 22, 2009 is visible from only a small portion of the Earth's surface. To see the total eclipse, you have to reside upon the long yet narrow and winding eclipse path that runs across Asia and the Pacific Ocean. For a map of the total eclipse path, click here.

Cool Animation of Eclipse

For a cool animation of this eclipse, click here. The small dark dot that traverses the globe from west-to-east (left to right) shows you where the moon's dark umbral shadow crosses the Earth's surface. The much larger shaded circle surrounding the dark dot shows you where a partial solar eclipse is visible from Earth. From start to finish, the Moon's dark umbral shadow travels atop the Earth's surface for a period of about 3.5 hours. Thereafter, the moon shadow falls into the vastness of space.

Point of Greatest Eclipse

The maximum possible duration of this total eclipse as seen from a single point on the total eclipse path is 6 minutes and 39 seconds - the maximum duration for any total solar eclipse for all the 21st century. However, you'd have to be in the middle of this total eclipse path (in the Pacific Ocean) to see the Sun totally eclipsed for this period of time. We zoom in on a more detailed view of the total eclipse path, whereby the red dot spotlights the point of the greatest eclipse.

Starts at Sunrise; Ends at Sunset

The total eclipse starts at sunrise just west of India and ends at sunset to the southeast of the Marshall Islands. On the eclipse path, the duration of totality is less when the totally eclipsed sun is lower in the sky (near sunrise or sunset). The duration of totality is greater at points along the total eclipse path whereby the totally eclipsed Sun is seen higher in the sky (at or around noontime). The maximum duration of totality (on land) appears to be at the Japanese island of Kitaio Jima, where the totally eclipsed Sun is not far from the zenith point in the sky.

What causes a long-lasting total eclipse of the Sun?

A long-lasting total eclipse of the Sun depends on the following:
1) Earth appreciably close to aphelion - its farthest point from the Sun for the year
2) Moon appreciably close to perigee - its closest point to Earth for the month
3) Totality eclipsed Sun near zenith point in sky

New Moon near Node

Of course, for the totally eclipsed Sun to be close to the zenith point, the New Moon has to be appreciably close to one of its two nodes - the points on the Moon's orbital path that intersect with the ecliptic (the plane of the Earth's orbit around the Sun). According to Guy Ottewell's Astronomical Calendar 2009, the New Moon falls at 2:34 Universal Time (UT) and the Moon crosses its descending node at 3:49 UT, for a time difference of 1 hour and 15 minutes. Relative to the center of the Earth, the center of the Moon is only 4 minutes of arc (1/15 of a degree) north of the center of the Sun at the moment of the greatest eclipse.
Contrast this with the total solar eclipse of one year ago, on August 1, 2008. The New Moon fell at 10:13 UT (on August 1, 2008), whereas the Moon crossed its descending node at 1:21 UT (on August 2, 2008). That's a time difference of 15 hours and 08 minutes between New Moon and the nodal crossing. At the moment of greatest eclipse, the center of the Moon was some 46 minutes (about 3/4 degree) north of the center of the Sun.
Hence, the duration of the August 1, 2008 total solar eclipse is much less than that of the upcoming July 22, 2009 production - the longest total solar eclipse of the 21st century!

copyright 2009 by Bruce McClure

June 2009 Feature * August 2009 Feature