Sunday, May 20, 2012

Annular Solar Eclipse, May 20-21, 2012

Annual Solar Eclipse in Taurus. The Moon crosses the descending node of its orbit meeting the apparent pathway of the Sun through Earth's sky just as the Sun moves through the very same line of sight, back-dropped by the familiar Hyades and Pleiades star clusters of the constellation Taurus. Because the Moon will have passed apogee only a day before, it's greatest distance from Earth, the apparent size of its disk will not not quite match the Sun's photosphere, and the result at totality is an annulus, a spectacular "ring of fire." The simulation above, showing the event from a perspective 12,700 km over South America, hints at the parts of North America, past sunset, where the celestial show will be invisible [Celesta].

Fred Espenak

The first solar eclipse of 2012 occurs at the Moon's descending node in central Taurus. An annular eclipse will be visible from a 240 to 300 kilometer-wide track that traverses eastern Asia, the northern Pacific Ocean and the western United States. A partial eclipse is seen within the much broader path of the Moon's penumbral shadow, that includes much of Asia, the Pacific and the western 2/3 of North America.

Path of Annularity, traced out on the sun-facing hemisphere of Earth, straddling the International Dateline in the North Pacific Ocean [F. Espenak/ NASA/GSFC].

The annular path begins in southern China at 22:06 UT. Because the Moon passed through apogee one day earlier (May 19 at 16:14 UT), its large distance from Earth produces a wide path of annularity. Traveling eastward, the shadow quickly sweeps along the southern coast of Japan as the central line duration of annularity grows from 4.4 to 5.0 minutes.

Tokyo lies 10 kilometers north of the central line. For the over 10 million residents within the metropolitan area, the annular phase will last 5 minutes beginning at 22:32 UT (on May 21 local time). The annular ring is quite thick because the Moon's apparent diameter is only 94% that of the Sun. Traveling with a velocity of 1.1 kilometers/second, the antumbral shadow leaves Japan and heads northeast across the Northern Pacific. The instant of greatest eclipse [1] occurs at 23:52:47 UT when the eclipse magnitude [2] reaches 0.9439. At that instant, the duration of annularity is 5 minutes 46 seconds, the path width is 237 kilometers and the Sun is 61° above the flat horizon formed by the open ocean.

The shadow passes just south of Alaska's Aleutian Islands as the central track slowly curves to the southeast. After a 7000 kilometer-long ocean voyage lasting nearly 2 hours, the antumbra finally reaches land again along the rugged coastlines of southern Oregon and northern California at 01:23 UT (May 20 local time).

Figure 2. [Fred Espenak / GSFC].
Redding, California lies 30 kilometers south of the central line. Nevertheless, it still experiences an annular phase lasting 4 1/2 minutes beginning at 01:26 UT. It is already late afternoon along this section of the eclipse path. The Sun's altitude is 20° during the annular phase and decreasing as the track heads southeast. Central Nevada, southern Utah, and northern Arizona are all within the annular path.

By the time the antumbra reaches Albuquerque, New Mexico (01:34 UT), the central duration is still 4 1/2 minutes, but the Sun's altitude has dropped to 5°. As its leading edge reaches the Texas Panhandle, the shadow is now an elongated ellipse extending all the way to Nevada. Seconds later, the antumbra begins its rise back into space above western Texas as the track and the annular eclipse end.

During the course of its 3.5-hour trajectory, the antumbral track is approximately 13,600 kilometers long and covers 0.74% of Earth's surface area. Path coordinates and central line circumstances are presented in Table 1.

Partial phases of the eclipse are visible primarily from the USA, Canada, the Pacific and East Asia. Local circumstances for a number of cities are found in Table 2 (Canada, Mexico and Asia) and Table 3 (USA). All times are given in Universal Time. The Sun's altitude and azimuth, the eclipse magnitude and obscuration are all given at the instant of maximum eclipse.

The NASA JavaScript Solar Eclipse Explorer is an interactive web page that can quickly calculate the local circumstances of the eclipse from any geographic location not included in Table 1:

This is the 33rd eclipse of Saros 128 (Espenak and Meeus, 2006). The family began with a series of 24 partial eclipses starting on A.D. 984 Aug 29. The first central eclipse was total and took place A.D. 1417 May 16. After three more totals and four hybrid eclipses, the series changed to annular A.D. 1561 Aug 11. Subsequent members of Saros 128 were all annular eclipses with increasing durations, the maximum of which was reached on Feb 1, 1834 and lasted 8 minutes 35 seconds. The duration of annularity of each succeeding eclipse is now dropping and will reach 4 minutes with the last annular eclipse of the series on July 25, 2120. Saros 128 terminates on November 1, 2282 after a string of 9 partial eclipses. Complete details for the 73 eclipses in the series (in the sequence of 24 partial, 4 total, 4 hybrid, 32 annular, and 9 partial) may be found HERE.

Additional details for the 2012 annular solar eclipse (including tables, maps and weather prospects) can be found HERE.

"Making eclipse magic," Emily Lakdawalla
The Planetary Society

Where to See the Annular Eclipse Online
Sky & Telescope

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