The world’s sky gazers will be holding their breath this morning as the century’s most dramatic total solar eclipse sweeps over parts of India, Nepal, Bangladesh, Bhutan, Myanmar and China. Impressive partial eclipses will also be seen in most of Southeast Asia, including Taiwan.
“While the moon eclipses the sun an average of 238 times every century, only 28 percent of those events are total eclipses, in which the sun is completely blocked from view,” said Sun Wei-hsin (孫維新), a professor at National Taiwan University’s (NTU) Graduate Institute of Astrophysics.
Although this means that a total solar eclipse can theoretically be observed every year-and-a-half, the blockage of the sun is visible from a different location on the Earth each time, so a total solar eclipse will only occur at any single location about every 450 years, he said.
The significance of today’s total solar eclipse — aside from the fact that the next one will not be seen in Taiwan until 2070 around Kenting — is its long duration, Sun said.
“Theoretically, a total solar eclipse can last a maximum of seven minutes and 31 seconds, so today’s eclipse, which will last six minutes and 39 seconds, is an extremely rare occurrence,” Sun said.
The previous total eclipse — which occurred on Aug. 1 last year — lasted two minutes and 27 seconds, and the next time that the Earth will see an eclipse lasting as long as today’s will be 123 years from now, on June 13, 2132, Sun said.
Although Taiwan is not on the narrow path that the moon’s shadow will trace over the Earth, Sun said that Taiwan’s proximity to the shadow zone would still result in a 85 percent partial eclipse.
People in Taipei can expect to see the moon start to eclipse the sun at 8:32am and obscure about 85 percent at 9:40am.
The moon will completely separate from the solar ring at 11:05am, Sun said.
What makes today’s spectacular event even more special, he said, is that the total eclipse will be visible over a long, narrow corridor spanning about 3,000km across Asia and the Pacific Ocean.
A chain of fortunate coincidences makes the rare occurrence possible, Sun said.
First, the moon yesterday arrived at the nearest point in its orbit to the Earth — its perigee — while the Earth reached its farthest point from the sun — its aphelion — at the beginning of this month, so the moon will appear to be 8 percent larger than the sun today, Sun said.
Second, the moon will enter a new moon phase today, which is essential because total solar eclipses only occur during a new moon.
The third coincidence is that shortly after the new moon phase begins, the moon will reach the descending node of its orbit, where it will come between the Earth and the sun and cast its shadow over the surface of the Earth, Sun said.
The Taipei Astronomical Museum, which has provided 200,000 pairs of eclipse-viewing glasses to students, will be open to the public from 8am today.
The museum warned people against looking at the sun directly, adding that regular sunglasses were insufficient to prevent permanent eye damage.
“If you do not have sun-observing glasses, project the eclipse with a mirror and look at the mirror instead,” a museum official said.