The astronomical event of the summer, if not for this entire year, occurs this Wednesday, July 22: A total eclipse of the sun visible in parts of India and China.
In fact, this will be one of the very best solar eclipses of the 21st century thanks to the near-coinciding of three events:
First, the moon arrives at perigee ? the nearest point in its orbit relative to Earth ? on July 21; a distance of 222,128 mi (357,463 km). Back on July 3, the Earth was at its farthest point from the sun (called aphelion). So while in some configurations the moon might barely cover the sun, this time the moon will appear 8-percent larger than the sun in terms of angular size, which is what we see in the sky.
Second, the moon will arrive at new moon phase on July 22.
And third, just 75-minutes after arriving at new phase, the moon reaches the descending node of its orbit, a point where it can come directly between the Earth and the sun cast its dark cone of shadow (called the umbra) upon the Earth's surface. The end result will be the solar eclipse with the longest duration of totality until the year 2132.
The path of the moon's dark umbral shadow, from where the panoply of phenomena associated with that magic word "totality" can be seen, will first touch the Earth over the Arabian Sea and Gulf of Khambhat (formerly the Gulf of Cambay), roughly between Ahmadabad to the north and Mumbai to the south.
The shadow then sweeps northeast across central India. The path of totality is a narrow swath, yet in crossing India, it could be visible to at least 13-million people (probably a very conservative estimate). The population centers range in size from the 4 million inhabitants of the metropolitan area of Surat ? practically on the eclipse center line ? to the 130,000 in the city of Darjeeling, internationally famous for its tea industry and the Darjeeling Himalayan Railway, a UNESCO World Heritage Site, down to countless smaller communities and hamlets.
Unfortunately, monsoon conditions typically prevail during July and the chances of getting a clear view of the sun is only 15 percent, based on climate records.
The moon's dark shadow will also sweep over the base of the Himalaya range in India, the Hindu Kingdom of Nepal, and Bhutan and will pass a scant 75 miles (121 km) south of the summit of Mount Everest where 97-percent of the sun's diameter will be covered. The umbra will also race over northern Bangladesh, extreme eastern India and southern and central Tibet.
Next stop, China
The umbra will then cut a west-to-east path across the middle of the People?s Republic of China, the most densely populated region on Earth. In fact, four of China?s ten largest cities are inside the totality zone. Among the many large cities that will experience totality, is Shanghai, the largest in the People?s Republic and with a population of over 14 million, recognized as the sixth largest city in the world. And yet, within the sprawling metropolitan region that encompasses the municipality of Chongqing ? also inside of the totality path ? there are estimated to be nearly 32 million people!
Certainly, when the umbra sweeps through here beginning at 01:13 UT (9:13 a.m. local time in China), more people will be experiencing the spectacle of a total solar eclipse at one moment then at anytime in recorded history!
Chengou (population nearly 10 million) and Wuhan (over 7 million) are also in the path of total eclipse. All told, at least 85-million ? perhaps the actual figure is closer to 100 million people . . . will be plunged into darkness as the core of the moon?s shadow races through China. Prospects for clear weather in China is about 30 to 40-percent, but offsetting these modest statistics for fair weather is the probability for haze and industrial smoke, creating smog, especially in Shanghai.
After departing China, the umbra moves out over the East China Sea, eventually passing over some of the Ryukyu (or Nansei) Islands of Japan which form an archipelago extending southwestward from Kyushu towards Taiwan. About 200 miles (325 km) east-southeast of Iwo Jima is the point of greatest eclipse. The umbra attains a maximum width of 161 miles (259 km), with totality on the center line reaching a peak of 6 minutes 39 seconds, with the sun almost directly overhead at an altitude of 86-degrees in the sky.
Many cruise ships are expected to congregate around this area on eclipse day.??
Thereafter, the umbra moves on to the southeast, its overall width gradually diminishing, its velocity slowly increasing and the duration of totality correspondingly diminishing. During mid afternoon, the shadow will pass over some of the Marshall and Gilbert Islands. Interestingly, its final landfall is the island of Nikumaroro. There is also a hypothesis that in July 1937 Amelia Earhart and Fred Noonan landed and died on Nikumaroro after failing to find Howland Island during the final stages of their ill-fated World Flight.
Upon crossing the International Date Line going east, the eclipse date transitions from July 22 back to July 21. The totality path finally comes to its end at 4:18 UT in the South Pacific Ocean amidst the northern group of the Cook Islands.
Local Circumstances (and be careful!)
The visibility zone for the associated partial eclipse will include much of central and eastern Asia.
Eclipses recur in a cycle known as the saros; one saros cycle is equal to 18-years, 11 and one-third days (give or take one day).
Hawaii, which was crossed by the totality path of the saros predescessor of this eclipse in July 1991, will see a small partial eclipse toward sunset. And a very small section of Australia, namely the northern and eastern portion of the Cape York Peninsula, juts just far enough into the moon's penumbral shadow to allow for small dent to appear on the lower right edge of the midday sun.
For maps depicting the zone of visibility of both the partial and total stages, including a listing of 385 local circumstances for selected cities, go to http://www.eclipse.org.uk/eclipse/0412009/.
IMPORTANT: To look at the sun without proper eye protection is dangerous. Even if you are in the path of the total eclipse you will need to protect your eyes during the partial phases. Learn safe viewing here.
The next total eclipse of the sun will be less than a year from now, on July 11, 2010. The umbral shadow will pass chiefly over the open ocean waters of the South Pacific, but will also make contact with Mangaia ? the second largest and most southerly of the Cook Islands, a number of small atolls of the Tuamotu Archipelago and later still along the track, the legendary Easter Island.
Finally, just as the shadow path is coming to its end, it makes landfall in South America along the rugged shoreline of southern Chile; finally slipping off the Earth?s surface in southern Argentina. At its peak, the moon will blot out the sun for 5 minutes 20 seconds.
North Americans must wait a bit longer for their chance at a total solar eclipse. On Aug. 21, 2017, the moon's shadow will sweep coast to coast across the contiguous United States, from Oregon, southeastward to South Carolina. It will be the first total solar eclipse for the mainland U.S. since Feb. 26, 1979.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York
- Video: How Eclipses Work
- Images: Total Lunar Eclipse Gallery
- All About Eclipses