Total eclipse — longest of the century

Six minutes 39 seconds of totality over India, China and the Pacific — unbeaten until 2132.

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The story

On 22 July 2009 the longest total solar eclipse of the twenty-first century began on India's west coast and crossed Nepal, Bhutan, Bangladesh and China before heading out over the Pacific. Maximum duration was 6 minutes 39 seconds over the ocean — a record that stands until 2132.

The path took in Shanghai, Chengdu, Wuhan and Hangzhou, making it record-breaking for the number of people beneath it. Shanghai, sadly, was under rain clouds and felt only the darkening, but hundreds of millions along the Yangtze experienced midday darkness; inland Zhejiang towns such as Anji and Tonglu, and parts of India, had clear skies.

The eclipse was so long because of the geometry of distances. The Moon was near perigee, so it looked large, while Earth was near aphelion, so the Sun looked small, and the Moon covered it with room to spare. The length of totality is set by this chance overlap of two elliptical orbits.

The theoretical maximum is 7 minutes 32 seconds, and 6 minutes 39 seconds came close to that limit. The sky view replay shows Shanghai's sky that day (without the clouds) and the Sun–Moon–Earth alignment.

Why it matters

The 2009 eclipse is the textbook example of why long totality is rare. The Moon at perigee, Earth at aphelion and the shadow passing near the centre of the Earth all have to coincide, and that happens only once or twice a century.

It was also the first mass eclipse observation held in China. The government opened observing stations along the path and distributed filters to schools, and it is credited with a large growth in Chinese amateur astronomy. The next chance there is 2 September 2035 across northern China, North Korea and Japan.

Long totality is valuable for coronal research: more than six minutes allowed the corona's changes over time to be tracked from the ground, and the quiet, equatorially stretched corona of the 2008–2009 solar minimum was recorded in detail.

How to watch

Choose the 2009 eclipse in the sky view's event list to replay totality over Shanghai at 09:36 local time on 22 July — the black Sun low in the eastern sky with Venus and Mercury beside it. Move the location to Chengdu or Wuhan and totality comes earlier.

The orbit view's event replay shows the Moon near perigee sliding between Sun and Earth; switching on the lunar orbit ring shows the Earth–Moon distance shorter than average at that moment.

The previous eclipse of the same Saros series (136) was the Hawaii–Mexico eclipse of 11 July 1991 (6 minutes 53 seconds), and the next is the Luxor eclipse of 2 August 2027 (6 minutes 23 seconds). All three can be compared in the sky view.

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Background

Saros 136 is the series responsible for the long eclipses of the twentieth and twenty-first centuries. Its 20 June 1955 eclipse over the Philippines (7 minutes 8 seconds) was the longest; the series has shortened slowly through 1973 in Africa (7:04), 1991 in Hawaii–Mexico (6:53), 2009 (6:39) and 2027 at Luxor (6:23).

In Japan the Ogasawara Islands and the Tokara Islands lay in the path. Observers crowded onto Akuseki in the Tokara chain but got rain, and only ships off Ogasawara saw totality. Tokyo had a 75 percent partial eclipse.

The Sun was passing through its deepest minimum since 1913 at the time. With almost no sunspots, the corona was simple — two large streamers stretched along the equator.

The 2009 path began at Surat in India, passed Varanasi and Patna, crossed Nepal, Bhutan and Bangladesh and entered China. Monsoon cloud covered most of India, but at Varanasi on the Ganges totality was seen, and tens of thousands gathered on the ghats at dawn watched the black Sun. The Chinese section ran through Chengdu, Chongqing, Wuhan, Hangzhou and Shanghai before heading into the Pacific, and the Tokara Islands south of Japan, forecast to see 6 minutes 25 seconds of totality close to the maximum, drew crowds of observers.

FAQ

How long was totality?

Up to 6 minutes 39 seconds — the century's longest, unbeaten until 2132.

Why was it so long?

The Moon was near perigee and looked large while Earth was near aphelion and the Sun looked small, so the Moon covered it with room to spare.

Was it seen from Shanghai?

Shanghai was under rain clouds and felt only the darkening; some inland parts of Zhejiang had clear skies.

What is the next eclipse of the series?

The Luxor eclipse of 2 August 2027, lasting 6 minutes 23 seconds.

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Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.