July eclipse is best chance to look for gravity anomaly

[lurkey]

July eclipse is best chance to look for gravity anomaly3


18:00 19 July 2009 by Phil McKenna

From remote observatories on the Tibetan plateau to a cave in a Shanghai suburb, Chinese researchers are poised to conduct an audacious once-in-a-century experiment. The plan is to test a controversial theory: the possibility that gravity drops slightly during a total eclipse.

Geophysicists from the Chinese Academy of Sciences are preparing an unprecedented array of highly sensitive instruments at six sites across the country to take gravity readings during the total eclipse due to pass over southern China on 22 July. The results, which will be analysed in the coming months, could confirm once and for all that anomalous fluctuations observed during past eclipses are real.

"It sounds like what is really necessary to break the uncertainty," says Chris Duif of Delft University of Technology in The Netherlands. "I'm not really convinced the anomaly exists, but it would be revolutionary if it turned out to be true," he says.

Pendulum anomaly
The first sign that gravity fluctuates during an eclipse was in 1954. French economist and physicist Maurice Allais noticed erratic behaviour in a swinging pendulum when an eclipse passed over Paris.

Pendulums typically swing back and forth as a result of gravity and the rotation of the Earth. At the start of the eclipse, however, the pendulum's swing direction shifted violently (see diagram), suggesting a sudden change in gravitational pull.

Fluctuations have since been measured during around 20 total solar eclipses, but the results still remain inconclusive.

Relative doubt
Most physicists doubt the anomaly's existence, because it would challenge our ideas about how gravity works.

As a result, a number of conventional explanations have been suggested. "There could be different reasons: atmospheric changes in temperature or air pressure, people suddenly moving or not moving, or other sudden changes," says C. S. Unnikrishnan of Tata Institute of Fundamental Research in Mumbai, India.

However, in 2004, Duif posted a theory online concluding that none of the suggested external factors could account for the magnitude and timing of observed anomalies (see http://www.arxiv.org/abs/0408023).

Best chance
In the run up to July's eclipse, Chinese researchers have prepared eight gravimeters and two pendulums spread across six monitoring sites. The team hopes that the vast distance between the sites (roughly 3000 kilometres (1864 miles) between the most easterly and westerly stations), as well as the number and diversity of instruments used, will eliminate the chance of instrument error or local atmospheric disturbances.

"If our equipment operates correctly, I believe we have a chance to say the anomaly is true beyond all doubt," says Tang Keyun, a geophysicist at the Chinese Academy of Sciences.

The opportunity won't come again soon. At over five minutes, the event will be the longest total solar eclipse predicted for this century. What's more, the event will occur when the sun is high in the sky; a time when, according to Tang, any potential gravitational anomaly should be greatest.

[HURAKAN]

Asia set for total solar eclipse

Millions of people in Asia will see the longest total solar eclipse this century on Wednesday as swaths of India and China are plunged into darkness.

Scores of amateur stargazers and scientists will travel long distances for the eclipse, which will last for about five minutes.

The eclipse will first appear in the Gulf of Khambhat just north of Mumbai.

It will move east across India, Nepal, Burma, Bangladesh, Bhutan and China before hitting the Pacific.

The eclipse will cross some southern Japanese islands and will last be visible from land at Nikumaroro Island in the South Pacific nation of Kiribati.

Elsewhere, a partial eclipse will be visible across much of Asia.

The previous total eclipse, in August 2008, lasted two minutes and 27 seconds. This one will last six minutes and 39 seconds at its maximum point.

Alphonse Sterling, a Nasa astrophysicist who will be following the eclipse from China, scientists are hoping data from the eclipse will help explain solar flares and other structures of the sun and why they erupt.

"We'll have to wait a few hundred years for another opportunity to observe a solar eclipse that lasts this long, so it's a very special opportunity," Shao Zhenyi, an astronomer at the Shanghai Astronomical Observatory in China told the Associated Press news agency.

Solar scientist Lucie Green, from University College London, is aboard an American cruise ship heading for that point near the Japanese island of Iwo Jima, where the axis of the Moon's shadow will pass closest to Earth.

"The [Sun's] corona has a temperature of 2 million degrees but we don't know why it is so hot," she said.

"What we are going to look for are waves in the corona. ... The waves might be producing the energy that heats the corona. That would mean we understand another piece of the science of the Sun."

The next total solar eclipse will occur on 11 July next year. It will be visible in a narrow corridor over the southern hemisphere, from the southern Pacific Ocean to Argentina.

TOTAL SOLAR ECLIPSE
# In the area covered by the umbra (the darkest part of the shadow), a total eclipse is seen
# In the region covered by the penumbra (where only some of the light source is obscured) a partial eclipse is seen

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Send your pictures to yourpics@bbc.co.uk or text them to +44 7725 100 100 . If you have a large file you can upload here.

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Story from BBC NEWS:
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[Dionne]

This is really interesting. I recall reading one of Kurt Vonneugts books.....where he suggested the possibility that the Chinese had discovered a method to change gravity.....one of my favorites lines...."on days of particularly light gravity, I might scamper to the top of the Empire State building and fling a manhole cover in New Jersey"....

[Aslkahuna]

Actually the next eclipse with a similar duration of totality will occur in 2132. It's in the same Saros as the March 1970 eclipse seen in the US and the upcoming 2024 eclipse with 4 minutes totality in the US. Three Saros intervals from 2132 (in 2186)will see a 7 minute 29 second total very close to the maximum possible. In 2045, a member of the current eclipse's Saros will produce a totality of just over 6 minutes near Florida.

Steve

[JonathanBelles]

Awesome eclipse in store for 2045 for FL!

[x-y-no]

This alleged gravity anomaly was new to me. It would be very interesting if it actually turns out to be real.

The link to the paper by Chris Duif is broken. The paper can be downloaded here:

http://arxiv.org/abs/gr-qc/0408023

It doesn't come to any definite conclusion, but does a nice job of evaluating proposed explanations that obey classical physics.

[somethingfunny]

This is the coolest picture I have seen in quite some time. It was taken by a Japanese satelite during last week's total eclipse.