Sunday, May 30, 2004

Transit of Venus

On tuesday June 8th, the sun will be fainter than usual. On the face of the sun will be a small, dark dot. The dot is Venus, passing directly between Earth and the sun for the first time since 1882

The interest in observing the transit of Venus led to the invention of the movie camera and to the discovery of the great barrier reef

Kepler first predicted a transit of Venus in 1631. Ever since scientists have keenly followed the transit of venus- first for measuring the distance from Earth to Sun and now for detecting life on extra solar planets.

Given the relative speeds of the two planets, transits should occur every one-and a half years, but are actually much rarer as Venus's orbit around the sun is tipped relative to that of Earth.

Scientists tried timing Venus's transit from widely separated points on Earth, from which the could easure the distance from earth to sun.

Measuring Venus's path in 1769 was one of the mission objectives of James Cook's first voyage. Once this official mission was accomplished, Cook explored the south Pacific, accurately mapping New Zealand and stumbling ( literally ) upon the Great Barrier Reef.

When all the results came in, the astronomical unit was calculated to be 153m kilometres, with an uncertainity of 1m kilometres. The uncertainity arose as it was difficult to measure the exact start and end of the transit, without recording equipment.

Pierre Janssen, a French astronomer, invent a multi-exposure camera with a slotted rotating wheel instead of an ordinary shutter, the forerunner of the movie camera.It did'nt help much.

Visible in both Europe and the United States, The 1882 transit was a public sensation. Thomas Hardy wrote a novel about it. Telescopes were set up in town squares and millions of people had a look. It was the last chance to see a transit of Venus until 6 June 2004.

Though we now know the value of AU with great precision, scientists still study transits to finetune techniques to understand planetary compositions of extra solar planets. By measuring the transit in different colours scientists can theorrize about the atmosphere of the transiting planet. Transits have thus become the best way to search for extra solar life


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