Scientists have made the first precise measurement of the size of a planet orbiting another star. They used a new camera so powerful that it could detect a moth flying in front of a lit window 1,000 miles away.

The planet, labelled WASP 10b is one discovered by a British robotic survey that was built with lenses sourced on the auction site eBay.

It orbits a star 300 light-years away from Earth in the constellation of Pegasus.

The team of astronomers used a giant telescope on Mauna Kea in Hawaii to measure the tiny fade in light as the planet passed in front of its home star in an eclipse.

They found its diameter is six per cent more than Jupiter, which is 89,000 miles wide and the largest planet in our own solar system. However the planet is much denser than Jupiter and would weigh three times as much if you could put it on a pair of scales.

The same transit technique has allowed astronomers to analyse the atmospheres of extrasolar planets. Experts say it is only a matter of time now before they are able to detect planets the size of Earth in transit across the face of other stars.

The special camera, called OPTIC, was mounted on the University of Hawaii’s 2.2-metre telescope to make the critical measurements.

The team’s leader, Dr John Johnson, said: “While we know of more than 330 planets orbiting other stars in our Milky Way galaxy, we can measure the physical sizes of only the few that line up just right to transit.”

Colleague Joshua Winn said: “This new detector design is really going to change the way we study planets. It’s the killer app for planet transits.”

The planet was originally found by sky survey project, called SuperWASP – short for Super Wide Angle Search for Planets – which watches millions of stars every night from sites in the Canary Islands and South Africa.

To complete SuperWASP, astronomers had to turn to eBay to track down 13 lenses, costing £4,000 each, after they learned that Canon no longer made them.

Picture: The observatory housing the 2.2 metre telescope on Mauna Kea. (Photo by Karen Teramura).

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