Astronomers are building telescopes powerful enough to watch alien TV channels.

New radio telescopes are being designed which could tune into signals from television transmitters around other stars.

Researchers in the USA tell New Scientist this week that our own civilisation is leaking signals into space from TV and FM radio stations and military radar.

Radio telescopes designed to study the earliest molecules in the universe are just the right type to eavesdrop on those sort of signals too.

The UK is involved in a project to build the world’s biggest radio telescope in Australia or South Africa. The Square Kilometre Array will have more collecting power than eight million Sky minidishes.

UK astronomer Ian Morison, of Jodrell Bank in Cheshire, told Skymania News that it will be powerful enough to pick up alien TV and radio broadcasts.

Dr Morison said: “The telescope should be able to detect the leakage of any signals from planets around nearby stars. The secret is to pick up the aliens’ early broadcasts before they go digital. That’s when the signals become more focused and leak into space less.”

He added: “It could also pick up radar signals which extraterrestrials might use to check approaching asteroids that threaten to collide with them.”

Abraham Loeb, of Harvard University, Massachusetts, tells New Scientist: “By a happy accident, the telescopes will be sensitive to just the kind of radio emission that our civilisation is leaking into space.” He says the latest radio telescopes are designed to pick up radio waves emitted by neutral hydrogen molecules in the early universe.

Today these have a wavelength corresponding to a frequency of tens or hundreds of megahertz. “This overlaps with our civilisation’s radio emissions, which are in the range 50 to 400 megehertz,” says Loeb.

Loeb and colleague Matias Zaldarriaga say the new generation of radio telescopes could pick up ET’s leaking TV signals from stars as far as 1,000 light years away.

Their big challenge would be to sort the aliens’ faint broadcasts from interference from channels here on Earth.

The image is a computer-generated artist’s impression of the planned Square Kilometre Array.