Shanghai's giant radio telescope could be a white elephant

Shanghai, you may have a problem. Municipal government officials have just attended a ceremony to mark the completion of a "landmark" radio telescope in the city.

The dish, with a diameter of 65 metres and weighing 2,700 tonnes, is the biggest, costliest and most technically advanced radio telescope ever built in China.

It's something that no other major city has - or would even contemplate having - and there's a good reason for that.

Many astronomers have questioned the project since its inception in 2008 because radio telescopes are designed to pick up extremely faint radio waves from celestial bodies such as stars and galaxies that could be more than 12 billion light years away.

Big cities such as Shanghai, which generate lots of radio noise from such things as cell phones, police radios and air traffic control are regarded as the worst possible place to put up a dish.

Nearly all of the world's largest radio telescope projects have been built in remote areas, far from human activity, with some even set atop high mountains to ward off unwanted interference. America's Very Large Array, for example, was built in New Mexico, 80 kilometres from the nearest city, which has a population of just 9,000.