Astronomers in America have been flying in supersonic fighter aeroplanes in order to get a better look at the stars.

The "top gun" scientists are able to fly over clouds, which might obscure a view, and easily reach remote vantage points, such as over the open ocean.

Using the military planes also means they can be "scrambled" to spy on short-lived astronomical events.

Flying observatories

The F-18 Hornets and modified WB-57 aircraft carry scientific instruments to become flying observatories.

A project demonstrating the feasibility of the concept has just been completed by the Southwest Research Institute (SwRI) in Texas, US, and the Nasa Dryden Flight Research Centre in California, US.

So far, 14 sorties have been flown. In the final flight, an F-18 fitted with an ultraviolet detector was used to observe an asteroid passing in front of a star.

Chief investigator Dr Alan Stern, director of the SwRI Department of Space Studies, said: "This observation will reveal the size of the asteroid 308 Polyxo, which like most asteroids, is too small for even the Hubble Space Telescope to resolve."

Dr Daniel Durda, the flight astronomer for the asteroid mission, added: "Our observation will be combined with three ground-based observations from other locations to deduce the asteroid's shape."

Spy planes

Using the jets is far less expensive than launching spacecraft and is also only a tenth of the cost per hour of hiring Boeing 707s and 747s as astronomical platforms.

Astronomers on the F-18 missions were given special flight training for fast jets and rode in the navigator's seat behind the pilot.

Further missions are planned, including flights up to 23,000m (75,000 ft) in two-seater U-2 spy planes.