Wilkes - named after computing pioneer Maurice Wilkes - will be used for development of the Square Kilometre Array (SKA).
When complete the SKA will be the biggest radio telescope ever made.
The computer's power is the equivalent of 4,000 typical desktop computers all working together, the university said.
While it is some way off being the most powerful in the world - it ranks at 166th - Wilkes was built to be efficient rather than powerful.
"Energy-efficiency is the biggest single challenge in supercomputing today and our new system makes an important step forward in this regard," said Dr Paul Calleja, director of the Cambridge High Performance Computing Service.
It has an energy efficiency of 3,361 Mega-flops per watt. In simple terms, "flops" (floating point operations per second) is a measure of how much computing a machine can handle at once.
Wilkes comes in 2nd place on the Green 500, a ranking of the most energy-efficient computers. However the leading machine, built by a team in Tokyo, requires an oil-cooling system, whereas Wilkes is cooled using air, making it the most efficient of its kind.
Maurice Wilkes was the man behind EDSAC, the first programmable computer to come into general use - it was designed in 1947 and ran its first program on 6 May 1949.
A team at the National Museum of Computing at Bletchley Park are currently in the process of building an authentic replica of EDSAC.
A supercomputer that is the "greenest of its kind" has been built at Cambridge University.