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The source of strange radio signals that have left astronomers at Australia's most famous radio telescope scratching their heads for 17 years has finally been discovered. It turns out that it was a microwave oven.

Mysterious interference by signals called perytons was first detected in 1998 "within 5km" of the Parkes Observatory in New South Wales, according to Simon Johnston, head of astrophysics at the scientific research agency CSIRO.


Once or twice a year, researchers would notice an odd signal, which was initially thought to be caused by lightning strikes. However, earlier this year, a new receiver was installed at the observatory, which picked up strong signals at a frequency of 2.4GHz -- the same as a microwave oven.

Immediate testing of the oven failed to detect any perytons -- until they opened the microwave door a few seconds before it had finished cooking. Johnston told The Guardian: "If you set it to heat and pull it open to have a look, it generates interference."

Although the telescope, known locally as "The Dish", is operated largely remotely, a few operational staff who maintain the facility would use the microwave oven to heat their lunch in the daytimes. Moreover, the interference would only occur when the telescope was pointed in the oven's direction, making the cause even harder to pinpoint. The findings have been published in the notices of the Royal Astronomical Society.

In recent years, the Parkes radio telescope, which gained attention after being used to relay signals from the 1969 moon landing, has been increasingly affected by radio disturbance -- from Wi-Fi to digital TVs -- as the once-remote area has become more urbanised.