The images of Io we have seen in recent years show a violently active little world. Its volcanoes and amazing surface bearing witness to its proximity to Jupiter and its powerful gravitational field. However there is another interaction that this satellite has with its planet, the interaction with its magnetosphere.

The interaction causes strong radio storms, and when the Earth is in the path of these directional emissions it is possible to observe them.

Ideally you would use a communications receiver with the automatic gain control (AGC) switched off, however it is possible to listen to these signals with any decent shortwave broadcast receiver. There is a "quiet band" set aside for radio astronomy between 25.55 and 25.67 MHz that may be used for this purpose, but any frequency clear of man-made signals or interference between 20 and 30 MHz is suitable. Many people use 21.0 MHz if it is clear in their part of the world.

You will also require a suitable antenna. Some people say that a small loop antenna will work, however we have to admit that our tests do not substantiate this and we would recommend using a half wave dipole - a simple design is provided.

NASA's Project Radio Jove and the Radio Sky Publishing CD will provide software for predicting likely times of Jovian radio storms and recording software. In addition Project Radio Jove can supply a receiver design or even a kit if you wish to build one for yourself.

We would recommend that you listen to samples of the types of storm, although if you hear something like waves breaking on a shingle beach you are probably listening to Jupiter.

Because the signals have wavelengths in the tens of metres, they are know as Jovian Decametric emissions. You will find a number of related sites in our links database .

These frequencies also contain radio emissions from the Sun and the Galaxy, but it has to be said that man-made interference is a great problem.