The European Radio Astronomy Club frequencies, the ionosphere is opaque. Here, two targets are possible: the Sun with its solar flares or Jupiter, which is also a very strong radio source, together with the moon Io, which is a very powerful natural radio wave transmitter. When Jupiter, Io and the Earth are aligned, it is possible to hear this radio source very clearly. The European Radio Astronomy Club The European Radio Astronomy club (ERAC) is Europe's only group coordinating the work of radio astronomers to jointly use radio waves to study the universe at radio wavelengths. It was founded in 1995 by Peter Wright, who
Atmospheric duct bent by atmospheric refraction. In over-the-horizon radar, ducting causes part of the radiated and target-reflection energy of a radar system to be guided over distances far greater than the normal radar range. It also causes long distance propagation of radio signals in bands that would normally be limited to line of sight. Normally radio "ground waves" propagate along the surface as creeping waves. That is, they are only diffracted around the curvature of the earth. This is one reason that early long distance radio communication used long wavelengths. The best known exception is that HF (3–30 MHz.) waves are reflected