The antenna in the valley

The construction of the 100-metre radio telescope four decades ago at Effelsberg bears witness to the fine art of engineering

When Galileo Galilei turned his modest “spy glass” towards the stars in the summer of 1609, he opened up new skies. He observed things which no one had ever seen before: mountains and craters on the moon, the phases of Venus, individual stars of the Milky Way. Galileo Galilei had pushed the window into space wide open. He had no way of knowing that his telescope observed only a tiny octave in the cosmic keyboard of light, because the electromagnetic spectrum we receive from space stretches across twelve orders of magnitude: at one end are the high-energy gamma rays with wavelengths of 0.01 nanometres (one billionth of a metre); at the other, the radio region with wavelengths of several metres.

Karl Jansky opened up this radio window in the early 1930s. The American engineer built a 30-metre monster from wood and wire on behalf of the Bell Phone telephone company and listened for interference signals in the short-wave band - and, lo and behold, a hiss actually got caught in Jansky’s antenna: but not from an intergalactic radio broadcast by aliens, but from the centre of the Milky Way.

Today, researchers from the Max Planck Institute for Radio Astronomy use high-tech dishes to search for signals from the long-wave end of the electromagnetic spectrum. At the heart of the Bonn-based Institute is the antenna that was inaugurated in 1971 near Effelsberg in the Eifel Mountains – with a diameter of 100 metres it was, for decades, the largest fully steerable radio telescope in the world. (The American Greenbank telescope, with an effective diameter of slightly over 100 metres outranked it a few years ago.)

Compared to other European countries, radio astronomy got off to a late start in Germany. This was down to the technical restrictions which the occupying forces imposed on researchers as a consequence of the Second World War. It was only in the middle of the 1950s that a fully steerable antenna with 25-metre diameter was built on Stockert Hill north of Bad Münstereifel. At the same time, the Heinrich-Hertz Institute in Berlin-Adlershof built a 36-metre transit instrument that was intended for galactic research.