Arecibo observatory

Arecibo observatory

Fig. 6.2 . The world's largest radio telescope is nestled into the hills near Arecibo, Puerto Rico. Its metal reflecting surface has a spherical shape with a diameter of 305 meters. The reflected radio signals are focused to detectors suspended on the triangular structure hanging from the three towers. The facility can also transmit powerful radio pulses, sending them off the metal surface into space. Such pulses, sent and received from this giant telescope, first measured Mercury's rotation period in 1965. Until then it had been wrongly thought that Mercury kept one side permanently facing the Sun, with a rotation period equal to its orbital period.

Copyright 2010, Professor Kenneth R. Lang, Tufts University