Radar-ranging to Venus

Radar-ranging to Venus

Fig. 1.19 . Accurate distances to the nearby planets have been determined by sending radio pulses from Earth to the planet, and timing their return several minutes later. The figure shows the emission of a pulse toward Venus; when it bounces from Venus the radiation spreads over the sky and we receive only a small fraction of the original signal, delayed by the round-trip travel time. If T is the round-trip time and c is the speed of light, the total distance traveled is cT and the distance to Venus is cT/2. For Venus, the round-trip time is 4.6 minutes when the planet is nearest Earth and increases to 28.7 minutes when it is furthest away from us.

Copyright 2010, Professor Kenneth R. Lang, Tufts University