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How did radar measurements of Venus test Einstein’s theory of general relativity?

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Radio telescope Lovell Telescope, a fully steerable radio telescope at Jodrell Bank, Macclesfield, Cheshire, England.

Radar measurements of Venus have served as a critical, independent test of Albert Einstein’s theory of general relativity by confirming the predicted effects of gravity on the propagation of light.1

When Venus is positioned on the opposite side of the Sun from Earth, radar signals transmitted from Earth must pass through the region of space near the Sun to reach the planet and return. According to general relativity, the Sun’s immense mass warps the surrounding space, causing these electromagnetic signals to slow down and follow a slightly different path than they would in the absence of such a massive body.123

By measuring the precise round-trip travel time of these radar pulses, astronomers have confirmed the additional time delay predicted by Einstein’s theory to within approximately 4 percent. Furthermore, radar measurements of the distances to planets like Venus have allowed scientists to estimate orbital precessions that align with the predictions of general relativity, providing additional empirical validation of the theory.2