The Sky at Night — Episode 5: When Mercury Crosses the Sun

You are watching the episode When Mercury Crosses the Sun On 9 May the tiny planet Mercury will be seen as a black dot in transit across the sun's disc. Because it orbits close to the sun, Mercury has always been difficult to observe, and astronomers can only guess at the nature of this planet. Patrick Moore explains how a spacecraft will fly past Mercury in 1973 and send back television pictures.