Transit of Venus The transit of Venus is a rare astronomical event in which the planet Venus passes across the face of the sun. In the mid 18th century, astronomers, Royal Society Fellows and gentlemen scientists anticipated with excitement the prospect of observing this phenomenon. The astronomer Edmund Halley predicted that transits would occur in 1761 and 1769. He urged those who would be observing the event to record the fullest details from different locations around the globe, because the data generated would enable astronomers to calculate the true distance between the earth and the sun. To do this, a first-class regulator clock, a telescope fitted with a micrometre, and a tent to protect these instruments from inclement weather were needed. In 1738, clockmaker John Ellicott was elected Fellow of the Royal Society, and in 1760 he produced regulator clocks which were used by astronomers to track the transit of Venus in 1761. Clockmaker John Shelton the Younger also made five astronomical regulators for the Royal Society which were used for timing the transits of Venus in 1769, and one was taken by James (later Captain) Cook to Tahiti for his transit observations there. Note that the tracking of Venus-events (its appearance, disappearance and transits across the sun) was first undertaken at least 3000 years ago by the Babylonians and perhaps as much as two thousand years ago by the Maya. Venus events were also extensively tracked and modelled by the Ancient Greeks. Although each culture had to make adjustments to account for leap years, remarkably, their Venus appearance predictions are accurate to within a few days. All were based on naked-eye observations. To learn more about Venus-watching in ancient cultures, read Stairways to the Stars: Skywatching in the three great ancient cultures by Prof Anthony Aveni.
