9th December 1874. Transit of Venus.
Two things helped the 17thc recording of the Transport of Venus across the sun: Firstly the development of the telescope and secondly Keppler’s astronomy of planetary motion.
Today in 1874 a tablet was placed in Westminster Abbey to the memory of the astronomer and Puritan parson, Jeremiah Horrocks.(1)
Horrocks had learned his astronomy in the summer holidays, and after working on The Transit of Venus, and planetary motion, by applying Keppler’s Laws, predicted, correctly to the day, that the next Transit would be in 1639.
Horrocks was part of a north-country group of astronomers which included William Crabtree.(2)
Both had interests which would not have featured in the Cambridge Curriculum at the time, confined as it was to little other than Scripture and Classics.
Also both had been given insight into their research from publications of the recently deceased Keppler who had spotted the 1631 Transit but failed to predict from his Rudolphine Charts (1627), that a second was due in 1639.
The problem for Horrocks and Crabtree was that the Transit though lasting over 5 hours would only be seen in the UK for 40 minutes, then there was the weather as a November, Lancashire afternoon is not the best time for astronomy.
Horrocks from Keppler’s Tables knew the Transit was due at 3.pm on that Sunday of the 24th of November and was prepared, as was Crabtree, with telescope, darkened room and white paper to reflect the image.
However Crabtree, it appeared, only managed a sketch after the event, whilst Horrocks, initially thwarted with cloud, recorded the observation, the data of which was later used to calculate relative distances of the Solar System, calculations confirmed later by Christopher Wren, Professor of Astronomy at Oxford.
Horrocks died early and his results were later recorded in ‘Venus Sole Visa’ (Sight of Venus and the Sun), published posthumously in 1662 and published by John Wallis as Jeremiae Horrocci opera posthuma (posthumous work) of 1678.
Despite this however much was lost due to the 1666 Great Fire of London and the disturbance of the Civil War.
The 17thc was a time of much speculation about astronomy and Christopher Wren, Robert Hooke and Edmund Halley all coffee-house friends, could not quite manage to work out the detailed maths of the planetary orbits.
Transits are separated by a period of 8 years, then over 100 years elapse before they are seen again.
(1) Horrocks typical of the age was a parson with time on his hands and with a talent for science had joined Emmanuel College (Cantab) on 11th May 1632 and matriculated as a member on 5th July 1632 as a Sizar, but left before graduating.
(2) Other group members were Richard Towneley and William Gasgoine.
commons.wikimedia.org/Pic of Etching.