A Year: Day to Day Men: 24th of November,  Solar Year 2018

One Facet of Life

November 24, 1639 marks the first known observation and recording of a transit of Venus.

By the 17th century, two developments allowed for the transits of planets across the face of the sun to be predicted and observed. One was the telescope of which the actual inventor is unknown; a patent for a refracting telescope was submitted in 1608 in the Netherlands by spectacle maker Hans Lippershey. Galileo heard about it, and in 1609 built his own version, making observations of celestial objects.

The second development was the new astronomy of Johannes Kepler, which assumed elliptical rather than circular orbits fro the planets. In 1627, Kepler published his “ Rudolphine Tables”, a star catalogue and planetary tables using some observational data collected by Danish astronomer Tycho Brahe. Two years later, Kepler published extracts from his tables concerning the transit of Mercury and of Venus for the year 1631. These occurred as predicted and were observed by several astronomers, vindicating Kepler’s approach to astronomical theory.

The first known observations and recording of the transit of Venus across the sun were made in 1639 by the English astronomers Jeremiah Horrocks and his friend and correspondent William Crabtree. These observations were made on November 24, under the Julian calendar then in use in England. This calendar was refined and gradually replaced by our Gregorian calendar initiated by Pope Gregory XIII, changing the observation date to December 4th of that year. Horrocks observed the event from the village of Much Hoole, Lancashire, and Crabtree, independently, observed the event from his home in Broughton, near Manchester.

Both men, followers of Kepler’s astronomy, were self-taught mathematical astronomers who methodically worked to correct and improve Kepler’s Tables by observation and measurement. In 1639, Horrocks was the only astronomer who realized that the transit of Venus was imminent; others became aware only upon receiving Horrocks’s report. The two men’s observations and later mathematical work were influential in establishing the size of the solar system. For their achievements, they are considered the founders fo British research astronomy.

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