Two young amateur astronomers were not only the first people to observe a Venus transit - they also predicted the transit in 2004!
by Anne Mette Sannes
At this location, in the tiny village of Much Hoole i Lancashire, UK, a Venus transit was observed for the first time.
Photo: N. Ritchie
The first predictions and observations of Venus transits
History tells us about an Arabic stargazer who, as early as in 639 B.C, witnessed a Venus transit. Whether or not this really happened is impossible to determine, what the stargazer actually saw might as well have been sunspots.
In the 1600s, the German astronomer and mathematician Johannes Kepler, predicted both a Mercury- and a Venus transit to take place in 1631.
Pierre Gassendi, a French naturalist and philosopher, planned to see both the Mercury transit on November 7th and the Venus transit a month later.
In terms of the Mercury transit, the luck was on his side – he was one of very few people to observe the phenomenon.
He published the very first data about the event, and exited he started to prepare for the predicted Venus transit to appear a month later.
To make sure he should not miss this phenomenon and also because he was afraid that Kepler’s calculations were not accurate enough, he started his observations on December 5th, two days before the expected transit. But December 7th passed without seeing anything.
What neither Kepler nor Gassendi knew, was that the phenomenon took place during the night on the northern hemisphere. Seen from France, the Sun was below the horizon.
No reports indicate that someone actually observed Venus’ journey across the solar disk in 1631.
But at least he was lucky to have a Moon crater named after him – the Gassendi Crater – a big crater in the northwestern corner of the Mare Humorum bassin. During the Apollo landings, it was in this particular crater NASA considered landing with Apollo 17.
The Gassendi Crater on the Moon.
A young, brilliant amateur astronomer
Nor did Kepler predict that Venus transits occur in pairs. In 1639, the English amateur astronomer, Jeremiah Horrocks, who also happened to be a first-class mathematician, took a closer look at Keplers calculations. Based on this, he managed to predict another Venus transit only two months later, on December 4th. He was not absolutely sure, it was also the possibility that Venus would go clear of the Sun. But Horrocks was right, and together with his colleague, William Crabtree, these two were the first to both predict, observe and register a Venus transit.
Using a telescope, Horrocks managed to make a projection of the Sun on a sheet of paper, and by using Crabtrees calculations, Horrocks estimated the size of Venus as best he could.
Using the observations, he estimated the distance Sun-Earth to be 2/3 of the correct distance which, by today’s knowledge, is 149.6 million kilometers.
But this is not all – these two men also managed to predict the Venus transit on June 8th 2004! Not bad of two young amateur astronomers – Horrocks twenty and Crabtree twenty-nine! Tragically enough, they both died shortly after, Horrocks from unknown reasons two years later only twenty-two years old – the day before he was going to meet his colleague. Crabtree died three years after Horrocks. It is not known whether these two ever met.
Horrocks’ dissertation, «In sub sole visa» was first published in 1662, twenty-one years after his death.
The observation of the Venus transit in 1639 is by many seen as the beginning of modern astronomy in the UK.
Jeremiah Horrocks managed to both predict and observe the Venus transit in 1639.
Photo: J.W. Lavender
Major celestial events in Norway 2010-2015