1639 transit of Venus

[1] The pair made their observations independently on 4 December that year (24 November under the Julian calendar then used in England); Horrocks from Carr House, then in the village of Much Hoole, Lancashire, and Crabtree from his home in Broughton, near Manchester.

Although the friends both died within five years of making their observations, their ground-breaking work was influential in establishing the size of the Solar System; for this and their other achievements Horrocks and Crabtree, along with their correspondent William Gascoigne, are considered to be the founding fathers of British research astronomy.

By the 17th century, two developments allowed for the transits of planets across the face of the Sun to be predicted and observed: the telescope and the new astronomy of Johannes Kepler, which assumed elliptical, rather than circular, planetary orbits.

[3] Although Kepler's calculations indicated that the 1631 transit of Venus would best be visible from the American continent, he was not fully confident of his prediction, and advised that European astronomers should be prepared to observe the event.

[7] Jeremiah joined Emmanuel College on 11 May 1632 and matriculated as a member of the University of Cambridge on 5 July 1632 as a sizar, which meant he did not have the means to fully support himself and was given specific duties to compensate for a reduction in fees.

[7][8] After leaving Cambridge, Horrocks returned to his home in Lancashire and began collecting books and instruments in order to pursue his main interest, the study of astronomy.

[13] It is not known whether Horrocks and Crabtree ever met in person but from 1636 they corresponded regularly, and, because of their shared interest in the work of Johannes Kepler, referred to themselves, along with William Gascoigne, as nos Keplari (we Keplarians).

By 1637, he had convinced Horrocks of the superiority of the Keplerian system, and, using their own planetary observations, both men made many corrections to Kepler's tables, which Crabtree converted to decimal form.

This remarkable assemblage of the planets (as if they were desirous of beholding, in common with ourselves, the wonders of the heavens, and of adding to the splendour of the scene), seemed to forebode great severity of weather.

In this apprehension I coincide with the opinion of the astrologers, because it is confirmed by experience; but in other respects I cannot help despising their more puerile vanities.At around midday on 23 November Horrocks darkened his room and focused the rays of sunlight coming through the window onto the paper where the image could be observed safely.

I then beheld a most agreeable spectacle, the object of my sanguine wishes, a spot of unusual magnitude and of a perfectly circular shape, which had already fully entered upon the Sun's disk on the left ... Not doubting that this was really the shadow of the planet, I immediately applied myself sedulously to observe it ... although Venus continued on the disk for several hours, she was not visible to me longer than half-an-hour, on account of [the Sun] so quickly setting ...

The inclination was the only point upon which I failed to attain the utmost precision; for, owing to the rapid motion of the Sun, it was difficult to observe with certainty to a single degree ...

But all the rest is sufficiently accurate, and as exact as I could desire.Crabtree made his observations using a similar set-up but had insufficient time to make any measurements, as it was cloudy in Broughton, and thus he only saw the transit briefly.

Horrocks's papers remained with his family for a short time; some were destroyed during the English Civil War, some were taken to Ireland by a brother, Jonas, and never seen again, and others passed into the collection of antiquarian and astronomer, Christopher Towneley, where they were consulted by Jeremy Shakerley, who wrote three books on astronomy in the mid-17th century.

[1] The publication of Venus in Sole Visa by Hevelius caused great consternation at the newly founded Royal Society when it was realised that such an elegant and important paper by an Englishman had been neglected in his own country for so long.

The mathematician John Wallis, who was a friend of Horrocks at Emmanuel College, and a founder member and leading light of the society, summed up the view of its members when he wrote: I cannot help being displeased, that this valuable observation, purchasable with no money, elegantly described and prepared for the press, should have laid for two-and-twenty years, and that no-one should have been found to take charge of so fair an offspring at its father's death, to bring to light a treatise of such importance to astronomy and to preserve a work for our country's credit and for the advantage of mankind.

[20] John Flamsteed later said he regarded Horrocks, Crabtree and Gascoigne as the founding fathers of British research astronomy and the intellectual heirs to Galileo and Kepler.

[24] In December 2005, a commemorative plaque was unveiled a few yards away near Ivy Cottage on Lower Broughton Road, which is thought to have been the home of Crabtree and his family at the time he was collaborating with Horrocks.

[24] The second transit of the pair occurred on 5 and 6 June 2012, and was marked by a celebration held in the church at Much Hoole, which was streamed live worldwide on the NASA website.

[25] A celebration was also held at Crabtree's former home in Broughton when NASA broadcast a re-creation of the observation at Ivy Cottage, inspired by the Ford Madox Brown mural, to millions of viewers, and projected a live video stream of the transit from Hawaii onto the side of the house.

This was the appearance in the dark apartment; therefore out of doors beneath the open sky, according to the laws of optics, the contrary would be the case, and Venus would be below the centre of the Sun, distant 620 30' from the lower limb, or the nadir, as the Arabians term it.