Jeremiah Horrocks

Jeremiah Horrocks
Jeremiah Horrocks
	; Making the first observation of; the transit of Venus in 1639
Born	1618; Lower Lodge, Otterspool,; Toxteth Park, Liverpool, England
Died	3 January 1641 (aged 22); Toxteth Park, Liverpool
Residence	England
Citizenship	English
Nationality	English
Fields	Astronomy; Mathematics; Mechanics
Alma mater	University of Cambridge
Known for	Transit of Venus; Tides; Elliptical orbit; Lunar orbit

Jeremiah Horrocks (1618 – 3 January 1641), sometimes given as Jeremiah Horrox (the Latinised version that he used on the Emmanuel College register and in his Latin manuscripts),^[1] was an English astronomer. He was the first person to demonstrate that the Moon moved around the Earth in an elliptical orbit and was the only person to predict the transit of Venus of 1639, an event which he and his friend William Crabtree were the only two people to observe and record. His treatise on the transit, Venus in sole visa, was almost lost to science due to his early death and the chaos brought about by the English civil war, but for this and his other work he has since been hailed as the father of British astronomy.

Early life and education [edit]

Jeremiah Horrocks was born at Lower Lodge farm, in Toxteth Park, a former royal deer park, near Liverpool.^[2] His father, James, was a watchmaker who had moved to Toxteth Park to be apprenticed to Thomas Aspinwall and subsequently married his master's daughter, Mary. Both families were well educated Puritans; the Horrocks' sent their younger sons to the University of Cambridge and the Aspinwalls favoured Oxford.^[3] The unorthodox beliefs of the Puritans excluded them from public office and pushed them towards trade and industry and thus, by 1600 the Aspinwalls had become a successful family of watchmakers.^[2] As a boy, Jeremiah had an early introduction to astronomy as one of his chores was to measure the local noon in order to set the watches accurately,^[4] and his Puritan upbringing gave him an inbuilt suspicion of witchcraft, magic and astrology.^[5]

Horrocks joined Emmanuel College on 11 May 1632 and matriculated as a member of the University of Cambridge on 5 July 1632 as a sizar. At Cambridge, he made friends with John Wallis and John Worthington. He was the only person at Cambridge to believe the revolutionary heliocentric theory of Copernicus and, in his spare time, used the college libraries to study the works of Johannes Kepler, Tycho Brahe and others.^[6] In 1635 he left without formally graduating, for reasons which are not clear.^[7] Marston (2007) has suggested that he may have wished to defer the cost of graduation until he had secured employment,^[1] whilst Aughton (2004) has speculated that he may have failed his exams due to concentrating too much on his own interests or that he didn't want to take Anglican orders and so a degree was of limited use to him.^[8]

Astronomical observations [edit]

Now committed to the study of astronomy, Horrocks began to build up a collection of astronomical books and equipment. In 1638 he bought the best telescope he could find, having found the cheap toy one he had bought some years earlier no longer practical. As nearby Liverpool was a seafaring town, navigational instruments such as the astrolabe and cross staff were relatively easy to obtain. There was, at this time, no market for more specialised astronomical instruments and so his only option was to make his own. As luck would have it, he was well placed to do this as his father and uncles were watchmakers with the tools and expertise in producing accurate instruments. It seems likely that he would have helped with the family business during the daylight hours and, in return, the watchmakers in his family advised and assisted him with the design and construction of instruments to study the stars at night.^[9] He obtained a three foot radius astronomicus (a development of the cross staff with two movable sights on the cross piece) which he used to measure the angle between two stars, but by January 1637 he had come up against the limitations of this instrument and had built himself a larger version, eleven feet in length, in order to measure the angles more accurately.^[10] He read most of the astronomical treatises of his day, found the weaknesses in them and was suggesting new lines of research by the age of seventeen.

The traditional view is that, when he left home, he supported himself financially by holding a curacy in Much Hoole, near Preston in Lancashire, but there is little evidence for this and it is more likely he was a tutor to the Stones' children.^[1] According to local tradition in Much Hoole, he lived at Carr House, within the Bank Hall Estate, Bretherton. Carr House was a substantial property owned by the Stones family who were prosperous farmers and merchants, and Horrocks was probably a tutor for the Stones' children.^[11]

Lunar research [edit]

Horrocks was the first to demonstrate that the Moon moved in an elliptical path around the Earth. He also claimed that comets followed elliptical orbits and supported his theory by analogy with the conical pendulum. He noted that if the bob was drawn back and released then it followed an elliptical path, and that the major axis rotated in the direction of revolution exactly as did the apsides of the moon's orbit.^[12] He anticipated Isaac Newton in suggesting an influence on the orbit from the Sun as well as the Earth and in the Principia^[13] Newton acknowledged Horrocks's work in relation to the theory of the Moon. In the final months of his life he also made detailed study of tides, in an attempt to explain the nature of lunar causation of tidal movements.^[14]

Transit of Venus [edit]

Main article: Transit of Venus, 1639

A representation of Horrocks' recording of the transit published in 1662 by Johannes Hevelius

Horrocks was convinced that Lansberg's tables were inaccurate when Kepler predicted that a near-miss of a transit of Venus would occur in 1639. Horrocks believed that the transit would indeed occur, having made his own observations of Venus for years.

Horrocks made himself a simple helioscope by focusing the image of the Sun through a telescope onto a piece of paper, where the image could be safely observed. From his location in Much Hoole, he calculated that the transit was to begin at approximately 3:00 pm on 24 November 1639 (Julian calendar, or 4 December in the Gregorian calendar). The weather was cloudy, but he first observed the tiny black shadow of Venus crossing the Sun on the paper at about 3:15 pm, and observed for half an hour until sunset. The 1639 transit was also observed by his friend and correspondent, William Crabtree, from his home in Broughton, near Manchester.

Horrocks' observations allowed him to make a well-informed guess as to the size of Venus (previously thought to be larger and closer to Earth), as well as to make an estimate of the distance between the Earth and the Sun, now known as the astronomical unit (AU). His figure of 95 million kilometres (59 million miles, 0.63 AU) was far from the 150 million kilometers (93 million miles) that it is known to be today but it was a more accurate figure than any suggested up to that time.

A treatise by Horrocks, Venus in sole visa (Venus seen on the Sun) was published by Johannes Hevelius at his own expense in 1662. This paper, which caused great excitement when revealed to members of the Royal Society 20 years after it was written, contained much evidence of Horrocks' enthusiastic and romantic nature, including humorous comments and passages of original poetry. When speaking of the century separating Venusian transits, he rhapsodised,

" ...Thy return

Posterity shall witness; years must roll

Away, but then at length the splendid sight

Again shall greet our distant children's eyes."

At a time of great uncertainty in astronomy, when the world's astronomers couldn't agree amongst themselves and theologians argued over contradictory Scriptural passages, Horrocks, although a pious man, came down firmly on the side of scientific determinism.^[15]

It is wrong to hold the most noble Science of the Stars guilty of uncertainty on account of some people's uncertain observations. Through no fault of its own it suffers these complaints which arise from the uncertainty and error not of the celestial motions but of human observations...I do not consider that any imperfections in the motions of the stars have so far been detected, nor do I believe that they are ever to be found. Far be it from me to allow that God has created the heavenly bodies more imperfectly than man has observed them. - Jeremiah Horrocks^[15]

Death and remembrance [edit]

Jeremiah Horrocks Observatory on Moor Park, Preston

Horrocks returned to Toxteth Park sometime in mid-1640 and died suddenly and from unknown causes on 3 January 1641, aged 22. As expressed by Crabtree, "What an incalculable loss!"^[16] He has been described as a bridge which connected Newton with Copernicus, Galileo, Brahe and Kepler.^[17]

Horrocks is remembered on a plaque in Westminster Abbey^[18] and the lunar crater Horrocks is named after him. In 1859 a marble tablet and stained-glass windows commemorating him were installed in The Parish Church of St Michael, Much Hoole.^[11]

In 1927, the Jeremiah Horrocks Observatory was built at Moor Park, Preston.^[19]

The 2012 Transit of Venus was marked by a celebration held in the church at Much Hoole, which was streamed live worldwide on the NASA website.^[20]