Jeremiah Horrocks

Jeremiah Horrocks is a astronomer English of the 17th (1619 (?) - January 3rd 1641).

Biography

There does not exist any more register of baptism to know with precision the day or even the year of its birth. But, to believe of it the mathematician John Wallis who knew it, the young astronomer would have been born in 1619, since, according to him, he dies suddenly at the time of his twenty-second year, the January 3rd 1641. The majority of the commentators sticks to this testimony, others, more rarely, gives birth to it in 1618 or 1617.

Passage in Cambridge

Jeremiah Horrocks returns to the Collège Emmanuel to Cambridge the May 18th 1632, as “a sizar”, i.e. as student in charge of an exchange of the exemption from payment of the courses. Horrocks remains four years there, until in 1635, before turning over at his place in the county of the Lancaster, to perhaps carry on a religious activity there. Horrocks between at the University at thirteen years, as it was the case for Tycho Brahé.

The matters studied in this school are mainly the traditional languages, the literature and the Théologie, and perhaps some elements of Astronomie and old Géométrie. But Horrocks sticks to an activity except program, namely the reading of the new astronomy, of which in particular Tabulae Motuum , of the Flemish Philip Van Lansberg. Horrocks thus counts twenty-four continental authors of astronomy from of which all, except the Anglo-Irish astronomer Sacrobosco, result from the continent.

To this difficulty of getting scientific works, another problem, the absence of qualified professor in astronomy is added. Jeremiah Horrocks complains some besides in these terms: These many obstacles and my inexperience made my study difficult. The lack of means discouraged me and despaired me… What grained me more was the fact that nobody could inform me on this discipline, nobody who could help me with sympathy in my efforts. I was taken of torpor and moroseness. But what was I to make? It was impossible for me to soften my labor and even less to increase my means. The worst of all was than I was unable to move whoever with astronomy. But, to give up the study of philosophy because of these difficulties would have seemed to me unworthy. I decided, consequently, that lassitude was to be overcome by assiduity, poverty by patience. There was not an other solution. And, in the absence of a professor, I was to resort to the books of astronomie.

In Cambridge, it meets in particular John Wallis which enters there the same year as him, and which, at the request of the Royal Society , published works of Horrocks in 1673, on a purely posthumous basis.

After having left the university, it makes, in 1636, the decisive meeting of William Crabtree, a merchant of textile which lives the village of Salford, close to Manchester. This one was a close friend but especially invaluable corresponding scientific.

The question of knowing if Horrocks, very pious, were ordered man of the church or were simple Vicaire, is still prone to controversy today. Although no direct or indirect testimony of its friendly close relations like Wallis or John Flamsteed - themselves ecclesiastical - seems convincing, an anecdote authenticates the fact of leaving its telescope several hours Sunday December 4th 1639, day of the Transit of Venus, “for extremely important reasons”, i.e. “professional” reasons and obviously more eminent than the cosmic phenomenon. Very believing, Horrocks could regard the celebration of the mass as a higher duty, even if, so it missed the totality of the transit.

Work and discovered

To mark the Venus transit of December 1874, the astronomers of the Royal Astronomical Society decided to set up a commemorative plaque with the memory of their compatriot who was the first to observe a Venus passage in front of the Sun. Present in the Abbey of Westminster, this plate mentions the problems of the astronomy on which the Horrocks young person leant, namely:

determination of the elliptic orbit of the moon;
its physical assumption of displacements of planets.

It does not mention however:

its desire to eliminate any source from possible error in the observations;
that he proposed a horizontal Parallaxe solar of 14" ;
that it corrected, following its reading of the Tables rudolphines of Kepler, inequalities of the average movements of two large known higher planets at the time;
that he discovered that the Comet S move around the Sun while following elliptic orbits;
or, that before its death, Horrocks undertook a study of the tides.

Let us announce that all papers concerning these investigations are now lost.

Observation of the Venus transit of December 4th, 1639

First steps and calculations

It is the major work of Horrocks by which it will reach the posterity. Horrocks is very early disappointed by the astronomical tables of its predecessors, who all seem in conflict the ones with the others, and particularly with those of Lansberg and Hortensius.

With his/her friend Crabtree that the aforementioned tables also oppose, Horrocks undertakes to carry out towards 1636 fastidious observations, thus collecting data on the orbits lunar and planet gears. In fact proper calculations of Horrocks made him discover that a Venus passage in front of the Sun is always followed of a second eight years afterwards, which Kepler had not provided. In the same way, an average combination of the tables of Copernic, Longomontanus and of Kepler leads Horrocks to note that Venus is constantly placed at 8 ' too in the south. Thanks to this deduction, it determines a Venus passage for at the end of November the 1639.

He writes on this subject: I trusted the Venus movements which I had recomputed, it seemed impossible to me that the phenomenon takes place before 15:00 on November 24th. And yet, according to the majority of the astronomers, the conjunction was to take place earlier, i.e. the day before. I was reticent to depend on my only opinion, opinion which was not strengthened. A breach of trust could have endangered the experiment. I was anxious mainly the 23 and all the day the 24 because of this business, and did not miss any occasion to observe the Venus entry in front of Soleil.

The history of this phenomenon is reported in the work of Horrocks entitled Venus in plate aimed . By this work, Horrocks comes to carry out at the same time the very first great succeeded research of the history of British astronomy and the first coordination of English astronomical observations. As of at the end of October, that is to say approximately a month before the event, it had solicited his/her friends to take part in his work. Because of the bad weather, his/her Jonas brother in Liverpool could not observe it. The measurement of the Venus diameter by Crabtree of 1 ' 03" , apparent diameter of the Sun is 7/100e, remained the measurement most used during more than one century.

The new measurement of the world

The Horrocks young person is on the point of modifying the values of the distances between the stars as soon as it notes the Venus shade, because, as soon as it sees it, it is astonished by its smallness. It finds a angular diameter indeed to him of 1 ' 16" , whereas one allotted the size of 3 traditionally to him '.

It is an observation which intrigued also Pierre Gassendi at the time of the transit of Mercure: I was far, indeed, to suspect Mercure of projecting a so small shade… I thought that it was rather a spot, which, although it was not noted there on the Sun the previous day, nevertheless could also have been born since this time, and I had learned this fait. elsewhere He also thought that the Venus diameter was as to appear smaller to him as than one considered, which confirmed Horrocks.

The data collected with 15:15, 15:35 and 15:45 must make it possible Horrocks to measure the apparent Venus size, the slope of planet, the exact position of the node, the total duration of the passage, just like the moments of entry and exit, not having been able to observe any of it. Horrocks estimated that the apparent Diamètre Venus was of 1 ' 16" ± 4" and the angle underlain by Venus since the Sun of 28". Horrocks considered, by error, that all the known planets had the same angle underlain since the Sun.
On the basis of this reasoning, it calculated that the distance to the Sun was, by rounding the figures, approximately of 15.000 terrestrial rays, whereas for Kepler it was of 3.500 times the ray of the Earth. The English still remains despite everything far from the true distance, of the 23.000 terrestrial rays separating our planet from the Sun.

An premature end

He is trying to want to remake the history of the astronomy of this 17th century by imagining which work could have still carried out Horrocks, and which discoveries he could have made, if he had not suddenly died in full youth.

All that one knows of dead of Horrocks, at the 22 years age, is what Crabtree wrote on a bundle of letters that it had received from Horrocks: Letters of Jeremiah Horrocks of years 1638,1639,1640 until the day of its death brutally which has occurred, in the morning of January 3rd; the day before it had been arranged to pass to see me. Thus God decides it end of any thing. I lost, alas, my dear Horrocks. Hinc illae lachrimae . Thus the tears run”. Loss irréparable.

See too

Internal bonds

Résolution of the equation of Kepler
the asteroid (3078) Horrocks was named in its honor.

External bonds

a more complete biography on planetastronomy.com
on Crabtree, companion of Horrocks

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