Background Transit of Venus, 1639

1 background

1.1 jeremiah horrocks
1.2 william crabtree
1.3 transit of mercury

background

kepler s de raris mirisque anni 1631 notice astronomers of impending transits of mercury , venus, 1631

by 17th century, 2 developments allowed transits of planets across face of sun predicted , observed: telescope , new astronomy of johannes kepler, assumed elliptical, rather circular, planetary orbits.

in 1627, kepler published rudolphine tables. 2 years later published extracts tables in pamphlet de raris mirisque anni 1631 included admonitio ad astronomos (warning astronomers) concerning transit of mercury in 1631 , transits of venus in 1631 , 1761. mercury transit occurred predicted , observed johann baptist cysat in innsbruck, johannes remus quietanus in rouffach , pierre gassendi in paris, vindicating keplerian approach. observations threw question previous theories solar system mercury shown smaller expected.

although kepler s calculations indicated 1631 transit of venus best visible american continent, not confident of prediction, , advised european astronomers should prepared observe event. gassendi , others in europe watched but, predicted, sun below horizon during transit. according modern calculations, observers in of italy , along eastern mediterranean should have been able view last stage of transit, no such observations recorded. kepler had predicted near miss venus transit in 1639 and, next full transit not expected 121 years, gassendi , other astronomers concentrated efforts in other areas.

jeremiah horrocks

jeremiah horrocks (1618 – 3 january 1641) born in lower lodge, toxteth park, part of liverpool; father, james watchmaker, , mother mary (née aspinwall) notable toxteth park family. several members of aspinwall family in watchmaking trade, , said watchmaker uncle first interested jeremiah in astronomy. jeremiah joined emmanuel college on 11 may 1632 , matriculated member of university of cambridge on 5 july 1632 sizar, meant did not have means support himself , given specific duties compensate reduction in fees. @ cambridge, have studied arts, classical languages, little geometry, , traditional astronomy, not latest work of galileo, tycho brahe , kepler. used spare time teach himself more demanding mathematical astronomy , familiarise himself latest thinking. horrocks read of astronomical treatises of day, found weaknesses in them, , suggesting new lines of research age of 17. in 1635, left cambridge without formally graduating, presumably owing cost of graduation.

after leaving cambridge, horrocks returned home in lancashire , began collecting books , instruments in order pursue main interest, study of astronomy. in summer of 1639, left home , moved 18 miles along coast village of hoole, thought took post tutor children of stones family, prosperous haberdashers living @ carr house, within bank hall estate, bretherton.

horrocks first demonstrate moon moved in elliptical path around earth. wrote treatise on keplerian astronomy , began explore mathematically properties of force became known gravity; isaac newton in principia acknowledged horrocks s work in relation theory of moon.

william crabtree


ivy cottage, broughton: house william crabtree thought have made observation of transit

william crabtree (1610–1644) cloth merchant broughton spout, hamlet in township of broughton near manchester, part of salford. son of john crabtree, lancashire farmer of comfortable means, , isabel crabtree (née pendleton), educated @ grammar school in manchester – forerunner of manchester grammar school, situated between collegiate church , chetham s school of music. worked in manchester, married wealthy family , in spare time studied mathematics , astronomy. measured movements of planets, undertook precise astronomical calculations , rewrote existing rudolphine tables improved accuracy. maintained active correspondence, of lost, horrocks, 2 other young astronomers – william gascoigne , christopher towneley – , samuel foster, professor of astronomy @ gresham college, london , alumnus of emmanuel college. not known whether horrocks , crabtree ever met in person 1636 corresponded regularly, and, because of shared interest in work of johannes kepler, referred themselves, along william gascoigne, nos keplari (we keplarians).

crabtree’s observations had convinced him that, despite errors, kepler’s rudolphine tables superior commonly used lansberg s tables, , became 1 of first converts kepler’s new astronomy. 1637, had convinced horrocks of superiority of keplerian system, and, using own planetary observations, both men made many corrections kepler s tables, crabtree converted decimal form.

transit of mercury

on 29 september 1638, horrocks wrote crabtree forthcoming transit of mercury on 21 october 1638 (old style) kepler had not predicted. explained intended construct later called helioscope attaching telescope oblong stick, carrying plane surface @ right angles on receive sun’s image , , draw circle numerical markings on sheet of paper on project image of sun. in event, no such transit took place mercury passed on sun outside limit transit, exercise proved important dry-run later observation of transit of venus.

in october 1639, horrocks had calculated transits of venus occur not singly, in pairs 8 years apart, , realised second transit occur in less 4 weeks. convinced measurement made of apparent diameter of planet within fraction of second of arc when seen dull black disk on face of sun, compared accuracy of around 1 minute of arc when seen in normal position bright morning star close sun. wrote younger brother , crabtree in broughton, advising them observe event on sunday, 24 november (4 december new style). quote horrocks: more accurate calculations of rudolphi confirmed expectations; , rejoiced exceedingly in prospect of seeing venus .

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