Ancient
Indian,
Greek,
Egyptian,
Babylonian, and
Chinese observers knew of Venus and recorded the planet's motions.
Pythagoras is credited with realizing that the so-called
morning and
evening stars were really both the planet Venus. There is no evidence that any of these cultures observed planetary transits. It has been proposed that
frescoes found at the
Maya site at
Mayapan may contain a pictorial representation of the 12th or 13th century transits. The Persian polymath
Avicenna claimed to have observed Venus as a spot on the Sun. There was a transit on 24 May 1032, but Avicenna did not give the date of his observation, and modern scholars have questioned whether he could have observed the transit from his location; he may have mistaken a
sunspot for Venus. He used his alleged transit observation to help establish that Venus was, at least sometimes, below the Sun in
Ptolemaic cosmology, i.e., the sphere of Venus comes before the sphere of the Sun when moving out from the Earth in the then prevailing
geocentric model.
1631 and 1639 transits ,
Jeremiah Horrocks (1618–1641) (1903),
Astley Hall Museum and Art Gallery The German astronomer
Johannes Kepler predicted the 1631 transit in 1627, but his methods were not sufficiently accurate to predict that it could not be seen throughout most of Europe. As a consequence, astronomers were unable to use his prediction to observe the event. The first recorded observation of a transit of Venus was made by the English astronomer
Jeremiah Horrocks from his home at
Carr House in
Much Hoole, near
Preston, on 4 December 1639 (24 November O.S.). His friend
William Crabtree observed the transit from nearby
Broughton. Kepler had predicted transits in 1631 and 1761 and a near miss in 1639. Horrocks corrected Kepler's calculation for the orbit of Venus, realized that transits of Venus would occur in pairs 8 years apart, and so predicted the transit of 1639. Although he was uncertain of the exact time, he calculated that the transit was to begin at approximately 15:00. Horrocks focused the image of the Sun through a simple
telescope and onto paper, where he could observe the Sun without damaging his eyesight. After waiting for most of the day, he eventually saw the transit when clouds obscuring the Sun cleared at about 15:15, half an hour before sunset. His observations allowed him to make a well-informed guess for the diameter of Venus and an estimate of the mean distance between the Earth and the Sun (). His observations were not published until 1661, well after Horrocks's death. In an attempt to observe the first transit of the pair, astronomers from Britain (
William Wales and
Captain James Cook), Austria (
Maximilian Hell), and France (
Jean-Baptiste Chappe d'Auteroche and
Guillaume Le Gentil) took part in expeditions to places that included
Siberia,
Newfoundland, and Madagascar. Most of them observed at least part of the transit.
Jeremiah Dixon and
Charles Mason succeeded in observing the transit at the
Cape of Good Hope, but
Nevil Maskelyne and
Robert Waddington were less successful on Saint Helena, although they put their voyage to good use by trialling the
lunar-distance method of finding longitude. Venus was generally thought to possess
an atmosphere prior to the transit of 1761, but the possibility that it could be detected during a transit seems not to have been considered. The discovery of the planet's atmosphere has long been attributed to the Russian scientist
Mikhail Lomonosov, after he observed the 1761 transit from the
Imperial Academy of Sciences of St. Petersburg. The attribution to Lomonosov seems to have arisen from comments made in 1966 by the astronomy writer
Willy Ley, who wrote that Lomonosov had inferred the existence of an atmosphere from his observation of a luminous arc. The attribution has since then been questioned.
1769 transit 's observations of the 1769 transit of Venus For the 1769 transit, scientists travelled to places all over the world. The Czech astronomer
Christian Mayer was invited by the Russian empress
Catherine the Great to observe the transit in
Saint Petersburg with
Anders Johan Lexell, while other members of the
Russian Academy of Sciences went to eight other locations in the
Russian Empire under the general coordination of
Stepan Rumovsky. King
George III of the United Kingdom had the
King's Observatory built near his summer residence at
Richmond Lodge, so that he and the
Astronomer Royal,
Stephen Demainbray, could observe the transit. Hell and his assistant
János Sajnovics travelled to
Vardø, Norway. Wales and
Joseph Dymond went to
Hudson Bay to observe the event. In
Philadelphia, the
American Philosophical Society erected three temporary observatories and appointed a committee led by
David Rittenhouse. Observations were made by a group led by Dr. Benjamin West in
Providence, Rhode Island,
Observations were also made from Tahiti by Captain James Cook and Charles Green at a location still known as
Point Venus. D'Auteroche went to San José del Cabo in what was then
New Spain to observe the transit with two Spanish astronomers (Vicente de Doz and Salvador de Medina). For his trouble he died in an epidemic of
yellow fever there shortly after completing his observations. Only 9 of 28 in the entire party returned home alive. Le Gentil spent over eight years travelling in an attempt to observe either of the transits. Whilst abroad he was declared dead, and as a result he lost his wife and possessions. Upon his return he regained his seat in the
French Academy and remarried. The American astronomer
Simon Newcomb combined the data from the last four transits, and he arrived at a value of . The participants' observations allowed a calculation of the astronomical unit (au) of , which differed from the accepted value by 0.007%. During the 2004 transit, scientists attempted to measure the loss of light as Venus blocked out some of the Sun's light, in order to refine techniques for discovering
extrasolar planets. The
2012 transit of Venus provided scientists with research opportunities as well, in particular in regard to the study of
exoplanets. The event additionally was the first of its kind to be documented from space, photographed aboard the International Space Station by NASA astronaut
Don Pettit. The measurement of the dips in a star's brightness during a transit is one observation that can help astronomers find exoplanets. Unlike the 2004 Venus transit, the 2012 transit occurred during an active phase of the 11-year activity cycle of the Sun, and it gave astronomers an opportunity to practise picking up a planet's signal around a "spotty" variable star. Measurements made of the apparent diameter of a planet such as Venus during a transit allows scientists to estimate exoplanet sizes. Observation made of the atmosphere of Venus from Earth-based telescopes and the
Venus Express gave scientists a better opportunity to understand the intermediate level of Venus's atmosphere than was possible from either viewpoint alone, and provided new information about the
climate of the planet. Spectrographic data of the atmosphere of Venus can be compared to studies of the atmospheres of exoplanets. The
Hubble Space Telescope used the
Moon as a mirror to study light from the atmosphere of Venus, and so determine its composition. == Future transits ==