Various Topics

General Literature on the Transits of Venus

Theory of Transits of Venus and Tables of their Circumstances

Transits observed from other Solar System Planets

The Black Drop and Related Phenomena

The Moon of Venus

In 1645 the Italian astronomer Francesco Fontana claimed that he had discovered a satellite in the vicinity of Venus through his telescope. Several other astronomers (including Jean Dominique Cassini) made similar claims during the 17th and 18th century but these claims could never be substantiated.

In 1773 the German astronomer Johann Heinrich Lambert announced an orbit for the supposed satellite which he assumed to revolve around Venus in an eccentric orbit in 11 days and 5 hours. However, no such satellite was seen during the transits of Venus in 1761, 1769, 1874 & 1882, although several observers searched diligently for a satellite near the disk of Venus as it crossed the solar disk.

In 1888 the Belgian astronomer Paul Stroobant published a memoir in which he convincingly argued that in most cases the observers had either been fooled by ghost images of Venus in their telescopes or a background star. Modern space missions to the planet Venus have up to now failed to detect any satellite.

Pre-Telescopic Transit of Venus Observations

In his biography of Charlemagne, the Frankish annalist Einhard reported that a few years before his death a black spot had been seen on the Sun’s disk for seven days (Vita Karoli Magni, cap. 32). Other contemporary sources placed the event in March 807 and averred that it had been the planet Mercury. Later, Islamic philosophers as Abu Yusuf Ya‘qub ibn Ishaq al-Sabbah al Kindi (c. 810 - c. 866), Abu ‘Ali al-Husayn ibn ‘Abdallah ibn Sina (Avicenna, 980 - 1037) and others cited similar observations as proof that the orbits of Mercury and Venus were situated below that of the Sun.

A transit of Mercury can only be seen with the aid of a telescope, but a transit of Venus should be visible to the naked eye when the sunlight is sufficiently tempered by thin clouds or dust or when the Sun is near to the horizon. So it is possible that amongst the many pre-telescopic observations of sunspots noted in Chinese, Islamic, European and other sources there may lurk an early record of a transit of Venus. However, many of these observations are only roughly dated, and those reports that are accurately dated do not coincide with a date for a transit of Venus.

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