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A transit of Venus takes place when Venus passes directly between the Sun and the Earth (or any other superior planet), becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus is visible as a small black circle moving across the face of the Sun. Transits of Venus reoccur periodically.
Kepler's De raris mirisque Anni 1631 Phaenomenis notice to astronomers of the impending transits of Mercury and Venus, 1631. By the 17th century, two developments allowed for the transits of planets across the face of the Sun to be predicted and observed: the telescope and the new astronomy of Johannes Kepler, which assumed elliptical, rather than circular, planetary orbits.
The first successful flyby Venus probe was the American Mariner 2 spacecraft, which flew past Venus in 1962, coming within 35,000 km. A modified Ranger Moon probe, it established that Venus has practically no intrinsic magnetic field and measured the temperature of the planet's atmosphere to be approximately 500 °C (773 K ; 932 °F ).
During a transit, Venus appears as a small black disc travelling across the Sun. Transits of Venus occur in a pattern that repeats itself every 243 years, with two transits that are eight years apart, separated by breaks of 121.5 and 105.5 years. [2]
2012 transit of Venus, projected to a white card by a telescope. A transit of Venus is the appearance of Venus in front of the Sun, during inferior conjunction. Since the orbit of Venus is slightly inclined relative to Earth's orbit, most inferior conjunctions with Earth, which occur every synodic period of 1.6 years, do not produce a transit ...
The black drop effect was long thought to be due to Venus's thick atmosphere, and indeed it was held to be the first real evidence that Venus had an atmosphere. However, it is now thought by many to be an optical effect caused by the combination of the extreme darkening of the Sun's disk near its apparent edge and the intrinsic imperfection of ...
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One type of transit involves the motion of a planet between a terrestrial observer and the Sun. This can happen only with inferior planets, namely Mercury and Venus (see transit of Mercury and transit of Venus). However, because a transit is dependent on the point of observation, the Earth itself transits the Sun if observed from Mars