Transit of Venus

:This article is about the astronomical phenomenon. For other meanings, see Transit of Venus (disambiguation).

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A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and the Earth, obscuring a small portion of the Sun's disc. During a transit, Venus can be seen from the Earth as a small black disc moving across the face of the Sun. A transit is similar to a solar eclipse by the Moon, but, although the diameter of Venus is almost 4 times that of the Moon, Venus appears much smaller because it is much further away from the Earth. Before modern astronomy, observations of transits of Venus helped scientists measure the distance between the Sun and the Earth using the method of parallax.

Related Topics:
Sun - Planet - Venus - Earth - Transit - Solar eclipse - Moon - Astronomy - Parallax

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Transits of Venus are rare and currently occur in a pattern that repeats every 243 years, with pairs of transits 8 years apart separated by long gaps of 121.5 years and 105.5 years. Before 2004, the last pair of transits of Venus were in December 1874 and December 1882. The first of a pair of transits of Venus in the beginning of the 21st century took place on June 8, 2004 (see Transit of Venus, 2004) and the next in this pair will be on June 6, 2012 (see Transit of Venus, 2012). After 2012, the next transits of Venus will be in December 2117 and December 2125.

Related Topics:
2004 - 1874 - 1882 - 21st century - June 8 - Transit of Venus, 2004 - June 6 - 2012 - Transit of Venus, 2012 - 2117 - 2125

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The pattern repeats every 243 years because 243 sidereal orbital periods of the Earth (365.25636 days, which is slightly different from the tropical year) is 88757.3 days, and 395 sidereal orbital periods of Venus (224.701 days) is 88756.9 days. Thus, after this time both Venus and Earth have returned to very nearly the same point in each of their respective orbits. This period of time corresponds to 152 synodic periods of Venus.

Related Topics:
Sidereal orbital period - Tropical year - Synodic period

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The pattern of 105.5, 8, 121.5 and 8 years is not the only pattern that is possible within the 243-year cycle. Prior to 1518, the pattern of transits was 8, 113.5 and 121.5 years, and prior to 546, transits always took place 121.5 years apart. The current pattern will continue until 2846, when it will be replaced by a pattern of 105.5, 129.5 and 8 years. Thus, the 243-year cycle is relatively stable, but the number of transits and their timing within the cycle will vary over time.

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The safest way to observe the event in 2012 would be to project the image of the Sun, as seen through a telescope, onto a screen. Nevertheless, the event can also be seen with free eyes using special stained glasses. Grade 14 of Welder?s glasses should be used. Observing the Sun without filters can cause a temporary or permanent loss of visual function, as it can damage and even destroy retinal cells.

Related Topics:
Telescope - Welder?s glasses - Retina

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