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See Nasa's or Transit of Venus Project safety pages.

Transits - of Mercury and Venus

Normally, when an inferior planet (Mercury or Venus) comes into inferior conjunction with the Sun, it will pass the Sun's disk at some apparent distance. But occasionally, it happens that it passes close enough to the disk's center that it will pass between Earth and Sun. On these occasions, a transit of the dark, small planetary disk can be seen on the bright, large disk of the Sun.

  • Mercury will transit across the Sun on May 7, 2003. Next transits will be in 2006, 2016, 2019.

  • Venus will pass across the Sun's disk on June 8, 2004. Next transit will be in 2012, then only in 2117.

    Mercury Transits

    Mercury transits occur every few years, about 13 a century. These events occur when Mercury's inferior conjunction happens to coincide with a crossing of the Earth's orbital plane, the Ecliptic, i.e. when the planet passes its orbit's ascending or descending node. At these times, Earth passes Mercury's orbit each early May (descending node; Mercury passes ecliptic from North to South) and early November (ascending node). If Mercury's inferior conjunction happens to occur at that time, a transit can be seen.

    Next Mercury transit will occur on May 7, 2003 between 5:13 and 10:32 UT, with its minimal separation from the solar disk's apparent center at 7:52.

    The following transit will be on November 8, 2006, 19:12 UT to 00:10 UT (Nov 9) with greatest approach at 21:41.

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    Venus Transits

    Venus transits are rare, occurring in pairs separated by 8 years, with 105.5 or 121.5 years to the next pair of transits. These events occur when Venus passes between Earth and sun just coincidently with both planets crossing the other's orbital plane (the ascending and descending nodes). These times, Earth always crosses Venus' orbit in early June and early December of each year; if an inferior conjunction happens to take place at these times, a transit can be observed.

    Because they are so rare, only six Venus transit have occurred since the invention of the telescope:

    The 20th century has passed without any Venus transit occurring. Next Venus transits will happen on The Venus transits of 1761 and 1769 have been utilized by astronomers to attempt a parallax measure for determining the length of the Astronomical Unit, AU, and thus the linear dimensions of the Solar System.

    Links:

    Hartmut Frommert [contact]
    [SEDS]