The 2004 Transit of Venus
Simulation © 2003 HL
(Click to play a larger avi movie)
IN 2004 and 2012 Venus Will Cross the Sun's Face
EVENTS are among the rarest of all planetary alignments. In
fact, the last such occurrence was in the year 1882. (See Fig.
1 on left for simulation of the 2004 transit.)
More than one century will elapse before these transits
occur again. Indeed, few humans have ever seen Venus cross the Sun's disk.
of Venus are easily seen only with telescopes and only six transits
of Venus have occurred since the telescope was invented in the
early seventeenth century: 1631, 1639, 1761, 1769, 1874, and 1882.
(Notice transits now occur in pairs with eight year separations
between the two transits in the pair. Intervals of about 105 or
122 years elapse before a pair of transits occurs again.)
only planets that can transit the Sun are planets with orbits smaller
than Earth's orbit. These planets are Mercury and Venus. Since their orbits are inside Earth's orbit, both planets can pass between the Sun and Earth. (See Fig. 2.)
However, because planetary orbits are tilted to the plane of the Earth's orbit, these planets usually appear to pass either above or below the Sun's disk.
Fig. 2. Seen from our planet only objects with orbits
smaller than Earth's can transit the Sun
transits of Mercury are common (thirteen to fourteen per century)
because the orbit of Venus is larger than the orbit of Mercury.
(Mercury orbits the Sun every 88 days; Venus requires 225 days.)
So, transits of Venus happen infrequently and most people never
see this remarkable event. (Also, the disk of Venus appears about
five times larger than the disk of Mercury making transits of this
planet far more spectacular and special than for Mercury.)