On the 8th of June 2004, Venus passes in front of the disc of the Sun for the first time in 121 years. This event occurs as the nodes of Venus's orbit pass between the Earth and the Sun, something that happens at intervals of 8, 121, 8 and 105 years. The reason that the event is so infrequent is that the orbit of Venus is tilted relative to the Earth's. Even though the planets are in the same point on their orbit every 583.9 days, Venus is usually above or below the plane of the ecliptic.

The following image, showing the stages of the transit, was generated using Planetary Visions' interactive CD-ROM, 3D Universe.

Although only the sixth time that man has been able to observe a transit of Venus, there is little scientific interest in this transit. The previous observations, in 1639, 1761, 1769, 1874 and 1882, were used (unsuccesfully) to measure the distance from the Earth to Venus and to the Sun. In the 19th century it was also thought that observers would see jungles and oceans on the Venusian surface.

The transits of the 18th century were observed by the surveyors Mason and Dixon, described by Thomas Pynchon in his book of the same name , and by Captain James Cook in Tahiti. Cook was employed primarily as an astronomer and surveyor, and it was incidental that on this voyage he also discovered Australia and claimed it for the British Crown.

3D Universe was developed in conjunction with United Soft Media, and with the European Southern Observatory. The CD-ROM contains an encyclopedia of 150,000 words, 2000 images, and an interactive flying mode which allows you to use a planetarium, or to see the solar system, a million stars, or 70,000 galaxies, from anywhere in the known universe.