The Venus Transit 2004 - The black drop effect (artist's impression)

On June 8, 2004, a rare event will be visible from the Earth. For the first time in 122 years Venus will pass in front of the disk of the Sun in a so-called transit. The transit will take about 6 hours and be visible from most of Europe, Africa and Asia.

Read more on the web pages of theVenus Transit 2004 collaboration.

In this close-up animation the so-called black drop effect can be seen. The effect has been the subject of considerable controversy, but is caused by a combination of many different contributing effects: Partly the diffraction of light inside the telescope, partly by the Sun?s limb darkening and partly by the smearing of the image by the terrestrial atmospheric. Note that the black drop effect has also been observed during Mercury transits (Mercury has no atmosphere), as well as during Mercury transits from space (where the terrestrial atmosphere plays no role).