Twice every 130 or so years, Venus crosses the disk of the Sun, as seen from Earth. The nineteenth century transits of Venus helped astronomers determine the scale of the solar system. Transits still have scientific use. For one thing, the backside of Venus is black compared to the surface of the Sun, much blacker than sunspots, which would be blinding if they were anywhere but the surface of the Sun. This gives us a handle on the true brightness of the Sun.
Information on this year's transit, which takes place early Tuesday Morning, EDT, is available on the Sun-Earth Day 2004 web page. Some of the links include:
- Information on live webcasts, useful for the Western Hemisphere since the transit starts at 1 am EDT.
- A link to NASA TV, which will carry some or all of the transit, live.
- John Phillip Sousa's Transit of Venus March, including piano scores and the Library of Congress's site, including a recording. (It sounds pretty much like every Sousa march you've ever heard.)
If you've just got to look at the transit directly, it's recommended that you use a welding hood with a #14 or darker filter. Otherwise, use one of these websites, or contact your local observatory.
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