Since Venus is closer to the Sun than is the Earth, Venus passes in front of the Sun fairly often. However, due to its orbital period (just 225 days) and its orbital angle (tilted by 3 degrees to Earth’s orbital angle), we don’t see this transit every time. The transits we can see come in pairs, separated by 8 years, in an alternating pattern of every 105.5 and 121.5 years. They are RARE events! Observed transits occurred in 1639, 1761/1769, 1874/1882, and now in 2004/2012. While I don’t usually link to Wikipedia, a good historical perspective of the modern observations is presented there. For whatever reason, I especially like the story of Guillaume Le Gentil – it’s wonderfully awful! Sometimes the stars do not align, even for astronomers.
I saw the 2004 transit telecast from the Lawrence Hall of Science at Berkeley, and now I’m looking forward to hosting an observing event at Albion College. The Venus transit will be seen by much of the world, from June 5 to June 6; only parts of South America and Africa won’t be able to see it. However, dozens of webcasts will show the event, and I’ll bet there will be millions, if not billions, of observers.
DO NOT LOOK DIRECTLY AT THE SUN! Be sure that you are either projecting the event, looking through telescopes equipped with special filters, or wearing eclipse glasses. The Sun’s intense radiation can temporarily damage your eyes if you are not protecting them!
This is a global observing event and the last good opportunity to see Venus transit the Sun from the surface of Earth (but click here to read about other viewing opportunities). Don’t miss it! Find a nearby viewing event or watch it on-line – and keep your fingers crossed for clear skies!
Everything you wanted to know about the Venus transit (Discover Magazine article)
History of Venus transit observations (NY Times article)
More history of Venus transit observations (Australian Geographic article)
Transits Explained (Sky & Telescope article)
Story of Captain James Cook’s first voyage, to observe the Venus transit (1769)
NASA Press Release, including a transit animation
NASA Webcast of transit
6 ways to observe the transit
June 6 (Update): That was certainly an amazing event! I hope you had a chance to see it, wherever you were. In Albion, the clouds parted and we had a solid four hours of observing sunspots and then Venus, all the way to the horizon. We had a fantastic turnout, with over 200 people attending. Enjoy the pictures.
Pictures from Albion College can be found here.
Battle Creek Enquirer newspaper article, with great pictures