Spent this chilly afternoon at the beach in South Haven MI photographing one of the rarest astronomical events...The transit of Venus across the disk of the Sun!  Such an even only occurs twice, 8 years apart, about every 200 years.

When this occurs, the planet actually blocks a portion of the sun. Unlike an eclipse, which covers the entire sun, a transit is similar but doesn't block the entire disk of the sun. So you get what looks like a shodow on the sun. Much like a bird or plan crossing the sun from your point of view!  ( I was lucky enough to capture both)

Given that this is 2012, and the recent hype about Mayan calendars etc... This is an excellent way to demonstrate how really cool that calendar was...You see more than a thousand years ago the ancient Maya were able to predict when these transits would occur, and actually based an element of their long count on it. (But without actually mentioning the transit itself) So it's probably no surprise that their long count ends on a year that venus transits the sun. Another part of the calendar is based on a venus...Every 9 months it completes an orbit relative to the Earth, which is also roughly the length of a full term pregnancy. The Lunar calendar, is 29 1/2 days from New to New moon, again, another element of the Maya Calendar.  Nothing in that calendar was ever meant to mean an 'end' to anything, but rather the beginning of another day, month, season, year, transit cycle, or eon.  Learn more here.
Photo from my February 2012 trip to Tulum, Mexico