It won't be visible from Earth again until 2117. Today the planet Venus will transit the sun and astute sky watchers in the Northern Hemisphere will see it as a tiny black dot moving across the sun's surface.
Transits of Venus happen in pairs eight years apart, with more than a century between cycles. During the pass, Venus appears as a small, dark round spot moving across the face of the sun, like a bug on a dinner plate.
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Tuesday's transit, which bookends a 2004-2012 pair, begins at 6:09pm EDT (2209 GMT) and lasts for six hours and 40 minutes. Times can vary by seven minutes depending on the location of the observer.
Skywatchers on seven continents, including Antarctica, will be able to see all or part of the Venus transit, which should only be observed with telescopes outfitted with solar filters to protect the eyes.
MSNBC has detailed information on how the sun can be viewed safely.