The transit begins at 6:09 p.m. EDT and lasts about 6 hours and 40 minutes.
Optics expert, Peter Emmel, tells Unofficial Networks more about todays Transit of Venus.
Hopefully some of you have noticed the planetary lineup after sunset for the past couple of months, as we’ve seen the Moon pass by a gauntlet formed by Jupiter and Venus in the west, then Mars and Saturn higher in the sky. If you’ve noticed this, then you might already be aware that we’re closing in on a rare astronomical event, and I’m not talking about Mayan calendar 2012 end-of-the-world hocus pocus. This is real once-in-a-lifetime astronomy and anyone in the right part of the globe – and with a clear sky and a little ingenuity (or an internet connection) – should be able to see at least part of it. The event is a “transit of Venus” … when we on Earth can see Venus pass right across the face of the Sun. It won’t happen again for more than a century.
Venus goes between us and the Sun about every 19 months (roughly every year and a half), but most of the time it’s a little above or below our exact line of sight so we don’t see it go by. On rare (but regular) occasions, Earth, Venus and the Sun line up just right. The last time this happened was in 2004, but the next time won’t be until 2117 – 105 years from now! (The “transitofvenus” site shown above explains the irregular intervals – in the FAQ section.)
Historically – beginning with Jeremiah Horrox in 1639 and including US ‘Founding Father’ Thomas Paine in the late 1790s – transits of Venus across the Sun have been used to confirm (or debunk) ideas about the Solar System and make measurements – including the Earth’s distance from the Sun (by triangulation based on transit data from different places on Earth).
I hope the sky is clear enough today so that you can at least see the Sun, even if you can’t actually see Venus. However, if it’s cloudy there’s a fall-back: The entire transit will be webcast live by NASA from an observatory in Hawaii where it’s almost never cloudy: