The second half of a twice-in-a-lifetime astronomical event takes place today — a transit of Venus across the face of the Sun. The planet will look like a small black dot slowly creeping across the Sun’s northern hemisphere. It’ll be visible across the entire United States — but you need eye protection to view it.
Venus crosses between Earth and the Sun every 19 months. Its orbit is tilted slightly with respect to Earth’s orbit, though, so most of the time Venus passes just above or below the Sun.
Occasionally, though, the geometry is just right, and Venus passes across the Sun. Such transits happen in pairs, with the two halves of the pair separated by eight years. There was a transit eight years ago, so today’s is the last half of a pair. The pairs are separated by either 105-and-a-half or 121-and-a-half years. So after today, the next transit isn’t until 2117.
Today’s transit begins shortly after 5 p.m. Central Time, when Venus first touches the Sun’s disk. It ends about six hours later. The Sun will set before then across the Lower 48 states. But the entire transit will be visible from Hawaii and Alaska.
To view it safely, look through special solar eclipse glasses or dark welder’s glass — number 14 or darker. Many groups, including the visitor center at McDonald Observatory, will offer viewing through telescopes equipped with special filters. And NASA and others will broadcast the entire transit on the web. We have links to several of those, plus much more on the transit, on our website — stardate.org.
Script by Damond Benningfield, Copyright 2012
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