It won't happen again until December 2117. On June 5th, 2012, Venus will transit(pass in front of) the face of the sun in an event of both historical and observational importance.
Jane Houston Jones: What's Up for June? The transit of Venus.
The dark disk of Venus crosses the sun on June 5 in the Western Hemisphere and on June 6 in the Eastern Hemisphere.
Hello and welcome. I'm Jane Houston Jones at NASA's Jet Propulsion Laboratory in Pasadena, California.
Did you catch the transit of Venus in 2004? If you lived in western North American, you missed it because the transit had ended before the sun rose.
Venus frequently passes nearly directly between the Earth and the sun.
That's when Venus appears closest to the sun from our vantage point on Earth.
But 'nearly' means the planet passes above or below the sun, not across the sun's disk.
A 'transit' of Venus happens when Venus passes directly between the Earth and the sun.
The side of Venus facing us will appear as a small black dot.
It will take about 6 hours and 40 minutes for Venus to pass completely across the disk of the sun.
Only 6 Venus transits have occurred since the invention of the telescope and no one saw the first one in 1631.
Two British astronomers, Jeremiah Horrocks and William Crabtree, saw the next transit in 1639.
Transits occur in pairs, with more than 100 years between each pair.
For safe transit viewing, in addition to solar telescopes and pinhole projection methods, you can use number 14 welder's glass from a welding supply store.
If you want to join a group of observers, you may find one near you on this world-wide event location map.
Or check with your local astronomy club, science center or planetarium.
You can read about how NASA spacecraft, like the Kepler mission, use transits around distant stars to discover new worlds at solarsystem dot nasa dot gov slash y s s, for Year of the Solar System.
And you can learn about all of NASA's missions at w w w dot nasa dot gov.
That's all for this month. I'm Jane Houston Jones.
NASA Jet Propulsion Laboratory, California Institute of Technology