By Kathy Waits
Try stargazing on most any day, and what object will you see? The sun, of course! But on June 5, 2012, something extra special happened in the daytime sky. The planet Venus moved right across the face of our star as it orbits between Earth and the sun.
This extraordinary phenomenon is called a “transit of Venus,” and it happens only when Venus, Earth, and the sun are all lined up just right: Venus must be exactly between the sun and Earth at exactly the same time (astronomers call this an “inferior conjunction”), and its orbit has to cross the sun’s path in the sky (“the ecliptic”).
A transit of Venus is basically the same thing as a solar eclipse, when the moon blots out the sunlight as it passes between Earth and the sun. Except in this case, it’s Venus that will do the blotting. But since the disk of Venus is only 1/30th the size of the disk of the sun, the planet won’t be blotting out very much.
These transits occur very rarely. The last one happened eight years ago, but if you missed this one, you’ll have to wait more than 100 years for the next one. There won’t be another transit of Venus until December 11, 2117!
In the San Francisco Bay Area, Venus ﬁrst touched the limb of the sun at 3:06 pm. The sun set before Venus came through to the other side. In the United States, only people in Alaska and Hawaii were able to see the entire event.
Here’s very important advice to any would-be daytime astronomers: Never look directly at the sun. The bright light can seriously damage your eyes. To safely watch solar events like the transit of Venus you need special equipment, such as ﬁltered glasses (not ordinary sunglasses!) or a projection screen. Check out Sunearthday.nasa.gov, or Transitofvenus.org for tips on observing the transit and protecting your eyes.
If you are a kid, don’t try any of these tips without help from a grownup. A safer and easier place to view celestial events is UC Berkeley’s Lawrence Hall of Science. In the plaza they often have a full display where you can watch the whole thing.
Or, easier still, your can watch the live webcast from the Mauna Kea Observatory atop the Mauna Kea volcano in Hawaii (sunearthday.nasa.gov/2012/transit/webcast.php). Aloha, Venus!