June 6, 2012
Community watches as Venus transits across the sun
Blinn College gave sky-watchers a once-in-a-lifetime opportunity Tuesday afternoon on its Bryan campus.
Just outside the Bookstore Building Blinn students, faculty and staff joined local astronomy buffs to watch Venus transit the sun, an event that happens just twice every 243 years. A transit of Venus across the sun takes place when the planet passes directly between the sun and Earth, becoming visible against the sun, much like the moon does during a solar eclipse. It is among the rarest of predictable astronomical phenomena.
The last time the event occurred, in 2006, it wasn’t viewable from North America, and it won’t occur again until 2117. Because the orbits of Earth and Venus aren’t on the same plane, the sun, Earth and Venus rarely line up. The pattern repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 and 105.5 years.
During the transit, Venus appears as a dark dot passing across the surface of the sun. The dot appears far smaller than that of a solar eclipse because even though Venus is much larger than the moon, it is so far from the Earth’s surface (261 million miles) that it appears smaller than the moon a mere 238,900 miles away.
"That’s what is cool about this – you get to see the size of the sun compared to the planets," said Physics and Astronomy Professor Kris Byboth. "The sun is just so much bigger that it dwarves Venus, which is about the same size as the Earth."
During the viewing, several methods of safely viewing the sun were demonstrated, including the use of a hydrogen alpha telescope designed especially for solar viewing, use of a glass filter mounted onto Blinn’s 10-inch Dobsonian telescope and a safe method of projecting the image of the sun onto a screen.
"People run the risk of going blind if they try to see this without proper instrumentation,"Byboth said. "It doesn’t take long looking at the sun to do a lot of damage."
The event was hosted by Blinn’s Physics Department and the Brazos Region Astronomy Service Society, a student organization with membership open to the public. Blinn hosts about four public astronomical viewings per year and is a member of the NASA Night Sky Network.
In addition to 11 telescopes on its Bryan campus, Blinn is also home to the Schaefer Observatory on its Schulenburg campus. The 27-foot tall galvanized metal structure was built in the 1940s by Schulenburg hardware store owner H.P. Schaefer and his sons to see the surface of the moon.