Transit Of Venus Across The Sun Occurs Today
December 21, 2012

Transit Of Venus Across The Sun Occurs Today, 12-21-12

Lawrence LeBlond for - Your Universe Online

So it´s December 21st and the world is still here. Does that mean the doomsayers were full of baloney? Or did they just misread the warnings? Perhaps the Mayans knew today´s date was special for some other reason than total annihilation. If so, then you may be happy to know they would have been right.

Phil Nicholson, a Cornell University scientist said this week that Venus will be making a second transit across the face of the Sun on December 21, 2012.

If you recall, Earthlings were treated to a once in a lifetime transit of Venus across the Sun back in June. The event was so rare that astronomers said it would not occur again for more than a hundred years.

But, it is in fact happening again today. However, the transit will not be viewable on Earth this time around, but from a much more distant planet: Saturn.

“On Friday, Dec. 21st, there will be a transit of Venus visible from Saturn, and we will be watching it using the Cassini spacecraft,” Nicholson, a scientist on the Cassini project, said in a statement. “This will be the first time a transit of Venus has been observed from deep space.”

But because Saturn is 10 times farther from the Sun than Earth, the transit of Venus will not be as easy to spot by Cassini. The planet will be just a tiny black speck crawling across the face of the Sun. While Cassini will be witness to this event, it is safe to say we will not get any great images from the Saturnian orbiter, if any at all. This doesn´t mean that groundbreaking science will not occur, however.

“As Venus crosses the face of the sun, we will see if we can detect chemical compounds in the planet's atmosphere by looking at the spectrum of sunlight filtered by Venus,” explained Nicholson.

Nicholson said it is similar to an experiment using NASA´s Kepler Space Telescope. Kepler routinely discovers new exoplanets orbiting distant stars by looking for a very small reduction in light that occurs during a planetary transit. Much in the same way, watching the Venus transit from the orbit of Saturn could provide a good similarity.

“We already know what Venus's atmosphere is made of,” said Nicholson. “But this will give us a chance to see if we can pull this information out of a faint, distant planetary transit.”

The experiment will rely on Cassini´s VIMS instrument. The VIMS instrument is an infrared spectrometer designed to unravel the chemical compositions of Saturn and its natural satellites. It isn´t designed for planetary transits, but Nicholson believes with a little ingenuity he and his team can gather useful data from the instrument.

“VIMS has a heavily-filtered 'solar port' 20 degrees off the main axis of the spectrometer. We use it to occasionally observe the sun for calibration purposes--or to watch the sun set in the atmosphere of Saturn's moon's Titan” Nicholson explained. “On Dec. 21st we'll be using the solar port to monitor the transit of Venus.”

While the images they receive won´t be impressive by any means, the researchers are more focused on the “spectra.” Nicholson noted that Venus´s atmosphere is made up mostly of carbon dioxide, which “has several absorption bands squarely inside our 1 to 5 micron observing window.”

The team expects the VIMS instrument will gather data for the entire 9 hours of the transit–as well as many hours both before and after the event for comparable data.

"Even with so much observing time, we still might not detect any chemical signatures," Nicholson cautioned. "The signals are going to be faint--only a few parts in a million--so this is an extremely difficult observation."

Nevertheless, it should be a great day for Cassini.

“While most people have to wait a hundred years for the next transit of Venus, we get to experience one right away. And if we make any discoveries at the same time... so much the better,” concluded Nicholson.