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Story last updated at 5:37 PM on Wednesday, June 6, 2012

Scientists replicate historic astronomical experiment



Photo by Michael Armstrong

Ron DiIulio, director of the University of North Texas, Denton, monitors photographs of the transit of Venus on Tuesday afternoon at Land's End Resort, Homer.

Astronomers and citizen scientists from the University of North Texas, Denton, visited the Homer Spit on Tuesday to replicate a historic experiment done by British explorer Capt. James Cook in Tahiti in 1769. With high-tech telescopes and cameras pointing at the sun from the beach by Land's End Resort, Ron DiIulio, director of the UNT astronomy program, took timed photographs of the planet Venus as it crossed the view of the sun.

At the same time at South Point, Hawaii, another UNT astronomer, Preston Starr, took similar measurements, duplicating an experiment first proposed by Edmond Halley, the discoverer of Halley's Comet, who died before the 1769 transit. Halley wrote that if observers took measurements from two places a known distance apart, and timed when Venus first crossed the view of the sun, using parallax measurements, the distance from earth to the sun can be calculated — now known to be 93 million miles.

Parallax error is the slight difference in view of the same object between two places. To see this, hold your thumb up and look at something like a tree with one eye closed, DiIulio said. Block your view with the thumb and then look at it with the other eye. Your thumb will appear to shift.

UNT observers originally planned to watch from the roof of a parking garage at the University of Alaska Anchorage, but after looking at weather records and predictions, decided Homer would have better viewing. Despite cloudy skies on Tuesday, that turned out right.

"We knew it would be fine," DiIulio said. "We ate the token halibut and knew the weather would clear up."

The transit of Venus occurs in pairs every eight years, with pairs separated by gaps of between 105 and 121 years. The last transit was in 2004 and the next transit will be in 2117, so this transit was the last chance of a lifetime. The last transits before that had been in 1874 and 1882.


Photo by Michael Armstrong

Taken through a TeleVu 85 mm telescope, Venus, the dot in the upper left, transits the sun at about 3:05 p.m. Tuesday as seen from Land's End Resort on the Homer Spit.

Although the methods were the same as for Cook, in the 21st century, the UNT scientists had better equipment. Cook had to make his observations with sketches and time it with a stand-up grandfather clock. DiIulio had better equipment: an Explorer Scientific 127 mm refracting telescope, a Televu 85 mm refracting telescope, and a Canon 5D Mark III camera with a GPS tracker, the GP-E2, so new it hasn't been released yet and was loaned by Canon just for the experiment. Special filters blocked harmful light from keep eyes and sensitive camera equipment.

"We're recreating it with the new technology," DiIulio said.

The 2004 transit was the first time the event was photographed. The 2012 transit takes it even further. Citizen scientists and observers around the world recorded measurements with smart phone and computer apps and shared them on scientific blogs and web pages.

"This second period we actually remembered and recorded the event digitally," DiIulio said.

Michael Armstrong can be reached at michael.armstrong@homernews.com.