Pluto plane chases shadow
StoryDiscussionImage (2)Pluto plane chases shadow
ERIC BETZ Sun Staff Reporter azdailysun.com | Posted: Sunday, July 10, 2011 5:15 am | (2) Comments
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The Stratospheric Observatory for Infrared Astronomy, or SOFIA, sat on the tarmac during nighttime telescope operations at NASA�s Dryden Aircraft Operations Facility in October 2010. (Photo courtesy of NASA)
..On June 23, astronomers from Lowell Observatory boarded an airplane in southern California and flew 1,800 miles out over the Pacific Ocean, positioning themselves to glimpse Pluto's shadow as it raced across Earth's surface at 53,000 MPH.
The aircraft was no ordinary plane, it was NASA's heavily modified Boeing 747 called the Stratospheric Observatory for Infrared Astronomy, which is equipped with a 8-foot-diameter telescope mirror as well an instrument designed by the Lowell astronomers themselves for exactly such an occasion.
Their instrument is called the High-Speed Imaging Photometer for Occultation. It's an incredibly fast and accurate electronic camera created to observe somewhat rare astronomical events called occultations.
Occultations happen when a planet -- or other object -- passes in front of another star in line of sight from the Earth.
"Occultations give us the ability to measure pressure, density, and temperature profiles of Pluto's atmosphere without leaving the Earth," said Lowell Observatory's Ted Dunham, who led the onboard team of scientists and is HIPO's principal investigator.
Dunham was also a member of the group that first discovered Pluto's atmosphere during a stellar occultation observed by SOFIA's predecessor, the Kuiper Airborne Observatory, in 1988.
The astronomers said that calculating exactly where the shadow would fall was tough and they could only get an accurate calculation a few hours before they were to start observing.
That night, Lowell astronomer Stephen Levine used facilities at the U.S. Naval Observatory's Flagstaff Station to image Pluto and the star. Those images were then sent to astronomers at the Massachusetts Institute of Technology, who refined the exact prediction of where the shadow would pass.
A mere two hours before the occultation started, the MIT scientists called the aircraft to say the shadow would pass 125 miles north of their intended flight plan. At 45,000 feet above the Earth, the pilots then had to refile a flight plan and wait 20 minutes for air traffic controllers to give them approval to change course.
"Because we were able to maneuver SOFIA so close to the center of the occultation, we observed an extended, small, but distinct brightening near the middle of the occultation," said Dunham. "This change will allow us to probe Pluto's atmosphere at lower altitudes than is usually possible with stellar occultations."
Eric Betz can be reached at ebetz@...
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