A Comet Movie

In August 2009, the Australian astronomer Gordon J. Garradd was working on a sky survey at the Siding Spring Observatory near Coonabarabran, New South Wales, when he discovered a comet. Comet discoveries aren’t unusual for Siding Spring; the observatory found no fewer than a dozen that year, two of them by Garradd.

[One of the black-and-white images of Comet Garradd that I took Saturday morning]
The Starry Night Pro planetarium program lists four different comets Garradd, named after their discoverer. The one he noticed two years ago this month, official designation Comet Garradd (C/2009 P1), just now is in a good position for telescopic viewing — high in the nighttime sky, slipping from the constellation Pegasus into Delphinus.
The “Cometography” web site maintained by Gary W. Kronk — click HERE — indicates that when Garradd sighted this primordial chunk of ice and dust, it was a dim magnitude 17.7 to 17.5. (The higher the number, the fainter the object; somewhat brighter than magnitude 6 is about as feeble a star as most people can detect with the naked eye.)
Around the time of discovery, the comet’s distance was estimated at eight astronomical units. An AU is the distance from the sun to Earth, 93 million miles, so the comet was about 744 million miles away.
As its long orbit carries it inward to loop around the sun, Comet Garradd is warming. Sol’s rays are heating the surface, causing particles to stream off. It has begun to develop a tail, and it is much brighter than before. According to NASA’s Astronomy Picture of the Day for last Saturday, the comet is now about 145 million miles distant.
“Shining faintly around 9th magnitude, comet Garradd will brighten in the coming months, predicted to be just below naked eye visibility near its peak in February 2012,” Gregg Ruppel wrote in the APOD caption to his photo of the comet. Experts predict it will glow a little brighter than sixth magnitude by then.
Meanwhile, Comet Garrard already makes an interesting view through a largish amateur telescope.
Late Friday afternoon I set up my scope at the dusty observing site nicknamed Lakeside. Located in Tooele County, it is reached by driving about an hour west from Salt Lake City on I-80, taking a side road back five miles to a turnoff, then making a left. Half a mile on, a berm from an abandoned reservoir marks the spot. The ground is dry, cracked dirt. Fine white powder invades shoes and trousers, mosquitoes drain your blood, but the light pollution isn’t bad.

[My portable observatory set up at Lakeside. Photo by Joe Bauman]

I knew Comet Garradd was not far from the direction of the beautiful globular cluster M15, yet when I directed the telescope to the cluster, I couldn’t find the comet. It was too dim to show up in the finder scope. I had to resort to plugging the main telescope into the Starry Night program, syncing on M15, and telling the program to swing the scope to Garradd. Immediately the fuzz ball dominated my computer screen.
I took views in black-and-white and a group of color images. The color views are worthless because of movement between filters.

With the black-and-white, termed luminosity exposures, I shot a couple of dozen two-minute views while the telescope guided on the comet. Following the moving comet meant that the star field behind it was smeared — the comet glided far enough during each exposure that the background stars were elongated — but the comet remained undistorted.
I took photos for three hours, most for processing purposes — such as darks, bias images and flats — which are used to remove static and other flaws from astrophotos.
Eventually, I made a 12-second movie that shows the comet sliding in front of the background stars.
To watch it, click HERE. Then wait — a bit longer — wait some more, because the file takes a while to load.
The coma that surrounds the nucleus glows against the blackness of space, while the broad, stubby tail isn’t as bright. The tail will probably expand as the sun’s heat boils off more material. Watching the little movie carefully, I seem to glimpse streams of material shooting from the comet.
Cometography says its closest approach to Earth will be on March 5, 2012, at 1.27 AU (about 118 million miles). Already interesting, Comet Garradd (C/2009 P1) could be a knockout by then.

[Followed by its shadow, a beetle struts across the desolate ground of Lakeside. Photo by Joe Bauman]

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