The Sea Monster and the Skull

For decades I enjoyed fishing, but that was before I empathized with the fish. Now I trawl the deep skies, searching out objects stranger than any fish in the ocean. For example: the Skull in the coils of the Sea Monster.

This past weekend, a group of astrophotographers set up on the driveway of our kindly hosts, Jerry and Cindy Foote, near Kanab in extreme southern Utah. Cindy and Jerry are extraordinary astronomers. She has helped discover something like half a dozen exoplanets. Besides scientific observations of cataclysmic variable stars with a 24-inch telescope, Jerry builds research grade telescopes, drives and housings at his business ScopeCraft.
Saturday evening began cool and breezy, and I had trouble aligning on north. I had decided to use a right-angle finder scope that I had discarded years ago, but it was worthless and I had to switch back to a straight-through model. I used blazing Jupiter to get the finder and main scopes aiming together.
By the time my scope equipment was running and aligned and the cameras were connected, the breeze had dozed off and the stars were steady. Thin clouds were dissipating, the slim young moon had set and an imposing dark cliff loomed in front of the lower western part of the Milky Way. I sat at my folding table, surrounded by great friends: Don Colton was imaging to my right, Tyler Allred back to my left, and Jerry came over to chat. We were plugged into the Footes’ power system so I had no need for my noisy generator, and their Internet connection let me check for autumn celestial objects on the Internet, while taking astrophotos. It was, in a word, heavenly.
I was casting about for interesting planetary nebulas to photograph, searching the Web, when I came upon one called NGC 246 in the southern constellation Cetus the Sea Monster. (Cetus is sometimes misrepresented as a whale, but Greek myths make it clear the creature that tried to kill Andromeda was a scarier beast.) The nebula is caught in the monster’s tail coils.
The nickname for NGC 246 is the Skull Nebula, and it does look like a vast skull glowing in outer space.

[View of the Skull Nebula that I took on 10-10-10]

I took images of it the early morning, a series of exposures that I later staked — seven luminosity views at five minutes each; six with the red filter, six through the green and six through the blue, duration of each of the color views four minutes, for a grand total of one hour, 47 minutes.
The Skull Nebula was featured as NASA’s Astronomy Picture of the Day on April 18, 2006. The view was by the Gemini South Observatory, and commentary was by Travis Rector, associate professor of physics and astronomy at the University of Alaska, Anchorage.
The nebula is appropriately nicknamed because it “really does surround a dying star some 1,600 light-years away in the constellation Cetus,” Rector wrote. “Expelled over a period of thousands of years, the lovely, intricate nebula is the outer atmosphere of a once sun-like star.”

An oblong “star” at the center of the nebula is actually a pair of binary stars so close together that they appear as a single misshapen orb. One of these is the former sun-like star. It’s traveling toward the upper left of my photo as the gas continues to expand. The brighter region along the top is where the star’s atmosphere is creating a shock wave as it blasts through the gas and dust of the interstellar medium.
NGC 246 is a dim object, rated about 11th magnitude. It barely showed on my computer screen as I began to image.
Eventually the nebula will thin out to nothing and the progenitor star will become a tiny white dwarf. In the far distant future, the white dwarf itself will cool and fade away.

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