Elementary Perceptions

(published April 2002 Journal)

My imagination has been captured by a single line from the book "The Universe Revealed" by Chris Impey and William K. Hartmann. Describing the elements produced in a supernova, the text reads, "Supernovae are the source of most of the rare elements and precious metals in the world -- the silver in the coins in our pockets and the gold in the jewelry on our bodies." I was fascinated by the concept that all elements heavier than iron can only be produced in a star with enough mass that it will eventually explode in a supernova, thus explaining the rarity of these heavy elements. Our sun does not contain enough mass to go through the funereal march of supernova nucleosynthesis, but the presence of elements heavier than iron in our solar system speak to the distant past. These precious elements tell us that everything in Sol’s domain (including ourselves) has been recycled from a cloud made partly of supernova stardust that was likely compressed in the increased density of a galactic spiral arm, approximately 5 billion years ago.

Supernova remnants (SNR) are the element-rich clouds of gas and dust that are left after a supernova explosion, and there are many examples of them that can be seen with small to moderately sized amateur telescopes. Some have been given names that refer to their discovery dates (e.g., SN1987A, the brightest and nearest supernova of the last three centuries, discovered by Canadian Ian Shelton). Many SNRs have made it onto lists of radio sources, so they have catalogue numbers beginning with 3C.

The only example of a SNR on the Messier list is M1 or the Crab Nebula. This remnant is the result of a supernova on July 4, 1054 (current era) that was well documented by Chinese observers of the Sung dynasty. With an estimated brightest magnitude of -4 it is surprising that there is only one European record of this event, that being by a Christian physician from Bagdad, Ibn Butlan. As a novice to the hobby I found M1 a difficult object to locate using my 4.5-inch reflector from a light polluted backyard, but find it I did. One of the biggest obstacles I had was a frustrating habit of always starting my search beside Beta Tau instead of Zeta Tau. As I gained experience I still carried this habit, along with a new 8-inch reflector, onto the hillsides around Kelowna for a much more rewarding view of M1. My sparse notes of the time describe it as a large but diffuse nebula, slightly flattened and extended northwest to southeast. Using my 12.5-inch reflector I re-observed with hopes of seeing some of the detail mentioned by Stephen James O’Meara in his book Deep-Sky Companions: The Messier Objects. The best I could do was to notice the two mis-aligned halves, which were described to me by Alan Whitman as forming a "fat S-shape."

The constellation Cygnus contains, in my opinion, the most dramatic example of a SNR. This is the Veil Nebula or Cygnus Loop. Here the lacy filaments of the scattered shell still glow from the tremendous energy released when a star blew up many thousands of years ago. (For Mackie’s description of the Veil see "Cygnus Delights" in the June 2000 issue of the Journal.)

Wanting to push the limits of my 12.5-inch Dobsonian, I went in search of fainter targets. My research indicated that there might be visual evidence of the remnants 3C58 (SN1181), 3C10 (SN 1572, and Cassiopeia A (SN1671). It was perhaps unrealistic to have these objects as targets for a 12.5-inch scope and I found no observational evidence of these objects, but I did enjoy the hunt. On August 7, 1181 the supernova 3C58 was reported by Fujiwara Kenezane, a courtier of the Japanese imperial court, as a guest star in the constellation Wang-liang, our constellation Cassiopeia. It was observed for 6 months and probably never rose in brightness above magnitude 0. Most are familiar with the story of Tycho’s star, 3C10, which was noticed by Tycho on an evening stroll home from a day in the alchemical laboratory on November 11, 1572. This supernova brightened to about -4 magnitude and was visible for close to a year. A slightly more recent event was Cassiopeia A (SN1671) which has been seen in visible light by the 200-inch reflector at Palomar, but not by a 12.5-inch Dobsonian -- big surprise. It probably rose to magnitude 5, but if any visual reports were made at the time, they have not survived.

I had better luck tracking down IC 443, a SNR in Gemini. The subject of numerous observing sessions, IC 443 stubbornly refused to yield a truly positive identification, until an exceptionally clear night in December of 2000. As with past observations, on this night I was drawn to a glow around a faint Y-shaped asterism east of Eta Geminorum. The glow within the Y is not likely part of the SNR, but using 63x and alternately a UHC and OIII filter I detected a gauzy fan extending from the leg of the Y to a catcher’s mitt of three stars (SAO 78203 and SAO 78194 are the brightest), 20' to the north. I concentrated on this area for some time without a satisfying identification. I increased the power to 88x using an OIII filter, which gave a darker background and made the area stand out better, but I was still not sure. I found that tube movement with my hands cupped around the eyepiece (no small feat) improved the view. On one of my sweeps I drifted off about 20' to the north-northwest of SAO 78194 and there was a distinct glowing patch! Careful observation revealed a flattened S-shaped arc lying east to west, approximately 12' to 15' in length and 4' in width. It broadened to 6' to 7' at the brighter west end. Switching to a UHC filter I could still detect a dim blush but it was very much muted. A photograph of IC 443 on page 944 of Burnham’s Celestial Handbook shows many of the details that I have mentioned. About one third of the way up the page on the left hand (east) side is the Y-shaped asterism. The brightest star above (north) and almost off the left side is SAO 78203, the easternmost of three stars in the catcher’s mitt. A flattened S-shape delineates the northernmost boundary of the nebulosity, which is most likely the area I observed.

If shown on your star maps, the huge rippled shell of Simeis 147 makes a tempting target; however this titan of Taurus is very faint and presents one of the most challenging objects for the amateur. I have made S147 a whimsical stop on many observing sessions with absolutely no luck at all. That is, until a beautiful night in November of 2000. I drove to my 3600-foot-high dark site with windows down and a cold (garage stored) mirror. Simeis 147 was my only target on this night, and I believe I was successful! During this observing session I spent more than two and a half hours studying the small area near SAO 77350 using a low power of 63x and an OIII filter. Two brief periods of superb seeing lasting less than 30 seconds in total are the basis for my positive identification of S147. On these two occasions the seeing improved to reveal dark striations, reminiscent of the intertwined tendrils of the Veil, in the portion near to SAO 77350. These striations were the most exciting part of the observation. Both times they appeared in averted vision and I could hold them there for a few seconds, before they melted in direct vision. The first time I saw them I was optimistic (read thrilled) but still not sure. When they repeated about 15 or 20 minutes later, I was ready, and I held them in averted vision till I was sure of the observation. On subsequent observations the seeing has never been as good as on that night, and the striations have not been seen by me again. There are however some areas that have repeatedly shown a subtle texture or stain, which agrees with other observing reports and photographic evidence of S147. Using a 20mm Meade Erfle eypiece to yield 80x and OIII filter, I can detect a dim stain extending from 5' south of SAO 77350 in an arc to finish in a point-shape near a faint double star at 05 37 20 +26 34.8. This stain breaks apart to the east of 77350 but there is a slight strengthening approaching SAO 77398. Traveling north to the area of SAO 77478 there is a definite texture to the sky between SAO 77478 and SAO 77466. Tube movement of 1 field or more highlights this area. The dim milky band starts northeast of 77478 and streams directly towards 77466. I would have overlooked a nebulous patch 30' southeast of SAO 77397, at 5 43 37 +28 15.1, were it not for an observing report by Jay McNiel. Here a sparse “clump” of 10th magnitude stars does seem to show an area of nebulosity extending further from the sparse cluster than the unfiltered view would lead you to expect. When attempting to observe S147 I wear a towel over my head as a light shield, I occasionally remove the filter to study the unfiltered star patterns and I refrain from making frequent checks of star charts to preserve my night vision. While I strongly believe that I have observed sections of S147 with my 12.5-inch scope, visual observations are a subjective experience and I accept contrary opinions as being legitimate and constructive.

When observing these diffuse, element-rich clouds I sometimes cast my thoughts into the distant future, to a time when these remnant clouds may again coalesce into a new solar system. Will they hold the genesis of yet another Klondike Gold Rush or galleons sailing an alien Spanish Main, as subsequent intelligent (?) life forms come to recognize the rarity of supernova elements?

I wonder.

I gaze upon the beauty of the stars and think of them as a garden of blossoms.

-- Moses Ibn Ezra (1070-1138)

Bibliography