The Lord of the Rings: Saturn and the Crab

by Randy Muller

Weather conditions could have been worse, but not much worse, as I traveled to Fiddletown, California on Saturday afternoon January 4th to meet a bunch of insanely photon-starved but proper TAC-SACos to view the transit of Saturn across the distant supernova remnant known as the Crab Nebula, also known as M1. The sky was thick with high, thin, broken clouds. I had no doubt I would be able to view bright planets, but wasn't sure about viewing any deep-sky objects. So I planned to observe mainly Saturn.

The short story: I was never able to see the nebula, as it was completely overwhelmed by glare from Saturn.

Jane Smith, Shneor Sherman, Gregg Blandin and Marsha Robinson were all there when I arrived. To our utter suprise and delight, Steve Gottlieb showed up at 6:30.

After several hours, it still wasn't very clear for deep sky viewing, so Gregg and Steve left. We knew that the sacrifice of Gregg's 8" would help clear the clouds, but there was a debate about whether Steve's sacrifice would be effective, since his scope was never set up. I thought it should count simply because he drove so far.

The hunt for the nebula was fun, rewarding and instructive. I observed Saturn (with a few breaks) from about 5:30pm to 12:30am (1:30 - 8:30 January 5 UT) under excellent seeing, which is the longest I have ever spent on any object in any observing session in my 6-year observing career. I observed only two other objects the entire night: Jupiter for a total of about 15 minutes, and M42, the Great Nebula in Orion, also for about 15 minutes. I concentrated on Saturn because of the transit and also because I had not taken a really good, long look at it yet this year.

Both the Crab Nebula and Saturn are among the more interesting objects in the sky.

The Crab Nebula

The Crab Nebula is the still expanding and glowing debris of a supernova that became visible on July 4, 1054. It was recorded by Chinese observers as a guest star. It was described as reddish-white and visible during the day like Venus for a total of 23 days.

It would have made an interesting sight when it was discovered in the morning before sunrise with the unaided eye: It was only 4 degrees west of what must have been a lovely waning 27-day old thin crescent moon. The event may have also been recorded by the Pueblo Native Americans in the south-west USA.

At the center of the nebula is a pulsar, a rotating neutron star with very strong magnetic field which is generating intense radio and x-ray pulses 30 times per second. Since the discovery of radio waves from this object in 1948 (and dubbed at that time as "Taurus A"), the Crab Nebula has been the fruitful subject of much study.

The nebula has a total integrated photographic magnitude of 8.4, but this is bit deceptive, because the brightness is spread more or less evenly over a 8x4 arcminute oval. From my backyard with a 10" dobsonian telescope in suburban Roseville, it is reasonably easy to see, and appears as a an utterly featureless and unimpressive gray thumbprint-like blob. From a dark site with my 18" dob, some variations in brightness and texture can be seen.

The Lord of the Rings

Saturn, a mini solar system unto itself, dazzled my eyes when I looked at its magnitude 0.4 brightness with my 18" dobsonian telescope. The rings are, of course, the most obvious feature of the planet, but the first thing I noticed were details on the surface of the planet itself. I generally observed the planet at 226x and 301x.

The Planet

The South Equatorial Belt, much wider but less contrasty than the corresponding belt on Jupiter, was showing a nice dark reddish-brown color and some mottling and perhaps some vague linear features. The color of the belt contrasted with the pale yellowish surface. As the planet got higher, the yellow color deepened slightly to a very pale pink.

I had to spend minutes and hours staring at the image throughout the night to get seconds and minutes of fine steady images. When that happened, usually suddenly, it was like someone drew a veil aside, and suddenly I was seeing it "in the clear".

Then, just as suddenly, it would go blurry again, and I would have to wait more minutes to get a few seconds of great views. The few great moments kept me glued to the eyepiece through the many minutes and hours of average or poor views.

In addition to the South Equatorial Belt, I noticed that that South Polar Region was also fairly prominent, though not as much as the belt. This grayish dark brown feature is a circular cap centered on the south pole. I could not see any details in it.

While studying the SPR, I noticed an interesting "squared off" illusion where the southern limb of the planet met the Cassini Division in the rings. It's possible there was also interplay between the shadow of the planet on the rings in the same area, but it was difficult to tell. It seemed like the planet had dark corners. The terminator was also clearly visible on the eastern (trailing) side of the planet. This gave the whole image a nice 3-d appearance.

The Rings

The Cassini Division separating the very bright B-ring from the outermost and darker A-ring was very prominent and wide, and I was able to trace it all the way around the ring. The innermost translucent and charcoal gray C-ring, also known as the Crepe Ring, was also easily visible. The planet was easily visible through the Crepe Ring, and in the vicinity of the northern side of the Crepe Ring, I was able to detect hints of systems of complicated ring shadows on the planet. These things were not immediately obvious, but after hours of observation, these features persisted.

On the southern side of the B-ring, a thin shadow of the planet was clearly present.

There appeared to be a smooth gradation of brightness from the inner part of the bright B-ring to the Crepe Ring. I had probably noticed this before, but it seemed very prominent Saturday night.

The A-ring did not have the solid appearance of the B-ring. Instead, it appeared to be constructed of several linear "furrows", concentric with the ring. I never saw the Encke Division directly, but it was undoubtedly contributing to this furrowed appearance.

The Moons

I observed a total of seven moons, and several of them moved significantly over the 7-hour period that I watched them. In order of brightness they were:

I missed Mimas, but on the chart generated by Sky Map Pro 9, it moved fully 1/4 of the way around its orbit during the time I was watching. Mimas was just too faint and too close to the intense glare of Saturn for this rather moisture-laden night.

The Transit

Finally, I tried to detect the Crab Nebula.

A quick view of the planet showed that if it was going to be visible at all, it was going to be extremely subtle. With a casual view, it was completely invisible.

At the beginning of the evening, Saturn was about a ring diameter or so away from the center. Just before I packed up, it was about 3 diameters away. After the quick view, I decided that the best chance of seeing anything at all would be to check for asymmetry in the glare of Saturn, and that this would be more prominent the further away from the Nebula Saturn was.

So I waited until the end of the session, and then I studied the glare of Saturn (with Saturn out of the field of view) on two sides: The side with Titan and the side away from Titan, since Titan was now in the same general direction as the center of the Crab Nebula.

At first I thought I detected greater nebulosity on the south-eastern side (i.e., Titan side) of Saturn than on the north-western side, but then I realized the extent of the change I was observing was significantly larger than the actual Crab Nebula itself, so I concluded I was fooling myself. It was also very difficult to see the difference and difficult to "measure".

At the end, I decided I wasn't seeing anything significant.

All in all, I had a lot of fun during the evening, even though I never saw the nebula. I learned alot and eagerly look forward to February 4, 2006, when Saturn finds itself inside M44, the Beehive!

DateJanuary 4, 2003 5:30pm-12:30am (Jan 5, 01:30-08:30 UT)
LocationNear Fiddletown, CA
Elevation2565 ft
InstrumentStarmaster 18" f/4.3 dob-newt
Eyepieces7.5, 10, 17, 26mm Sirius Plossls; 1.15x Tele Vue Paracorr
Seeing8 Very steady
TransparencyStarting 4/10, ending 6/10