More observing comet C/2002 C1 Ikeya-Zhang

by Randy Muller

On Friday evening March 15th, I observed Comet Ikeya-Zhang with my 18" dob from my severely light-polluted backyard.

I observed it from about 6:50 local time (2:45 UTC 16 Mar 2002), when it became visible in binoculars, until about 7:40 (3:40 UTC 16 Mar 2002) when it set behind my neighbor's house.

I was pretty excited by the view I had of it on Thursday night through my 10x50 binoculars, and I really wanted to get some more aperture on it to look for any detail in the coma. So, I went all out and set up my 18" dob instead of my slightly more portable but much smaller 10" dob. I really wanted all the aperture I could get.

Prior to observing the comet, I was waiting for it to get dark, and I turned my scope on the moon and Saturn, which are always nice targets from any light-polluted site.

The Moon

The thin cresent moon low in the sky with dazzling Venus made a marvelous naked-eye sight. The "dark side" of the moon was easily visible, shining with reflected ghostly bluish earth light.

I scanned the lit part of the crescent, which represented the first time I have looked at the moon with my 18", and immediately noticed two prominent craters near the terminator. They were aligned north-south, and the southern one had a central peak, while the northern one was flat on the inside.

After checking Antonin Rukl's Atlas of the Moon and calculating the co-longitude (ie., where the terminator was at the time I was viewing it), I determined that these two craters were Berosus (north) and Hahn (south) on Rukl chart 16.

Nothing else caught my attention, but I have to admit I was more eager to view the comet!

Saturnalia on the Ides of March

Still waiting for the comet to appear, I turned the scope on Saturn.

Saturn presented a lovely view of its cloud tops, rings and its little "solar system within a solar system" swarm of moons. The fat South Equatorial Belt was easily visible had a definite pinkish or reddish hue which was somewhat richer and darker than the pinkish-reddish hue of the rest of the planet. The color in the clouds contrasted sharply with the very bright white color of the A-ring. There was also some texture visible in the belt--a slight nonuniformity of color and intensity.

This belt and planet color fades to shades of yellow in my 10".

The rings were a study in contrast. The A-ring was brilliant white. The Cassini Division was sharp and wide. The yellowish B-ring was dimmer than the A-ring and the Encke Division in the outer 3/4 of the B-ring was barely visible intermittently.

The shadow of the planet on the ring was very prominent, and gave the whole scene a nice 3-d look.

I neglected to identify any of the moons, except for Titan, which was obvious by its brightness and pale orange color.

Comet C/2002 C1 Ikeya-Zhang

Finally, I saw the comet with binoculars. The tail appeared to be about 1 degree long, as it was on Thursday night.

The comet was about 1.5 degrees west and .5 degrees north of Eta Piscium. Eta Psc is the naked-eye mag 3.6 star I use to star hop to one of my favorite backyard Messier challenges for my 10" dob, M74.

(M74 has never been a challenge in my 18" from my backyard, but this night it eluded me, being located not only in twilight skies, but also in some of the worst light pollution from my backyard location.)

Eta Psc was visible only very intermittently to my unaided eye, demonstrating how bad the light pollution and twilight was in this part of the sky. It was much darker in the zenith, but by no means "dark".

The view of the comet at 87x (26mm plossl) was wonderful. Surrounding the very bright central condensation (nucleus) was the coma. As a very rough guess, the coma was about half an arcminute in diameter. The color of the coma and nucleus was bluish-white.

The coma blended smoothly into the tail, and lost its brightness and color rapidly. The width of the tail was about the same as the diamter of the coma. My impression was that the tail had a yellowish or "warm" complexion, in contrast to the cold bluish light from the coma, but I am not sure there was enough light in it to stimulate the color receptors in my eye.

At 301x (7.5mm plossl), I could see that the nucleus was not a simple starlike point, but had an actual extent. It was circular, and in the center of the coma. Unexpectedly, the tail became a lot less visible at this power.

I looked for, and saw nothing like the spiral streams I saw in Hale-Bopp. Overall, the best view of the comet was at 87x.

Over the duration of the session, I was able to detect the movement of the comet to the north against the background stars. Initially, the comet was making an almost equilateral triangle with a mag 9.5 star and a mag 10.5 star. Later, it was obviously no longer almost equilateral, and the comet was approaching a mag 11.9 star.

This is one fabulous comet!

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