G A R Y   W.   K R O N K ' S   C O M E T O G R A P H Y


Past, Present, and Future Orbits by Kazuo Kinoshita

Michael Jäger photograph of Ikeya-Zhang on March 30
Copyright © 2002 by Michael Jäger (Austria)

This photograph was obtained by Michael Jäger on 2002 March 30.81. It is a composite of two 4-minute exposures obtained with a 200/300 Schmidt camera and Kodak Ektachrome 100 film. The field of view measures 6° by 3.5°.


This comet was discovered in the evening sky by three amateur astronomers on 2002 February 1. Kaoru Ikeya (Mori, Shuchi, Shizuoka, Japan) found the comet on February 1.41, while using a 25-cm reflector (39x). He described it as magnitude 9.0, with a weak condensed coma about 2 arcmin in diameter. About an hour and a half later, Daqing Zhang (near Kaifeng, Henan province, China) independently discovered the comet while using a 20-cm reflector). He described the comet as magnitude 8.5 and about 3 arcmin across. Paulo M. Raymundo (Salvador, Brazil) found the comet on February 1.91, while using his 25-cm reflector. He described it as about magnitude 7.5 with a coma 5 arcmin across.

Historical Highlights

  • The first published orbit came on February 2, when S. Nakano (Japan) and B. G. Marsden (Central Bureau for Astronomical Telegrams) independently calculated parabolic orbits about an hour apart. Nakano used 26 positions obtained on February 1 and 2, and determined the perihelion date as March 7.75 and the perihelion distance as 0.49 AU. Marsden followed with a very similar orbit, which used 24 positions from February 1 and 2, and found a perihelion date of March 8.91. After acquiring additional positions, Nakano calculated a revised orbit on February 3, which used 52 positions obtained on February 1 to 3. This orbit slightly rotated the Argument of Perihelion and Ascending Node, as well as moved the perihelion date to March 18.42. Nakano pointed out that this orbit was now very similar in every respect to the orbit calculated for comet C/1532 R1. The next day Marsden determined a very similar orbit using 63 positions spanning the period of February 1 to 4. The question as to whether this comet was identical to one seen in 1532 continued to be on the minds of several astronomers as February progressed. On the 15th, Marsden announced the following, "A parabolic orbit no longer adequately fits the observations, and a revolution period of 400-500 years is likely. There is a possibility that the comet is identical with C/1532 R1, as first suggested by S. Nakano...."
  • Despite this, additional observations continued to reduce the likely orbital period for C/2002 C1 and on February 21 Nakano announced that a possible link with C/1532 R1 had become unlikely and suggested, instead, that C/2002 C1 was more likely related to C/1661 C1. He even produced an orbit that roughly linked C/2002 C1 with C/1661 C1 using 264 precise positions from the 2002 comet and 7 very rough positions from the 1661 comet. Nakano obtained essentially the same numbers when additional positions from 2002 were added on February 25, although the fit was improved. The resulting orbital period for C/2002 C1 was then determined as 365.45 years. On the same date, Nakano computed an orbit using only the positions from 2002 and obtained a period of 367.44 years. Marsden released his revised orbit on February 26. Using 309 positions spanning the period of February 1 to 24, he determined the period as 367.17 years.

  • The comet steadily brightened after discovery, but its low altitude and partial involvement in evening twilight made it somewhat difficult to observe. The result was typically a wide range of brightness estimates each day. Taking the averages of these estimates, it would seem the comet became brighter than magnitude 7 around February 16 and brighter than magnitude 6.5 on February 22. The comet was between magnitude 6 and 6.5 on February 24, when moonlight began causing serious problems. Widespread observations resumed on February 27, at which time observers were reporting the magnitude as 5.0 to 5.4. The reported range had increased to 4.9 to 5.3 by the 28th, at which time several observers were reporting the comet was visible to the naked eye. The apparent jump in brightness caused Andrew Pearce (Australia) to remark that a "marked increase in brightness" had occurred during the last day or so.
  • By early March the comet was steadily becoming easier to see and the tail was being spotted with the help of binoculars even in light polluted areas. Most observers were reporting the brightness as around magnitude 4 on the 12th, with an average visible tail length of 1.5° to 2°. The longest reported tail lengths for observers with very dark western horizons were typically near 4°. Even more interesting, however, was the occurrence of tail disruption events. The first was detected on the 3rd and is illustrated in the image archives by the images of Michael Jäger (Austria) and Andrea Aletti and Simone Di Filippo (Italy). The second event occurred on the 11th and is illustrated in the image archives by the images of Paolo Candy (Italy), Gilbert Jones (USA), and Alfredo Garcia, Jr. (USA). During the second half of March, most observers were reporting the comet's brightness holding at between magnitude 3.3 and 3.5. Most visual estimates of the tail length were between 2.5° and 4°. Moonlight interfered with observations during the this same period, but after is had left the early evening sky during the last few days of March, observers were reporting a larger coma and the increasing prominence of the dust tail.
  • The comet's brightness was still holding at magnitude 3.3 to 3.5 as April began, while the coma diameter generally fell within the range of 5 to 10 arcmin, as seen in binoculars. The tail length was typically estimated as between 3 and 5 degrees. The comet faded as April progressed and was between magnitude 4.5 and 4.8 by month's end. The coma had increased to a diameter between 15 and 20 arcmin, while the tail had decreased in length to about 2 degrees.

  • Magnitude estimates on May 1 typically fell within the range of 4.6 and 4.8, while the coma diameter was between 15 and 22 arcmin. Estimates of the visual tail length were virtually non-existent, with the few available ranging from 0.5 to 5 degrees. By mid-month, magnitude estimates typically ranged from 5.5 to 6.0, while the coma diameter was still maintaining a large diameter of between 13 and 18 arcmin. Again, estimates of the visual tail length were scarce, with the few available indicating it extended less than 1 degree. As May came to an end, magnitude estimates ranged from 6.1 to 6.7. Coma diameter estimates spanning a larger range than before, with a fairly even distribution between 9 and 20 arcmin. No estimates of the visual tail length were reported.


    Archive: February

    Archive: March 1-10

    Archive: March 11-20

    Archive: March 21-31

    Archive: April 1-10

    Archive: April 11-20

    Archive: April 21-30

    Archive: May 1-31

    Best Images of Comet Ikeya-Zhang

    Michael Karrar animation of Ikeya-Zhang on March 11
    Copyright © 2002 by Michael Karrar (Graz, Austria)

    The image above is clickable and will take you to a 636KB animation obtained by Michael Karrar on 2002 March 11. The images were obtained with a 4" f/8 Takahashi Refractor and a Starlight Xpress MX916 CCD camera. Note that some of the streamers are not only moving away from the comet's head, but are also moving from the lower portion of the tail toward the top portion, giving the tail a sort of corkscrew rotation. (Thanks to Michael Jäger for sending this to me!)

    Shigemi Numazawa photograph of Ikeya-Zhang on April 18
    Copyright © 2002 by Shigemi Numazawa (Kamijinai, Shibata-city, Niigata, Japan)

    These four photographs were obtained within a 37-minute period on April 18 and reveal a tail disconnection event. The images were obtained with a 200/220,300 F/1.5 Schmidt Camera. Click here to see a larger version.