Catch a Star! …and discover all its secrets! Comet Ikeya-Zhang (C/2002 C1) Valery Shaimuhametov Vladimir Golendukhin Anton Lavrov Arsen Babayan

 

Astrospace school of Astrocosmic association Sirius-86, Rezh, Sverdlovsk region, Lenina 76/5 str., Russia,

623750, sirius86@rezh.ru

Comet Ikeya-Zhang well seen from Russia (article to newsletter “GNOMON” AAE-UK)

Vladimir Golendukhin –astrocosmic association Sirius-86

The comet Ikeya-Zhang, which received the designation Ñ / 2002 Ñ1, immediately attracted special attention by astronomers. It was soon found that it has a large period, and the elements of its orbit were reminiscent of Comet C / 1532 R1, which had attracted similar attention. However, as the astrometric data was obtained, it appeared closer to another comet - C/ 1661 Ñ1. The latest information gave an estimated orbital period of 367.17 years, which rules out the possibility that it marked the return of any of the historical comets mentioned. Amateur observers in our area of Russia were immediately excited by the news that the comet would soon be visible with the unaided eyes, having already reached magnitude 4.5 - 4. The comet rapidly "inflamed", and we were soon reassured that forecasts of comet magnitudes are not always mistaken when its magnitude reached 3,5. At the beginning of March it had got a small tail, and though not far from the Sun, about 30-40 °, the plane of a tail was almost perpendicular to the line of sight, so it could be seen at its maximum angular extent. The first magnitude estimate of the comet was approximately 8.1. In two weeks it had grown in size, and by February 20 - 24 had passed the naked eye visibility threshold (mag. 6.5 - 6). At the beginning of March it was already perfectly visible by a unaided eye, and the gas tail was also well seen. It had an angular width at the head of about 3arcmin with the coma, but poorly extended from the head. In binoculars it could be observed across 3 - 5°. By the end of March the comet has reached the maximum magnitude. Visibility improved as it gradually passed from the evening sky to morning. In especially dark places and with good sky transparency, the length of tail exceeded 10°. In the same time the tail appeared dusty and bent. Even though very weak, the tail could be distinguished, in large binoculars and wide angle telescopes. In large instruments it was possible to make out detail of the nucleus. The coma had the normal greenish colour, marked by many observers. The gas tail had a light-blue shade, easy to make out on colour film as well as the colour of the head. Even in small instruments observers could make out the jets, frequently wavy, almost of a sinusoidal form in the tail, due to the rotation of the nucleus, and they could study the most active areas of jets. Comet Ikeya-Zhang passed through the constellation of Cetus, into Pisces. On March 25, it passed by M33, only 3° away in Triangulum. At the end of March it was already in Andromeda, and during April 4 and 5 passed near to the Great Galaxy in Andromeda (Ì31), presenting lucky observers with a fine sight. It continued in a western direction, through Cassiopeia, Cepheus and Draco, when the visible length of the tail of the comet gradually decreased as its longitudinal axis (the radius - vector of a comet) gradually came nearer to the line of sight, and the magnitude decreased insignificantly. At the beginning of May, the comet was passing through the head of Draco. At dawn, it appeared almost at the zenith and was easily visible to the unaided eye at a magnitude about 5. In binoculars, a small (about 10 - 20arcmin) thin direct gas tail could be seen, and in telescopes it was possible to make out a second, more diffusive and dusty. The angle between the tails at this time was between 60° and 70°, giving photographs taken at that time a distinctly unusual look. During May 16 and 17 the comet passed as close as 2.5° to the globular cluster Ì13 in Hercules. Observers at this time noted that, outwardly, the comet and M13 appeared very similar. It moved on through the constellations of Corona Borealis and Serpens. Finally, the comet dimmed to end the period of unaided visibility. From the end of May it was quickly dropping in magnitude, and by middle of June was difficult to spot in binoculars. Now comet Ikeya-Zhang is moving far from the Sun and the Earth, and will soon disappear once more in the depths of the Solar System.

 

 

 

 

Gary W. Kronk’s Cometography Discovery

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.

 

·     Photo 1,2: Comet Ikeya -Zhang – March 24

·     Photo 3: Comet Ikeya -Zhang and the Great Galaxy M31 in Andromeda – April 4

·     Photo 4: Comet Ikeya -Zhang – April 19

·     Photographs was obtained by Vladimir Golendukhin and Andrei Rybin on 2002