|This page is a web version of the article "Can Comet Hunters survive?" written by Shigeki Murakami and published in the April 2003 issue of the Oriental Astronomical Association Journal, the Heavens.|
Can comet hunters survive?
|altitude skies. This will still make it possible to sweep the skies which
do not overlap with LINEAR's coverage. (This will be discussed in the next
-To use magnifications twice the aperture in centimeters, as the minimum effective power would show objects of one or two magnitudes brighter than the limiting magnitude of the aperture.
-To observe from sites with low light-pollution and at a high elevation, even if it means a longer driving time. It is reported that every 3000 feet (914m) the visibility of the object will increase by 0.5 to 1 magnitude4). This agrees with my own experience.
I would like to stress that more efforts are required for future discoveries. This is inevitable to avoid wasteful efforts facing a threat from the high-tech observing instrument SWAN. I passed this conclusion on to Mr. Utsunomiya. In the subsequent mails from him I have sensed his strong desire for a large aperture telescope to find fainter comets.
For many days both us had searched for strategies against SWAN; apertures, eyepieces, mountings, telescope makers, maintenance of instruments, methods of searching, an so on, and exchanged practical views based on our own experiences.
A telescope manufacturer sells inexpensive large aperture telescopes, but the thin mirrors worry us. It is an idea to build an German equatorial which is based on a Yamasaki-type mounting*, but the weight of the tube may cause some vibration. Can we use an equatorial without a tube rotation device? What is the quality of super wide-angle and long focal eyepieces on the market? Large mirrors tend to attract mold. These were the questions and concerns we discussed.
Mr. Utsunomiya actually tested a 35-cm equatorial reflector owned by his friend Mr. Tetsuo Kudo (the discover of C/2002 X5) for its practicality.
*Yamasaki-type mounting: An improvement on a reflector by attaching a counter weight at the front end of the telescope so that the position of the eyepiece does not change vertically. It rotates only horizontally.
3. A simple question
Afraid of SWAN? ...I feel exhausted...What's come over me? My mind had been occupied with measures against SWAN. Suddenly a very simple question crossed my uneasy mind.
Availability of SWAN images to the public is not a recent occurrence. It became well-known after the observations of C/1973 E1 (Kohoutek) by rockets5),6)that comets emit Lyman-alpha lines. C/1997 K2 and C/2000 S5 had been discovered from SWAN images before Mr. Suzuki's discovery7). Why haven't they paid much attention to the capability of SWAN to discover comets? Amateurs around the world have been finding many comets from images produced by LASCO (coronagraph), which is one of many instruments carried by SOHO. Has NASA, which manages SOHO, overlooked visually detectable bright comets up to now? Or is the discovery of comets not regarded highly among professional astronomers? Has SWAN really captured all of the comets bright enough for visual discovery? It just doesn't make sense....Maybe I should examine SWAN images myself instead of relying on what other people have written.
4. No need to be afraid of SWAN!
SWAN images are displayed by ecliptic coordinate. SOHO is stationary at the Laglangian point 1.5 million kilometers from the earth toward the sun. The directions to the earth and the sun are excluded from observation of Lyman alpha emissions, which correspond to areas of approximately 30°x30°and 30°x130°. The skies other than these areas are observed three times a week. Observation from the ground is affected by weather, latitudes, and the phase of the moon, but SOHO is an awesome new weapon to capture comets almost at any part of the sky regardless of these factors. Had this new instrument really captured new comets before they were discovered visually? I tried to find if SWAN images had caught all of the new comets which had been visually discovered since 2001. The following is the summary of the results of research by Mr. Masayuki Suzuki, Mr. Hirohisa Sato, and me, based on the Comet-Obs mailing-list discussions. Incidentally I have received advice from Mr. Masayuki Suzuki since I met him at the 2002 Oriental Astronomical Association Himeji Conference (October 26 to 27).
- C/2001 Q2 Petriew (discovered on August 18, 2001 UT)
It is barely visible in the image of August 5. In the images of August 8 and 9 it is faintly visible, but it seems difficult to determine if it is a comet. It is also seen in the images of August 14 and 16, located in the area interfered with a lot of noise (or Lyman-alpha emissions). It is difficult to identify it as a comet.
|In the image of February 19 it is barely visible. From February 21 on it
has become faint but discernible.
Around February 28 it is still faint but relatively easy to identify. It is located slightly above the bright C/2000 WM1 LINEAR. In the images of March 9 it has become very difficult temporarily but in March 12 and 14 images it is discernible though faint. Around February 28 it is most noticeable but difficult to determine its true nature.
- C/2002 F1 Utsunomiya (discovered on March 18 UT)
At the time of the discovery it was in the area in the vicinity of the sun which lacks data. Even if bright light was emitted near the boundary of this area it would be difficult to determine if it is a comet or solar flare. On April 7 it is clearly seen.
- C/2002 O4 Honig (discovered on July 22, 2002 UT)
In the images of July 16 and 18 a stain-like spot is seen shifting its positions, but it is difficult to differentiate it from noise. In the image of July 20 it is not detectable. In the July 25 image it brightens suddenly. It will be difficult, however, to identify the comet if you use only the July 16 and 18 images.
- C/2002 X5 Kudo-Fujikawa (discovered on December 13, 2002 UT)
SWAN images are available only to November 13 as of December 15 and to November 23 as of December 22; therefore, there is no way to use images to find the comet before their visual discovery. According to Mr. Suzuki, the comet was not visible in the images of around November 13, but a faint moving object was seen in the November 21 and 23 images. The comet's magnitude is estimated to be visually about 10. In the images of November 21 and 23 it is extremely faint and impossible to discover only from these two images.
With these results I have come to the conclusion that, out of 6 comets visually discovered since 2001, only 153P Ikeya-Zhang is possible to discover using SWAN images before its visual discovery. Even excluding C/2002 F1, which was outside the observable area, and C/2002 X5, whose images immediately before the discovery are still not available, only one (153P) out of the four comets was possibly to be found from the SWAN images prior to the visual discovery.
Then, what do the articles by Mr. Kojima (Gekkan Tenmon2) ) and Mr. Yoshida (Gekkan Hoshi Navi3)) mean? They were not groundless claims, of course. Many comets were certainly visible in the SWAN images before their visual discoveries, but it is not the same as to say they were discoverable as comets.
I think this simply indicates the difference in views between observers and searchers. Trying to identify a comet with its position well known is totally different from finding a comet whose existence is completely unknown. It is the same with visual or photographic discoveries, or use of SWAN images.
SWAN images contain a lot of noise or Lyman-alpha emissions. As these disappear and appear with time, it is difficult to determine if the seen object is a comet, except the bright comets like 153P and C/2002 O6. Also, the magnitudes determined by Lyman-alpha emissions and visual magnitudes are naturally different. Visually discoverable comets are not necessarily discoverable from SWAN images.
"No need to be afraid of SWAN!". I sent email so titled to Mr. Utsunomiya on October 20.
5. A reply from Mr. Utsunomiya
I am quite relieved. I am afraid that many comet searchers may have given up after reading Mr. Kojima's article in Gekkan Tenmon's October issue and Mr Seiichi Yoshida's article in Hoshi Navi November issue.
I am thinking of telling Mr. Takemoto and others from Tenmon Guide magazine, when they visit me tomorrow, that I have a burning passion for finding new comets now.
After discoveries of comets by LINEAR and SOHO as well as Mr. Suzuki' discovery from SWAN images, some people may tell me: "Are you still searching for comets with a telescope? You are like a living fossil!" I admit it has become more difficult, but do not believe there is no room for visual discovery. Whether this belief is right or not will become clear only in 3 to 5 years from now. The LASCO in SOHO and SWAN do not operate forever and their successors will replace them with much higher sensitivity and produce better quality images. This will make visual discovery much more difficult. If it is true, the amateurs' dream of finding new comets, a tradition since Messier's discovery of comets, will last only a few more years. This is the last chance we have. I want to trust my observing instruments and my own eyes.
I am grateful to Mr. Syogo Utsunomiya for permitting me to quote personal email correspondence, and Messers. Masayuki Suzuki and Hirohisa Sato for allowing me to use contents of discussions in Comet observers mailing list Comet-Obs.
1) http://sohowww.nascom.nasa.gov/ SOHO Home Page.
2) Takuo Kojima. 2002. Gekkan Tenmon, (Sky Traveler) October. pp.38-40. ChijinShokan.
3) Seiichi Yoshida. 2002. Gekkan Hoshi Navi, November. pp.38-39. AstroArts.
4) O'Meara, S.J. 2000. The Messier Objects. pp.29-32. Cambridge University Press.
5) Opal, C.B., Carruthers, G.R., Prinz, D.K., and Meier, R.R. 1974. Comet Kohoutek: Ultraviolet images and spectrograms, Science 185 pp.702-705
6) Feldman, P.D., Takacs, P.Z., Fastie, W.G., and Donn, B. 1974. Rocket ultraviolet spectrophotometry of Comet Kohoutek (1973f). Science 185. pp.705-707.
7) Oriental Astronomical Association 2002: Raiman-arufa kisen chohsade hakkensareta suisei (Comets discovered by investigation of Lyman-alpha emission lines). Tenkai (The Heavens) 83 (926) p.442.
The original article was written by Shigeki Murakami in the Japanese language.
This web version in English was translated by Eiji Kato.
Shigeki Murakami's web-page:
Translator: Eiji Kato
An amateur astronomer living in Australia. He runs the following web sites: