Comet Machholz observing report Begin: 20041217 7:29 UTC | 20041216 11:23PM Local Time (MST) End: 20041217 8:45 UTC | 20041217 0:45AM Local Time (MST) By: Kurt Fisher, SLAS member (canopus56@yahoo.com) Location: North Fork Winter Trailhead Parking Lot (Off Mirror Lake Highway, approx. 12 miles east of Kamas, Utah) 40 deg 35.75'N, 111 deg 5.78'W Elevation: 7500 ft. Temp: 4 deg C Target: Comet C/2004 Q2 (Machholz) was at approx. local alt 25 deg (hand measured), azm transiting on meridian. Limiting magnitude: ZLM: 6.2 per IMO Limiting Magnitude Area 2 (Perseus) (15 stars) NELM at Machholz: 6.0 per IMO Limiting Magnitude Area 22 (Lep) (14-15 stars) Seeing: Antoniadi II; Pickering 7-8 Observed with: Scope - SLAS Loaner scope #2 - 6" Newt 1120mm fl. Dob Lenses - 40mm - 28x 1.25 TFOV 30mm - 37x 15mm - 75x 9mm - 124x 9mm Graduated reticule Other - 8 x 35 Binoculars Rough sketch: 20041217 8:30 UTC 28x 1.25 deg TFOV http://members.csolutions.net/fisherka/astronote/observed/C2004Q2/20041217_M... Comments: After initially locating this comet in the early morning hours of December 16, local time, low in the extinction zone, I decided to try again from a truly dark skies site in the Unita Mountains. Arrival at the observing point was timed for the comet's transit and the setting of the Moon. The comet's magnitude is probably between 5.0-5.5, as reported by ICQ observers, but no attempt was made to estimate magnitude during this session, due to the cold weather using the in/out method. Currently the comet is passing through Eri. Because of the lack of bright stars in Eri, location of this fast-moving comet was more difficult than expected. Initially I confused it with 53 Eri. Until the comet reaches omi1-omi2 Eri around December 23, just look for the brightest object south of omi1-omi2 Eri, but above the declination of gam Eri. Unlike other comments seen in recent years, Comet Machholz is distinguished by its lack of an easily discernible tail. The 1-2 deg extended wispy ion tail seen in astrophotographs posted on the web was not seen, probably due to the small aperature size used, e.g. - http://antwrp.gsfc.nasa.gov/apod/ap041213.html (aperature not stated) http://galaxyphoto.com/temp/jw_comet12_14_.jpg (with a 12" Schmidt) Nonetheless, at low magnification (28x), it is a subtle and beautiful object to follow. With six inches of aperture a faint bow shockwave could be seen. The shockwave had a slight brightness above the background sky brightness. (It appeared similar to a faint nebula, like the California nebulae with a hydrogen filter.) The bright central coma is embedded in the shockwave. See drawing. The ability to see a bowwave was probably a result of very dark skies at the observing site. Low magnification (40mm-28x or 30mm-37x) was the most effective. Computed size from a visual estimate in the 40mm lens at 28x ( without a reticule ) for the 1/2 brightness limit - the coma diameter - (the outer circle in the figure) was 10.5 arcminutes. This is consistent with the most recent International Comet Quarterly Reports. << http://cfa-www.harvard.edu/icq/CometMags.html >> Every five to ten seconds, a bright extended glint and/or a point glint could be seen within the center of the bright coma. The averted image impression was one of a tiny hourglass shape; however, this was visual impression only and no definite detection occurred. Using a 9mm graduated reticule lens, a brighter area within the central coma was measured and estimated at 1.3 arcminutes. When driving back to Salt Lake City, I briefly stopped on, East Canyon Highway below Little Mountain and above East Canyon Reservoir, to check the visibility of the comet in urban skies. The comet was detectable from East Canyon, although it was more difficult to locate because of the relative lack of guide stars. Similarly, I could locate the comet using 10x 50 binoculars in the Avenues, but only because I had previously located the comet at a dark skies site. In an urban sky, it appears only as a faint fuzzy brightness above the urban background sky brightness. Again, as the comet approaches omi1 Eri around December 23, locating the comet under an urban or suburban-rural sky should be less difficult. Although the Moon increasingly will wash out the sky through Jan. 3rd, 2005, wide-field astrophotographers should have a good day around Jan. 8, when the comet passes with a few degrees of the Pleiades. The comet is predicted to reach its maximum brightness beginning around Jan. 3rd and continuing through Jan. 10. There will be an early evening observing window around Jan. 8 before the Moon rises. All in all, this is a great comet and is worth driving to a dark skies site to see, at least once through Jan. 10. Rough finder charts were plotted using the Minor Planet Center ephemerides service. << http://cfa-www.harvard.edu/iau/Ephemerides/Comets/index.html

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These charts are available at:

Overview 70 deg finder to 1/10/2005 with Moon phase and transit notes http://members.csolutions.net/fisherka/astronote/finder/CometC2004Q47... 25 deg finder with Lep orientation - good through 12/23/2004 Stars to mag 10 http://members.csolutions.net/fisherka/astronote/finder/CometC2004Q4L... 25 deg finder with Eri orientation - good through 12/27/2004 Stars to mag 10 http://members.csolutions.net/fisherka/astronote/finder/CometC2004Q4E... Ephemerides can be found at: http://cfa-www.harvard.edu/iau/Ephemerides/Comets/index.html http://ssd.jpl.nasa.gov/cgi-bin/eph - Canopus56 P.S. - I'm not quite sure what causes a wispy "ion" trail as opposed to the "streak" tails I have seen on previous comets. Any guesses? __________________________________ Do you Yahoo!? Send holiday email and support a worthy cause. Do good. http://celebrity.mail.yahoo.com