20041217 Comet Machholz obs. report The following is my observer report from the Unita Mtns, east of Salt Lake City. A rough sketch of what I saw is at: 20041217 8:30 UTC 28x 1.25 deg TFOV http://members.csolutions.net/fisherka/astronote/observed/C2004Q2/200... Begin: 20041217 7:29 UTC | 20041216 11:23PM Local Time (MST) End: 20041217 8:45 UTC | 20041217 0:45AM Local Time (MST) Supplement: 20041219 8:30 UTC | 20041219 0:30AM Local Time (MST) By: fisherka@csolutions.net 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 Bortle: 2 Observed with: Scope - 6" Newt 1120mm fl. Dob Lenses - 40mm - 28x 1.25 TFOV 30mm - 37x 15mm - 75x 9mm - 124x 12mm graduated reticule - 93x Other - 8 x 35 Binoculars 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 using the in/out method due to the cold weather. 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. An initial measurement using the 12mm graduated reticule lens was botched but was repeated on 20041219 8:30 UTC. (I'm still working through the math on the angular size of the smaller and brighter central coma seen at 93x.) For you high-end scope users at there, 6" of aperature was too dim at 90x. You really need more aperature to see anything at that power. 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 city, but only because I had previously located the comet at a dark skies site. It was visible only in the early morning hours when the city lights were low. In an urban sky, it appears only as a faint fuzzy brightness above the urban background sky brightness. When city lights are brighter in the early evening hours (7:00-8:00 local time) of 12/18, for example, I could not see it. As the comet approaches omi1 Eri around December 23, locating the comet under an urban or suburban-rural sky should be less difficult due to the presence of guide stars. 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. 12. 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. 12. I'm not quite sure what causes a wispy "ion" trail as opposed to the "streak" tails I have seen on previous comets. - K. Fisher fisherka@csolutions.net Supplemental observing report on 20041219 8:30am: I wasn't satisfied with my diameter measurement taken on 20041217, so I went back to the same site and retook a measurement at 20041219 8:30AM and after manually rechecking the apparent fields of my lenses. At 20041219 8:30am, the comet had an estimated diameter of 16.8 arcminutes at 27.5 magnification. Repeated measurements were not taken, so I'd assign an arbitrary confidence interval of +- 2.2 arcminutes (13%). This size was estimated visually as 1/7 the TFOV of a 40mm lens with a 54 deg AFOV used in an scope with an 1100mm fl, or 27.5x. This 16.8 arcminute measurement comported with an asterism in a nearby stellar field. Machholz was within 1 1/2 degs of "Y" shaped asterism involving HD27113 (v8.4) and HD27217 (v8.4). The 16.8 arcminute measurement appeared portional to the 22.3 arcminute distance between HD27113 (v8.4) and HD27217 (v8.4) reported by planetarium software. A 12mm graduated reticule was used to remeasure the size of the bright core of the comet at 91.6 power. A bright core seen at this magnification was measured at approx. 1.75 arcminutes. Repeated measurements were not taken, so I'd assign an arbitrary confidence interval of 0.6 arcminutes or (30%). This corresponds to one-tick mark on the linear scale of the reticule.