20060226 Comet Pojmanski (C/2006 A1) Obs Rep 41N Lat K. Fisher fisherka@csolutions.net In December 2004, observers were treated to the flyby of C/2004 Q2 (Comet Machholz), a tailess maximum mag. v4.1, comet with a high inclination (~34 degs). Mag v5.1 Comet C/2006 A1 (Comet Pomjanski) is (for northern hemisphere observers) a new apparition much like comet Machholz - only this time with the promise of a tail: Photos (with tail) by John Drummond, Possum Observatory, New Zealand - http://www.possumobservatory.co.nz/comet_2006a1_pojmanski.htm Southern hemisphere track charts (going north) through March 2,2006 from the Comet Section of the Royal Astronomical Society of New Zealand: - http://www.rasnz.org.nz/Comets/C2006A1.htm#Chart2 I believe that we are currently seeing Comet Pojmanski on its inbound turn. The JPL-MPC Ephemeris shows C/2006 A1 holding at its current brightness (estimated at v6.5) through March 7 at which point it will begin its dimming phase. Harvard-MPC Ephemeris and plotting input file - http://cfa-www.harvard.edu/iau/Ephemerides/Comets/2006A1.html JPL-MPC Ephemeris generator - for generating local topocentric ephemerides - http://ssd.jpl.nasa.gov/cgi-bin/eph Southern observers have been watching this comet - that is moving at 93 degs inclination to the ecliptic - for some time. They report its 5-6 arcminute diameter brightening from v7.5 on 1/30/2006 to v5.4 on Feb. 26. See reports at ICQ-MPC Recent Comet Magnitudes webpage http://cfa-www.harvard.edu/iau/icq/CometMags.html Comet Pojmanski is coming into view for north latitude observers but at an time that makes observing this bright comet a challenge for 40N observers. The comet rises between 12:15 UTC - 12:30 UTC (5:15am-5:30am local time) at 41N, low in the south east horizon at az 120, alt 0. Rough 41N courtesy charts generated from Cartes du Ciel through March 7, 2006. 90 deg Eq chart http://members.csolutions.net/fisherka/astronote/finder/Comet2001A6_9... 90 deg Alt az chart http://members.csolutions.net/fisherka/astronote/finder/Comet2001A6_9... 30 deg Alt az chart http://members.csolutions.net/fisherka/astronote/finder/Comet2001A6_3... Sky and Telescope Online Article with chart http://skyandtelescope.com/observing/objects/comets/article_1684_1.asp But astonomical twilight ends abruptly between 12:35 and 12:45 UTC (5:35-5:45 local time). To further complicate the picture, Venus is currently about 7-8 degrees away and has an extraordinary brillance of v-4.8. Venus is bright enough to cast shadows and creates a 5-8 deg light wash-out zone around its position. Comet Pojmanski is travelling past alf Cap tonight (2/27/2006) and towards Aquila. But Venus is also travelling towards alf Cap through March 7. The problem of astronomical twilight and the small observing window is illustrated by the following rising table for my op: *********************************************** Date__(UT)__HR:MN Azi_(a-appr)_Elev T-mag *********************************************** 2006-Feb-25 12:15 111.9655 -2.4042 6.52 2006-Feb-25 12:30 r 114.3784 0.2290 6.52 2006-Feb-25 12:45 A 116.8454 2.8126 6.52 2006-Feb-25 13:00 Am 119.3758 5.3406 6.52 2006-Feb-25 13:15 Nm 121.9783 7.8064 6.52 2006-Feb-25 13:30 Nm 124.6616 10.2033 6.52 2006-Feb-25 13:45 Cm 127.4341 12.5235 6.52 2006-Feb-25 14:00 Cm 130.3040 14.7591 6.52 *********************************************** My own experience is that by 12:45 UTC (5:45 am) the comet was whited out and not visible. Finally, this comet is low on the horizon and rises out of the atmospheric zone. A consequence of these motions for 41N observers - and the first key to seeing Comet Pojmanski - is that there is a very narrow observing window beginning at 5:15 that lasts about 15 minutes. The following is a table of rising tables for my op at 41N through March 7. If you arrive at 5:20 to begin observing - you'll miss the comet in end of astonomical twilight. The key is to arrive and set up by 5:00 am local time and begin tracking the rise of alf Cap before the comet rises. The following is a table of altitude times at 12:15 UTC (5:15am) for Comet C/2006 A1 through March 7 for my op: *********************************************************************** Date__(UT)__HR:MN R.A._(ICRF/J2000.0)_DEC Azi_(a-appr)_Elev T-mag *********************************************************************** 2006-Feb-26 12:15 20 18 00.35 -15 36 17.1 110.4982 -0.3053 6.52 2006-Feb-27 12:15 20 19 50.41 -13 02 27.6 108.9579 1.8074 6.53 2006-Feb-28 12:15 20 21 53.47 -10 25 22.7 107.3458 3.9236 6.54 2006-Mar-01 12:15 20 24 09.21 -07 45 44.3 105.6642 6.0323 6.56 2006-Mar-02 12:15 20 26 37.28 -05 04 18.3 103.9162 8.1218 6.59 2006-Mar-03 12:15 20 29 17.26 -02 21 53.2 102.1059 10.1803 6.63 2006-Mar-04 12:15 20 32 08.67 +00 20 41.0 100.2386 12.1957 6.68 2006-Mar-05 12:15 20 35 11.01 +03 02 34.5 98.3204 14.1566 6.74 2006-Mar-06 12:15 20 38 23.74 +05 42 58.7 96.3583 16.0524 6.80 2006-Mar-07 12:15 20 41 46.30 +08 21 08.0 94.3600 17.8736 6.87 2006-Mar-08 12:15 20 45 18.12 +10 56 20.4 92.3338 19.6121 6.95 2006-Mar-09 12:15 20 48 58.62 +13 27 58.5 90.2884 21.2613 7.03 2006-Mar-10 12:15 20 52 47.22 +15 55 30.2 88.2329 22.8165 7.11 2006-Mar-11 12:15 Am 20 56 43.34 +18 18 29.2 86.1761 24.2746 7.21 *********************************************************************** From the proceeding table, note that the comet becomes progressively twilight limited as we proceed into March - although you can see it by arriving earlier. The second key to seeing Comet Pojmanski is a good ephemeris table showing rising times at your observing point. Make a geographic specific epheremis for your observing point before you leave. Show up early enough to be tracking on the horizon as the comet rises. The Moon is favorably positioned below the horizon at 12:15 UTC through March 10 at which point Moonlight washout will begin to be a problem. On Feb. 26, 2006 at 12:30-12:45 (UTC), a fellow observer and I watched this comet rise on the south eastern horizon near bet Cap from our op at Little Mtn, Utah (approx. 41 N, 111.8 W). First, we tracked alf Cap's rise off the horizon, and then a few minutes later, bet Cap. From our mountain horizon blocked op, Comet Pojmanski finally rose at approx~ 12:25 UTC (5:25am) and was high enough to be observable by 12:30 UTC (5:30am local time). C/2006 A1 is very similar in appearance to last year's Comet Machholz and is strikingly beautiful. Because of light-wash out from Venus, it was difficult to estimate the diameter or magnitude of the comet. Even so, the comet was distinct and bright - a promise for things to come on future mornings. The nucleus has a DC5 concentration and its bright nucleus 3' arcsize was easily compared to the 3' arcsize of nearby double bet Cap. ( DC=5 Still more condensed; the central condensation strongly influences m1, hampering the use of the In-out method. ) The size of the outer coma and magnitude was foregone due to the sky wash-out from nearby Venus. However, the outer coma appeared to give a total comet size have a total comet size of about 5-6' - similar to reports by southern hemisphere observers. Sky wash-out from Venus also prevented seeing the comet's tail other than as a suspected averted vision detection close to the nucleus. I expect the tail will become more visible as Comet Pojmanski pulls away from Venus and gains more altitude. Although currently there is only a narrow observing window of 15-20mins, subjective time, it seemed like we watched for 30 minutes. This was more than enough to enjoy the show. The observing window should improve through March 7, by which time there may be close to an hour to watch the comet before astronomical twilight ends. Weather is a factor in northern latitudes at this time of year. But if you have a weather window, I strongly recommend making an early morning sojourn to take a long at this new bright comet. Do not be deterred by its low altitude near the extinction zone. It is worth the trip. K. Fisher fisherka@csolutions.net