------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 2001 2004 May 28 16.53UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK GMH at AST.STAR.RL.AC.UK WORLD WIDE WEB http://www.theastronomer.org ------------------------------------------------------------------- COMET C/2004 H6 (SWAN) As long ago as May 13, the Central Bureau was informed apparently independently by X.-m. Zhou, K. Cernis, and M. Mattiazzo of the existence of a possible unknown comet on the low-resolution ultraviolet SWAN images taken from the SOHO spacecraft. However initial attempts by Dan Green to reconcile all positions with one object and produce search ephemerides failed suggesting some positions may not relate to the comet. 2004 UT R.A. (2000.0) Decl. Mag. Observer Apr. 29 4 09 - 9.4 SWAN May 2 4 05 -10.3 " 5 3 59 -10.6 " 8 3 56 -11.4 " 14.388 3 45 56 -11 47.5 7.8 Mattiazzo 14.444 3 46.0 -11 44 7.9 Pearce 16.37777 3 42 51.52 -12 01 01.7 9.2 Mattiazzo 21.84565 3 33 47.86 -12 37 44.4 " 22.807 3 32 18 -12 41.2 7.5 Drescher 25.84159 3 26 56.59 -12 57 13.4 Mattiazzo The following tentative ephemeris by Dan Green has appeared on IAUC 8347: 2004 TT R. A. (2000) Decl. Delta r Elong. Phase Mag. May 25 3 28.40 -12 53.6 1.391 0.812 35.2 46.0 7.5 30 3 19.57 -13 11.5 1.346 0.845 38.9 48.8 7.6 June 4 3 10.28 -13 21.6 1.291 0.887 43.2 51.5 7.7 9 3 00.35 -13 25.7 1.227 0.936 48.2 54.0 7.7 14 2 49.45 -13 25.1 1.156 0.991 53.8 55.9 7.8 19 2 37.12 -13 21.5 1.079 1.050 60.0 57.0 7.8 24 2 22.73 -13 15.6 0.998 1.112 67.0 57.3 7.8 Martin Mobberley comments: Comet C/2004 H6 (SWAN) is currently observable in the southern hemisphere as a 6th magnitude object in the pre-dawn morning sky. Currently in Eridanus it will move westwards into Cetus from mid June. By mid- July it should still be a 6th or 7th mag object as it moves into Aquarius. Although Perihelion (0.776 AU) occurred on May 12th it is now moving closer to the Earth. Closest approach is predicted to be on July 26th when it will be 0.61 AU from the Earth and 1.54 AU from the Sun. From a UK standpoint the comet will crawl out of the dawn nautical twilight in the second week of July, attaining an altitude of 10 degrees in the southeast by July 12th. By July 18th it will be a healthy 20 degrees in altitude in morning nautical UK twilight. The CBAT/MPC ephemeris suggests it may still be mag 6.6 by this time. In theory we could have three comets of at least 7th mag in UK skies in July, i.e. 2003 K4, 2001 Q4 and 2004 H6. On July 28th, 2004 H6 passes 1 degree to the north of Uranus. By late July, 2004 H6 will be visible by midnight UT, low in the southeast from UK skies. The moon is not a problem in the UK pre-dawn sky from July 15th to the 30th. But by Full Moon (31st) it will interfere. On August 11th the comet crosses from Aquarius to Aquila by which time it will probably have faded to mag 8. The comet will stay in Aquila for the rest of the year, gradually drifting in the direction of Altair. Guy M Hurst