Electronic Telegram No. 5630 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET P/2025 U1 (HOGAN) Joshua K. Hogan, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet on CCD images obtained on Oct. 30 with the Mt. Lemmon 1.5-m reflector (discovery observations tabulated below). He notes that four 30-s exposures show a "faint fuzziness" toward p.a. about 315 degrees; he then examined another three stacked 60-s exposures to find what appears to be a small "triangular" tail about 7".5 long in p.a. 310-320 deg. 2025 UT R.A. (2000) Decl. Mag. Observer Oct. 30.47835 8 35 37.63 - 3 43 07.8 20.6 Hogan 30.48258 8 35 37.73 - 3 43 09.9 21.3 " 30.48678 8 35 37.85 - 3 43 12.0 20.6 " 30.49102 8 35 37.96 - 3 43 14.0 20.6 " 30.50074 8 35 38.20 - 3 43 18.2 20.8 " 30.50790 8 35 38.42 - 3 43 22.0 21.0 " 30.51520 8 35 38.62 - 3 43 26.1 21.1 " After the comet was posted on the Minor Planet Center's PCCP webpage, H. Sato (Bunkyo-ku, Tokyo, Japan) reported that sixteen stacked 60-s CCD exposures taken on Nov. 2.7 UT with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show a strongly condensed coma 8" in diameter with no tail; the magnitude was 20.4 as measured within a circular aperture of radius 4".3. The available astrometry appears on MPEC 2025-V41. The following very preliminary orbital elements by S. Nakano (Central Bureau) are from 24 observations spanning 2025 Oct. 30-Nov. 4 (mean residual 0".3). Nakano notes that a parabola also still closely fits the observations (T = 2025 May 19.46179 TT, Peri. = 216.49836 deg, Node = 240.56326 deg, i = 24.84056 deg, equinox J2000.0), q = 4.3659934 AU). T = 2026 Jan. 24.85422 TT Peri. = 255.65928 e = 0.3339389 Node = 235.58987 2000.0 q = 4.2298553 AU Incl. = 23.93707 a = 6.3505515 AU n = 0.06158670 P = 16.0 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 10 12 08 25.17 -01 14.8 4.482 4.260 70.8 12.8 20.3 2025 10 22 08 31.30 -02 34.6 4.342 4.255 78.4 13.2 20.2 2025 11 01 08 36.31 -03 55.4 4.199 4.250 86.1 13.5 20.1 2025 11 11 08 40.07 -05 15.6 4.057 4.245 94.1 13.5 20.1 2025 11 21 08 42.45 -06 33.6 3.918 4.241 102.4 13.2 20.0 2025 12 01 08 43.36 -07 47.2 3.787 4.238 110.8 12.6 19.9 2025 12 11 08 42.76 -08 54.0 3.666 4.235 119.3 11.7 19.8 2025 12 21 08 40.68 -09 51.3 3.559 4.233 127.7 10.6 19.8 2025 12 31 08 37.24 -10 36.5 3.471 4.232 135.7 9.3 19.7 2026 01 10 08 32.71 -11 07.4 3.405 4.230 142.8 8.1 19.7 2026 01 20 08 27.44 -11 22.4 3.363 4.230 148.0 7.1 19.6 2026 01 30 08 21.90 -11 21.0 3.347 4.230 150.1 6.7 19.6 2026 02 09 08 16.59 -11 04.4 3.358 4.230 148.5 7.0 19.6 2026 02 19 08 11.99 -10 34.7 3.395 4.232 143.7 8.0 19.7 2026 03 01 08 08.48 -09 55.1 3.455 4.233 136.9 9.2 19.7 2026 03 11 08 06.37 -09 09.5 3.537 4.235 129.2 10.5 19.8 2026 03 21 08 05.78 -08 21.2 3.638 4.238 121.1 11.6 19.8 2026 03 31 08 06.78 -07 33.8 3.752 4.242 112.9 12.5 19.9 2026 04 10 08 09.31 -06 49.6 3.878 4.245 104.8 13.2 20.0 2026 04 20 08 13.27 -06 10.9 4.011 4.250 96.9 13.6 20.0 2026 04 30 08 18.54 -05 38.9 4.147 4.255 89.2 13.7 20.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 November 5 (CBET 5630) Daniel W. E. Green