Electronic Telegram No. 5501 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 C/2025 B2 (BORISOV) Gennady Borisov, Nauchnij, Crimea, reports his discovery of another comet in three 120-s unfiltered CCD survey images taken on Jan. 20 with a 0.5-m f/1.9 reflector (discovery observations tabulated below); the discovery frames show the object as asteroidal in appearance. 2025 UT R.A. (2000) Decl. Mag. Observer Jan. 20.77696 4 09 34.27 +71 18 15.6 20.3 Borisov 20.80215 4 09 32.69 +71 18 11.5 20.5 " 20.82726 4 09 31.02 +71 18 09.1 20.2 " 20.91481 4 09 25.20 +71 17 57.5 20.2 " 20.92925 4 09 24.27 +71 17 55.4 20.3 " 20.94366 4 09 23.34 +71 17 53.9 20.6 " On Jan. 21.7 UT, Borisov took a deep exposure (220 minutes) with the same telescope, which showed a very condensed coma of size 2".5-4" with no tail. After the comet was posted on the Minor Planet Center's PCCP webpage, T. Chen, Beijing, reported that CCD images obtained with a 0.50-m f/8.1 reflector at Jiamaerdeng Observatory in Tibet on Jan. 26.65-26.67 UT show a small diffuse coma with an apparent 0'.2 tail in p.a. 43 degrees (measured by J.-L. Yang, Central University of Taiwan, and Chen). Fifteen stacked 60-s exposures taken remotely on Feb. 2.26 by H. Sato (Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show only a stellar appearance; the magnitude was 20.2 as measured within a circular aperture of radius 4".9. The available astrometry appears on MPEC 2025-C153. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 139 observations spanning Jan. 8-Feb. 8 (mean residual 0".4). There are no close approaches to any major planets. T = 2026 Sept.10.08844 TT Peri. = 78.72986 Node = 84.87811 2000.0 q = 8.2455794 AU Incl. = 91.75695 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 7.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 01 25 04 05.21 +71 09.0 8.498 8.968 115.7 5.7 19.8 2025 02 04 03 56.85 +70 44.3 8.572 8.945 109.2 6.0 19.8 2025 02 14 03 51.22 +70 17.9 8.658 8.923 102.5 6.2 19.8 2025 02 24 03 48.17 +69 52.4 8.750 8.901 95.6 6.4 19.8 2025 03 06 03 47.46 +69 30.0 8.845 8.879 88.7 6.4 19.8 2025 03 16 03 48.82 +69 12.0 8.940 8.857 82.0 6.4 19.8 2025 03 26 03 51.96 +68 59.5 9.031 8.836 75.6 6.3 19.8 2025 04 05 03 56.66 +68 52.9 9.114 8.815 69.6 6.1 19.9 2025 04 15 04 02.70 +68 52.6 9.187 8.794 64.0 5.9 19.9 2025 04 25 04 09.89 +68 58.6 9.248 8.774 59.1 5.6 19.9 2025 05 05 04 18.08 +69 10.9 9.295 8.754 54.9 5.4 19.9 2025 05 15 04 27.15 +69 29.2 9.327 8.734 51.5 5.2 19.9 2025 05 25 04 36.98 +69 53.5 9.343 8.715 49.2 5.0 19.9 2025 06 04 04 47.50 +70 23.4 9.342 8.696 48.0 5.0 19.9 2025 06 14 04 58.60 +70 58.8 9.325 8.677 47.9 5.0 19.9 2025 06 24 05 10.24 +71 39.5 9.292 8.659 49.0 5.1 19.8 2025 07 04 05 22.36 +72 25.5 9.243 8.641 51.1 5.3 19.8 2025 07 14 05 34.90 +73 16.5 9.181 8.624 54.0 5.5 19.8 2025 07 24 05 47.82 +74 12.6 9.106 8.606 57.7 5.7 19.8 2025 08 03 06 01.07 +75 13.6 9.020 8.590 61.9 6.0 19.7 2025 08 13 06 14.62 +76 19.6 8.926 8.573 66.6 6.2 19.7 2025 08 23 06 28.45 +77 30.4 8.825 8.557 71.5 6.4 19.7 2025 09 02 06 42.49 +78 46.0 8.719 8.541 76.6 6.6 19.7 2025 09 12 06 56.74 +80 06.2 8.613 8.526 81.7 6.7 19.6 2025 09 22 07 11.20 +81 30.6 8.507 8.511 86.8 6.8 19.6 2025 10 02 07 25.83 +82 58.9 8.406 8.497 91.8 6.8 19.6 2025 10 12 07 40.70 +84 30.4 8.312 8.483 96.5 6.7 19.5 2025 10 22 07 56.00 +86 04.3 8.227 8.469 100.7 6.6 19.5 2025 11 01 08 12.42 +87 39.7 8.153 8.455 104.4 6.5 19.5 2025 11 11 08 37.39 +89 15.2 8.093 8.442 107.4 6.4 19.5 2025 11 21 20 22.28 +89 10.1 8.048 8.430 109.5 6.3 19.4 2025 12 01 20 45.61 +87 38.3 8.018 8.418 110.7 6.3 19.4 2025 12 11 21 01.58 +86 10.6 8.004 8.406 110.9 6.3 19.4 2025 12 21 21 16.35 +84 48.5 8.006 8.394 110.1 6.3 19.4 2025 12 31 21 30.59 +83 33.6 8.022 8.383 108.3 6.4 19.4 2026 01 10 21 44.43 +82 26.9 8.051 8.373 105.8 6.5 19.4 2026 01 20 21 57.96 +81 29.6 8.092 8.363 102.7 6.6 19.4 2026 01 30 22 11.18 +80 42.5 8.141 8.353 99.1 6.7 19.4 2026 02 09 22 24.05 +80 06.1 8.196 8.344 95.2 6.8 19.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 February 10 (CBET 5501) Daniel W. E. Green