Electronic Telegram No. 5641 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 W1 (SANKOVICH) An apparently asteroidal object that was discovered via images obtained remotely on Nov. 20 by Anatoly Vasilyevich Sankovich of Moscow using his own 0.50-m telescope (+ QHY camera) located at the Santel Observatory, El Leoncito, Argentina, has been found to show cometary appearance by observers elsewhere after it was posted to the Minor Planet Center's NEOCP and PCCP webpages. The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. Mag. Observer Nov. 20.16224 5 54 02.68 -53 33 03.8 19.8 Sankovich 20.20373 5 53 59.71 -53 33 00.7 19.6 " 20.24479 5 53 56.68 -53 32 55.6 19.2 " 20.24921 5 53 56.35 -53 32 55.1 19.4 " 20.27378 5 53 54.61 -53 32 52.8 19.2 " 20.29730 5 53 52.92 -53 32 50.3 19.2 " 20.30312 5 53 52.49 -53 32 49.4 19.2 " 21.29527 5 52 42.14 -53 30 58.1 19.5 " 21.29895 5 52 41.94 -53 30 56.8 19.7 " 21.30370 5 52 41.53 -53 30 56.6 19.5 " One-hundred stacked 30-s CMOS exposures taken by C. Jacques (Belo Horizonte, Brazil) on Nov. 22.1 UT with a 0.45-m f/2.9 reflector at the SONEAR site at Serra da Piedade show a condensed coma of size 10" and no tail. Twelve stacked 60-s CCD exposures obtained on Nov. 27.34 remotely by H. Sato (Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, show a strongly condensed coma 6" in diameter with no tail; the magnitude was 19.5 as measured within a circular aperture of radius 3".6. Ten stacked 120-s CCD images obtained remotely on Nov. 30.7 by T. Prystavski (Lviv, Ukraine) using an iTelescope 0.51-m f/6.8 "corrected Dall-Kirkham" astrograph located at Siding Spring, NSW, Australia, show a very condensed coma of total mag 19.2 with a tail about 0'.2 long in p.a. 264 degrees. The available astrometry appears on MPEC 2025-X33. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 72 observations spanning Nov. 20-Dec. 1 (mean residual 0".4). T = 2025 Feb. 17.61630 TT Peri. = 250.61371 Node = 95.88498 2000.0 q = 4.1697906 AU Incl. = 79.80345 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 08 13 06 05.64 -48 56.2 4.520 4.424 78.1 12.9 18.4 2025 08 23 06 13.89 -49 14.4 4.526 4.452 79.4 12.9 18.5 2025 09 02 06 20.39 -49 42.1 4.526 4.482 81.1 12.9 18.5 2025 09 12 06 24.97 -50 17.4 4.522 4.513 83.1 12.8 18.5 2025 09 22 06 27.48 -50 58.1 4.514 4.545 85.4 12.7 18.5 2025 10 02 06 27.70 -51 41.4 4.504 4.579 88.0 12.6 18.6 2025 10 12 06 25.51 -52 23.6 4.491 4.613 90.7 12.5 18.6 2025 10 22 06 20.81 -53 00.6 4.479 4.649 93.6 12.3 18.6 2025 11 01 06 13.63 -53 27.6 4.469 4.686 96.5 12.2 18.6 2025 11 11 06 04.23 -53 39.5 4.463 4.723 99.2 11.9 18.6 2025 11 21 05 53.05 -53 31.5 4.464 4.762 101.6 11.7 18.7 2025 12 01 05 40.81 -52 59.8 4.474 4.802 103.6 11.5 18.7 2025 12 11 05 28.34 -52 02.2 4.495 4.843 104.9 11.3 18.7 2025 12 21 05 16.48 -50 38.5 4.530 4.884 105.4 11.2 18.8 2025 12 31 05 05.96 -48 50.7 4.580 4.927 105.0 11.1 18.8 2026 01 10 04 57.28 -46 42.7 4.645 4.970 103.7 11.1 18.9 2026 01 20 04 50.67 -44 19.1 4.726 5.015 101.4 11.1 19.0 2026 01 30 04 46.19 -41 45.2 4.822 5.060 98.3 11.1 19.0 2026 02 09 04 43.73 -39 06.0 4.932 5.105 94.5 11.1 19.1 2026 02 19 04 43.10 -36 25.9 5.055 5.152 90.1 11.1 19.2 2026 03 01 04 44.10 -33 48.8 5.187 5.199 85.2 10.9 19.3 2026 03 11 04 46.48 -31 17.5 5.326 5.247 80.1 10.7 19.4 2026 03 21 04 50.01 -28 54.1 5.469 5.295 74.7 10.5 19.5 2026 03 31 04 54.52 -26 40.4 5.614 5.344 69.3 10.1 19.6 2026 04 10 04 59.79 -24 37.1 5.757 5.394 64.0 9.6 19.7 2026 04 20 05 05.68 -22 45.0 5.896 5.444 58.8 9.1 19.7 2026 04 30 05 12.03 -21 04.1 6.028 5.495 53.8 8.5 19.8 2026 05 10 05 18.72 -19 34.6 6.151 5.546 49.3 7.9 19.9 2026 05 20 05 25.63 -18 16.2 6.262 5.597 45.3 7.4 20.0 2026 05 30 05 32.64 -17 08.5 6.360 5.650 42.1 6.9 20.0 2026 06 09 05 39.67 -16 11.3 6.444 5.702 39.9 6.6 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 December 2 (CBET 5641) Daniel W. E. Green