Electronic Telegram No. 5638 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 UX_109 (YE) Quan-Zhi Ye, University of Maryland, reports his discovery of a comet on images obtained on Oct. 20 UT with the "Zwicky Transient Facility" camera on the 1.2-m Schmidt telescope at Palomar (discovery observations tabulated below). There was no visible coma but there was a straight 9"-long tail (he measured position angles 300 and 330 degrees). He subsequently identified pre-discovery observations obtained with the same instrumentation on nine additional dates back to Oct. 1 2025 UT R.A. (2000) Decl. Mag. Oct. 1.52507 9 39 08.44 +11 28 04.4 19.4 1.52905 9 39 08.73 +11 28 03.7 18.9 2.51983 9 40 45.24 +11 19 42.9 19.8 2.52381 9 40 45.65 +11 19 41.2 19.5 2.52779 9 40 46.05 +11 19 38.6 19.8 3.52223 9 42 22.36 +11 11 15.5 19.5 3.52619 9 42 22.85 +11 11 13.9 20.1 4.52651 9 43 59.35 +11 02 47.2 19.9 5.52264 9 45 35.01 +10 54 21.1 19.6 5.52650 9 45 35.34 +10 54 19.8 19.8 5.53038 9 45 35.74 +10 54 17.7 19.4 9.52203 9 51 54.86 +10 20 23.7 19.6 9.52599 9 51 55.27 +10 20 23.8 20.1 12.52284 9 56 35.22 + 9 54 54.0 19.6 12.52671 9 56 35.64 + 9 54 51.2 19.9 12.53058 9 56 36.01 + 9 54 49.3 20.2 18.52604 10 05 43.20 + 9 03 48.4 19.8 18.52994 10 05 43.65 + 9 03 45.0 19.8 19.52548 10 07 12.77 + 8 55 17.8 19.7 19.52937 10 07 13.21 + 8 55 16.5 19.7 19.53327 10 07 13.53 + 8 55 14.4 19.7 20.52721 10 08 42.04 + 8 46 48.8 19.6 20.53111 10 08 42.39 + 8 46 45.1 19.8 20.53502 10 08 42.78 + 8 46 43.4 19.5 Additional astrometry appears on MPEC 2025-W42. The following unperturbed orbital elements by S. Nakano (Central Bureau) are from 67 observations spanning 2025 Oct. 1-Nov. 4 (mean residual 0".5). The comet passed 0.95 AU from Jupiter on 1985 October. T = 2025 Aug. 15.12517 TT Peri. = 276.31832 e = 0.3303525 Node = 198.04022 2000.0 q = 2.5729105 AU Incl. = 3.17985 a = 3.8421865 AU n = 0.13086889 P = 7.53 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 10 12 09 55.78 +09 59.4 3.107 2.597 51.0 17.4 19.6 2025 10 22 10 10.87 +08 34.3 3.013 2.606 56.9 18.7 19.6 2025 11 01 10 25.08 +07 10.6 2.912 2.617 63.1 19.8 19.5 2025 11 11 10 38.30 +05 49.7 2.805 2.629 69.6 20.7 19.4 2025 11 21 10 50.39 +04 33.4 2.694 2.642 76.4 21.3 19.4 2025 12 01 11 01.19 +03 23.4 2.580 2.656 83.5 21.6 19.3 2025 12 11 11 10.51 +02 21.6 2.464 2.672 91.1 21.6 19.2 2025 12 21 11 18.12 +01 30.0 2.349 2.688 99.2 21.2 19.1 2025 12 31 11 23.81 +00 50.7 2.238 2.706 107.8 20.2 19.1 2026 01 10 11 27.36 +00 25.5 2.134 2.725 117.0 18.8 19.0 2026 01 20 11 28.61 +00 16.1 2.040 2.745 126.8 16.7 18.9 2026 01 30 11 27.51 +00 23.5 1.960 2.766 137.3 14.0 18.9 2026 02 09 11 24.20 +00 47.0 1.900 2.788 148.3 10.7 18.8 2026 02 19 11 19.05 +01 25.0 1.862 2.810 159.8 7.0 18.8 2026 03 01 11 12.70 +02 13.4 1.850 2.834 171.4 3.0 18.9 2026 03 11 11 05.95 +03 06.6 1.867 2.858 175.6 1.5 18.9 2026 03 21 10 59.66 +03 58.9 1.911 2.883 164.4 5.3 19.0 2026 03 31 10 54.59 +04 44.5 1.982 2.909 153.1 8.9 19.1 2026 04 10 10 51.27 +05 19.8 2.077 2.935 142.3 12.0 19.3 2026 04 20 10 49.97 +05 42.4 2.193 2.962 132.1 14.6 19.4 2026 04 30 10 50.74 +05 51.5 2.325 2.989 122.5 16.5 19.6 2026 05 10 10 53.46 +05 47.6 2.469 3.017 113.4 17.9 19.8 2026 05 20 10 57.96 +05 31.6 2.623 3.045 104.9 18.7 19.9 2026 05 30 11 04.01 +05 04.7 2.783 3.074 96.9 19.1 20.1 2026 06 09 11 11.36 +04 28.1 2.945 3.103 89.2 19.1 20.3 2026 06 19 11 19.82 +03 43.1 3.109 3.132 81.9 18.7 20.4 2026 06 29 11 29.19 +02 51.0 3.271 3.162 74.9 18.1 20.6 2026 07 09 11 39.30 +01 52.9 3.429 3.191 68.0 17.2 20.7 2026 07 19 11 50.03 +00 49.8 3.582 3.222 61.4 16.1 20.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 November 18 (CBET 5638) Daniel W. E. Green