Electronic Telegram No. 5668 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 A1 (LEMMON) An apparently asteroidal 20th-mag object with a nearly parabolic orbit was discovered on 2025 Jan. 2 by the Mt. Lemmon survey (cf. CBET 5494) and was given the designation A/2025 A1. The discovery observations are tabulated below. 2025 UT R.A. (2000) Decl. Mag. Jan. 2.27772 6 46 48.05 +22 41 04.8 20.5 2.28296 6 46 47.91 +22 41 05.5 20.5 2.28822 6 46 47.81 +22 41 06.2 20.3 2.29347 6 46 47.69 +22 41 07.3 20.3 2.36372 6 46 45.94 +22 41 17.6 20.2 2.37735 6 46 45.60 +22 41 19.4 20.3 2.39087 6 46 45.26 +22 41 21.6 20.3 2.40447 6 46 44.92 +22 41 23.4 20.2 Single-night pre-discovery astrometry from 2024 Dec. 20 UT obtained with the Bok 2.25-m reflector at Kitt Peak were identified in the Minor Planet Center's "isolated tracklet file" (ITF). R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the identification of many nights of pre-discovery observations of this comet obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala -- including on 2021 Nov. 11.5 UT (at mag 23.1-23.3), 2021 Nov. 27.5 (mag 23.2-23.7), 2023 Dec. 4.53-4.57 (mag 21.7-23.0), 2023 Dec. 7.53-7.56 (mag 21.6-22.8), 2023 Dec. 12.5 (mag 22.1- 23.7), and 2023 Dec. 30.44-30.48 (mag 22.2-22.9). He also identified the comet in pre-discovery images obtained with the Pan-STARRS2 1.8-m reflector at Haleakala on 2023 Dec. 16.33-16.35 (mag 21.8-22.3) and on 2024 Feb. 12.3 (mag 21.8). Additional Pan-STARRS2 observations were found from 2024 Nov. 2.54-2.58 (mag 21.0-21.2) and 2024 Nov. 27.46-27.56 (mag 21.0-22.4). Additional Mt. Lemmon pre-discovery images were found from 2024 Oct. 28 and Nov. 14, and on Bok telescope images from 2024 Dec. 20.45-20.46 (mag 20.6- 20.7) and 2025 Oct. 2.5 (mag 20.0-20.2). Four 45-s w-band Pan-STARRS1 survey images from 2025 Dec. 13.5 taken in 1".0-1".2 seeing show no coma but a head of size 1".5 (full-width-at-half-maximum) and a 1" tail toward p.a. 110 deg. Four 45-s w-band Pan-STARRS2 survey images from 2026 Jan. 16.42-16.46 taken in 1".6-1".8 seeing show no coma but a head of size 2".0-2".1 (FWHM) and a broad tail 4" long spanning p.a. 110-170 deg. D. Rankin, Lunar and Planetary Laboratory, University of Arizona, writes that Bok telescope images taken on 2026 Jan. 14.3 show it to be clearly a comet with a coma diameter of 15".4 (mag 18.7). CCD images taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) using a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) on 2025 Dec. 30.55 UT show only a stellar appearance (mag 18.4). Unfiltered CCD images taken on 2026 Mar. 6.97 by D. Buczynski (Portmahomack, Scotland) with a Celestron 14 telescope show a small coma and a 10"-long tail in p.a. 108 degrees. One-hundred-twenty-eight stacked 30-s unfiltered CCD exposures taken remotely by A. Aletti on 2026 Mar. 8.9 using a 0.36-m f/7.5 reflector located at Hakos, Namibia, show a condensed 8" coma extended toward p.a. 135 degrees. The available astrometry appears on MPEC 2026-F30 and includes two single-night observations obtained on 2025 Oct. 29 (at mag 20.3-20.8) with the 2.5-m Wide Field Survey Telescope at Lenghu, China, which were apparently found in the ITF. The following orbital elements by S. Nakano (Central Bureau) are from 324 observations spanning 2021 Nov. 11-2026 Mar. 11 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.000133 and +0.001693 (+/- 0.000001) AU**-1, respectively. The comet passed 2.03 AU from Jupiter on 2026 Jan. 22 UT. Epoch = 2027 Mar. 16.0 TT T = 2027 Mar. 15.81834 TT Peri. = 68.45550 e = 0.9977281 Node = 101.27241 2000.0 q = 5.3350054 AU Incl. = 33.38847 The following ephemeris by Nakano from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 12 31 08 49.06 +33 17.0 5.363 6.233 150.0 4.5 18.5 2026 01 10 08 45.82 +34 11.1 5.272 6.197 158.3 3.4 18.4 2026 01 20 08 41.88 +35 02.9 5.212 6.161 163.3 2.6 18.4 2026 01 30 08 37.55 +35 49.9 5.182 6.125 161.8 2.9 18.4 2026 02 09 08 33.20 +36 30.5 5.182 6.090 155.0 3.9 18.3 2026 02 19 08 29.19 +37 03.3 5.210 6.056 146.1 5.2 18.3 2026 03 01 08 25.87 +37 27.7 5.264 6.022 136.5 6.5 18.3 2026 03 11 08 23.53 +37 43.8 5.340 5.989 126.9 7.6 18.4 2026 03 21 08 22.36 +37 52.3 5.433 5.957 117.3 8.5 18.4 2026 03 31 08 22.50 +37 53.8 5.539 5.925 108.0 9.2 18.4 2026 04 10 08 23.99 +37 49.4 5.654 5.894 99.0 9.7 18.4 2026 04 20 08 26.79 +37 39.9 5.772 5.863 90.2 9.9 18.5 2026 04 30 08 30.85 +37 26.1 5.891 5.833 81.8 9.8 18.5 2026 05 10 08 36.06 +37 08.7 6.007 5.804 73.7 9.6 18.5 2026 05 20 08 42.32 +36 48.3 6.116 5.776 65.9 9.2 18.5 2026 05 30 08 49.50 +36 25.3 6.216 5.749 58.3 8.6 18.5 2026 06 09 08 57.48 +36 00.1 6.304 5.722 51.1 7.9 18.6 2026 06 19 09 06.15 +35 33.0 6.380 5.696 44.2 7.1 18.6 2026 06 29 09 15.40 +35 04.4 6.441 5.671 37.7 6.3 18.6 2026 09 17 10 39.72 +31 11.0 6.329 5.499 31.7 5.5 18.4 2026 09 27 10 50.44 +30 49.8 6.240 5.482 37.7 6.4 18.4 2026 10 07 11 00.99 +30 32.7 6.137 5.465 44.2 7.3 18.3 2026 10 17 11 11.27 +30 20.8 6.022 5.450 51.0 8.2 18.3 2026 10 27 11 21.21 +30 14.9 5.896 5.435 58.0 8.9 18.2 2026 11 06 11 30.73 +30 15.8 5.761 5.421 65.3 9.6 18.2 2026 11 16 11 39.72 +30 24.5 5.619 5.409 72.8 10.1 18.1 2026 11 26 11 48.07 +30 41.8 5.473 5.397 80.4 10.4 18.0 2026 12 06 11 55.68 +31 08.0 5.327 5.386 88.2 10.5 18.0 2026 12 16 12 02.40 +31 43.5 5.183 5.377 96.1 10.5 17.9 2026 12 26 12 08.13 +32 28.0 5.044 5.368 104.0 10.2 17.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 March 17 (CBET 5668) Daniel W. E. Green