Electronic Telegram No. 5660 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/2026 B2 (SUN-GAO) Guoyou Sun (Wenzhou, Zhejiang, China) writes that he has discovered a comet on CCD images taken on Jan. 19 by Xing Gao (Urumqi, Xinjiang, China) using a 0.28-m f/2.2 Schmidt telescope at Xingming Observatory, Nanshan, in the course of their search for comets near the sun. The object is distinctly cometary on the discovery images, showing a diffuse coma 15" in diameter with no tail. The discovery observations are tabulated below. 2026 UT R.A. (2000) Decl. Mag. Observer Jan. 19.00251 18 55 24.41 + 3 55 34.4 15.5 Gao 19.00669 18 55 25.22 + 3 55 42.7 15.3 " 19.01085 18 55 26.16 + 3 55 49.5 15.4 " 19.01501 18 55 27.06 + 3 55 59.6 15.3 " After the comet was posted on the Minor Planet Center's PCCP webpage, other astrometrists commented on the cometary appearance. A. Aletti, Varese, Italy, reports that sixty-nine 15-s unfiltered CCD exposures taken on Jan. 21.2 UT with a 0.36-m f/7.5 reflector show a slightly condensed coma 25" wide with no tail. CCD images obtained on Jan. 21.9 by K. Kadota with a 0.25-m f/5 reflector at Ageo, Japan, show a coma of diameter 1'.0 (total mag 14.7) with a central condensation but no tail. Four stacked 30-s CMOS exposures taken on Jan. 22.57 by Hidetaka Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/3 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show a moderately condensed comet with an outer coma 30" in diameter and no tail; the magnitude was 14.8 as measured within a circular aperture of radius 16".3. Fifty stacked 30-s CCD exposures obtained by Hirohisa Sato with a 0.25-m f/4.5 reflector located at Sukagawa, Japan, on Jan. 24.85-24.86 show a condensed a coma about 24" in diameter (total mag 15.7), but no tail. The available astrometry appears on MPEC 2026-B203. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 70 observations spanning 2026 Jan. 19-26 (mean residual 0".8). The comet will pass 3.40 AU from Saturn on 2029 Jan. 26 UT. T = 2026 Jan. 10.17309 TT Peri. = 47.34601 Node = 234.64568 2000.0 q = 1.2847728 AU Incl. = 59.57351 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 12.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2025 12 31 17 48.30 -04 56.5 2.152 1.294 22.0 16.6 15.1 2026 01 10 18 23.05 -00 27.6 2.092 1.285 26.2 19.7 15.0 2026 01 20 18 59.04 +04 25.7 2.052 1.293 29.8 22.2 15.0 2026 01 30 19 35.99 +09 32.3 2.036 1.319 32.7 23.8 15.0 2026 02 09 20 13.54 +14 38.1 2.048 1.361 34.9 24.5 15.1 2026 02 19 20 51.17 +19 29.0 2.087 1.418 36.3 24.4 15.3 2026 03 01 21 28.30 +23 53.7 2.152 1.486 37.0 23.6 15.5 2026 03 11 22 04.37 +27 45.5 2.238 1.564 37.0 22.5 15.8 2026 03 21 22 38.92 +31 02.7 2.340 1.649 36.5 21.1 16.1 2026 03 31 23 11.61 +33 47.5 2.450 1.741 35.8 19.6 16.4 2026 04 10 23 42.23 +36 03.5 2.565 1.838 35.1 18.3 16.7 2026 04 20 00 10.73 +37 55.6 2.678 1.938 34.6 17.1 16.9 2026 04 30 00 37.08 +39 28.0 2.786 2.040 34.7 16.3 17.2 2026 05 10 01 01.34 +40 44.6 2.885 2.145 35.5 15.9 17.5 2026 05 20 01 23.56 +41 48.6 2.972 2.251 37.2 15.8 17.7 2026 05 30 01 43.77 +42 42.6 3.046 2.357 39.7 15.9 17.9 2026 06 09 02 02.02 +43 28.5 3.105 2.464 43.1 16.4 18.1 2026 06 19 02 18.30 +44 07.9 3.148 2.571 47.4 16.9 18.3 2026 06 29 02 32.55 +44 41.8 3.175 2.679 52.4 17.5 18.4 2026 07 09 02 44.71 +45 11.0 3.186 2.786 58.1 18.0 18.6 2026 07 19 02 54.67 +45 35.8 3.183 2.893 64.4 18.5 18.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 January 29 (CBET 5660) Daniel W. E. Green