Electronic Telegram No. 5718 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 161P/HARTLEY-IRAS This comet has apparently been recovered independently by at least two observers. CCD images taken remotely on June 23.8 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) using a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, show a strongly condensed coma 10" in diameter; the magnitude was 18.6 as measured within a circular aperture of radius 5".4. M. Masek (Institute of Physics, Czech Academy of Sciences) reports his recovery of this comet as a stellar object on CCD images obtained on June 25.4 UT with the 0.30-m FRAM telescope at Pierre Auger Observatory in Argentina (cf. CBETs 5658, 5710). The astrometry of both observers is tabulated below. 2026 UT R.A. (2000) Decl. Mag. Observer June 23.79867 3 07 53.22 -22 40 11.8 Sato 23.80384 3 07 53.42 -22 40 09.5 18.6 " 25.36697 3 08 50.14 -22 29 40.1 18.4 Masek 25.40366 3 08 51.46 -22 29 25.6 18.2 " Sato later relayed that an apparent accidental recovery was made on CCD images taken on July 15.1 UT with a 0.5-m f/2 Schmidt reflector at Sutherland, South Africa, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program, whence the V magnitude was given as 18.1-18.6; that had been posted on the Minor Planet Center's NEOCP webpage as an apparently new object. These and other astrometry from July 8-16 were published on MPEC 2026-O09 on July 17. The residuals for the 2026 observations were +3.62 deg in R.A. and -7.03 deg in Decl. from the prediction in NK 1184 (and ICQ Comet Handbook 2026), with a corresponding correction of Delta(T) = +28.4 days. This is the third recorded apparition of this comet (cf. IAUC 8428). The following linked orbital elements by S. Nakano (Central Bureau) are from 332 observations spanning 1983 Dec. 1-2026 July 15 (mean residual 1".2), with corresponding non-gravitational parameters A1 = +0.66 +/- 0.04, A2 = -0.0329 +/- 0.0000. The comet will pass 0.40 AU from Jupiter on 2028 June 2 UT. Epoch = 1984 Jan. 21.0 TT T = 1984 Jan. 8.70735 TT Peri. = 47.11314 e = 0.8338199 Node = 1.49913 2000.0 q = 1.2824312 AU Incl. = 95.73171 a = 7.7171153 AU n = 0.04597498 P = 21.44 years Epoch = 2005 July 9.0 TT T = 2005 June 20.84299 TT Peri. = 47.07440 e = 0.8350660 Node = 1.39776 2000.0 q = 1.2751398 AU Incl. = 95.69797 a = 7.7312138 AU n = 0.04584928 P = 21.50 years Epoch = 2026 Nov. 16.0 TT T = 2026 Nov. 27.18959 TT Peri. = 47.06559 e = 0.8361792 Node = 1.47535 2000.0 q = 1.2651626 AU Incl. = 95.79207 a = 7.7228465 AU n = 0.04592382 P = 21.46 years Epoch = 2047 Mar. 31.0 TT T = 2047 Apr. 13.05668 TT Peri. = 45.69825 e = 0.8357811 Node = 1.51485 2000.0 q = 1.2286604 AU Incl. = 96.89573 a = 7.4818470 AU n = 0.04816048 P = 20.46 years The comet is some 2-3 magnitudes fainter now than predicted from the 2004-2005 apparition, and that apparition was roughly 1.5 mag fainter than was predicted from the magnitude parameters of the first apparition in 1983-1984. The following ephemeris by the undersigned from the above orbital elements thus uses photometric power-law parameters H = 11.5, 2.5n = 12 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 06 09 02 58.09 -24 31.7 2.910 2.503 56.8 19.8 18.6 2026 06 19 03 04.86 -23 13.9 2.726 2.409 61.3 21.7 18.3 2026 06 29 03 10.95 -22 06.3 2.526 2.315 66.4 23.7 17.9 2026 07 09 03 16.08 -21 08.5 2.312 2.220 72.0 25.8 17.5 2026 07 19 03 19.83 -20 20.6 2.086 2.126 78.3 27.9 17.0 2026 07 29 03 21.56 -19 42.0 1.848 2.033 85.2 29.8 16.5 2026 08 08 03 20.31 -19 11.7 1.602 1.940 93.0 31.5 16.0 2026 08 18 03 14.38 -18 47.6 1.351 1.850 102.1 32.4 15.4 2026 08 28 03 00.69 -18 22.9 1.101 1.761 113.0 31.9 14.7 2026 09 07 02 33.35 -17 38.8 0.862 1.675 127.1 28.7 13.9 2026 09 17 01 41.12 -15 38.1 0.655 1.594 146.7 20.2 13.0 2026 09 27 00 11.11 -10 03.8 0.522 1.518 168.5 7.6 12.3 2026 10 07 22 20.89 -00 31.4 0.521 1.449 142.5 24.8 12.0 2026 10 17 20 58.05 +07 26.9 0.644 1.388 113.7 41.1 12.3 2026 10 27 20 10.23 +12 08.7 0.826 1.337 94.1 47.8 12.6 2026 11 06 19 43.43 +15 03.7 1.023 1.299 80.3 48.8 12.9 2026 11 16 19 27.87 +17 12.2 1.213 1.275 69.9 46.8 13.2 2026 11 26 19 18.46 +19 02.4 1.384 1.265 61.8 43.5 13.4 2026 12 06 19 12.63 +20 47.8 1.531 1.271 55.7 39.8 13.7 2026 12 16 19 08.95 +22 37.0 1.649 1.292 51.6 36.6 13.9 2026 12 26 19 06.53 +24 36.3 1.735 1.327 49.5 34.3 14.2 2027 01 05 19 04.74 +26 51.5 1.791 1.375 49.6 33.0 14.4 2027 01 15 19 02.99 +29 28.6 1.817 1.433 51.7 32.6 14.7 2027 01 25 19 00.63 +32 33.3 1.816 1.501 55.7 32.8 14.9 2027 02 04 18 56.85 +36 11.4 1.794 1.575 61.1 33.2 15.1 2027 02 14 18 50.48 +40 28.0 1.756 1.655 67.7 33.5 15.4 2027 02 24 18 39.69 +45 24.6 1.711 1.740 75.0 33.3 15.6 2027 03 06 18 21.55 +50 55.8 1.667 1.828 82.7 32.6 15.8 2027 03 16 17 51.17 +56 40.6 1.635 1.918 90.3 31.2 16.0 2027 03 26 17 01.73 +61 49.0 1.626 2.011 97.1 29.5 16.2 2027 04 05 15 49.41 +64 56.5 1.650 2.104 102.3 27.7 16.5 2027 04 15 14 27.18 +64 44.3 1.712 2.198 105.0 26.2 16.8 2027 04 25 13 19.74 +61 25.9 1.815 2.292 105.0 25.1 17.1 2027 05 05 12 35.60 +56 28.1 1.954 2.386 102.6 24.4 17.5 2027 05 15 12 09.42 +51 04.3 2.126 2.480 98.2 23.8 17.9 2027 05 25 11 54.69 +45 52.4 2.321 2.574 92.6 23.1 18.3 2027 06 04 11 47.08 +41 06.6 2.534 2.668 86.3 22.3 18.6 2027 06 14 11 44.02 +36 50.0 2.758 2.761 79.6 21.2 19.0 2027 06 24 11 43.96 +33 01.0 2.986 2.853 72.6 19.9 19.3 2027 07 04 11 45.96 +29 36.4 3.215 2.945 65.6 18.3 19.7 2027 07 14 11 49.40 +26 32.7 3.439 3.036 58.6 16.6 20.0 2027 07 24 11 53.85 +23 46.8 3.655 3.126 51.5 14.7 20.3 2027 08 03 11 59.02 +21 15.9 3.860 3.215 44.5 12.8 20.5 2027 08 13 12 04.70 +18 57.9 4.049 3.304 37.5 10.8 20.8 2027 08 23 12 10.72 +16 51.1 4.222 3.392 30.7 8.8 21.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 July 18 (CBET 5718) Daniel W. E. Green