Electronic Telegram No. 5391 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/2024 G5 (LEONARD) G. J. Leonard reports his discovery of a comet on CCD images obtained on Apr. 5 with the Mt. Lemmon Survey's 1.5-m reflector in Arizona (discovery observations tabulted below); four 30-s co-added images showed a moderately condensed coma 8" across with a straight tail 6" long in p.a. 90 degrees. 2024 UT R.A. (2000) Decl. Mag. Observer Apr. 5.13126 7 44 13.51 +29 28 22.6 20.8 Leonard 5.13876 7 44 13.61 +29 28 17.4 20.9 " 5.14407 7 44 13.65 +29 28 12.1 20.3 " 5.14940 7 44 13.67 +29 28 07.5 " 5.15838 7 44 13.84 +29 28 00.3 19.9 " 5.16979 7 44 13.90 +29 27 51.0 19.9 " 5.18147 7 44 14.05 +29 27 41.5 19.9 " 5.19316 7 44 14.18 +29 27 31.7 20.3 " After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists also commented on the cometary appearance. Eight stacked 120-s exposurse taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) on Apr. 10.2 UT with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) showed only a stellar appearance; the magnitude was 20.3 as measured within a circular aperture of radius 3".8. K. Wierzchos writes that four 30-s unfiltered exposures taken with the Mt. Lemmon 1.5-m reflector on Apr. 21.2 show a condensed 6" coma with no tail. Numerous single-night, previously unconnected observations (all with the comet presumably stellar in appearance) were subsequently identified in the MPC's "isolated tracklet file", including astrometry obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala on 2023 Dec. 15.6 UT (mag 21.7-22.1), 2024 Jan. 3.5 (mag 21.2-21.3), and Feb. 5.4 (mag 20.6- 20.9); with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on 2024 Jan. 6.5 (mag21.2-21.5); and with the Mt. Lemmon 1.5-m reflector on Feb. 17.2 (mag 20.1-20.8). S. Deen (Simi Valley, CA, USA) also identified a several pre-discovery observations (all of which showed the comet as stellar in appearance) in publicly available images obtained with the 1.2-m Oschin Schmidt reflector at Palomar (ZTF program) from 2024 Jan. 6.4 (mag r = 21.2), Jan. 13.4 (r = 20.4), Jan. 15.3 (r = 20.2), Jan. 17.4 (g = 20.9), and Jan. 31.4. The available astrometry appears on MPEC 2024-J126. The following orbital elements by S. Nakano (Central Bureau) are from 92 observations spanning 2023 Dec. 15-2024 May 5 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.002396 and +0.001629 (+/- 0.000008) AU**-1, respectively. There are no close approaches to any major planets. Epoch = 2024 Sept. 7.0 TT T = 2024 Sept. 7.00060 TT Peri. = 209.56253 e = 0.9945486 Node = 316.39844 2000.0 q = 2.9528710 AU Incl. = 50.38911 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 08 01.93 +21 45.3 3.410 3.184 68.6 17.2 19.7 2024 05 15 08 05.91 +20 40.8 3.459 3.166 64.9 16.8 19.7 2024 05 20 08 10.16 +19 36.5 3.507 3.148 61.3 16.4 19.7 2024 05 25 08 14.65 +18 32.2 3.552 3.132 57.8 15.9 19.7 2024 05 30 08 19.35 +17 27.8 3.596 3.116 54.3 15.3 19.7 2024 06 04 08 24.24 +16 23.2 3.638 3.100 50.9 14.7 19.7 2024 06 09 08 29.32 +15 18.1 3.677 3.086 47.7 14.1 19.7 2024 06 14 08 34.55 +14 12.5 3.713 3.072 44.4 13.4 19.7 2024 06 19 08 39.92 +13 06.3 3.747 3.058 41.3 12.7 19.8 2024 11 06 11 28.04 -26 42.7 3.603 3.013 46.8 13.9 19.6 2024 11 11 11 33.69 -28 30.4 3.570 3.023 49.5 14.4 19.6 2024 11 16 11 39.22 -30 19.3 3.537 3.034 52.3 14.9 19.6 2024 11 21 11 44.64 -32 09.3 3.503 3.046 55.0 15.4 19.6 2024 11 26 11 49.91 -34 00.4 3.470 3.058 57.7 15.8 19.6 2024 12 01 11 55.02 -35 52.2 3.436 3.072 60.4 16.2 19.6 2024 12 06 11 59.94 -37 44.8 3.403 3.085 63.1 16.6 19.6 2024 12 11 12 04.64 -39 37.8 3.370 3.100 65.9 16.8 19.6 2024 12 16 12 09.09 -41 31.0 3.337 3.116 68.6 17.1 19.6 2024 12 21 12 13.27 -43 24.2 3.306 3.132 71.3 17.3 19.6 2024 12 26 12 17.12 -45 17.2 3.275 3.148 73.9 17.5 19.6 2024 12 31 12 20.61 -47 09.6 3.246 3.166 76.6 17.6 19.6 2025 01 05 12 23.68 -49 01.1 3.217 3.184 79.2 17.7 19.6 2025 01 10 12 26.27 -50 51.2 3.190 3.202 81.8 17.7 19.6 2025 01 15 12 28.33 -52 39.6 3.165 3.221 84.4 17.7 19.6 2025 01 20 12 29.78 -54 25.7 3.142 3.241 86.9 17.6 19.6 2025 01 25 12 30.55 -56 09.2 3.120 3.262 89.4 17.6 19.6 2025 01 30 12 30.55 -57 49.3 3.100 3.283 91.8 17.5 19.6 2025 02 04 12 29.70 -59 25.5 3.083 3.304 94.2 17.3 19.6 2025 02 09 12 27.93 -60 57.0 3.067 3.326 96.5 17.1 19.6 2025 02 14 12 25.15 -62 23.1 3.054 3.349 98.7 17.0 19.6 2025 02 19 12 21.33 -63 43.2 3.044 3.372 100.8 16.7 19.6 2025 02 24 12 16.40 -64 56.4 3.036 3.395 102.8 16.5 19.7 2025 03 01 12 10.40 -66 01.9 3.031 3.419 104.7 16.3 19.7 2025 03 06 12 03.37 -66 59.0 3.028 3.444 106.5 16.0 19.7 2025 03 11 11 55.46 -67 47.1 3.028 3.468 108.2 15.8 19.7 2025 03 16 11 46.85 -68 25.8 3.031 3.494 109.7 15.5 19.8 2025 03 21 11 37.80 -68 54.9 3.036 3.520 111.1 15.3 19.8 2025 03 26 11 28.61 -69 14.5 3.045 3.546 112.3 15.1 19.8 2025 03 31 11 19.61 -69 24.7 3.056 3.572 113.4 14.9 19.8 2025 04 05 11 11.11 -69 26.2 3.071 3.599 114.2 14.7 19.9 2025 04 10 11 03.41 -69 19.8 3.088 3.626 115.0 14.5 19.9 2025 04 15 10 56.71 -69 06.6 3.108 3.654 115.5 14.4 20.0 2025 04 20 10 51.16 -68 47.6 3.132 3.682 115.8 14.2 20.0 2025 04 25 10 46.84 -68 23.9 3.158 3.710 115.9 14.1 20.1 2025 04 30 10 43.80 -67 56.4 3.187 3.739 115.9 14.0 20.1 2025 05 05 10 42.00 -67 26.2 3.220 3.768 115.7 14.0 20.1 2025 05 10 10 41.40 -66 54.3 3.255 3.797 115.3 13.9 20.2 2025 05 15 10 41.91 -66 21.4 3.293 3.826 114.7 13.9 20.3 2025 05 20 10 43.45 -65 48.1 3.334 3.856 113.9 13.9 20.3 2025 05 25 10 45.94 -65 15.0 3.377 3.886 113.0 13.9 20.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 May 10 (CBET 5391) Daniel W. E. Green