Electronic Telegram No. 5077 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/2021 A1 (LEONARD) This comet has continued to brighten roughly as predicted on CBET 4907. K. Yoshimoto (Kumage, Yamaguchi, Japan) provides the following CCD astrometry obtained with a 0.20-m f/8 Ritchey-Chretien reflector. He noted the following coma diameters and tail lengths/p.a.: Nov. 25.8 UT, 8'.8, > 40' in p.a. 315 deg; 26.8, 10'.1, > 40' in p.a. 315 deg; 28.8, 10'.5, > 40' in p.a. 312 deg. 2021 UT R.A. (2000) Decl. Mag. Observer Nov. 25.81185 12 48 36.60 +32 04 09.5 Yoshimoto 25.81858 12 48 38.46 +32 04 03.7 8.2 " 26.84319 12 53 44.37 +31 46 44.0 " 26.84983 12 53 46.46 +31 46 37.6 8.0 " 28.82418 13 05 15.32 +31 04 23.0 " 28.83091 13 05 17.90 +31 04 12.8 7.6 " Hirohisa Sato, Sukagawa, Japan, provides the following CCD astrometry obtained with a 0.25-m reflector: 2021 UT R.A. (2000) Decl. Mag. Observer Nov. 29.75559 13 11 36.11 +30 39 01.0 Sato 29.75936 13 11 37.71 +30 38 54.6 " 29.76314 13 11 39.36 +30 38 47.8 8.3 " The following observations have been posted by F. Kugel, Dauban, France, from CCD exposures taken with a 0.4-m f/2.8 reflector: 2021 UT R.A. (2000) Decl. Mag. Observer Dec. 1.10158 13 22 05.67 +29 53 52.6 13.0 Kugel 1.11340 13 22 11.72 +29 53 25.2 12.6 " 1.11433 13 22 12.13 +29 53 23.6 12.6 " 1.11526 13 22 12.61 +29 53 21.9 8.4 " 1.14986 13 22 30.23 +29 52 02.9 13.0 " 1.15682 13 22 33.80 +29 51 46.7 12.8 " 1.16469 13 22 37.77 +29 51 29.9 13.0 " 1.17210 13 22 41.55 +29 51 12.2 8.7 " 2.17943 13 31 51.67 +29 08 15.3 11.8 " 2.18828 13 31 56.79 +29 07 50.5 12.4 " 2.19280 13 31 59.44 +29 07 37.9 12.3 " 2.19609 13 32 01.29 +29 07 28.9 12.5 " 2.19744 13 32 02.04 +29 07 25.6 12.7 " 2.19895 13 32 03.01 +29 07 20.2 12.2 " 2.20045 13 32 03.88 +29 07 16.0 12.4 " 2.20180 13 32 04.69 +29 07 12.4 12.3 " 2.20424 13 32 06.16 +29 07 05.3 12.2 " 2.20701 13 32 07.74 +29 06 57.6 8.8 " 2.21298 13 32 11.14 +29 06 40.9 12.5 " 2.21576 13 32 12.77 +29 06 33.1 9.5 " 2.22270 13 32 16.85 +29 06 13.0 12.4 " CCD astrometry by M. Suzuki with a 0.43-m f/4.5 telescope near Mayhill, NM: 2021 UT R.A. (2000) Decl. Mag. Observer Dec. 1.52058 13 25 43.81 +29 37 23.3 8.3 Suzuki 1.52145 13 25 44.26 +29 37 21.2 8.3 " 1.52229 13 25 44.75 +29 37 18.8 8.3 " S. Nakano (CBAT) notes that the Crowson observations (Animas, NM, USA) and the Mayhill observations from Nov. 29 published on MPEC 2021-W138 are bad. The following updated orbital elements by Nakano are from 1808 observations spanning 2020 Apr. 11-2021 Dec. 2 (mean residual 0".6), with corresponding original and future values of 1/a being +0.000500 and -0.000105 AU**-1, respectively (mean error +/- 0.000001 AU**-1). There are no obvious non-gravitational forces visible in the astrometric observations. The comet will pass 0.23 AU from the earth on 2021 Dec. 12.6 UT and 0.029 AU from Venus on 2021 Dec. 18.1 UT; on the latter date, the comet will be located 5.1 deg from Venus in p.a. 217.7 degrees (geocentric location). Epoch = 2022 Jan. 21.0 TT T = 2022 Jan. 3.29850 TT Peri. = 225.09198 e = 1.0000279 Node = 255.89560 2000.0 q = 0.6152614 AU Incl. = 132.68630 Selected total CCD magnitudes reported to the Central Bureau: May 9.58 UT, 17.0 (K. Kadota, Ageo, Japan, 0.25-m reflector); July 16.50, 16.1 (Kadota); Sept. 19.81, 13.1 (Kadota); 23.82, 13.8, 1'.0 (K. Yoshimoto, Yamaguchi, Japan, 0.20-m reflector; coma diameter 1'.0); Oct. 4.82, 12.5 (Kadota); 10.82, 13.3 (Hirohisa Sato, Sukagawa, Japan, 0.25-m reflector); 14.83, 11.9 (Kadota); 17.49, 13.4 (H. Sato, Tokyo, Japan, remotely with a 0.43-m astrograph near Mayhill, NM, USA; coma diameter 1'.2); 25.84, 11.1 (Yoshimoto; coma diameter 4'.1); Nov. 4.84, 10.0 (Yoshimoto, 180-mm f/2.8 lens + Canon EOS Kiss X7i digital camera; coma diameter 4'.7); 10.82, 9.4 (Kadota); 14.84, 9.1 (Yoshimoto, 0.08-m refractor + CMOS camera; coma diameter 9'.2); 16.85, 8.8 (Yoshimoto, 0.20-m reflector; coma diameter 9'.4); 19.81, 8.6 (Kadota); 25.82, 8.2 (Yoshimoto; coma diameter 8'.8); 28.83, 7.6 (Yoshimoto; coma diameter 10'.5). Visual total-magnitude and coma-diameter estimates: Oct. 7.20 UT, 11.2, 5' (J. J. Gonzalez, Leon, Spain, 0.20-m reflector); Nov. 5.23, 9.7, 5' (Gonzalez); 6.83, 9.8, 5' (K. Yoshimoto, Yamaguchi, Japan, 20x100 binoculars); 11.22, 8.7, 8' (Gonzalez, Asturias, Spain, 25x100 binoculars); 14.83, 8.7, 7' (Yoshimoto); 18.24, 7.9, 8' (Gonzalez); 22.84, 8.4, 7' (Yoshimoto). The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 10 for the total magnitudes. Forward scattering of dusty particles near perihelion may cause the comet to appear brighter. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 11 22 12 33.31 +32 51.5 0.846 1.067 70.7 60.9 8.4 2021 11 24 12 40.70 +32 29.4 0.774 1.036 70.9 64.2 8.1 2021 11 26 12 49.49 +32 01.2 0.701 1.006 70.8 68.0 7.8 2021 11 28 13 00.15 +31 23.7 0.629 0.976 70.4 72.2 7.4 2021 11 30 13 13.36 +30 31.8 0.558 0.946 69.3 77.2 7.0 2021 12 02 13 30.12 +29 16.7 0.488 0.917 67.4 83.2 6.6 2021 12 04 13 51.87 +27 23.5 0.420 0.888 64.2 90.6 6.1 2021 12 06 14 20.66 +24 25.7 0.356 0.859 59.2 100.0 5.6 2021 12 08 14 59.04 +19 39.0 0.299 0.832 51.4 112.3 5.1 2021 12 10 15 49.15 +12 06.2 0.256 0.805 39.9 128.4 4.6 2021 12 12 16 49.92 +01 32.3 0.235 0.779 25.4 147.2 4.3 2021 12 14 17 54.38 -09 57.9 0.241 0.755 15.0 160.3 4.2 2021 12 16 18 52.73 -19 15.4 0.273 0.731 18.9 154.2 4.3 2021 12 18 19 39.32 -25 22.0 0.324 0.709 26.6 141.5 4.6 2021 12 20 20 14.12 -29 05.7 0.387 0.689 32.4 130.1 4.8 2021 12 22 20 39.52 -31 23.3 0.456 0.671 36.0 120.4 5.1 2021 12 24 20 58.02 -32 51.4 0.529 0.655 38.2 111.9 5.3 2021 12 26 21 11.55 -33 50.8 0.604 0.641 39.2 104.3 5.5 2021 12 28 21 21.45 -34 32.6 0.680 0.631 39.5 97.2 5.7 2021 12 30 21 28.67 -35 03.1 0.757 0.622 39.3 90.4 5.8 2022 01 01 21 33.88 -35 26.1 0.832 0.617 38.6 84.0 6.0 2022 01 11 21 42.71 -36 20.0 1.187 0.638 32.5 55.9 6.9 2022 01 21 21 39.84 -36 21.7 1.479 0.724 25.3 35.6 7.9 2022 01 31 21 34.94 -36 00.7 1.698 0.851 20.7 24.1 8.9 2022 02 10 21 30.50 -35 33.6 1.852 0.997 21.0 20.8 9.8 2022 02 20 21 26.59 -35 09.8 1.951 1.150 26.2 22.3 10.6 2022 03 02 21 22.70 -34 54.7 2.002 1.305 34.1 25.2 11.2 2022 03 12 21 18.06 -34 51.5 2.013 1.459 43.3 27.9 11.7 2022 03 22 21 11.83 -35 02.5 1.990 1.611 53.5 29.8 12.1 2022 04 01 21 03.10 -35 29.2 1.941 1.760 64.5 30.8 12.4 2022 04 11 20 50.72 -36 11.6 1.874 1.907 76.4 30.7 12.7 2022 04 21 20 33.42 -37 06.8 1.799 2.050 89.3 29.3 12.9 2022 05 01 20 09.96 -38 06.5 1.727 2.191 103.3 26.6 13.1 2022 05 11 19 39.57 -38 54.6 1.672 2.329 118.5 22.4 13.3 2022 05 21 19 03.00 -39 08.4 1.647 2.464 134.5 17.0 13.5 2022 05 31 18 23.17 -38 28.1 1.666 2.597 150.7 11.0 13.8 2022 06 10 17 44.60 -36 50.4 1.737 2.728 164.4 5.7 14.1 2022 06 20 17 11.31 -34 32.8 1.861 2.857 165.7 5.1 14.4 2022 06 30 16 45.09 -32 02.1 2.034 2.983 154.3 8.5 14.8 2022 07 10 16 25.91 -29 39.4 2.248 3.108 141.4 11.8 15.2 2022 07 20 16 12.73 -27 36.1 2.493 3.230 129.0 14.1 15.6 2022 07 30 16 04.33 -25 55.2 2.760 3.351 117.5 15.6 16.0 2022 08 09 15 59.66 -24 35.7 3.041 3.470 106.7 16.3 16.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 December 2 (CBET 5077) Daniel W. E. Green