Electronic Telegram No. 5008 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 O1 (NISHIMURA) Further to CBET 5004, the following additional astrometric observations have been reported to the Central Bureau: 2021 UT R.A. (2000) Decl. Mag. Observer July 25.79789 6 57 02.65 +31 13 50.0 10.5 Yoshimoto 25.80154 6 57 04.08 +31 13 51.6 " 25.80559 6 57 05.67 +31 13 53.3 " 26.06836 6 58 47.71 +31 15 33.4 12.8 Jaeger 26.07063 6 58 48.60 +31 15 33.3 12.9 " 26.07288 6 58 49.44 +31 15 35.5 12.7 " 26.07833 6 58 51.65 +31 15 37.0 12.3 " 26.08141 6 58 52.92 +31 15 37.3 12.3 " 27.76235 7 09 52.12 +31 24 17.8 Kadota 27.76542 7 09 53.33 +31 24 18.5 " 27.76870 7 09 54.61 +31 24 19.2 9.7 " 30.07253 7 25 10.95 +31 30 05.5 11.9 Jaeger 30.07553 7 25 12.24 +31 30 03.5 12.3 " 30.07807 7 25 13.25 +31 30 04.3 12.2 " K. Yoshimoto (Kumage, Yamaguchi, Japan). 0.20-m f/8.0 Ritchey-Chretien reflector + CCD. Condensed coma 1'.8 in diameter and straight tail 4'.5 long in p.a. 290 deg. M. Jaeger, E. Prosperi, and S. Prosperi (Stixendorf, Austria). 0.3-m f/4 reflector + CCD (July 26) and 0.2-m f/2.0 reflector + CCD (July 30). K. Kadota (Ageo, Japan). 0.25-m f/5 reflector + CCD. Revised parabolic orbital elements by S. Nakano (CBAT) from 65 observations spanning 2021 July 22-30: T = 2021 Aug. 13.92185 TT Peri. = 74.44011 Node = 41.60330 2000.0 q = 0.7870368 AU Incl. = 27.57029 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 8.5 and 2.5n = 8 for the magnitudes. The comet will remain within 20 degrees of the sun from early August until early December as it slowly fades in brightness (to total mag perhaps 13-14 in December). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 05 06 01 55.54 +03 41.6 2.820 1.893 18.8 9.9 13.0 2021 05 11 02 05.90 +05 14.8 2.739 1.826 20.3 11.1 12.8 2021 05 16 02 16.82 +06 51.4 2.656 1.757 21.7 12.3 12.6 2021 05 21 02 28.36 +08 31.4 2.573 1.689 23.1 13.6 12.4 2021 05 26 02 40.60 +10 15.0 2.490 1.621 24.2 14.9 12.2 2021 05 31 02 53.65 +12 02.3 2.407 1.552 25.3 16.2 11.9 2021 06 05 03 07.61 +13 53.3 2.325 1.484 26.1 17.5 11.7 2021 06 10 03 22.62 +15 47.7 2.245 1.415 26.8 18.9 11.5 2021 06 15 03 38.83 +17 45.1 2.167 1.347 27.3 20.2 11.2 2021 06 20 03 56.39 +19 44.5 2.092 1.280 27.5 21.5 11.0 2021 06 25 04 15.51 +21 44.6 2.021 1.214 27.5 22.8 10.7 2021 06 30 04 36.39 +23 43.6 1.955 1.149 27.3 23.9 10.4 2021 07 05 04 59.21 +25 38.5 1.894 1.087 26.8 24.9 10.2 2021 07 10 05 24.15 +27 25.6 1.840 1.027 26.0 25.7 9.9 2021 07 15 05 51.30 +29 00.1 1.793 0.971 25.0 26.2 9.7 2021 07 20 06 20.61 +30 16.3 1.755 0.920 23.7 26.4 9.4 2021 07 25 06 51.89 +31 08.2 1.726 0.875 22.3 26.1 9.2 2021 07 30 07 24.69 +31 30.1 1.706 0.838 20.7 25.4 9.0 2021 08 04 07 58.36 +31 17.5 1.697 0.810 19.1 24.3 8.9 2021 08 09 08 32.10 +30 28.6 1.698 0.793 17.6 22.7 8.8 2021 08 14 09 05.06 +29 04.5 1.709 0.787 16.1 20.9 8.8 2021 08 19 09 36.57 +27 09.2 1.728 0.793 14.8 19.0 8.9 2021 08 24 10 06.12 +24 49.0 1.757 0.811 13.7 17.1 9.0 2021 08 29 10 33.51 +22 11.0 1.794 0.839 12.8 15.4 9.2 2021 09 03 10 58.69 +19 22.3 1.838 0.876 12.0 13.9 9.4 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 July 31 (CBET 5008) Daniel W. E. Green