C/2021 O1 (Nishimura)
| Parameter |
Value |
| Designation |
C/2021 O1 (Nishimura) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-08-13T22:16:11.570880Z |
| Orbit solution date (soln_date, UTC) |
2023-04-24T19:06:44Z |
| Obs used |
59 |
| NEO |
- |
| M1 |
10.800 |
| K1 |
10.000 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-07-21T18:47:36.384000Z |
| Discovery magnitude (MPC) |
10.70 T |
| Discovery observatory (MPC) |
247 · Roving Observer |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-07-26.0000000 |
| e |
1.00305367 |
| q (au) |
0.787409 |
| a (au) |
-257.856271 |
| i (deg) |
27.567888 |
| Ω (om, deg) |
41.631614 |
| ω (w, deg) |
74.438198 |
| M (ma, deg) |
-0.004505 |
Magnitude
Scatter + Global Linear
$$
M_a = (9.855 + 3.673\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
9.855 |
| n |
3.673 |
| gf |
1.000 |
| gb |
-0.500 |
| k |
1.000 |
| δ90 |
10.000 |
| Parameter |
Symbol |
Range |
Description |
| Absolute magnitude at 1 AU from Sun and Earth |
H0 |
-5 to 20 |
Intrinsic brightness of the comet |
| Photometric slope parameter |
n |
2 to 6 |
Rate of brightness change with heliocentric distance |
| Forward scattering asymmetry factor |
gf |
0.8 to 1 |
Degree of forward scattering |
| Backward scattering asymmetry factor |
gb |
-1 to -0.5 |
Degree of backward scattering |
| Partitioning coefficient |
k |
0.8 to 1 |
Ratio between forward/backward scattering contributions |
| Dust-to-gas brightness ratio |
δ90 |
1 to 10 |
Relative contribution of dust scattering to gas emission |
Reference: EPSC-DPS2025-160
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-02-03 00:00 |
17:51:19.95 |
-42:25:15.6 |
HIP 87337 |
6.99 |
| 2026-02-03 12:00 |
17:51:28.08 |
-42:25:48.1 |
HIP 87337 |
8.28 |
| 2026-02-04 00:00 |
17:51:36.14 |
-42:26:20.9 |
HIP 87337 |
9.64 |
| 2026-02-04 12:00 |
17:51:44.15 |
-42:26:53.8 |
HIP 87337 |
11.05 |
| 2026-02-05 00:00 |
17:51:52.09 |
-42:27:26.9 |
HIP 87337 |
12.49 |
| 2026-02-05 12:00 |
17:51:59.97 |
-42:28:00.2 |
HIP 87337 |
13.95 |
| 2026-02-06 00:00 |
17:52:07.79 |
-42:28:33.7 |
HIP 87337 |
15.41 |
| 2026-02-06 12:00 |
17:52:15.54 |
-42:29:07.4 |
HIP 87337 |
16.87 |
| 2026-02-07 00:00 |
17:52:23.23 |
-42:29:41.3 |
HIP 87554 |
17.52 |
| 2026-02-07 12:00 |
17:52:30.85 |
-42:30:15.4 |
HIP 87554 |
17.34 |
| 2026-02-08 00:00 |
17:52:38.41 |
-42:30:49.7 |
HIP 87554 |
17.30 |
| 2026-02-08 12:00 |
17:52:45.90 |
-42:31:24.2 |
HIP 87554 |
17.40 |
| 2026-02-09 00:00 |
17:52:53.32 |
-42:31:58.8 |
HIP 87554 |
17.63 |
| 2026-02-09 12:00 |
17:53:00.68 |
-42:32:33.6 |
HIP 87646 |
16.39 |
| 2026-02-10 00:00 |
17:53:07.97 |
-42:33:08.7 |
HIP 87646 |
14.99 |
| 2026-02-10 12:00 |
17:53:15.19 |
-42:33:43.9 |
HIP 87646 |
13.61 |
| 2026-02-11 00:00 |
17:53:22.34 |
-42:34:19.3 |
HIP 87646 |
12.25 |
| 2026-02-11 12:00 |
17:53:29.43 |
-42:34:54.8 |
HIP 87646 |
10.92 |
| 2026-02-12 00:00 |
17:53:36.44 |
-42:35:30.6 |
HIP 87646 |
9.63 |
| 2026-02-12 12:00 |
17:53:43.38 |
-42:36:06.5 |
HIP 87646 |
8.38 |
| 2026-02-13 00:00 |
17:53:50.25 |
-42:36:42.6 |
HIP 87646 |
7.20 |
| 2026-02-13 12:00 |
17:53:57.05 |
-42:37:18.9 |
HIP 87646 |
6.12 |
| 2026-02-14 00:00 |
17:54:03.78 |
-42:37:55.4 |
HIP 87646 |
5.17 |
| 2026-02-14 12:00 |
17:54:10.44 |
-42:38:32.0 |
HIP 87646 |
4.46 |
| 2026-02-15 00:00 |
17:54:17.02 |
-42:39:08.8 |
HIP 87646 |
4.09 |
| 2026-02-15 12:00 |
17:54:23.53 |
-42:39:45.8 |
HIP 87646 |
4.14 |
| 2026-02-16 00:00 |
17:54:29.96 |
-42:40:22.9 |
HIP 87646 |
4.59 |
| 2026-02-16 12:00 |
17:54:36.32 |
-42:41:00.2 |
HIP 87646 |
5.33 |
| 2026-02-17 00:00 |
17:54:42.61 |
-42:41:37.7 |
HIP 87646 |
6.25 |
| 2026-02-17 12:00 |
17:54:48.82 |
-42:42:15.4 |
HIP 87646 |
7.27 |
| 2026-02-18 00:00 |
17:54:54.96 |
-42:42:53.2 |
HIP 87646 |
8.36 |
| 2026-02-18 12:00 |
17:55:01.01 |
-42:43:31.2 |
HIP 87646 |
9.49 |
| 2026-02-19 00:00 |
17:55:06.99 |
-42:44:09.3 |
HIP 87646 |
10.64 |
| 2026-02-19 12:00 |
17:55:12.90 |
-42:44:47.6 |
HIP 87699 |
11.57 |
| 2026-02-20 00:00 |
17:55:18.72 |
-42:45:26.0 |
HIP 87699 |
11.47 |
| 2026-02-20 12:00 |
17:55:24.47 |
-42:46:04.7 |
HIP 87699 |
11.49 |
| 2026-02-21 00:00 |
17:55:30.14 |
-42:46:43.4 |
HIP 87699 |
11.64 |
| 2026-02-21 12:00 |
17:55:35.73 |
-42:47:22.3 |
HIP 87699 |
11.89 |
| 2026-02-22 00:00 |
17:55:41.24 |
-42:48:01.4 |
HIP 87699 |
12.25 |
| 2026-02-22 12:00 |
17:55:46.67 |
-42:48:40.6 |
HIP 87699 |
12.70 |
| 2026-02-23 00:00 |
17:55:52.03 |
-42:49:19.9 |
HIP 87699 |
13.22 |
| 2026-02-23 12:00 |
17:55:57.30 |
-42:49:59.4 |
HIP 87699 |
13.81 |
| 2026-02-24 00:00 |
17:56:02.49 |
-42:50:39.1 |
HIP 87699 |
14.46 |