| Parameter |
Value |
| Designation |
C/2021 A2 (NEOWISE) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-01-22T15:13:06.119040Z |
| Orbit solution date (soln_date, UTC) |
2025-01-02T20:12:26Z |
| Obs used |
980 |
| NEO |
- |
| M1 |
15.000 |
| K1 |
4.500 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-01-03T00:31:00.192000Z |
| Discovery magnitude (MPC) |
15.00 R |
| Discovery observatory (MPC) |
C51 · WISE |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-02-20.0000000 |
| e |
0.99451672 |
| q (au) |
1.412974 |
| a (au) |
257.687917 |
| i (deg) |
106.978275 |
| Ω (om, deg) |
125.238283 |
| ω (w, deg) |
338.849015 |
| M (ma, deg) |
0.006759 |
Magnitude
Scatter + Global Linear
$$
M_a = (14.158 + 2.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
14.158 |
| n |
2.000 |
| gf |
1.000 |
| gb |
-1.000 |
| k |
0.991 |
| 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
Residuals (Piecewise)
$$\epsilon = a \log_{10} r_{\mathrm{au}} + b$$
| Start (UTC) |
End (UTC) |
a |
b |
| 2021-01-23 |
2021-05-09 |
+4.2062 |
-1.270 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
20:28:48.53 |
+37:10:47.1 |
HIP 101147 |
16.04 |
| 2026-09-20 12:00 |
20:28:43.21 |
+37:09:12.0 |
HIP 101118 |
16.54 |
| 2026-09-21 00:00 |
20:28:37.97 |
+37:07:36.6 |
HIP 101118 |
16.47 |
| 2026-09-21 12:00 |
20:28:32.79 |
+37:06:00.9 |
HIP 101118 |
16.60 |
| 2026-09-22 00:00 |
20:28:27.69 |
+37:04:24.8 |
HIP 101118 |
16.93 |
| 2026-09-22 12:00 |
20:28:22.65 |
+37:02:48.4 |
HIP 101118 |
17.45 |
| 2026-09-23 00:00 |
20:28:17.69 |
+37:01:11.8 |
HIP 101118 |
18.14 |
| 2026-09-23 12:00 |
20:28:12.79 |
+36:59:34.8 |
HIP 101118 |
18.98 |
| 2026-09-24 00:00 |
20:28:07.96 |
+36:57:57.6 |
HIP 101118 |
19.95 |
| 2026-09-24 12:00 |
20:28:03.21 |
+36:56:20.1 |
HIP 101118 |
21.04 |
| 2026-09-25 00:00 |
20:27:58.52 |
+36:54:42.3 |
HIP 101118 |
22.21 |
| 2026-09-25 12:00 |
20:27:53.91 |
+36:53:04.3 |
HIP 100826 |
23.37 |
| 2026-09-26 00:00 |
20:27:49.37 |
+36:51:26.0 |
HIP 100826 |
21.54 |
| 2026-09-26 12:00 |
20:27:44.89 |
+36:49:47.5 |
HIP 100826 |
19.72 |
| 2026-09-27 00:00 |
20:27:40.50 |
+36:48:08.7 |
HIP 100826 |
17.92 |
| 2026-09-27 12:00 |
20:27:36.17 |
+36:46:29.8 |
HIP 100826 |
16.14 |
| 2026-09-28 00:00 |
20:27:31.91 |
+36:44:50.5 |
HIP 100826 |
14.39 |
| 2026-09-28 12:00 |
20:27:27.73 |
+36:43:11.1 |
HIP 100826 |
12.68 |
| 2026-09-29 00:00 |
20:27:23.62 |
+36:41:31.5 |
HIP 100826 |
11.03 |
| 2026-09-29 12:00 |
20:27:19.58 |
+36:39:51.6 |
HIP 100826 |
9.47 |
| 2026-09-30 00:00 |
20:27:15.62 |
+36:38:11.6 |
HIP 100826 |
8.03 |
| 2026-09-30 12:00 |
20:27:11.73 |
+36:36:31.4 |
HIP 100826 |
6.82 |
| 2026-10-01 00:00 |
20:27:07.91 |
+36:34:51.0 |
HIP 100826 |
5.96 |
| 2026-10-01 12:00 |
20:27:04.16 |
+36:33:10.4 |
HIP 100826 |
5.60 |
| 2026-10-02 00:00 |
20:27:00.49 |
+36:31:29.7 |
HIP 100826 |
5.84 |
| 2026-10-02 12:00 |
20:26:56.90 |
+36:29:48.8 |
HIP 100826 |
6.61 |
| 2026-10-03 00:00 |
20:26:53.38 |
+36:28:07.7 |
HIP 100826 |
7.76 |
| 2026-10-03 12:00 |
20:26:49.93 |
+36:26:26.5 |
HIP 100826 |
9.13 |
| 2026-10-04 00:00 |
20:26:46.55 |
+36:24:45.2 |
HIP 100826 |
10.65 |
| 2026-10-04 12:00 |
20:26:43.26 |
+36:23:03.7 |
HIP 100826 |
12.25 |
| 2026-10-05 00:00 |
20:26:40.03 |
+36:21:22.1 |
HIP 100826 |
13.91 |
| 2026-10-05 12:00 |
20:26:36.89 |
+36:19:40.4 |
HIP 100826 |
15.60 |
| 2026-10-06 00:00 |
20:26:33.81 |
+36:17:58.7 |
HIP 100826 |
17.32 |
| 2026-10-06 12:00 |
20:26:30.82 |
+36:16:16.8 |
HIP 100826 |
19.05 |
| 2026-10-07 00:00 |
20:26:27.89 |
+36:14:34.8 |
HIP 100826 |
20.80 |
| 2026-10-07 12:00 |
20:26:25.05 |
+36:12:52.7 |
HIP 100826 |
22.55 |
| 2026-10-08 00:00 |
20:26:22.28 |
+36:11:10.6 |
HIP 100777 |
22.91 |
| 2026-10-08 12:00 |
20:26:19.59 |
+36:09:28.4 |
HIP 100777 |
21.14 |
| 2026-10-09 00:00 |
20:26:16.97 |
+36:07:46.1 |
HIP 100777 |
19.37 |
| 2026-10-09 12:00 |
20:26:14.43 |
+36:06:03.8 |
HIP 100777 |
17.60 |
| 2026-10-10 00:00 |
20:26:11.96 |
+36:04:21.4 |
HIP 100777 |
15.84 |
| 2026-10-10 12:00 |
20:26:09.58 |
+36:02:39.1 |
HIP 100777 |
14.08 |
| 2026-10-11 00:00 |
20:26:07.26 |
+36:00:56.6 |
HIP 100777 |
12.34 |