| 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) |
| 2026-03-26 00:00 |
20:56:40.07 |
+35:38:40.4 |
HIP 103387 |
7.90 |
| 2026-03-26 12:00 |
20:56:45.16 |
+35:39:51.3 |
HIP 103387 |
6.62 |
| 2026-03-27 00:00 |
20:56:50.20 |
+35:41:02.5 |
HIP 103387 |
5.49 |
| 2026-03-27 12:00 |
20:56:55.18 |
+35:42:14.0 |
HIP 103387 |
4.62 |
| 2026-03-28 00:00 |
20:57:00.11 |
+35:43:25.9 |
HIP 103387 |
4.15 |
| 2026-03-28 12:00 |
20:57:04.97 |
+35:44:38.0 |
HIP 103387 |
4.23 |
| 2026-03-29 00:00 |
20:57:09.77 |
+35:45:50.3 |
HIP 103387 |
4.83 |
| 2026-03-29 12:00 |
20:57:14.51 |
+35:47:03.0 |
HIP 103387 |
5.78 |
| 2026-03-30 00:00 |
20:57:19.19 |
+35:48:16.0 |
HIP 103387 |
6.93 |
| 2026-03-30 12:00 |
20:57:23.81 |
+35:49:29.2 |
HIP 103387 |
8.20 |
| 2026-03-31 00:00 |
20:57:28.37 |
+35:50:42.7 |
HIP 103387 |
9.55 |
| 2026-03-31 12:00 |
20:57:32.86 |
+35:51:56.4 |
HIP 103387 |
10.93 |
| 2026-04-01 00:00 |
20:57:37.30 |
+35:53:10.4 |
HIP 103387 |
12.34 |
| 2026-04-01 12:00 |
20:57:41.67 |
+35:54:24.6 |
HIP 103387 |
13.77 |
| 2026-04-02 00:00 |
20:57:45.98 |
+35:55:39.1 |
HIP 103387 |
15.20 |
| 2026-04-02 12:00 |
20:57:50.22 |
+35:56:53.9 |
HIP 103387 |
16.65 |
| 2026-04-03 00:00 |
20:57:54.41 |
+35:58:08.8 |
HIP 103387 |
18.09 |
| 2026-04-03 12:00 |
20:57:58.53 |
+35:59:24.0 |
HIP 103387 |
19.54 |
| 2026-04-04 00:00 |
20:58:02.58 |
+36:00:39.5 |
HIP 103387 |
20.99 |
| 2026-04-04 12:00 |
20:58:06.57 |
+36:01:55.1 |
HIP 103387 |
22.44 |
| 2026-04-05 00:00 |
20:58:10.50 |
+36:03:11.0 |
HIP 103387 |
23.89 |
| 2026-04-05 12:00 |
20:58:14.37 |
+36:04:27.0 |
HIP 103387 |
25.34 |
| 2026-04-06 00:00 |
20:58:18.16 |
+36:05:43.3 |
HIP 103594 |
23.91 |
| 2026-04-06 12:00 |
20:58:21.90 |
+36:06:59.8 |
HIP 103594 |
22.43 |
| 2026-04-07 00:00 |
20:58:25.56 |
+36:08:16.5 |
HIP 103594 |
20.96 |
| 2026-04-07 12:00 |
20:58:29.16 |
+36:09:33.3 |
HIP 103594 |
19.49 |
| 2026-04-08 00:00 |
20:58:32.70 |
+36:10:50.3 |
HIP 103594 |
18.03 |
| 2026-04-08 12:00 |
20:58:36.17 |
+36:12:07.6 |
HIP 103594 |
16.57 |
| 2026-04-09 00:00 |
20:58:39.57 |
+36:13:24.9 |
HIP 103594 |
15.12 |
| 2026-04-09 12:00 |
20:58:42.90 |
+36:14:42.5 |
HIP 103594 |
13.68 |
| 2026-04-10 00:00 |
20:58:46.17 |
+36:16:00.2 |
HIP 103594 |
12.25 |
| 2026-04-10 12:00 |
20:58:49.37 |
+36:17:18.1 |
HIP 103594 |
10.83 |
| 2026-04-11 00:00 |
20:58:52.50 |
+36:18:36.1 |
HIP 103594 |
9.43 |
| 2026-04-11 12:00 |
20:58:55.56 |
+36:19:54.3 |
HIP 103594 |
8.05 |
| 2026-04-12 00:00 |
20:58:58.55 |
+36:21:12.5 |
HIP 103594 |
6.70 |
| 2026-04-12 12:00 |
20:59:01.48 |
+36:22:31.0 |
HIP 103594 |
5.42 |
| 2026-04-13 00:00 |
20:59:04.33 |
+36:23:49.5 |
HIP 103594 |
4.24 |
| 2026-04-13 12:00 |
20:59:07.12 |
+36:25:08.2 |
HIP 103594 |
3.28 |
| 2026-04-14 00:00 |
20:59:09.83 |
+36:26:27.0 |
HIP 103594 |
2.77 |
| 2026-04-14 12:00 |
20:59:12.48 |
+36:27:45.9 |
HIP 103594 |
2.96 |
| 2026-04-15 00:00 |
20:59:15.05 |
+36:29:04.9 |
HIP 103594 |
3.73 |
| 2026-04-15 12:00 |
20:59:17.56 |
+36:30:24.0 |
HIP 103594 |
4.80 |
| 2026-04-16 00:00 |
20:59:19.99 |
+36:31:43.1 |
HIP 103594 |
6.02 |