| 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) |
| 2026-05-12 00:00 |
20:59:44.37 |
+37:39:43.8 |
HIP 103706 |
13.67 |
| 2026-05-12 12:00 |
20:59:42.83 |
+37:40:58.7 |
HIP 103706 |
14.07 |
| 2026-05-13 00:00 |
20:59:41.20 |
+37:42:13.3 |
HIP 103706 |
14.60 |
| 2026-05-13 12:00 |
20:59:39.50 |
+37:43:27.7 |
HIP 103580 |
13.33 |
| 2026-05-14 00:00 |
20:59:37.73 |
+37:44:41.8 |
HIP 103580 |
12.05 |
| 2026-05-14 12:00 |
20:59:35.87 |
+37:45:55.6 |
HIP 103580 |
10.78 |
| 2026-05-15 00:00 |
20:59:33.94 |
+37:47:09.1 |
HIP 103580 |
9.50 |
| 2026-05-15 12:00 |
20:59:31.93 |
+37:48:22.4 |
HIP 103580 |
8.23 |
| 2026-05-16 00:00 |
20:59:29.84 |
+37:49:35.4 |
HIP 103580 |
6.95 |
| 2026-05-16 12:00 |
20:59:27.68 |
+37:50:48.1 |
HIP 103580 |
5.68 |
| 2026-05-17 00:00 |
20:59:25.44 |
+37:52:00.4 |
HIP 103580 |
4.41 |
| 2026-05-17 12:00 |
20:59:23.12 |
+37:53:12.5 |
HIP 103580 |
3.15 |
| 2026-05-18 00:00 |
20:59:20.72 |
+37:54:24.2 |
HIP 103580 |
1.92 |
| 2026-05-18 12:00 |
20:59:18.25 |
+37:55:35.7 |
HIP 103580 |
0.85 |
| 2026-05-19 00:00 |
20:59:15.70 |
+37:56:46.7 |
HIP 103580 |
1.02 |
| 2026-05-19 12:00 |
20:59:13.08 |
+37:57:57.5 |
HIP 103580 |
2.16 |
| 2026-05-20 00:00 |
20:59:10.37 |
+37:59:07.9 |
HIP 103580 |
3.40 |
| 2026-05-20 12:00 |
20:59:07.60 |
+38:00:17.9 |
HIP 103580 |
4.67 |
| 2026-05-21 00:00 |
20:59:04.74 |
+38:01:27.6 |
HIP 103580 |
5.95 |
| 2026-05-21 12:00 |
20:59:01.81 |
+38:02:37.0 |
HIP 103580 |
7.23 |
| 2026-05-22 00:00 |
20:58:58.80 |
+38:03:45.9 |
HIP 103540 |
6.50 |
| 2026-05-22 12:00 |
20:58:55.72 |
+38:04:54.5 |
HIP 103540 |
5.22 |
| 2026-05-23 00:00 |
20:58:52.57 |
+38:06:02.7 |
HIP 103540 |
3.96 |
| 2026-05-23 12:00 |
20:58:49.33 |
+38:07:10.5 |
HIP 103540 |
2.70 |
| 2026-05-24 00:00 |
20:58:46.03 |
+38:08:17.9 |
HIP 103540 |
1.52 |
| 2026-05-24 12:00 |
20:58:42.64 |
+38:09:24.9 |
HIP 103540 |
0.81 |
| 2026-05-25 00:00 |
20:58:39.19 |
+38:10:31.5 |
HIP 103540 |
1.54 |
| 2026-05-25 12:00 |
20:58:35.66 |
+38:11:37.7 |
HIP 103540 |
2.73 |
| 2026-05-26 00:00 |
20:58:32.05 |
+38:12:43.5 |
HIP 103540 |
3.99 |
| 2026-05-26 12:00 |
20:58:28.37 |
+38:13:48.9 |
HIP 103540 |
5.27 |
| 2026-05-27 00:00 |
20:58:24.62 |
+38:14:53.8 |
HIP 103540 |
6.56 |
| 2026-05-27 12:00 |
20:58:20.79 |
+38:15:58.3 |
HIP 103540 |
7.86 |
| 2026-05-28 00:00 |
20:58:16.89 |
+38:17:02.4 |
HIP 103540 |
9.16 |
| 2026-05-28 12:00 |
20:58:12.92 |
+38:18:06.0 |
HIP 103540 |
10.46 |
| 2026-05-29 00:00 |
20:58:08.87 |
+38:19:09.1 |
HIP 103540 |
11.77 |
| 2026-05-29 12:00 |
20:58:04.76 |
+38:20:11.8 |
HIP 103540 |
13.08 |
| 2026-05-30 00:00 |
20:58:00.57 |
+38:21:14.1 |
HIP 103540 |
14.40 |
| 2026-05-30 12:00 |
20:57:56.30 |
+38:22:15.8 |
HIP 103540 |
15.71 |
| 2026-05-31 00:00 |
20:57:51.97 |
+38:23:17.1 |
HIP 103540 |
17.03 |
| 2026-05-31 12:00 |
20:57:47.56 |
+38:24:18.0 |
HIP 103540 |
18.35 |
| 2026-06-01 00:00 |
20:57:43.08 |
+38:25:18.3 |
HIP 103540 |
19.68 |
| 2026-06-01 12:00 |
20:57:38.53 |
+38:26:18.1 |
HIP 103540 |
21.00 |
| 2026-06-02 00:00 |
20:57:33.91 |
+38:27:17.5 |
HIP 103540 |
22.33 |