| Parameter |
Value |
| Designation |
C/2021 A4 (NEOWISE) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-03-20T00:53:23.712000Z |
| Orbit solution date (soln_date, UTC) |
2022-03-08T19:43:19Z |
| Obs used |
683 |
| NEO |
- |
| M1 |
13.600 |
| K1 |
28.500 |
| PC |
0.030 |
| Discovery observation (MPC, UTC) |
2021-01-03T22:02:49.632000Z |
| Discovery magnitude (MPC) |
20.00 R |
| Discovery observatory (MPC) |
C51 · WISE |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-02-16.0000000 |
| e |
0.97324748 |
| q (au) |
1.145476 |
| a (au) |
42.817518 |
| i (deg) |
111.569834 |
| Ω (om, deg) |
307.084762 |
| ω (w, deg) |
204.665566 |
| M (ma, deg) |
359.887300 |
Magnitude
Scatter + Global Linear
$$
M_a = (14.236 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
14.236 |
| n |
6.000 |
| 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
Residuals (Piecewise)
$$\epsilon = a \log_{10} r_{\mathrm{au}} + b$$
| Start (UTC) |
End (UTC) |
a |
b |
| 2021-01-03 |
2021-03-19 |
+14.1648 |
-1.643 |
| 2021-03-21 |
2021-07-07 |
-3.2765 |
-1.725 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-06-01 00:00 |
21:03:19.54 |
-21:12:04.1 |
HIP 103808 |
18.49 |
| 2026-06-01 12:00 |
21:03:15.18 |
-21:12:18.6 |
HIP 103808 |
17.47 |
| 2026-06-02 00:00 |
21:03:10.76 |
-21:12:33.3 |
HIP 103808 |
16.43 |
| 2026-06-02 12:00 |
21:03:06.26 |
-21:12:48.3 |
HIP 103808 |
15.39 |
| 2026-06-03 00:00 |
21:03:01.71 |
-21:13:03.4 |
HIP 103808 |
14.33 |
| 2026-06-03 12:00 |
21:02:57.09 |
-21:13:18.8 |
HIP 103808 |
13.27 |
| 2026-06-04 00:00 |
21:02:52.41 |
-21:13:34.4 |
HIP 103808 |
12.20 |
| 2026-06-04 12:00 |
21:02:47.66 |
-21:13:50.2 |
HIP 103808 |
11.12 |
| 2026-06-05 00:00 |
21:02:42.85 |
-21:14:06.3 |
HIP 103808 |
10.05 |
| 2026-06-05 12:00 |
21:02:37.97 |
-21:14:22.5 |
HIP 103808 |
8.97 |
| 2026-06-06 00:00 |
21:02:33.04 |
-21:14:39.0 |
HIP 103808 |
7.92 |
| 2026-06-06 12:00 |
21:02:28.04 |
-21:14:55.6 |
HIP 103808 |
6.89 |
| 2026-06-07 00:00 |
21:02:22.98 |
-21:15:12.5 |
HIP 103808 |
5.91 |
| 2026-06-07 12:00 |
21:02:17.85 |
-21:15:29.5 |
HIP 103808 |
5.03 |
| 2026-06-08 00:00 |
21:02:12.67 |
-21:15:46.8 |
HIP 103808 |
4.31 |
| 2026-06-08 12:00 |
21:02:07.42 |
-21:16:04.2 |
HIP 103808 |
3.86 |
| 2026-06-09 00:00 |
21:02:02.11 |
-21:16:21.9 |
HIP 103808 |
3.80 |
| 2026-06-09 12:00 |
21:01:56.74 |
-21:16:39.7 |
HIP 103808 |
4.15 |
| 2026-06-10 00:00 |
21:01:51.31 |
-21:16:57.7 |
HIP 103808 |
4.84 |
| 2026-06-10 12:00 |
21:01:45.82 |
-21:17:16.0 |
HIP 103808 |
5.76 |
| 2026-06-11 00:00 |
21:01:40.27 |
-21:17:34.4 |
HIP 103808 |
6.82 |
| 2026-06-11 12:00 |
21:01:34.66 |
-21:17:53.0 |
HIP 103808 |
7.97 |
| 2026-06-12 00:00 |
21:01:28.98 |
-21:18:11.7 |
HIP 103808 |
9.19 |
| 2026-06-12 12:00 |
21:01:23.25 |
-21:18:30.7 |
HIP 103808 |
10.45 |
| 2026-06-13 00:00 |
21:01:17.47 |
-21:18:49.8 |
HIP 103808 |
11.76 |
| 2026-06-13 12:00 |
21:01:11.62 |
-21:19:09.1 |
HIP 103808 |
13.09 |
| 2026-06-14 00:00 |
21:01:05.71 |
-21:19:28.6 |
HIP 103808 |
14.45 |
| 2026-06-14 12:00 |
21:00:59.75 |
-21:19:48.3 |
HIP 103808 |
15.83 |
| 2026-06-15 00:00 |
21:00:53.73 |
-21:20:08.1 |
HIP 103808 |
17.23 |
| 2026-06-15 12:00 |
21:00:47.65 |
-21:20:28.1 |
HIP 103808 |
18.65 |
| 2026-06-16 00:00 |
21:00:41.52 |
-21:20:48.2 |
HIP 103808 |
20.09 |
| 2026-06-16 12:00 |
21:00:35.33 |
-21:21:08.5 |
HIP 103808 |
21.55 |
| 2026-06-17 00:00 |
21:00:29.08 |
-21:21:29.0 |
HIP 103808 |
23.02 |
| 2026-06-17 12:00 |
21:00:22.78 |
-21:21:49.6 |
HIP 103808 |
24.51 |
| 2026-06-18 00:00 |
21:00:16.43 |
-21:22:10.4 |
HIP 103808 |
26.01 |
| 2026-06-18 12:00 |
21:00:10.02 |
-21:22:31.3 |
HIP 103507 |
27.16 |
| 2026-06-19 00:00 |
21:00:03.56 |
-21:22:52.4 |
HIP 103507 |
25.69 |
| 2026-06-19 12:00 |
20:59:57.04 |
-21:23:13.6 |
HIP 103507 |
24.23 |
| 2026-06-20 00:00 |
20:59:50.47 |
-21:23:34.9 |
HIP 103507 |
22.76 |
| 2026-06-20 12:00 |
20:59:43.85 |
-21:23:56.4 |
HIP 103507 |
21.30 |
| 2026-06-21 00:00 |
20:59:37.18 |
-21:24:18.0 |
HIP 103507 |
19.85 |
| 2026-06-21 12:00 |
20:59:30.45 |
-21:24:39.7 |
HIP 103507 |
18.41 |
| 2026-06-22 00:00 |
20:59:23.68 |
-21:25:01.6 |
HIP 103507 |
16.98 |