| Parameter |
Value |
| Designation |
C/2021 A7 (NEOWISE) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-07-15T07:52:29.438400Z |
| Orbit solution date (soln_date, UTC) |
2022-06-28T01:12:46Z |
| Obs used |
295 |
| NEO |
- |
| M1 |
11.600 |
| K1 |
9.500 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-01-09T02:37:24.384000Z |
| Discovery magnitude (MPC) |
20.00 R |
| Discovery observatory (MPC) |
C51 · WISE |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-04-15.0000000 |
| e |
0.99972271 |
| q (au) |
1.967689 |
| a (au) |
7096.234707 |
| i (deg) |
78.149198 |
| Ω (om, deg) |
154.518746 |
| ω (w, deg) |
356.065440 |
| M (ma, deg) |
359.999849 |
Magnitude
Scatter + Global Linear
$$
M_a = (11.691 + 4.023\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
11.691 |
| n |
4.023 |
| gf |
1.000 |
| gb |
-0.500 |
| k |
0.800 |
| δ90 |
9.995 |
| 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 |
| 2021-01-09 |
2021-07-08 |
-0.1334 |
-0.114 |
| 2021-11-10 |
2022-06-25 |
-4.5627 |
+3.915 |
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 |
20:51:00.04 |
+31:26:07.8 |
HIP 102863 |
9.21 |
| 2026-06-01 12:00 |
20:50:56.07 |
+31:27:02.3 |
HIP 102863 |
9.07 |
| 2026-06-02 00:00 |
20:50:52.03 |
+31:27:56.3 |
HIP 102863 |
9.08 |
| 2026-06-02 12:00 |
20:50:47.93 |
+31:28:49.7 |
HIP 102863 |
9.24 |
| 2026-06-03 00:00 |
20:50:43.75 |
+31:29:42.6 |
HIP 102863 |
9.54 |
| 2026-06-03 12:00 |
20:50:39.50 |
+31:30:34.9 |
HIP 102863 |
9.99 |
| 2026-06-04 00:00 |
20:50:35.19 |
+31:31:26.7 |
HIP 102863 |
10.55 |
| 2026-06-04 12:00 |
20:50:30.81 |
+31:32:17.8 |
HIP 102863 |
11.22 |
| 2026-06-05 00:00 |
20:50:26.36 |
+31:33:08.4 |
HIP 102863 |
11.97 |
| 2026-06-05 12:00 |
20:50:21.84 |
+31:33:58.5 |
HIP 102863 |
12.79 |
| 2026-06-06 00:00 |
20:50:17.25 |
+31:34:47.9 |
HIP 102863 |
13.68 |
| 2026-06-06 12:00 |
20:50:12.59 |
+31:35:36.8 |
HIP 102863 |
14.61 |
| 2026-06-07 00:00 |
20:50:07.87 |
+31:36:25.1 |
HIP 102863 |
15.59 |
| 2026-06-07 12:00 |
20:50:03.08 |
+31:37:12.7 |
HIP 102863 |
16.61 |
| 2026-06-08 00:00 |
20:49:58.23 |
+31:37:59.8 |
HIP 102863 |
17.66 |
| 2026-06-08 12:00 |
20:49:53.31 |
+31:38:46.2 |
HIP 102732 |
16.50 |
| 2026-06-09 00:00 |
20:49:48.32 |
+31:39:32.1 |
HIP 102732 |
15.22 |
| 2026-06-09 12:00 |
20:49:43.27 |
+31:40:17.3 |
HIP 102732 |
13.95 |
| 2026-06-10 00:00 |
20:49:38.15 |
+31:41:01.9 |
HIP 102732 |
12.68 |
| 2026-06-10 12:00 |
20:49:32.97 |
+31:41:45.8 |
HIP 102732 |
11.43 |
| 2026-06-11 00:00 |
20:49:27.72 |
+31:42:29.1 |
HIP 102732 |
10.19 |
| 2026-06-11 12:00 |
20:49:22.41 |
+31:43:11.8 |
HIP 102732 |
8.99 |
| 2026-06-12 00:00 |
20:49:17.03 |
+31:43:53.8 |
HIP 102732 |
7.83 |
| 2026-06-12 12:00 |
20:49:11.59 |
+31:44:35.2 |
HIP 102732 |
6.74 |
| 2026-06-13 00:00 |
20:49:06.09 |
+31:45:15.9 |
HIP 102732 |
5.77 |
| 2026-06-13 12:00 |
20:49:00.53 |
+31:45:55.9 |
HIP 102732 |
5.00 |
| 2026-06-14 00:00 |
20:48:54.91 |
+31:46:35.2 |
HIP 102732 |
4.52 |
| 2026-06-14 12:00 |
20:48:49.22 |
+31:47:13.9 |
HIP 102732 |
4.45 |
| 2026-06-15 00:00 |
20:48:43.47 |
+31:47:51.9 |
HIP 102732 |
4.80 |
| 2026-06-15 12:00 |
20:48:37.67 |
+31:48:29.2 |
HIP 102732 |
5.50 |
| 2026-06-16 00:00 |
20:48:31.80 |
+31:49:05.8 |
HIP 102732 |
6.44 |
| 2026-06-16 12:00 |
20:48:25.87 |
+31:49:41.7 |
HIP 102732 |
7.53 |
| 2026-06-17 00:00 |
20:48:19.89 |
+31:50:16.9 |
HIP 102732 |
8.72 |
| 2026-06-17 12:00 |
20:48:13.85 |
+31:50:51.4 |
HIP 102623 |
7.49 |
| 2026-06-18 00:00 |
20:48:07.75 |
+31:51:25.2 |
HIP 102623 |
6.10 |
| 2026-06-18 12:00 |
20:48:01.59 |
+31:51:58.3 |
HIP 102623 |
4.71 |
| 2026-06-19 00:00 |
20:47:55.38 |
+31:52:30.6 |
HIP 102623 |
3.35 |
| 2026-06-19 12:00 |
20:47:49.11 |
+31:53:02.3 |
HIP 102623 |
2.07 |
| 2026-06-20 00:00 |
20:47:42.78 |
+31:53:33.2 |
HIP 102623 |
1.23 |
| 2026-06-20 12:00 |
20:47:36.40 |
+31:54:03.3 |
HIP 102623 |
1.71 |
| 2026-06-21 00:00 |
20:47:29.97 |
+31:54:32.8 |
HIP 102623 |
2.93 |
| 2026-06-21 12:00 |
20:47:23.48 |
+31:55:01.4 |
HIP 102623 |
4.31 |
| 2026-06-22 00:00 |
20:47:16.94 |
+31:55:29.4 |
HIP 102623 |
5.73 |