| 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 |
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 |
| 2021-01-09 |
2021-07-08 |
-0.1334 |
-0.114 |
| 2021-11-10 |
2022-06-25 |
-4.5628 |
+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) |
| 2026-05-12 00:00 |
20:52:38.51 |
+30:43:28.9 |
HIP 103015 |
7.77 |
| 2026-05-12 12:00 |
20:52:37.53 |
+30:44:40.4 |
HIP 103015 |
8.59 |
| 2026-05-13 00:00 |
20:52:36.47 |
+30:45:51.5 |
HIP 103015 |
9.48 |
| 2026-05-13 12:00 |
20:52:35.34 |
+30:47:02.3 |
HIP 103015 |
10.42 |
| 2026-05-14 00:00 |
20:52:34.12 |
+30:48:12.8 |
HIP 103015 |
11.40 |
| 2026-05-14 12:00 |
20:52:32.84 |
+30:49:23.0 |
HIP 103015 |
12.41 |
| 2026-05-15 00:00 |
20:52:31.47 |
+30:50:32.8 |
HIP 103015 |
13.44 |
| 2026-05-15 12:00 |
20:52:30.02 |
+30:51:42.3 |
HIP 103115 |
14.48 |
| 2026-05-16 00:00 |
20:52:28.50 |
+30:52:51.5 |
HIP 103115 |
14.40 |
| 2026-05-16 12:00 |
20:52:26.90 |
+30:54:00.4 |
HIP 103115 |
14.44 |
| 2026-05-17 00:00 |
20:52:25.23 |
+30:55:08.8 |
HIP 103115 |
14.60 |
| 2026-05-17 12:00 |
20:52:23.48 |
+30:56:17.0 |
HIP 103115 |
14.87 |
| 2026-05-18 00:00 |
20:52:21.65 |
+30:57:24.7 |
HIP 103115 |
15.24 |
| 2026-05-18 12:00 |
20:52:19.74 |
+30:58:32.1 |
HIP 103115 |
15.71 |
| 2026-05-19 00:00 |
20:52:17.76 |
+30:59:39.1 |
HIP 103115 |
16.27 |
| 2026-05-19 12:00 |
20:52:15.70 |
+31:00:45.7 |
HIP 103115 |
16.91 |
| 2026-05-20 00:00 |
20:52:13.56 |
+31:01:51.9 |
HIP 103115 |
17.62 |
| 2026-05-20 12:00 |
20:52:11.35 |
+31:02:57.7 |
HIP 103115 |
18.40 |
| 2026-05-21 00:00 |
20:52:09.07 |
+31:04:03.2 |
HIP 103115 |
19.23 |
| 2026-05-21 12:00 |
20:52:06.70 |
+31:05:08.2 |
HIP 103115 |
20.11 |
| 2026-05-22 00:00 |
20:52:04.27 |
+31:06:12.7 |
HIP 103115 |
21.03 |
| 2026-05-22 12:00 |
20:52:01.75 |
+31:07:16.9 |
HIP 103115 |
21.99 |
| 2026-05-23 00:00 |
20:51:59.17 |
+31:08:20.6 |
HIP 102876 |
22.41 |
| 2026-05-23 12:00 |
20:51:56.50 |
+31:09:23.9 |
HIP 102876 |
22.62 |
| 2026-05-24 00:00 |
20:51:53.77 |
+31:10:26.8 |
HIP 102863 |
22.06 |
| 2026-05-24 12:00 |
20:51:50.95 |
+31:11:29.2 |
HIP 102863 |
21.04 |
| 2026-05-25 00:00 |
20:51:48.07 |
+31:12:31.1 |
HIP 102863 |
20.02 |
| 2026-05-25 12:00 |
20:51:45.11 |
+31:13:32.6 |
HIP 102863 |
19.02 |
| 2026-05-26 00:00 |
20:51:42.08 |
+31:14:33.6 |
HIP 102863 |
18.03 |
| 2026-05-26 12:00 |
20:51:38.97 |
+31:15:34.2 |
HIP 102863 |
17.05 |
| 2026-05-27 00:00 |
20:51:35.79 |
+31:16:34.3 |
HIP 102863 |
16.10 |
| 2026-05-27 12:00 |
20:51:32.54 |
+31:17:33.9 |
HIP 102863 |
15.16 |
| 2026-05-28 00:00 |
20:51:29.22 |
+31:18:33.0 |
HIP 102863 |
14.26 |
| 2026-05-28 12:00 |
20:51:25.82 |
+31:19:31.6 |
HIP 102863 |
13.39 |
| 2026-05-29 00:00 |
20:51:22.35 |
+31:20:29.8 |
HIP 102863 |
12.56 |
| 2026-05-29 12:00 |
20:51:18.81 |
+31:21:27.4 |
HIP 102863 |
11.79 |
| 2026-05-30 00:00 |
20:51:15.20 |
+31:22:24.5 |
HIP 102863 |
11.08 |
| 2026-05-30 12:00 |
20:51:11.51 |
+31:23:21.1 |
HIP 102863 |
10.45 |
| 2026-05-31 00:00 |
20:51:07.76 |
+31:24:17.2 |
HIP 102863 |
9.92 |
| 2026-05-31 12:00 |
20:51:03.93 |
+31:25:12.8 |
HIP 102863 |
9.50 |
| 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 |