| Parameter |
Value |
| Designation |
C/2015 X8 (NEOWISE) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2015-10-23T02:58:51.087360Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:33:20Z |
| Obs used |
116 |
| NEO |
Yes |
| M1 |
16.200 |
| K1 |
4.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2016-01-22.0000000 |
| e |
0.93911400 |
| q (au) |
1.190273 |
| a (au) |
19.549200 |
| i (deg) |
155.281698 |
| Ω (om, deg) |
191.111870 |
| ω (w, deg) |
20.400527 |
| M (ma, deg) |
1.036236 |
Magnitude
Scatter + Global Linear
$$
M_a = (15.395 + 4.524\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
15.395 |
| n |
4.524 |
| gf |
0.999 |
| gb |
-0.984 |
| k |
0.971 |
| 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
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
00:34:54.06 |
+02:17:24.4 |
HIP 2703 |
12.59 |
| 2026-09-20 12:00 |
00:34:48.81 |
+02:16:47.8 |
HIP 2703 |
12.33 |
| 2026-09-21 00:00 |
00:34:43.56 |
+02:16:11.1 |
HIP 2703 |
12.23 |
| 2026-09-21 12:00 |
00:34:38.30 |
+02:15:34.5 |
HIP 2703 |
12.31 |
| 2026-09-22 00:00 |
00:34:33.03 |
+02:14:57.7 |
HIP 2703 |
12.55 |
| 2026-09-22 12:00 |
00:34:27.75 |
+02:14:21.0 |
HIP 2703 |
12.95 |
| 2026-09-23 00:00 |
00:34:22.46 |
+02:13:44.2 |
HIP 2703 |
13.50 |
| 2026-09-23 12:00 |
00:34:17.17 |
+02:13:07.4 |
HIP 2680 |
13.15 |
| 2026-09-24 00:00 |
00:34:11.87 |
+02:12:30.6 |
HIP 2680 |
12.13 |
| 2026-09-24 12:00 |
00:34:06.56 |
+02:11:53.8 |
HIP 2680 |
11.21 |
| 2026-09-25 00:00 |
00:34:01.25 |
+02:11:16.9 |
HIP 2680 |
10.41 |
| 2026-09-25 12:00 |
00:33:55.93 |
+02:10:40.0 |
HIP 2680 |
9.77 |
| 2026-09-26 00:00 |
00:33:50.61 |
+02:10:03.1 |
HIP 2680 |
9.31 |
| 2026-09-26 12:00 |
00:33:45.28 |
+02:09:26.2 |
HIP 2680 |
9.07 |
| 2026-09-27 00:00 |
00:33:39.95 |
+02:08:49.3 |
HIP 2680 |
9.07 |
| 2026-09-27 12:00 |
00:33:34.62 |
+02:08:12.3 |
HIP 2680 |
9.30 |
| 2026-09-28 00:00 |
00:33:29.28 |
+02:07:35.4 |
HIP 2680 |
9.75 |
| 2026-09-28 12:00 |
00:33:23.94 |
+02:06:58.5 |
HIP 2680 |
10.39 |
| 2026-09-29 00:00 |
00:33:18.60 |
+02:06:21.5 |
HIP 2680 |
11.18 |
| 2026-09-29 12:00 |
00:33:13.25 |
+02:05:44.6 |
HIP 2680 |
12.11 |
| 2026-09-30 00:00 |
00:33:07.91 |
+02:05:07.7 |
HIP 2680 |
13.13 |
| 2026-09-30 12:00 |
00:33:02.56 |
+02:04:30.7 |
HIP 2680 |
14.24 |
| 2026-10-01 00:00 |
00:32:57.21 |
+02:03:53.8 |
HIP 2680 |
15.40 |
| 2026-10-01 12:00 |
00:32:51.86 |
+02:03:16.9 |
HIP 2680 |
16.62 |
| 2026-10-02 00:00 |
00:32:46.51 |
+02:02:40.1 |
HIP 2680 |
17.87 |
| 2026-10-02 12:00 |
00:32:41.16 |
+02:02:03.2 |
HIP 2680 |
19.15 |
| 2026-10-03 00:00 |
00:32:35.81 |
+02:01:26.4 |
HIP 2458 |
20.44 |
| 2026-10-03 12:00 |
00:32:30.47 |
+02:00:49.6 |
HIP 2458 |
19.03 |
| 2026-10-04 00:00 |
00:32:25.12 |
+02:00:12.8 |
HIP 2458 |
17.62 |
| 2026-10-04 12:00 |
00:32:19.78 |
+01:59:36.0 |
HIP 2458 |
16.22 |
| 2026-10-05 00:00 |
00:32:14.44 |
+01:58:59.3 |
HIP 2458 |
14.83 |
| 2026-10-05 12:00 |
00:32:09.10 |
+01:58:22.6 |
HIP 2458 |
13.47 |
| 2026-10-06 00:00 |
00:32:03.76 |
+01:57:46.0 |
HIP 2458 |
12.13 |
| 2026-10-06 12:00 |
00:31:58.43 |
+01:57:09.4 |
HIP 2458 |
10.82 |
| 2026-10-07 00:00 |
00:31:53.11 |
+01:56:32.8 |
HIP 2458 |
9.56 |
| 2026-10-07 12:00 |
00:31:47.78 |
+01:55:56.3 |
HIP 2458 |
8.36 |
| 2026-10-08 00:00 |
00:31:42.47 |
+01:55:19.9 |
HIP 2458 |
7.27 |
| 2026-10-08 12:00 |
00:31:37.16 |
+01:54:43.4 |
HIP 2458 |
6.33 |
| 2026-10-09 00:00 |
00:31:31.85 |
+01:54:07.1 |
HIP 2458 |
5.61 |
| 2026-10-09 12:00 |
00:31:26.55 |
+01:53:30.8 |
HIP 2458 |
5.21 |
| 2026-10-10 00:00 |
00:31:21.26 |
+01:52:54.6 |
HIP 2458 |
5.20 |
| 2026-10-10 12:00 |
00:31:15.98 |
+01:52:18.4 |
HIP 2458 |
5.58 |
| 2026-10-11 00:00 |
00:31:10.70 |
+01:51:42.4 |
HIP 2458 |
6.28 |