| Parameter |
Value |
| Designation |
361P/Spacewatch |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2018-07-02T14:46:57.017280Z |
| Orbit solution date (soln_date, UTC) |
2023-02-13T23:14:08Z |
| Obs used |
381 |
| NEO |
- |
| M1 |
4.600 |
| K1 |
23.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2017-09-16.0000000 |
| e |
0.43788752 |
| q (au) |
2.780030 |
| a (au) |
4.945682 |
| i (deg) |
13.882834 |
| Ω (om, deg) |
203.277939 |
| ω (w, deg) |
219.242791 |
| M (ma, deg) |
334.047022 |
Magnitude
Scatter + Global Linear
$$
M_a = (7.723 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
7.723 |
| 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 |
| 2017-09-11 |
2018-01-27 |
+17.2864 |
-8.358 |
| 2018-08-25 |
2020-03-21 |
+2.3797 |
-1.430 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
18:25:35.31 |
-08:50:53.7 |
HIP 90436 |
23.15 |
| 2026-09-20 12:00 |
18:25:39.02 |
-08:52:01.5 |
HIP 90436 |
22.17 |
| 2026-09-21 00:00 |
18:25:42.90 |
-08:53:09.1 |
HIP 90436 |
21.20 |
| 2026-09-21 12:00 |
18:25:46.95 |
-08:54:16.5 |
HIP 90436 |
20.26 |
| 2026-09-22 00:00 |
18:25:51.17 |
-08:55:23.8 |
HIP 90436 |
19.34 |
| 2026-09-22 12:00 |
18:25:55.57 |
-08:56:30.8 |
HIP 90382 |
18.19 |
| 2026-09-23 00:00 |
18:26:00.13 |
-08:57:37.7 |
HIP 90382 |
16.65 |
| 2026-09-23 12:00 |
18:26:04.87 |
-08:58:44.3 |
HIP 90382 |
15.12 |
| 2026-09-24 00:00 |
18:26:09.77 |
-08:59:50.7 |
HIP 90382 |
13.58 |
| 2026-09-24 12:00 |
18:26:14.85 |
-09:00:57.0 |
HIP 90382 |
12.07 |
| 2026-09-25 00:00 |
18:26:20.09 |
-09:02:03.0 |
HIP 90382 |
10.58 |
| 2026-09-25 12:00 |
18:26:25.50 |
-09:03:08.8 |
HIP 90382 |
9.17 |
| 2026-09-26 00:00 |
18:26:31.08 |
-09:04:14.3 |
HIP 90382 |
7.88 |
| 2026-09-26 12:00 |
18:26:36.82 |
-09:05:19.6 |
HIP 90382 |
6.82 |
| 2026-09-27 00:00 |
18:26:42.73 |
-09:06:24.7 |
HIP 90382 |
6.12 |
| 2026-09-27 12:00 |
18:26:48.81 |
-09:07:29.5 |
HIP 90382 |
5.95 |
| 2026-09-28 00:00 |
18:26:55.06 |
-09:08:34.1 |
HIP 90382 |
6.38 |
| 2026-09-28 12:00 |
18:27:01.46 |
-09:09:38.5 |
HIP 90382 |
7.32 |
| 2026-09-29 00:00 |
18:27:08.04 |
-09:10:42.5 |
HIP 90382 |
8.63 |
| 2026-09-29 12:00 |
18:27:14.78 |
-09:11:46.3 |
HIP 90382 |
10.19 |
| 2026-09-30 00:00 |
18:27:21.68 |
-09:12:49.9 |
HIP 90382 |
11.91 |
| 2026-09-30 12:00 |
18:27:28.75 |
-09:13:53.1 |
HIP 90382 |
13.74 |
| 2026-10-01 00:00 |
18:27:35.98 |
-09:14:56.1 |
HIP 90382 |
15.67 |
| 2026-10-01 12:00 |
18:27:43.37 |
-09:15:58.8 |
HIP 90382 |
17.67 |
| 2026-10-02 00:00 |
18:27:50.93 |
-09:17:01.3 |
HIP 90529 |
19.45 |
| 2026-10-02 12:00 |
18:27:58.65 |
-09:18:03.4 |
HIP 90529 |
17.84 |
| 2026-10-03 00:00 |
18:28:06.53 |
-09:19:05.2 |
HIP 90529 |
16.35 |
| 2026-10-03 12:00 |
18:28:14.57 |
-09:20:06.7 |
HIP 90529 |
15.04 |
| 2026-10-04 00:00 |
18:28:22.77 |
-09:21:07.9 |
HIP 90529 |
13.97 |
| 2026-10-04 12:00 |
18:28:31.13 |
-09:22:08.8 |
HIP 90529 |
13.22 |
| 2026-10-05 00:00 |
18:28:39.66 |
-09:23:09.4 |
HIP 90529 |
12.87 |
| 2026-10-05 12:00 |
18:28:48.34 |
-09:24:09.6 |
HIP 90529 |
12.95 |
| 2026-10-06 00:00 |
18:28:57.18 |
-09:25:09.6 |
HIP 90633 |
12.20 |
| 2026-10-06 12:00 |
18:29:06.18 |
-09:26:09.1 |
HIP 90633 |
11.35 |
| 2026-10-07 00:00 |
18:29:15.34 |
-09:27:08.4 |
HIP 90633 |
10.96 |
| 2026-10-07 12:00 |
18:29:24.65 |
-09:28:07.3 |
HIP 90633 |
11.10 |
| 2026-10-08 00:00 |
18:29:34.13 |
-09:29:05.8 |
HIP 90633 |
11.78 |
| 2026-10-08 12:00 |
18:29:43.76 |
-09:30:04.0 |
HIP 90633 |
12.93 |
| 2026-10-09 00:00 |
18:29:53.54 |
-09:31:01.8 |
HIP 90633 |
14.45 |
| 2026-10-09 12:00 |
18:30:03.48 |
-09:31:59.3 |
HIP 90633 |
16.26 |
| 2026-10-10 00:00 |
18:30:13.58 |
-09:32:56.3 |
HIP 90633 |
18.29 |
| 2026-10-10 12:00 |
18:30:23.83 |
-09:33:53.0 |
HIP 90633 |
20.48 |
| 2026-10-11 00:00 |
18:30:34.23 |
-09:34:49.4 |
HIP 90633 |
22.80 |