| Parameter |
Value |
| Designation |
389P/Siding Spring |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2020-01-02T20:23:08.842560Z |
| Orbit solution date (soln_date, UTC) |
2022-07-31T01:43:35Z |
| Obs used |
103 |
| NEO |
- |
| M1 |
14.300 |
| K1 |
19.500 |
| PC |
0.030 |
| Discovery observation (MPC, UTC) |
2019-09-25T12:36:33.696000Z |
| Discovery magnitude (MPC) |
20.50 w |
| Discovery observatory (MPC) |
F51 · Pan-STARRS 1, Haleakala |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2013-11-08.0000000 |
| e |
0.70466929 |
| q (au) |
1.659623 |
| a (au) |
5.619542 |
| i (deg) |
160.071918 |
| Ω (om, deg) |
218.811242 |
| ω (w, deg) |
249.490302 |
| M (ma, deg) |
193.763391 |
Magnitude
Scatter + Global Linear
$$
M_a = (14.922 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
14.922 |
| n |
6.000 |
| gf |
1.000 |
| gb |
-0.937 |
| k |
0.999 |
| 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) |
| 2026-05-12 00:00 |
10:23:59.68 |
+30:01:45.1 |
HIP 50926 |
10.49 |
| 2026-05-12 12:00 |
10:23:54.32 |
+30:01:13.8 |
HIP 50926 |
11.13 |
| 2026-05-13 00:00 |
10:23:49.09 |
+30:00:41.9 |
HIP 50926 |
11.88 |
| 2026-05-13 12:00 |
10:23:43.98 |
+30:00:09.4 |
HIP 50926 |
12.71 |
| 2026-05-14 00:00 |
10:23:38.99 |
+29:59:36.3 |
HIP 50926 |
13.60 |
| 2026-05-14 12:00 |
10:23:34.12 |
+29:59:02.6 |
HIP 50926 |
14.53 |
| 2026-05-15 00:00 |
10:23:29.37 |
+29:58:28.3 |
HIP 50926 |
15.50 |
| 2026-05-15 12:00 |
10:23:24.74 |
+29:57:53.5 |
HIP 50926 |
16.49 |
| 2026-05-16 00:00 |
10:23:20.23 |
+29:57:18.1 |
HIP 50926 |
17.50 |
| 2026-05-16 12:00 |
10:23:15.84 |
+29:56:42.1 |
HIP 50926 |
18.51 |
| 2026-05-17 00:00 |
10:23:11.58 |
+29:56:05.6 |
HIP 50926 |
19.53 |
| 2026-05-17 12:00 |
10:23:07.43 |
+29:55:28.5 |
HIP 50904 |
19.96 |
| 2026-05-18 00:00 |
10:23:03.40 |
+29:54:50.8 |
HIP 50904 |
19.74 |
| 2026-05-18 12:00 |
10:22:59.49 |
+29:54:12.6 |
HIP 50904 |
19.54 |
| 2026-05-19 00:00 |
10:22:55.70 |
+29:53:33.9 |
HIP 50904 |
19.39 |
| 2026-05-19 12:00 |
10:22:52.03 |
+29:52:54.7 |
HIP 50904 |
19.27 |
| 2026-05-20 00:00 |
10:22:48.48 |
+29:52:14.9 |
HIP 50904 |
19.18 |
| 2026-05-20 12:00 |
10:22:45.05 |
+29:51:34.7 |
HIP 50904 |
19.12 |
| 2026-05-21 00:00 |
10:22:41.74 |
+29:50:53.9 |
HIP 50904 |
19.09 |
| 2026-05-21 12:00 |
10:22:38.54 |
+29:50:12.6 |
HIP 50904 |
19.08 |
| 2026-05-22 00:00 |
10:22:35.46 |
+29:49:30.8 |
HIP 50904 |
19.11 |
| 2026-05-22 12:00 |
10:22:32.50 |
+29:48:48.6 |
HIP 50904 |
19.15 |
| 2026-05-23 00:00 |
10:22:29.65 |
+29:48:05.9 |
HIP 50904 |
19.22 |
| 2026-05-23 12:00 |
10:22:26.92 |
+29:47:22.6 |
HIP 50904 |
19.31 |
| 2026-05-24 00:00 |
10:22:24.31 |
+29:46:39.0 |
HIP 50904 |
19.42 |
| 2026-05-24 12:00 |
10:22:21.81 |
+29:45:54.8 |
HIP 50904 |
19.54 |
| 2026-05-25 00:00 |
10:22:19.42 |
+29:45:10.2 |
HIP 50904 |
19.68 |
| 2026-05-25 12:00 |
10:22:17.15 |
+29:44:25.2 |
HIP 50904 |
19.84 |
| 2026-05-26 00:00 |
10:22:15.00 |
+29:43:39.7 |
HIP 50904 |
20.01 |
| 2026-05-26 12:00 |
10:22:12.96 |
+29:42:53.8 |
HIP 50904 |
20.19 |
| 2026-05-27 00:00 |
10:22:11.03 |
+29:42:07.5 |
HIP 50904 |
20.38 |
| 2026-05-27 12:00 |
10:22:09.21 |
+29:41:20.7 |
HIP 50904 |
20.58 |
| 2026-05-28 00:00 |
10:22:07.51 |
+29:40:33.5 |
HIP 50904 |
20.79 |
| 2026-05-28 12:00 |
10:22:05.92 |
+29:39:45.9 |
HIP 50642 |
20.54 |
| 2026-05-29 00:00 |
10:22:04.44 |
+29:38:57.9 |
HIP 50642 |
20.03 |
| 2026-05-29 12:00 |
10:22:03.07 |
+29:38:09.5 |
HIP 50642 |
19.57 |
| 2026-05-30 00:00 |
10:22:01.81 |
+29:37:20.6 |
HIP 50642 |
19.16 |
| 2026-05-30 12:00 |
10:22:00.67 |
+29:36:31.4 |
HIP 50642 |
18.80 |
| 2026-05-31 00:00 |
10:21:59.63 |
+29:35:41.8 |
HIP 50642 |
18.50 |
| 2026-05-31 12:00 |
10:21:58.70 |
+29:34:51.9 |
HIP 50642 |
18.25 |
| 2026-06-01 00:00 |
10:21:57.88 |
+29:34:01.5 |
HIP 50642 |
18.07 |
| 2026-06-01 12:00 |
10:21:57.17 |
+29:33:10.8 |
HIP 50642 |
17.95 |
| 2026-06-02 00:00 |
10:21:56.57 |
+29:32:19.7 |
HIP 50642 |
17.89 |