| Parameter |
Value |
| Designation |
C/2010 A4 (Siding Spring) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2010-10-08T17:46:24.746880Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:31:39Z |
| Obs used |
140 |
| NEO |
- |
| M1 |
7.100 |
| K1 |
15.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2010-05-04.0000000 |
| e |
0.99062596 |
| q (au) |
2.737996 |
| a (au) |
292.082906 |
| i (deg) |
96.730138 |
| Ω (om, deg) |
346.685502 |
| ω (w, deg) |
271.685276 |
| M (ma, deg) |
359.968855 |
Magnitude
Scatter + Global Linear
$$
M_a = (7.590 + 5.685\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
7.590 |
| n |
5.685 |
| gf |
1.000 |
| gb |
-1.000 |
| k |
0.998 |
| 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 |
20:39:43.19 |
+44:54:14.8 |
HIP 102098 |
28.95 |
| 2026-09-20 12:00 |
20:39:39.76 |
+44:53:35.6 |
HIP 102098 |
29.84 |
| 2026-09-21 00:00 |
20:39:36.37 |
+44:52:56.2 |
HIP 101703 |
29.36 |
| 2026-09-21 12:00 |
20:39:33.02 |
+44:52:16.6 |
HIP 101703 |
28.82 |
| 2026-09-22 00:00 |
20:39:29.70 |
+44:51:36.7 |
HIP 101703 |
28.30 |
| 2026-09-22 12:00 |
20:39:26.42 |
+44:50:56.7 |
HIP 101703 |
27.81 |
| 2026-09-23 00:00 |
20:39:23.17 |
+44:50:16.4 |
HIP 101703 |
27.34 |
| 2026-09-23 12:00 |
20:39:19.96 |
+44:49:35.9 |
HIP 101703 |
26.90 |
| 2026-09-24 00:00 |
20:39:16.79 |
+44:48:55.2 |
HIP 101703 |
26.49 |
| 2026-09-24 12:00 |
20:39:13.65 |
+44:48:14.3 |
HIP 101703 |
26.11 |
| 2026-09-25 00:00 |
20:39:10.54 |
+44:47:33.3 |
HIP 101703 |
25.76 |
| 2026-09-25 12:00 |
20:39:07.48 |
+44:46:52.0 |
HIP 101703 |
25.44 |
| 2026-09-26 00:00 |
20:39:04.45 |
+44:46:10.5 |
HIP 101703 |
25.16 |
| 2026-09-26 12:00 |
20:39:01.46 |
+44:45:28.8 |
HIP 101703 |
24.91 |
| 2026-09-27 00:00 |
20:38:58.50 |
+44:44:47.0 |
HIP 101703 |
24.70 |
| 2026-09-27 12:00 |
20:38:55.58 |
+44:44:05.0 |
HIP 101703 |
24.52 |
| 2026-09-28 00:00 |
20:38:52.70 |
+44:43:22.7 |
HIP 101838 |
24.33 |
| 2026-09-28 12:00 |
20:38:49.86 |
+44:42:40.4 |
HIP 101838 |
23.51 |
| 2026-09-29 00:00 |
20:38:47.06 |
+44:41:57.8 |
HIP 101838 |
22.70 |
| 2026-09-29 12:00 |
20:38:44.29 |
+44:41:15.1 |
HIP 101838 |
21.89 |
| 2026-09-30 00:00 |
20:38:41.56 |
+44:40:32.2 |
HIP 101838 |
21.08 |
| 2026-09-30 12:00 |
20:38:38.87 |
+44:39:49.1 |
HIP 101838 |
20.28 |
| 2026-10-01 00:00 |
20:38:36.22 |
+44:39:05.9 |
HIP 101838 |
19.48 |
| 2026-10-01 12:00 |
20:38:33.60 |
+44:38:22.6 |
HIP 101838 |
18.69 |
| 2026-10-02 00:00 |
20:38:31.03 |
+44:37:39.0 |
HIP 101838 |
17.90 |
| 2026-10-02 12:00 |
20:38:28.49 |
+44:36:55.4 |
HIP 101838 |
17.11 |
| 2026-10-03 00:00 |
20:38:26.00 |
+44:36:11.6 |
HIP 101838 |
16.33 |
| 2026-10-03 12:00 |
20:38:23.54 |
+44:35:27.6 |
HIP 101838 |
15.56 |
| 2026-10-04 00:00 |
20:38:21.13 |
+44:34:43.5 |
HIP 101838 |
14.79 |
| 2026-10-04 12:00 |
20:38:18.75 |
+44:33:59.3 |
HIP 101838 |
14.04 |
| 2026-10-05 00:00 |
20:38:16.41 |
+44:33:14.9 |
HIP 101838 |
13.29 |
| 2026-10-05 12:00 |
20:38:14.11 |
+44:32:30.4 |
HIP 101838 |
12.55 |
| 2026-10-06 00:00 |
20:38:11.86 |
+44:31:45.8 |
HIP 101838 |
11.82 |
| 2026-10-06 12:00 |
20:38:09.64 |
+44:31:01.1 |
HIP 101838 |
11.11 |
| 2026-10-07 00:00 |
20:38:07.47 |
+44:30:16.3 |
HIP 101838 |
10.41 |
| 2026-10-07 12:00 |
20:38:05.33 |
+44:29:31.3 |
HIP 101838 |
9.74 |
| 2026-10-08 00:00 |
20:38:03.24 |
+44:28:46.3 |
HIP 101838 |
9.09 |
| 2026-10-08 12:00 |
20:38:01.19 |
+44:28:01.1 |
HIP 101838 |
8.47 |
| 2026-10-09 00:00 |
20:37:59.17 |
+44:27:15.8 |
HIP 101838 |
7.88 |
| 2026-10-09 12:00 |
20:37:57.20 |
+44:26:30.5 |
HIP 101838 |
7.34 |
| 2026-10-10 00:00 |
20:37:55.28 |
+44:25:45.0 |
HIP 101838 |
6.85 |
| 2026-10-10 12:00 |
20:37:53.39 |
+44:24:59.5 |
HIP 101838 |
6.42 |
| 2026-10-11 00:00 |
20:37:51.54 |
+44:24:13.9 |
HIP 101838 |
6.08 |