C/2012 S1 (ISON)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2012 S1 (ISON) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2013-11-28T18:20:55.495680Z |
| Orbit solution date (soln_date, UTC) | 2025-11-21T13:42:48Z |
| Obs used | 6684 |
| NEO | - |
| M1 | 10.400 |
| K1 | 4.500 |
| PC | - |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2013-05-01.0000000 |
| e | 1.00000509 |
| q (au) | 0.012467 |
| a (au) | -2446.893404 |
| i (deg) | 62.162896 |
| Ω (om, deg) | 295.686541 |
| ω (w, deg) | 345.541197 |
| M (ma, deg) | -0.001724 |
Magnitude
Scatter + Global Linear
$$ M_a = (11.695 + 2.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 11.695 |
| n | 2.000 |
| gf | 1.000 |
| gb | -0.791 |
| k | 0.951 |
| 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 |
|---|---|---|---|
| 2011-09-30 | 2013-11-13 | +0.7784 | -0.530 |
| 2013-11-13 | 2013-11-28 | +7.8926 | -0.124 |
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 | 07:33:54.85 | +36:40:46.5 | HIP 36704 | 23.65 |
| 2026-09-20 12:00 | 07:33:56.61 | +36:40:55.8 | HIP 36704 | 23.68 |
| 2026-09-21 00:00 | 07:33:58.34 | +36:41:05.2 | HIP 36704 | 23.70 |
| 2026-09-21 12:00 | 07:34:00.03 | +36:41:14.7 | HIP 36704 | 23.73 |
| 2026-09-22 00:00 | 07:34:01.69 | +36:41:24.3 | HIP 36704 | 23.76 |
| 2026-09-22 12:00 | 07:34:03.31 | +36:41:34.0 | HIP 36704 | 23.79 |
| 2026-09-23 00:00 | 07:34:04.90 | +36:41:43.9 | HIP 36704 | 23.83 |
| 2026-09-23 12:00 | 07:34:06.46 | +36:41:53.8 | HIP 36704 | 23.86 |
| 2026-09-24 00:00 | 07:34:07.98 | +36:42:03.9 | HIP 36704 | 23.89 |
| 2026-09-24 12:00 | 07:34:09.46 | +36:42:14.0 | HIP 36704 | 23.92 |
| 2026-09-25 00:00 | 07:34:10.92 | +36:42:24.3 | HIP 36704 | 23.95 |
| 2026-09-25 12:00 | 07:34:12.33 | +36:42:34.7 | HIP 36704 | 23.97 |
| 2026-09-26 00:00 | 07:34:13.71 | +36:42:45.2 | HIP 36704 | 24.00 |
| 2026-09-26 12:00 | 07:34:15.06 | +36:42:55.8 | HIP 36704 | 24.03 |
| 2026-09-27 00:00 | 07:34:16.37 | +36:43:06.5 | HIP 36704 | 24.05 |
| 2026-09-27 12:00 | 07:34:17.65 | +36:43:17.4 | HIP 36704 | 24.07 |
| 2026-09-28 00:00 | 07:34:18.89 | +36:43:28.3 | HIP 36704 | 24.09 |
| 2026-09-28 12:00 | 07:34:20.09 | +36:43:39.3 | HIP 36704 | 24.11 |
| 2026-09-29 00:00 | 07:34:21.26 | +36:43:50.5 | HIP 36704 | 24.13 |
| 2026-09-29 12:00 | 07:34:22.39 | +36:44:01.7 | HIP 36704 | 24.14 |
| 2026-09-30 00:00 | 07:34:23.49 | +36:44:13.1 | HIP 36704 | 24.15 |
| 2026-09-30 12:00 | 07:34:24.55 | +36:44:24.5 | HIP 36704 | 24.16 |
| 2026-10-01 00:00 | 07:34:25.58 | +36:44:36.1 | HIP 36704 | 24.17 |
| 2026-10-01 12:00 | 07:34:26.56 | +36:44:47.7 | HIP 36704 | 24.17 |
| 2026-10-02 00:00 | 07:34:27.52 | +36:44:59.5 | HIP 36704 | 24.17 |
| 2026-10-02 12:00 | 07:34:28.43 | +36:45:11.4 | HIP 36704 | 24.16 |
| 2026-10-03 00:00 | 07:34:29.31 | +36:45:23.3 | HIP 36704 | 24.15 |
| 2026-10-03 12:00 | 07:34:30.15 | +36:45:35.4 | HIP 36704 | 24.14 |
| 2026-10-04 00:00 | 07:34:30.95 | +36:45:47.6 | HIP 36704 | 24.13 |
| 2026-10-04 12:00 | 07:34:31.72 | +36:45:59.8 | HIP 36704 | 24.11 |
| 2026-10-05 00:00 | 07:34:32.45 | +36:46:12.2 | HIP 36704 | 24.08 |
| 2026-10-05 12:00 | 07:34:33.14 | +36:46:24.7 | HIP 36704 | 24.05 |
| 2026-10-06 00:00 | 07:34:33.80 | +36:46:37.2 | HIP 36704 | 24.02 |
| 2026-10-06 12:00 | 07:34:34.41 | +36:46:49.9 | HIP 36704 | 23.99 |
| 2026-10-07 00:00 | 07:34:34.99 | +36:47:02.6 | HIP 36704 | 23.94 |
| 2026-10-07 12:00 | 07:34:35.53 | +36:47:15.5 | HIP 36704 | 23.90 |
| 2026-10-08 00:00 | 07:34:36.04 | +36:47:28.4 | HIP 36704 | 23.85 |
| 2026-10-08 12:00 | 07:34:36.50 | +36:47:41.5 | HIP 36704 | 23.79 |
| 2026-10-09 00:00 | 07:34:36.93 | +36:47:54.6 | HIP 36704 | 23.73 |
| 2026-10-09 12:00 | 07:34:37.32 | +36:48:07.8 | HIP 36704 | 23.67 |
| 2026-10-10 00:00 | 07:34:37.67 | +36:48:21.1 | HIP 36704 | 23.60 |
| 2026-10-10 12:00 | 07:34:37.98 | +36:48:34.5 | HIP 36704 | 23.52 |
| 2026-10-11 00:00 | 07:34:38.25 | +36:48:48.0 | HIP 36704 | 23.44 |