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) |
|---|---|---|---|---|
| 2026-07-29 00:00 | 07:28:16.93 | +36:36:03.9 | HIP 36313 | 28.68 |
| 2026-07-29 12:00 | 07:28:21.09 | +36:36:00.1 | HIP 36313 | 28.55 |
| 2026-07-30 00:00 | 07:28:25.24 | +36:35:56.4 | HIP 36313 | 28.45 |
| 2026-07-30 12:00 | 07:28:29.39 | +36:35:52.8 | HIP 36313 | 28.37 |
| 2026-07-31 00:00 | 07:28:33.52 | +36:35:49.3 | HIP 36313 | 28.32 |
| 2026-07-31 12:00 | 07:28:37.64 | +36:35:46.0 | HIP 36313 | 28.29 |
| 2026-08-01 00:00 | 07:28:41.75 | +36:35:42.7 | HIP 36313 | 28.29 |
| 2026-08-01 12:00 | 07:28:45.85 | +36:35:39.6 | HIP 36313 | 28.32 |
| 2026-08-02 00:00 | 07:28:49.94 | +36:35:36.6 | HIP 36313 | 28.37 |
| 2026-08-02 12:00 | 07:28:54.02 | +36:35:33.8 | HIP 36313 | 28.45 |
| 2026-08-03 00:00 | 07:28:58.09 | +36:35:31.0 | HIP 36313 | 28.56 |
| 2026-08-03 12:00 | 07:29:02.14 | +36:35:28.4 | HIP 36313 | 28.68 |
| 2026-08-04 00:00 | 07:29:06.18 | +36:35:25.9 | HIP 36313 | 28.83 |
| 2026-08-04 12:00 | 07:29:10.21 | +36:35:23.5 | HIP 36313 | 29.01 |
| 2026-08-05 00:00 | 07:29:14.23 | +36:35:21.2 | HIP 36313 | 29.21 |
| 2026-08-05 12:00 | 07:29:18.23 | +36:35:19.0 | HIP 36313 | 29.43 |
| 2026-08-06 00:00 | 07:29:22.22 | +36:35:17.0 | HIP 36313 | 29.67 |
| 2026-08-06 12:00 | 07:29:26.19 | +36:35:15.1 | HIP 36313 | 29.93 |
| 2026-08-07 00:00 | 07:29:30.15 | +36:35:13.3 | HIP 36313 | 30.21 |
| 2026-08-07 12:00 | 07:29:34.10 | +36:35:11.7 | HIP 36313 | 30.51 |
| 2026-08-08 00:00 | 07:29:38.03 | +36:35:10.1 | HIP 36313 | 30.83 |
| 2026-08-08 12:00 | 07:29:41.95 | +36:35:08.7 | HIP 36313 | 31.16 |
| 2026-08-09 00:00 | 07:29:45.85 | +36:35:07.4 | HIP 36313 | 31.52 |
| 2026-08-09 12:00 | 07:29:49.74 | +36:35:06.2 | HIP 36313 | 31.88 |
| 2026-08-10 00:00 | 07:29:53.61 | +36:35:05.2 | HIP 36313 | 32.27 |
| 2026-08-10 12:00 | 07:29:57.47 | +36:35:04.2 | HIP 36627 | 32.17 |
| 2026-08-11 00:00 | 07:30:01.31 | +36:35:03.4 | HIP 36627 | 31.58 |
| 2026-08-11 12:00 | 07:30:05.13 | +36:35:02.8 | HIP 36627 | 31.01 |
| 2026-08-12 00:00 | 07:30:08.94 | +36:35:02.2 | HIP 36627 | 30.45 |
| 2026-08-12 12:00 | 07:30:12.73 | +36:35:01.8 | HIP 36627 | 29.90 |
| 2026-08-13 00:00 | 07:30:16.50 | +36:35:01.5 | HIP 36627 | 29.37 |
| 2026-08-13 12:00 | 07:30:20.25 | +36:35:01.3 | HIP 36627 | 28.85 |
| 2026-08-14 00:00 | 07:30:23.99 | +36:35:01.3 | HIP 36627 | 28.34 |
| 2026-08-14 12:00 | 07:30:27.71 | +36:35:01.3 | HIP 36627 | 27.85 |
| 2026-08-15 00:00 | 07:30:31.41 | +36:35:01.5 | HIP 36627 | 27.38 |
| 2026-08-15 12:00 | 07:30:35.09 | +36:35:01.9 | HIP 36627 | 26.92 |
| 2026-08-16 00:00 | 07:30:38.75 | +36:35:02.3 | HIP 36627 | 26.48 |
| 2026-08-16 12:00 | 07:30:42.40 | +36:35:02.9 | HIP 36627 | 26.05 |
| 2026-08-17 00:00 | 07:30:46.02 | +36:35:03.6 | HIP 36627 | 25.65 |
| 2026-08-17 12:00 | 07:30:49.63 | +36:35:04.4 | HIP 36627 | 25.26 |
| 2026-08-18 00:00 | 07:30:53.21 | +36:35:05.4 | HIP 36627 | 24.89 |
| 2026-08-18 12:00 | 07:30:56.78 | +36:35:06.5 | HIP 36627 | 24.54 |
| 2026-08-19 00:00 | 07:31:00.32 | +36:35:07.7 | HIP 36627 | 24.21 |