C/2025 A6 (Lemmon)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2025 A6 (Lemmon) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2025-11-08T12:56:43.054080Z |
| Orbit solution date (soln_date, UTC) | 2026-08-07T12:42:14Z |
| Obs used | 2099 |
| NEO | - |
| M1 | 10.400 |
| K1 | 8.750 |
| PC | - |
| Discovery observation (MPC, UTC) | 2025-01-03T08:12:42.537600Z |
| Discovery magnitude (MPC) | 21.65 G |
| Discovery observatory (MPC) | G96 · University of Arizona Mt. Lemmon Survey |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2025-10-31.0000000 |
| e | 0.99553621 |
| q (au) | 0.529904 |
| a (au) | 118.711819 |
| i (deg) | 143.663707 |
| Ω (om, deg) | 108.097987 |
| ω (w, deg) | 132.968841 |
| M (ma, deg) | 359.993493 |
Magnitude
Scatter + Global Linear
$$ M_a = (8.634 + 5.215\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 8.634 |
| n | 5.215 |
| gf | 0.999 |
| gb | -0.517 |
| k | 0.800 |
| 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 |
|---|---|---|---|
| 2024-11-12 | 2025-09-20 | +5.9437 | -0.967 |
| 2025-09-20 | 2025-11-08 | -3.5465 | -0.096 |
| 2025-11-08 | 2026-01-23 | -6.8624 | -1.865 |
| 2026-01-23 | 2026-03-23 | +13.1613 | -6.217 |
| 2026-03-23 | 2026-08-03 | -2.2246 | +0.365 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Finding Chart
Ephemeris
| Date/Time (UTC) | RA (J2000) | Dec (J2000) | Nearest HIP | Dist from HIP (arcmin) |
|---|---|---|---|---|
| 2026-09-20 00:00 | 11:43:17.60 | -31:23:19.3 | HIP 57085 | 14.67 |
| 2026-09-20 12:00 | 11:43:36.02 | -31:25:00.0 | HIP 57246 | 15.54 |
| 2026-09-21 00:00 | 11:43:54.40 | -31:26:41.7 | HIP 57246 | 12.06 |
| 2026-09-21 12:00 | 11:44:12.73 | -31:28:24.5 | HIP 57246 | 9.23 |
| 2026-09-22 00:00 | 11:44:31.02 | -31:30:08.3 | HIP 57246 | 7.82 |
| 2026-09-22 12:00 | 11:44:49.26 | -31:31:53.1 | HIP 57246 | 8.55 |
| 2026-09-23 00:00 | 11:45:07.46 | -31:33:39.0 | HIP 57246 | 11.00 |
| 2026-09-23 12:00 | 11:45:25.62 | -31:35:25.9 | HIP 57309 | 12.11 |
| 2026-09-24 00:00 | 11:45:43.73 | -31:37:13.8 | HIP 57309 | 12.67 |
| 2026-09-24 12:00 | 11:46:01.79 | -31:39:02.7 | HIP 57309 | 14.49 |
| 2026-09-25 00:00 | 11:46:19.80 | -31:40:52.5 | HIP 57481 | 15.38 |
| 2026-09-25 12:00 | 11:46:37.77 | -31:42:43.4 | HIP 57481 | 12.01 |
| 2026-09-26 00:00 | 11:46:55.68 | -31:44:35.2 | HIP 57481 | 9.37 |
| 2026-09-26 12:00 | 11:47:13.55 | -31:46:28.0 | HIP 57481 | 8.17 |
| 2026-09-27 00:00 | 11:47:31.36 | -31:48:21.8 | HIP 57481 | 9.01 |
| 2026-09-27 12:00 | 11:47:49.13 | -31:50:16.6 | HIP 57481 | 11.45 |
| 2026-09-28 00:00 | 11:48:06.84 | -31:52:12.2 | HIP 57481 | 14.71 |
| 2026-09-28 12:00 | 11:48:24.50 | -31:54:08.9 | HIP 57481 | 18.35 |
| 2026-09-29 00:00 | 11:48:42.11 | -31:56:06.4 | HIP 57481 | 22.19 |
| 2026-09-29 12:00 | 11:48:59.66 | -31:58:04.9 | HIP 57481 | 26.14 |
| 2026-09-30 00:00 | 11:49:17.16 | -32:00:04.3 | HIP 57672 | 27.13 |
| 2026-09-30 12:00 | 11:49:34.61 | -32:02:04.7 | HIP 57672 | 24.62 |
| 2026-10-01 00:00 | 11:49:52.00 | -32:04:05.9 | HIP 57672 | 22.62 |
| 2026-10-01 12:00 | 11:50:09.33 | -32:06:08.1 | HIP 57672 | 21.24 |
| 2026-10-02 00:00 | 11:50:26.61 | -32:08:11.1 | HIP 57672 | 20.61 |
| 2026-10-02 12:00 | 11:50:43.83 | -32:10:15.1 | HIP 57672 | 20.81 |
| 2026-10-03 00:00 | 11:51:00.99 | -32:12:19.9 | HIP 57672 | 21.80 |
| 2026-10-03 12:00 | 11:51:18.09 | -32:14:25.6 | HIP 57672 | 23.48 |
| 2026-10-04 00:00 | 11:51:35.13 | -32:16:32.2 | HIP 57692 | 25.43 |
| 2026-10-04 12:00 | 11:51:52.11 | -32:18:39.7 | HIP 57692 | 27.53 |
| 2026-10-05 00:00 | 11:52:09.03 | -32:20:48.0 | HIP 57692 | 30.05 |
| 2026-10-05 12:00 | 11:52:25.88 | -32:22:57.2 | HIP 58078 | 31.82 |
| 2026-10-06 00:00 | 11:52:42.67 | -32:25:07.2 | HIP 58078 | 29.96 |
| 2026-10-06 12:00 | 11:52:59.40 | -32:27:18.1 | HIP 58078 | 28.61 |
| 2026-10-07 00:00 | 11:53:16.06 | -32:29:29.8 | HIP 58078 | 27.85 |
| 2026-10-07 12:00 | 11:53:32.65 | -32:31:42.3 | HIP 58078 | 27.71 |
| 2026-10-08 00:00 | 11:53:49.18 | -32:33:55.7 | HIP 58078 | 28.20 |
| 2026-10-08 12:00 | 11:54:05.64 | -32:36:09.9 | HIP 58078 | 29.30 |
| 2026-10-09 00:00 | 11:54:22.03 | -32:38:24.8 | HIP 58100 | 26.29 |
| 2026-10-09 12:00 | 11:54:38.35 | -32:40:40.6 | HIP 58100 | 23.29 |
| 2026-10-10 00:00 | 11:54:54.59 | -32:42:57.2 | HIP 58100 | 20.67 |
| 2026-10-10 12:00 | 11:55:10.77 | -32:45:14.6 | HIP 58100 | 18.58 |
| 2026-10-11 00:00 | 11:55:26.87 | -32:47:32.7 | HIP 58100 | 17.20 |