C/2021 T4 (Lemmon)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2021 T4 (Lemmon) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2023-07-31T12:38:55.115520Z |
| Orbit solution date (soln_date, UTC) | 2025-04-14T09:29:19Z |
| Obs used | 1259 |
| NEO | - |
| M1 | 12.400 |
| K1 | 4.500 |
| PC | - |
| Discovery observation (MPC, UTC) | 2021-10-07T08:22:46.128000Z |
| Discovery magnitude (MPC) | 20.27 G |
| Discovery observatory (MPC) | G96 · University of Arizona Mt. Lemmon Survey |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2023-04-14.0000000 |
| e | 0.99991819 |
| q (au) | 1.483298 |
| a (au) | 18131.786728 |
| i (deg) | 160.777409 |
| Ω (om, deg) | 257.882312 |
| ω (w, deg) | 329.813930 |
| M (ma, deg) | 359.999956 |
Magnitude
Scatter + Global Linear
$$ M_a = (12.728 + 3.054\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 12.728 |
| n | 3.054 |
| gf | 0.999 |
| gb | -0.748 |
| 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 |
|---|---|---|---|
| 2021-08-07 | 2023-07-28 | +2.7531 | -2.268 |
| 2023-07-31 | 2024-04-13 | +9.0393 | -3.499 |
| 2024-04-13 | 2025-03-24 | -0.2550 | +1.251 |
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) |
|---|---|---|---|---|
| 2026-06-01 00:00 | 10:23:33.08 | +29:41:10.0 | HIP 50904 | 4.62 |
| 2026-06-01 12:00 | 10:23:32.65 | +29:40:12.3 | HIP 50904 | 3.81 |
| 2026-06-02 00:00 | 10:23:32.32 | +29:39:14.3 | HIP 50904 | 3.07 |
| 2026-06-02 12:00 | 10:23:32.10 | +29:38:16.0 | HIP 50904 | 2.48 |
| 2026-06-03 00:00 | 10:23:31.98 | +29:37:17.4 | HIP 50904 | 2.15 |
| 2026-06-03 12:00 | 10:23:31.97 | +29:36:18.6 | HIP 50904 | 2.22 |
| 2026-06-04 00:00 | 10:23:32.06 | +29:35:19.4 | HIP 50904 | 2.67 |
| 2026-06-04 12:00 | 10:23:32.24 | +29:34:20.0 | HIP 50904 | 3.34 |
| 2026-06-05 00:00 | 10:23:32.53 | +29:33:20.2 | HIP 50904 | 4.14 |
| 2026-06-05 12:00 | 10:23:32.92 | +29:32:20.2 | HIP 50904 | 5.00 |
| 2026-06-06 00:00 | 10:23:33.41 | +29:31:20.0 | HIP 50904 | 5.91 |
| 2026-06-06 12:00 | 10:23:34.00 | +29:30:19.5 | HIP 50904 | 6.84 |
| 2026-06-07 00:00 | 10:23:34.69 | +29:29:18.7 | HIP 50904 | 7.80 |
| 2026-06-07 12:00 | 10:23:35.47 | +29:28:17.7 | HIP 50904 | 8.77 |
| 2026-06-08 00:00 | 10:23:36.36 | +29:27:16.4 | HIP 50904 | 9.75 |
| 2026-06-08 12:00 | 10:23:37.34 | +29:26:14.9 | HIP 50904 | 10.75 |
| 2026-06-09 00:00 | 10:23:38.42 | +29:25:13.1 | HIP 50904 | 11.76 |
| 2026-06-09 12:00 | 10:23:39.59 | +29:24:11.1 | HIP 50904 | 12.78 |
| 2026-06-10 00:00 | 10:23:40.86 | +29:23:08.9 | HIP 50904 | 13.81 |
| 2026-06-10 12:00 | 10:23:42.23 | +29:22:06.5 | HIP 50904 | 14.85 |
| 2026-06-11 00:00 | 10:23:43.69 | +29:21:03.8 | HIP 50904 | 15.90 |
| 2026-06-11 12:00 | 10:23:45.25 | +29:20:01.0 | HIP 50904 | 16.95 |
| 2026-06-12 00:00 | 10:23:46.90 | +29:18:57.9 | HIP 50904 | 18.02 |
| 2026-06-12 12:00 | 10:23:48.64 | +29:17:54.6 | HIP 50904 | 19.10 |
| 2026-06-13 00:00 | 10:23:50.47 | +29:16:51.1 | HIP 50904 | 20.19 |
| 2026-06-13 12:00 | 10:23:52.40 | +29:15:47.4 | HIP 50904 | 21.29 |
| 2026-06-14 00:00 | 10:23:54.42 | +29:14:43.6 | HIP 50904 | 22.40 |
| 2026-06-14 12:00 | 10:23:56.53 | +29:13:39.5 | HIP 50904 | 23.52 |
| 2026-06-15 00:00 | 10:23:58.73 | +29:12:35.3 | HIP 50904 | 24.64 |
| 2026-06-15 12:00 | 10:24:01.02 | +29:11:30.9 | HIP 50904 | 25.78 |
| 2026-06-16 00:00 | 10:24:03.40 | +29:10:26.3 | HIP 50904 | 26.93 |
| 2026-06-16 12:00 | 10:24:05.87 | +29:09:21.6 | HIP 50904 | 28.09 |
| 2026-06-17 00:00 | 10:24:08.42 | +29:08:16.7 | HIP 50904 | 29.26 |
| 2026-06-17 12:00 | 10:24:11.07 | +29:07:11.7 | HIP 50904 | 30.44 |
| 2026-06-18 00:00 | 10:24:13.80 | +29:06:06.5 | HIP 50904 | 31.62 |
| 2026-06-18 12:00 | 10:24:16.61 | +29:05:01.2 | HIP 50904 | 32.82 |
| 2026-06-19 00:00 | 10:24:19.51 | +29:03:55.7 | HIP 50904 | 34.03 |
| 2026-06-19 12:00 | 10:24:22.50 | +29:02:50.1 | HIP 50904 | 35.25 |
| 2026-06-20 00:00 | 10:24:25.57 | +29:01:44.4 | HIP 50904 | 36.49 |
| 2026-06-20 12:00 | 10:24:28.72 | +29:00:38.5 | HIP 50904 | 37.73 |
| 2026-06-21 00:00 | 10:24:31.95 | +28:59:32.6 | HIP 50904 | 38.98 |
| 2026-06-21 12:00 | 10:24:35.27 | +28:58:26.5 | HIP 50904 | 40.24 |
| 2026-06-22 00:00 | 10:24:38.67 | +28:57:20.3 | HIP 50904 | 41.51 |