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 · 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 | 1.000 |
| 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) |
|---|---|---|---|---|
| 2026-03-26 00:00 | 10:42:01.68 | +30:22:28.5 | HIP 52275 | 17.61 |
| 2026-03-26 12:00 | 10:41:46.07 | +30:23:06.2 | HIP 52275 | 15.46 |
| 2026-03-27 00:00 | 10:41:30.54 | +30:23:42.8 | HIP 52275 | 13.83 |
| 2026-03-27 12:00 | 10:41:15.09 | +30:24:18.4 | HIP 52275 | 12.91 |
| 2026-03-28 00:00 | 10:40:59.74 | +30:24:53.0 | HIP 52275 | 12.82 |
| 2026-03-28 12:00 | 10:40:44.46 | +30:25:26.5 | HIP 52275 | 13.57 |
| 2026-03-29 00:00 | 10:40:29.28 | +30:25:58.9 | HIP 52275 | 15.03 |
| 2026-03-29 12:00 | 10:40:14.18 | +30:26:30.4 | HIP 52275 | 16.99 |
| 2026-03-30 00:00 | 10:39:59.17 | +30:27:00.8 | HIP 52275 | 19.29 |
| 2026-03-30 12:00 | 10:39:44.26 | +30:27:30.1 | HIP 52275 | 21.81 |
| 2026-03-31 00:00 | 10:39:29.43 | +30:27:58.5 | HIP 52234 | 23.29 |
| 2026-03-31 12:00 | 10:39:14.70 | +30:28:25.8 | HIP 52234 | 24.45 |
| 2026-04-01 00:00 | 10:39:00.06 | +30:28:52.1 | HIP 51978 | 23.66 |
| 2026-04-01 12:00 | 10:38:45.52 | +30:29:17.4 | HIP 51978 | 20.53 |
| 2026-04-02 00:00 | 10:38:31.07 | +30:29:41.6 | HIP 51978 | 17.43 |
| 2026-04-02 12:00 | 10:38:16.72 | +30:30:04.9 | HIP 51978 | 14.37 |
| 2026-04-03 00:00 | 10:38:02.46 | +30:30:27.1 | HIP 51978 | 11.37 |
| 2026-04-03 12:00 | 10:37:48.31 | +30:30:48.4 | HIP 51978 | 8.47 |
| 2026-04-04 00:00 | 10:37:34.25 | +30:31:08.6 | HIP 51978 | 5.77 |
| 2026-04-04 12:00 | 10:37:20.29 | +30:31:27.9 | HIP 51978 | 3.67 |
| 2026-04-05 00:00 | 10:37:06.43 | +30:31:46.1 | HIP 51978 | 3.47 |
| 2026-04-05 12:00 | 10:36:52.68 | +30:32:03.4 | HIP 51978 | 5.34 |
| 2026-04-06 00:00 | 10:36:39.03 | +30:32:19.7 | HIP 51978 | 7.89 |
| 2026-04-06 12:00 | 10:36:25.48 | +30:32:35.0 | HIP 51878 | 10.58 |
| 2026-04-07 00:00 | 10:36:12.03 | +30:32:49.3 | HIP 51878 | 9.40 |
| 2026-04-07 12:00 | 10:35:58.69 | +30:33:02.6 | HIP 51878 | 9.02 |
| 2026-04-08 00:00 | 10:35:45.46 | +30:33:15.0 | HIP 51878 | 9.52 |
| 2026-04-08 12:00 | 10:35:32.33 | +30:33:26.4 | HIP 51878 | 10.76 |
| 2026-04-09 00:00 | 10:35:19.31 | +30:33:36.9 | HIP 51878 | 12.50 |
| 2026-04-09 12:00 | 10:35:06.40 | +30:33:46.4 | HIP 51878 | 14.55 |
| 2026-04-10 00:00 | 10:34:53.60 | +30:33:54.9 | HIP 51878 | 16.79 |
| 2026-04-10 12:00 | 10:34:40.90 | +30:34:02.5 | HIP 51878 | 19.13 |
| 2026-04-11 00:00 | 10:34:28.32 | +30:34:09.2 | HIP 51652 | 20.24 |
| 2026-04-11 12:00 | 10:34:15.85 | +30:34:14.9 | HIP 51652 | 18.01 |
| 2026-04-12 00:00 | 10:34:03.49 | +30:34:19.7 | HIP 51652 | 15.93 |
| 2026-04-12 12:00 | 10:33:51.24 | +30:34:23.5 | HIP 51652 | 14.09 |
| 2026-04-13 00:00 | 10:33:39.10 | +30:34:26.5 | HIP 51652 | 12.56 |
| 2026-04-13 12:00 | 10:33:27.08 | +30:34:28.5 | HIP 51652 | 11.44 |
| 2026-04-14 00:00 | 10:33:15.18 | +30:34:29.6 | HIP 51652 | 10.86 |
| 2026-04-14 12:00 | 10:33:03.38 | +30:34:29.8 | HIP 51652 | 10.88 |
| 2026-04-15 00:00 | 10:32:51.71 | +30:34:29.1 | HIP 51652 | 11.48 |
| 2026-04-15 12:00 | 10:32:40.15 | +30:34:27.5 | HIP 51652 | 12.56 |
| 2026-04-16 00:00 | 10:32:28.70 | +30:34:25.0 | HIP 51565 | 13.40 |