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) |
|---|---|---|---|---|
| 2026-07-29 00:00 | 10:31:51.73 | +27:35:19.1 | HIP 51664 | 21.94 |
| 2026-07-29 12:00 | 10:31:59.45 | +27:34:15.8 | HIP 51664 | 21.09 |
| 2026-07-30 00:00 | 10:32:07.20 | +27:33:12.7 | HIP 51664 | 20.39 |
| 2026-07-30 12:00 | 10:32:14.99 | +27:32:09.8 | HIP 51664 | 19.86 |
| 2026-07-31 00:00 | 10:32:22.81 | +27:31:07.0 | HIP 51664 | 19.52 |
| 2026-07-31 12:00 | 10:32:30.67 | +27:30:04.5 | HIP 51664 | 19.38 |
| 2026-08-01 00:00 | 10:32:38.55 | +27:29:02.1 | HIP 51664 | 19.44 |
| 2026-08-01 12:00 | 10:32:46.47 | +27:28:00.0 | HIP 51664 | 19.71 |
| 2026-08-02 00:00 | 10:32:54.42 | +27:26:57.9 | HIP 51664 | 20.18 |
| 2026-08-02 12:00 | 10:33:02.40 | +27:25:56.1 | HIP 51664 | 20.84 |
| 2026-08-03 00:00 | 10:33:10.41 | +27:24:54.5 | HIP 51664 | 21.66 |
| 2026-08-03 12:00 | 10:33:18.44 | +27:23:53.1 | HIP 51664 | 22.64 |
| 2026-08-04 00:00 | 10:33:26.51 | +27:22:51.9 | HIP 51664 | 23.75 |
| 2026-08-04 12:00 | 10:33:34.60 | +27:21:50.9 | HIP 51823 | 23.56 |
| 2026-08-05 00:00 | 10:33:42.73 | +27:20:50.1 | HIP 51823 | 21.52 |
| 2026-08-05 12:00 | 10:33:50.88 | +27:19:49.6 | HIP 51823 | 19.49 |
| 2026-08-06 00:00 | 10:33:59.05 | +27:18:49.2 | HIP 51823 | 17.47 |
| 2026-08-06 12:00 | 10:34:07.26 | +27:17:49.1 | HIP 51823 | 15.45 |
| 2026-08-07 00:00 | 10:34:15.48 | +27:16:49.2 | HIP 51823 | 13.45 |
| 2026-08-07 12:00 | 10:34:23.74 | +27:15:49.5 | HIP 51823 | 11.46 |
| 2026-08-08 00:00 | 10:34:32.01 | +27:14:50.0 | HIP 51823 | 9.52 |
| 2026-08-08 12:00 | 10:34:40.31 | +27:13:50.8 | HIP 51823 | 7.65 |
| 2026-08-09 00:00 | 10:34:48.64 | +27:12:51.8 | HIP 51823 | 5.93 |
| 2026-08-09 12:00 | 10:34:56.98 | +27:11:53.1 | HIP 51823 | 4.52 |
| 2026-08-10 00:00 | 10:35:05.35 | +27:10:54.5 | HIP 51823 | 3.81 |
| 2026-08-10 12:00 | 10:35:13.74 | +27:09:56.3 | HIP 51823 | 4.16 |
| 2026-08-11 00:00 | 10:35:22.15 | +27:08:58.3 | HIP 51823 | 5.38 |
| 2026-08-11 12:00 | 10:35:30.58 | +27:08:00.5 | HIP 51823 | 7.03 |
| 2026-08-12 00:00 | 10:35:39.03 | +27:07:03.0 | HIP 51823 | 8.88 |
| 2026-08-12 12:00 | 10:35:47.50 | +27:06:05.8 | HIP 51823 | 10.82 |
| 2026-08-13 00:00 | 10:35:55.98 | +27:05:08.8 | HIP 51893 | 12.32 |
| 2026-08-13 12:00 | 10:36:04.49 | +27:04:12.1 | HIP 51893 | 13.00 |
| 2026-08-14 00:00 | 10:36:13.01 | +27:03:15.7 | HIP 51893 | 13.97 |
| 2026-08-14 12:00 | 10:36:21.54 | +27:02:19.6 | HIP 51893 | 15.17 |
| 2026-08-15 00:00 | 10:36:30.09 | +27:01:23.7 | HIP 51893 | 16.56 |
| 2026-08-15 12:00 | 10:36:38.66 | +27:00:28.1 | HIP 51893 | 18.08 |
| 2026-08-16 00:00 | 10:36:47.24 | +26:59:32.8 | HIP 51893 | 19.71 |
| 2026-08-16 12:00 | 10:36:55.83 | +26:58:37.8 | HIP 51893 | 21.42 |
| 2026-08-17 00:00 | 10:37:04.44 | +26:57:43.1 | HIP 51893 | 23.20 |
| 2026-08-17 12:00 | 10:37:13.06 | +26:56:48.7 | HIP 52051 | 24.14 |
| 2026-08-18 00:00 | 10:37:21.69 | +26:55:54.6 | HIP 52051 | 22.38 |
| 2026-08-18 12:00 | 10:37:30.33 | +26:55:00.7 | HIP 52051 | 20.68 |
| 2026-08-19 00:00 | 10:37:38.99 | +26:54:07.2 | HIP 52051 | 19.08 |