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) |
|---|---|---|---|---|
| 2026-09-20 00:00 | 10:46:48.86 | +26:09:52.4 | HIP 52667 | 25.80 |
| 2026-09-20 12:00 | 10:46:56.98 | +26:09:25.1 | HIP 52667 | 26.07 |
| 2026-09-21 00:00 | 10:47:05.07 | +26:08:58.3 | HIP 52667 | 26.48 |
| 2026-09-21 12:00 | 10:47:13.14 | +26:08:32.1 | HIP 52667 | 27.01 |
| 2026-09-22 00:00 | 10:47:21.18 | +26:08:06.3 | HIP 52667 | 27.67 |
| 2026-09-22 12:00 | 10:47:29.19 | +26:07:41.0 | HIP 52667 | 28.43 |
| 2026-09-23 00:00 | 10:47:37.16 | +26:07:16.3 | HIP 52667 | 29.29 |
| 2026-09-23 12:00 | 10:47:45.11 | +26:06:52.0 | HIP 52667 | 30.24 |
| 2026-09-24 00:00 | 10:47:53.03 | +26:06:28.3 | HIP 52667 | 31.27 |
| 2026-09-24 12:00 | 10:48:00.92 | +26:06:05.1 | HIP 52667 | 32.37 |
| 2026-09-25 00:00 | 10:48:08.77 | +26:05:42.4 | HIP 52667 | 33.53 |
| 2026-09-25 12:00 | 10:48:16.60 | +26:05:20.2 | HIP 52667 | 34.75 |
| 2026-09-26 00:00 | 10:48:24.39 | +26:04:58.6 | HIP 52667 | 36.01 |
| 2026-09-26 12:00 | 10:48:32.14 | +26:04:37.5 | HIP 52994 | 36.54 |
| 2026-09-27 00:00 | 10:48:39.87 | +26:04:16.9 | HIP 52994 | 35.60 |
| 2026-09-27 12:00 | 10:48:47.56 | +26:03:56.8 | HIP 52998 | 34.34 |
| 2026-09-28 00:00 | 10:48:55.21 | +26:03:37.3 | HIP 52998 | 32.96 |
| 2026-09-28 12:00 | 10:49:02.83 | +26:03:18.3 | HIP 52998 | 31.63 |
| 2026-09-29 00:00 | 10:49:10.42 | +26:02:59.9 | HIP 52998 | 30.36 |
| 2026-09-29 12:00 | 10:49:17.96 | +26:02:42.0 | HIP 52998 | 29.15 |
| 2026-09-30 00:00 | 10:49:25.47 | +26:02:24.6 | HIP 52998 | 28.00 |
| 2026-09-30 12:00 | 10:49:32.95 | +26:02:07.8 | HIP 52998 | 26.93 |
| 2026-10-01 00:00 | 10:49:40.38 | +26:01:51.6 | HIP 52998 | 25.93 |
| 2026-10-01 12:00 | 10:49:47.78 | +26:01:35.9 | HIP 52998 | 25.03 |
| 2026-10-02 00:00 | 10:49:55.13 | +26:01:20.7 | HIP 52998 | 24.21 |
| 2026-10-02 12:00 | 10:50:02.45 | +26:01:06.1 | HIP 52998 | 23.50 |
| 2026-10-03 00:00 | 10:50:09.73 | +26:00:52.1 | HIP 52998 | 22.90 |
| 2026-10-03 12:00 | 10:50:16.97 | +26:00:38.6 | HIP 52998 | 22.42 |
| 2026-10-04 00:00 | 10:50:24.16 | +26:00:25.7 | HIP 52998 | 22.06 |
| 2026-10-04 12:00 | 10:50:31.32 | +26:00:13.3 | HIP 52998 | 21.82 |
| 2026-10-05 00:00 | 10:50:38.43 | +26:00:01.6 | HIP 52998 | 21.71 |
| 2026-10-05 12:00 | 10:50:45.49 | +25:59:50.4 | HIP 52998 | 21.73 |
| 2026-10-06 00:00 | 10:50:52.52 | +25:59:39.8 | HIP 52998 | 21.88 |
| 2026-10-06 12:00 | 10:50:59.50 | +25:59:29.8 | HIP 52998 | 22.14 |
| 2026-10-07 00:00 | 10:51:06.43 | +25:59:20.3 | HIP 52998 | 22.52 |
| 2026-10-07 12:00 | 10:51:13.32 | +25:59:11.4 | HIP 52998 | 23.00 |
| 2026-10-08 00:00 | 10:51:20.16 | +25:59:03.2 | HIP 52998 | 23.58 |
| 2026-10-08 12:00 | 10:51:26.96 | +25:58:55.5 | HIP 52998 | 24.25 |
| 2026-10-09 00:00 | 10:51:33.71 | +25:58:48.4 | HIP 52998 | 24.99 |
| 2026-10-09 12:00 | 10:51:40.40 | +25:58:41.9 | HIP 52998 | 25.81 |
| 2026-10-10 00:00 | 10:51:47.05 | +25:58:36.0 | HIP 52998 | 26.68 |
| 2026-10-10 12:00 | 10:51:53.66 | +25:58:30.7 | HIP 53262 | 26.67 |
| 2026-10-11 00:00 | 10:52:00.21 | +25:58:26.1 | HIP 53262 | 25.47 |