C/2021 A1 (Leonard)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2021 A1 (Leonard) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2022-01-03T07:01:27.517440Z |
| Orbit solution date (soln_date, UTC) | 2025-01-02T20:12:26Z |
| Obs used | 2422 |
| NEO | - |
| M1 | 12.500 |
| K1 | 4.500 |
| PC | - |
| Discovery observation (MPC, UTC) | 2021-01-03T13:00:51.696000Z |
| Discovery magnitude (MPC) | 19.00 G |
| Discovery observatory (MPC) | G96 · University of Arizona Mt. Lemmon Survey |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2021-07-11.0000000 |
| e | 1.00010048 |
| q (au) | 0.615230 |
| a (au) | -6122.881779 |
| i (deg) | 132.685813 |
| Ω (om, deg) | 255.889104 |
| ω (w, deg) | 225.087713 |
| M (ma, deg) | -0.000363 |
Magnitude
Scatter + Global Linear
$$ M_a = (11.021 + 5.164\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 11.021 |
| n | 5.164 |
| gf | 0.800 |
| gb | -0.920 |
| k | 0.834 |
| 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 |
|---|---|---|---|
| 2020-04-11 | 2021-10-30 | +1.5118 | -0.912 |
| 2021-10-30 | 2021-12-06 | -9.8456 | +0.200 |
| 2021-12-06 | 2022-01-03 | +28.4757 | +3.588 |
| 2022-01-03 | 2022-05-28 | +0.7618 | -1.274 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) | RA (J2000) | Dec (J2000) | Nearest HIP | Dist from HIP (arcmin) |
|---|---|---|---|---|
| 2026-09-20 00:00 | 15:53:40.21 | -04:28:36.4 | HIP 77843 | 0.70 |
| 2026-09-20 12:00 | 15:53:43.44 | -04:29:07.3 | HIP 77843 | 0.93 |
| 2026-09-21 00:00 | 15:53:46.73 | -04:29:38.2 | HIP 77843 | 1.76 |
| 2026-09-21 12:00 | 15:53:50.08 | -04:30:09.1 | HIP 77843 | 2.70 |
| 2026-09-22 00:00 | 15:53:53.47 | -04:30:40.1 | HIP 77843 | 3.67 |
| 2026-09-22 12:00 | 15:53:56.91 | -04:31:11.0 | HIP 77843 | 4.67 |
| 2026-09-23 00:00 | 15:54:00.41 | -04:31:41.9 | HIP 77843 | 5.67 |
| 2026-09-23 12:00 | 15:54:03.96 | -04:32:12.9 | HIP 77843 | 6.69 |
| 2026-09-24 00:00 | 15:54:07.55 | -04:32:43.8 | HIP 77843 | 7.72 |
| 2026-09-24 12:00 | 15:54:11.20 | -04:33:14.8 | HIP 77843 | 8.77 |
| 2026-09-25 00:00 | 15:54:14.89 | -04:33:45.7 | HIP 77843 | 9.82 |
| 2026-09-25 12:00 | 15:54:18.64 | -04:34:16.6 | HIP 77843 | 10.89 |
| 2026-09-26 00:00 | 15:54:22.43 | -04:34:47.5 | HIP 77843 | 11.96 |
| 2026-09-26 12:00 | 15:54:26.27 | -04:35:18.4 | HIP 77843 | 13.05 |
| 2026-09-27 00:00 | 15:54:30.16 | -04:35:49.3 | HIP 77843 | 14.15 |
| 2026-09-27 12:00 | 15:54:34.10 | -04:36:20.1 | HIP 77843 | 15.25 |
| 2026-09-28 00:00 | 15:54:38.09 | -04:36:51.0 | HIP 77843 | 16.37 |
| 2026-09-28 12:00 | 15:54:42.12 | -04:37:21.8 | HIP 77843 | 17.50 |
| 2026-09-29 00:00 | 15:54:46.20 | -04:37:52.6 | HIP 77843 | 18.64 |
| 2026-09-29 12:00 | 15:54:50.33 | -04:38:23.3 | HIP 77843 | 19.79 |
| 2026-09-30 00:00 | 15:54:54.50 | -04:38:54.1 | HIP 77843 | 20.95 |
| 2026-09-30 12:00 | 15:54:58.72 | -04:39:24.8 | HIP 77843 | 22.12 |
| 2026-10-01 00:00 | 15:55:02.98 | -04:39:55.4 | HIP 77843 | 23.30 |
| 2026-10-01 12:00 | 15:55:07.29 | -04:40:26.0 | HIP 77843 | 24.48 |
| 2026-10-02 00:00 | 15:55:11.65 | -04:40:56.6 | HIP 77843 | 25.68 |
| 2026-10-02 12:00 | 15:55:16.05 | -04:41:27.2 | HIP 77843 | 26.89 |
| 2026-10-03 00:00 | 15:55:20.50 | -04:41:57.7 | HIP 77843 | 28.11 |
| 2026-10-03 12:00 | 15:55:24.98 | -04:42:28.1 | HIP 77899 | 29.17 |
| 2026-10-04 00:00 | 15:55:29.52 | -04:42:58.5 | HIP 77899 | 30.17 |
| 2026-10-04 12:00 | 15:55:34.09 | -04:43:28.9 | HIP 77899 | 31.18 |
| 2026-10-05 00:00 | 15:55:38.71 | -04:43:59.2 | HIP 77899 | 32.22 |
| 2026-10-05 12:00 | 15:55:43.38 | -04:44:29.4 | HIP 77899 | 33.28 |
| 2026-10-06 00:00 | 15:55:48.08 | -04:44:59.6 | HIP 78089 | 33.42 |
| 2026-10-06 12:00 | 15:55:52.83 | -04:45:29.7 | HIP 78089 | 33.43 |
| 2026-10-07 00:00 | 15:55:57.62 | -04:45:59.8 | HIP 78089 | 33.49 |
| 2026-10-07 12:00 | 15:56:02.45 | -04:46:29.8 | HIP 78089 | 33.60 |
| 2026-10-08 00:00 | 15:56:07.33 | -04:46:59.7 | HIP 78190 | 33.28 |
| 2026-10-08 12:00 | 15:56:12.24 | -04:47:29.6 | HIP 78190 | 32.60 |
| 2026-10-09 00:00 | 15:56:17.19 | -04:47:59.3 | HIP 78190 | 31.94 |
| 2026-10-09 12:00 | 15:56:22.19 | -04:48:29.0 | HIP 78190 | 31.32 |
| 2026-10-10 00:00 | 15:56:27.22 | -04:48:58.6 | HIP 78190 | 30.74 |
| 2026-10-10 12:00 | 15:56:32.29 | -04:49:28.2 | HIP 78190 | 30.20 |
| 2026-10-11 00:00 | 15:56:37.40 | -04:49:57.6 | HIP 78190 | 29.71 |