C/2021 U4 (Leonard)
| Parameter |
Value |
| Designation |
C/2021 U4 (Leonard) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-12-21T23:21:30.078720Z |
| Orbit solution date (soln_date, UTC) |
2025-01-14T17:42:12Z |
| Obs used |
37 |
| NEO |
- |
| M1 |
18.800 |
| K1 |
4.500 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-10-31T07:11:48.940800Z |
| Discovery magnitude (MPC) |
19.87 G |
| Discovery observatory (MPC) |
G96 · Mt. Lemmon Survey |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-10-27.0000000 |
| e |
0.95934634 |
| q (au) |
1.787292 |
| a (au) |
43.963864 |
| i (deg) |
152.875238 |
| Ω (om, deg) |
241.798913 |
| ω (w, deg) |
237.287717 |
| M (ma, deg) |
359.810748 |
Magnitude
Scatter + Global Linear
$$
M_a = (19.361 + 2.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
19.361 |
| n |
2.000 |
| gf |
0.990 |
| gb |
-0.500 |
| k |
0.800 |
| δ90 |
5.672 |
| 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
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-02-03 00:00 |
15:26:56.94 |
-11:33:25.6 |
HIP 75554 |
15.11 |
| 2026-02-03 12:00 |
15:26:57.34 |
-11:32:59.1 |
HIP 75554 |
15.44 |
| 2026-02-04 00:00 |
15:26:57.65 |
-11:32:32.3 |
HIP 75554 |
15.77 |
| 2026-02-04 12:00 |
15:26:57.89 |
-11:32:05.1 |
HIP 75554 |
16.09 |
| 2026-02-05 00:00 |
15:26:58.04 |
-11:31:37.5 |
HIP 75554 |
16.40 |
| 2026-02-05 12:00 |
15:26:58.11 |
-11:31:09.6 |
HIP 75554 |
16.71 |
| 2026-02-06 00:00 |
15:26:58.10 |
-11:30:41.3 |
HIP 75554 |
17.02 |
| 2026-02-06 12:00 |
15:26:58.01 |
-11:30:12.7 |
HIP 75554 |
17.32 |
| 2026-02-07 00:00 |
15:26:57.83 |
-11:29:43.8 |
HIP 75554 |
17.62 |
| 2026-02-07 12:00 |
15:26:57.57 |
-11:29:14.5 |
HIP 75554 |
17.91 |
| 2026-02-08 00:00 |
15:26:57.23 |
-11:28:44.8 |
HIP 75554 |
18.21 |
| 2026-02-08 12:00 |
15:26:56.81 |
-11:28:14.8 |
HIP 75554 |
18.51 |
| 2026-02-09 00:00 |
15:26:56.30 |
-11:27:44.4 |
HIP 75554 |
18.80 |
| 2026-02-09 12:00 |
15:26:55.71 |
-11:27:13.7 |
HIP 75554 |
19.10 |
| 2026-02-10 00:00 |
15:26:55.04 |
-11:26:42.6 |
HIP 75729 |
19.29 |
| 2026-02-10 12:00 |
15:26:54.28 |
-11:26:11.2 |
HIP 75729 |
19.49 |
| 2026-02-11 00:00 |
15:26:53.44 |
-11:25:39.5 |
HIP 75729 |
19.72 |
| 2026-02-11 12:00 |
15:26:52.52 |
-11:25:07.4 |
HIP 75729 |
19.99 |
| 2026-02-12 00:00 |
15:26:51.51 |
-11:24:34.9 |
HIP 75729 |
20.29 |
| 2026-02-12 12:00 |
15:26:50.42 |
-11:24:02.2 |
HIP 75729 |
20.63 |
| 2026-02-13 00:00 |
15:26:49.24 |
-11:23:29.0 |
HIP 75729 |
21.00 |
| 2026-02-13 12:00 |
15:26:47.98 |
-11:22:55.5 |
HIP 75729 |
21.40 |
| 2026-02-14 00:00 |
15:26:46.63 |
-11:22:21.7 |
HIP 75729 |
21.83 |
| 2026-02-14 12:00 |
15:26:45.20 |
-11:21:47.6 |
HIP 75729 |
22.30 |
| 2026-02-15 00:00 |
15:26:43.68 |
-11:21:13.1 |
HIP 75554 |
22.68 |
| 2026-02-15 12:00 |
15:26:42.08 |
-11:20:38.2 |
HIP 75554 |
23.06 |
| 2026-02-16 00:00 |
15:26:40.39 |
-11:20:03.0 |
HIP 75554 |
23.45 |
| 2026-02-16 12:00 |
15:26:38.62 |
-11:19:27.5 |
HIP 75554 |
23.85 |
| 2026-02-17 00:00 |
15:26:36.76 |
-11:18:51.7 |
HIP 75554 |
24.27 |
| 2026-02-17 12:00 |
15:26:34.82 |
-11:18:15.5 |
HIP 75663 |
24.62 |
| 2026-02-18 00:00 |
15:26:32.79 |
-11:17:39.0 |
HIP 75663 |
24.40 |
| 2026-02-18 12:00 |
15:26:30.68 |
-11:17:02.1 |
HIP 75663 |
24.21 |
| 2026-02-19 00:00 |
15:26:28.48 |
-11:16:25.0 |
HIP 75663 |
24.05 |
| 2026-02-19 12:00 |
15:26:26.20 |
-11:15:47.5 |
HIP 75663 |
23.94 |
| 2026-02-20 00:00 |
15:26:23.83 |
-11:15:09.6 |
HIP 75487 |
23.39 |
| 2026-02-20 12:00 |
15:26:21.37 |
-11:14:31.5 |
HIP 75487 |
22.52 |
| 2026-02-21 00:00 |
15:26:18.83 |
-11:13:53.0 |
HIP 75487 |
21.63 |
| 2026-02-21 12:00 |
15:26:16.21 |
-11:13:14.2 |
HIP 75487 |
20.72 |
| 2026-02-22 00:00 |
15:26:13.50 |
-11:12:35.1 |
HIP 75487 |
19.79 |
| 2026-02-22 12:00 |
15:26:10.70 |
-11:11:55.6 |
HIP 75487 |
18.84 |
| 2026-02-23 00:00 |
15:26:07.82 |
-11:11:15.9 |
HIP 75487 |
17.87 |
| 2026-02-23 12:00 |
15:26:04.86 |
-11:10:35.8 |
HIP 75487 |
16.88 |
| 2026-02-24 00:00 |
15:26:01.81 |
-11:09:55.4 |
HIP 75487 |
15.87 |