| Parameter |
Value |
| Designation |
C/2018 U1 (Lemmon) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-11-02T19:19:13.019520Z |
| Orbit solution date (soln_date, UTC) |
2025-04-11T14:44:11Z |
| Obs used |
2459 |
| NEO |
- |
| M1 |
6.400 |
| K1 |
8.750 |
| PC |
0.030 |
| Discovery observation (MPC, UTC) |
2018-10-27T04:27:14.112000Z |
| Discovery magnitude (MPC) |
20.00 G |
| Discovery observatory (MPC) |
G96 · University of Arizona Mt. Lemmon Survey |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2020-09-11.0000000 |
| e |
1.00080698 |
| q (au) |
4.993873 |
| a (au) |
-6188.361643 |
| i (deg) |
108.301379 |
| Ω (om, deg) |
75.476939 |
| ω (w, deg) |
180.420486 |
| M (ma, deg) |
-0.000846 |
Magnitude
Scatter + Global Linear
$$
M_a = (5.983 + 3.665\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
5.983 |
| n |
3.665 |
| gf |
0.858 |
| gb |
-0.500 |
| k |
0.942 |
| δ90 |
2.036 |
| 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 |
| 2018-10-27 |
2019-05-30 |
+10.1321 |
-9.496 |
| 2019-05-30 |
2021-10-08 |
-0.4295 |
+0.235 |
| 2022-02-03 |
2023-06-21 |
+3.8998 |
-2.549 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-06-01 00:00 |
07:10:33.69 |
-44:32:52.5 |
HIP 34634 |
1.50 |
| 2026-06-01 12:00 |
07:10:42.47 |
-44:31:14.8 |
HIP 34634 |
3.73 |
| 2026-06-02 00:00 |
07:10:51.29 |
-44:29:37.9 |
HIP 34634 |
5.98 |
| 2026-06-02 12:00 |
07:11:00.16 |
-44:28:02.1 |
HIP 34634 |
8.23 |
| 2026-06-03 00:00 |
07:11:09.08 |
-44:26:27.2 |
HIP 34634 |
10.47 |
| 2026-06-03 12:00 |
07:11:18.04 |
-44:24:53.2 |
HIP 34634 |
12.71 |
| 2026-06-04 00:00 |
07:11:27.04 |
-44:23:20.2 |
HIP 34634 |
14.94 |
| 2026-06-04 12:00 |
07:11:36.09 |
-44:21:48.2 |
HIP 34634 |
17.17 |
| 2026-06-05 00:00 |
07:11:45.18 |
-44:20:17.1 |
HIP 34634 |
19.39 |
| 2026-06-05 12:00 |
07:11:54.32 |
-44:18:46.9 |
HIP 34634 |
21.61 |
| 2026-06-06 00:00 |
07:12:03.50 |
-44:17:17.8 |
HIP 34634 |
23.83 |
| 2026-06-06 12:00 |
07:12:12.72 |
-44:15:49.6 |
HIP 34868 |
23.84 |
| 2026-06-07 00:00 |
07:12:21.97 |
-44:14:22.4 |
HIP 34868 |
21.98 |
| 2026-06-07 12:00 |
07:12:31.27 |
-44:12:56.1 |
HIP 34868 |
20.20 |
| 2026-06-08 00:00 |
07:12:40.61 |
-44:11:30.9 |
HIP 34868 |
18.54 |
| 2026-06-08 12:00 |
07:12:49.99 |
-44:10:06.6 |
HIP 34868 |
17.01 |
| 2026-06-09 00:00 |
07:12:59.41 |
-44:08:43.3 |
HIP 34868 |
15.65 |
| 2026-06-09 12:00 |
07:13:08.86 |
-44:07:20.9 |
HIP 34868 |
14.52 |
| 2026-06-10 00:00 |
07:13:18.35 |
-44:05:59.6 |
HIP 34868 |
13.67 |
| 2026-06-10 12:00 |
07:13:27.87 |
-44:04:39.2 |
HIP 34868 |
13.14 |
| 2026-06-11 00:00 |
07:13:37.44 |
-44:03:19.8 |
HIP 34868 |
12.98 |
| 2026-06-11 12:00 |
07:13:47.03 |
-44:02:01.4 |
HIP 34868 |
13.20 |
| 2026-06-12 00:00 |
07:13:56.66 |
-44:00:44.0 |
HIP 34868 |
13.77 |
| 2026-06-12 12:00 |
07:14:06.32 |
-43:59:27.6 |
HIP 34868 |
14.65 |
| 2026-06-13 00:00 |
07:14:16.02 |
-43:58:12.2 |
HIP 34868 |
15.80 |
| 2026-06-13 12:00 |
07:14:25.74 |
-43:56:57.8 |
HIP 35047 |
14.33 |
| 2026-06-14 00:00 |
07:14:35.50 |
-43:55:44.4 |
HIP 35047 |
12.64 |
| 2026-06-14 12:00 |
07:14:45.29 |
-43:54:32.0 |
HIP 35047 |
11.14 |
| 2026-06-15 00:00 |
07:14:55.11 |
-43:53:20.6 |
HIP 35047 |
9.88 |
| 2026-06-15 12:00 |
07:15:04.95 |
-43:52:10.2 |
HIP 35047 |
8.99 |
| 2026-06-16 00:00 |
07:15:14.82 |
-43:51:00.8 |
HIP 35047 |
8.56 |
| 2026-06-16 12:00 |
07:15:24.72 |
-43:49:52.4 |
HIP 35047 |
8.66 |
| 2026-06-17 00:00 |
07:15:34.65 |
-43:48:45.0 |
HIP 35047 |
9.27 |
| 2026-06-17 12:00 |
07:15:44.60 |
-43:47:38.6 |
HIP 35047 |
10.30 |
| 2026-06-18 00:00 |
07:15:54.58 |
-43:46:33.3 |
HIP 35047 |
11.64 |
| 2026-06-18 12:00 |
07:16:04.58 |
-43:45:28.9 |
HIP 35047 |
13.18 |
| 2026-06-19 00:00 |
07:16:14.60 |
-43:44:25.6 |
HIP 35047 |
14.87 |
| 2026-06-19 12:00 |
07:16:24.65 |
-43:43:23.2 |
HIP 35047 |
16.66 |
| 2026-06-20 00:00 |
07:16:34.72 |
-43:42:21.9 |
HIP 35047 |
18.51 |
| 2026-06-20 12:00 |
07:16:44.81 |
-43:41:21.6 |
HIP 35047 |
20.42 |
| 2026-06-21 00:00 |
07:16:54.92 |
-43:40:22.2 |
HIP 35327 |
22.02 |
| 2026-06-21 12:00 |
07:17:05.05 |
-43:39:23.9 |
HIP 35327 |
22.20 |
| 2026-06-22 00:00 |
07:17:15.19 |
-43:38:26.6 |
HIP 35387 |
22.01 |