C/2018 U1 (Lemmon)
| 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 · 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
$$
M_a = (5.982 + 3.665\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
5.982 |
| n |
3.665 |
| gf |
0.858 |
| gb |
-0.500 |
| k |
0.942 |
| δ90 |
2.042 |
| 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) |
| 2026-02-03 00:00 |
07:23:40.61 |
-54:20:51.1 |
HIP 35719 |
14.06 |
| 2026-02-03 12:00 |
07:23:21.96 |
-54:19:06.0 |
HIP 35719 |
12.38 |
| 2026-02-04 00:00 |
07:23:03.41 |
-54:17:19.6 |
HIP 35719 |
11.42 |
| 2026-02-04 12:00 |
07:22:44.96 |
-54:15:31.9 |
HIP 35719 |
11.36 |
| 2026-02-05 00:00 |
07:22:26.61 |
-54:13:42.9 |
HIP 35719 |
12.20 |
| 2026-02-05 12:00 |
07:22:08.37 |
-54:11:52.7 |
HIP 35719 |
13.80 |
| 2026-02-06 00:00 |
07:21:50.23 |
-54:10:01.1 |
HIP 35546 |
15.39 |
| 2026-02-06 12:00 |
07:21:32.20 |
-54:08:08.3 |
HIP 35546 |
13.31 |
| 2026-02-07 00:00 |
07:21:14.27 |
-54:06:14.2 |
HIP 35546 |
11.80 |
| 2026-02-07 12:00 |
07:20:56.46 |
-54:04:18.8 |
HIP 35546 |
11.08 |
| 2026-02-08 00:00 |
07:20:38.75 |
-54:02:22.3 |
HIP 35546 |
11.31 |
| 2026-02-08 12:00 |
07:20:21.16 |
-54:00:24.5 |
HIP 35546 |
12.43 |
| 2026-02-09 00:00 |
07:20:03.68 |
-53:58:25.4 |
HIP 35546 |
14.23 |
| 2026-02-09 12:00 |
07:19:46.31 |
-53:56:25.2 |
HIP 35546 |
16.50 |
| 2026-02-10 00:00 |
07:19:29.07 |
-53:54:23.8 |
HIP 35546 |
19.07 |
| 2026-02-10 12:00 |
07:19:11.94 |
-53:52:21.1 |
HIP 35546 |
21.83 |
| 2026-02-11 00:00 |
07:18:54.92 |
-53:50:17.3 |
HIP 35223 |
20.54 |
| 2026-02-11 12:00 |
07:18:38.03 |
-53:48:12.3 |
HIP 35223 |
19.37 |
| 2026-02-12 00:00 |
07:18:21.26 |
-53:46:06.2 |
HIP 35223 |
18.72 |
| 2026-02-12 12:00 |
07:18:04.62 |
-53:43:58.9 |
HIP 35223 |
18.65 |
| 2026-02-13 00:00 |
07:17:48.09 |
-53:41:50.5 |
HIP 35131 |
18.89 |
| 2026-02-13 12:00 |
07:17:31.69 |
-53:39:41.0 |
HIP 35131 |
15.98 |
| 2026-02-14 00:00 |
07:17:15.42 |
-53:37:30.4 |
HIP 35131 |
13.25 |
| 2026-02-14 12:00 |
07:16:59.28 |
-53:35:18.6 |
HIP 35131 |
10.81 |
| 2026-02-15 00:00 |
07:16:43.26 |
-53:33:05.8 |
HIP 35131 |
8.94 |
| 2026-02-15 12:00 |
07:16:27.38 |
-53:30:51.9 |
HIP 35131 |
8.02 |
| 2026-02-16 00:00 |
07:16:11.62 |
-53:28:36.9 |
HIP 35131 |
8.38 |
| 2026-02-16 12:00 |
07:15:56.00 |
-53:26:20.9 |
HIP 35131 |
9.88 |
| 2026-02-17 00:00 |
07:15:40.51 |
-53:24:03.9 |
HIP 35131 |
12.09 |
| 2026-02-17 12:00 |
07:15:25.15 |
-53:21:45.8 |
HIP 35131 |
14.71 |
| 2026-02-18 00:00 |
07:15:09.93 |
-53:19:26.8 |
HIP 35131 |
17.55 |
| 2026-02-18 12:00 |
07:14:54.84 |
-53:17:06.7 |
HIP 35131 |
20.52 |
| 2026-02-19 00:00 |
07:14:39.90 |
-53:14:45.6 |
HIP 34788 |
23.13 |
| 2026-02-19 12:00 |
07:14:25.09 |
-53:12:23.6 |
HIP 34788 |
20.87 |
| 2026-02-20 00:00 |
07:14:10.41 |
-53:10:00.6 |
HIP 34788 |
18.91 |
| 2026-02-20 12:00 |
07:13:55.88 |
-53:07:36.7 |
HIP 34788 |
17.36 |
| 2026-02-21 00:00 |
07:13:41.49 |
-53:05:11.9 |
HIP 34788 |
16.33 |
| 2026-02-21 12:00 |
07:13:27.24 |
-53:02:46.1 |
HIP 34788 |
15.93 |
| 2026-02-22 00:00 |
07:13:13.13 |
-53:00:19.5 |
HIP 34788 |
16.20 |
| 2026-02-22 12:00 |
07:12:59.16 |
-52:57:51.9 |
HIP 34788 |
17.11 |
| 2026-02-23 00:00 |
07:12:45.34 |
-52:55:23.5 |
HIP 34847 |
14.54 |
| 2026-02-23 12:00 |
07:12:31.66 |
-52:52:54.2 |
HIP 34847 |
12.13 |
| 2026-02-24 00:00 |
07:12:18.12 |
-52:50:24.1 |
HIP 34847 |
10.18 |