261P/Larson
| Parameter |
Value |
| Designation |
261P/Larson |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2019-06-18T10:37:49.324800Z |
| Orbit solution date (soln_date, UTC) |
2026-01-07T15:43:02Z |
| Obs used |
1303 |
| NEO |
- |
| M1 |
6.300 |
| K1 |
30.750 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2016-07-12.0000000 |
| e |
0.41609321 |
| q (au) |
2.062403 |
| a (au) |
3.532077 |
| i (deg) |
6.079315 |
| Ω (om, deg) |
295.237633 |
| ω (w, deg) |
61.517431 |
| M (ma, deg) |
200.915465 |
Magnitude
Scatter + Global Linear
$$
M_a = (11.348 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
11.348 |
| n |
6.000 |
| gf |
1.000 |
| gb |
-0.500 |
| k |
1.000 |
| 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 |
| 2025-05-25 |
2025-09-28 |
+18.8143 |
-6.709 |
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 |
23:34:23.32 |
+02:14:06.4 |
HIP 116410 |
14.94 |
| 2026-02-03 12:00 |
23:35:27.44 |
+02:20:47.4 |
HIP 116410 |
7.40 |
| 2026-02-04 00:00 |
23:36:31.57 |
+02:27:28.6 |
HIP 116463 |
9.17 |
| 2026-02-04 12:00 |
23:37:35.72 |
+02:34:10.1 |
HIP 116660 |
23.05 |
| 2026-02-05 00:00 |
23:38:39.88 |
+02:40:51.8 |
HIP 116786 |
24.09 |
| 2026-02-05 12:00 |
23:39:44.07 |
+02:47:33.7 |
HIP 116786 |
6.96 |
| 2026-02-06 00:00 |
23:40:48.27 |
+02:54:15.8 |
HIP 116786 |
10.97 |
| 2026-02-06 12:00 |
23:41:52.49 |
+03:00:58.1 |
HIP 116786 |
28.22 |
| 2026-02-07 00:00 |
23:42:56.72 |
+03:07:40.6 |
HIP 116866 |
38.87 |
| 2026-02-07 12:00 |
23:44:00.97 |
+03:14:23.2 |
HIP 117148 |
34.98 |
| 2026-02-08 00:00 |
23:45:05.24 |
+03:21:06.0 |
HIP 117245 |
21.16 |
| 2026-02-08 12:00 |
23:46:09.53 |
+03:27:48.9 |
HIP 117245 |
3.76 |
| 2026-02-09 00:00 |
23:47:13.83 |
+03:34:32.0 |
HIP 117245 |
13.63 |
| 2026-02-09 12:00 |
23:48:18.15 |
+03:41:15.2 |
HIP 117474 |
16.67 |
| 2026-02-10 00:00 |
23:49:22.49 |
+03:47:58.4 |
HIP 117474 |
16.43 |
| 2026-02-10 12:00 |
23:50:26.84 |
+03:54:41.8 |
HIP 117474 |
29.45 |
| 2026-02-11 00:00 |
23:51:31.21 |
+04:01:25.3 |
HIP 117530 |
33.62 |
| 2026-02-11 12:00 |
23:52:35.59 |
+04:08:08.8 |
HIP 117656 |
36.44 |
| 2026-02-12 00:00 |
23:53:39.99 |
+04:14:52.4 |
HIP 117804 |
33.96 |
| 2026-02-12 12:00 |
23:54:44.41 |
+04:21:36.0 |
HIP 118013 |
28.28 |
| 2026-02-13 00:00 |
23:55:48.84 |
+04:28:19.6 |
HIP 118013 |
11.77 |
| 2026-02-13 12:00 |
23:56:53.29 |
+04:35:03.3 |
HIP 118054 |
8.58 |
| 2026-02-14 00:00 |
23:57:57.76 |
+04:41:47.0 |
HIP 118054 |
17.64 |
| 2026-02-14 12:00 |
23:59:02.24 |
+04:48:30.6 |
HIP 118235 |
32.13 |
| 2026-02-15 00:00 |
00:00:06.73 |
+04:55:14.3 |
HIP 129 |
35.67 |
| 2026-02-15 12:00 |
00:01:11.24 |
+05:01:57.9 |
HIP 129 |
21.60 |
| 2026-02-16 00:00 |
00:02:15.77 |
+05:08:41.4 |
HIP 129 |
16.35 |
| 2026-02-16 12:00 |
00:03:20.31 |
+05:15:24.9 |
HIP 129 |
25.98 |
| 2026-02-17 00:00 |
00:04:24.86 |
+05:22:08.3 |
HIP 579 |
39.52 |
| 2026-02-17 12:00 |
00:05:29.43 |
+05:28:51.6 |
HIP 538 |
25.82 |
| 2026-02-18 00:00 |
00:06:34.02 |
+05:35:34.9 |
HIP 538 |
13.95 |
| 2026-02-18 12:00 |
00:07:38.61 |
+05:42:18.0 |
HIP 538 |
18.15 |
| 2026-02-19 00:00 |
00:08:43.22 |
+05:49:00.9 |
HIP 593 |
32.37 |
| 2026-02-19 12:00 |
00:09:47.85 |
+05:55:43.8 |
HIP 907 |
26.27 |
| 2026-02-20 00:00 |
00:10:52.48 |
+06:02:26.4 |
HIP 907 |
9.99 |
| 2026-02-20 12:00 |
00:11:57.13 |
+06:09:08.9 |
HIP 907 |
10.77 |
| 2026-02-21 00:00 |
00:13:01.79 |
+06:15:51.2 |
HIP 1095 |
21.27 |
| 2026-02-21 12:00 |
00:14:06.46 |
+06:22:33.3 |
HIP 1095 |
13.87 |
| 2026-02-22 00:00 |
00:15:11.15 |
+06:29:15.2 |
HIP 1095 |
23.20 |
| 2026-02-22 12:00 |
00:16:15.84 |
+06:35:56.9 |
HIP 1130 |
36.43 |
| 2026-02-23 00:00 |
00:17:20.55 |
+06:42:38.3 |
HIP 1535 |
43.38 |
| 2026-02-23 12:00 |
00:18:25.27 |
+06:49:19.4 |
HIP 1535 |
29.55 |
| 2026-02-24 00:00 |
00:19:30.00 |
+06:56:00.3 |
HIP 1535 |
21.67 |