| Parameter |
Value |
| Designation |
261P/Larson |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2019-06-17T05:55:39.953280Z |
| Orbit solution date (soln_date, UTC) |
2026-03-31T09:42:39Z |
| Obs used |
1333 |
| NEO |
- |
| M1 |
5.800 |
| K1 |
32.250 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2016-09-27.0000000 |
| e |
0.41834775 |
| q (au) |
2.050551 |
| a (au) |
3.525389 |
| i (deg) |
6.053412 |
| Ω (om, deg) |
294.373787 |
| ω (w, deg) |
62.549411 |
| M (ma, deg) |
212.105953 |
Magnitude
Scatter + Global Linear
$$
M_a = (10.802 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
10.802 |
| 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 |
2026-02-13 |
+27.6125 |
-9.326 |
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 |
03:49:59.88 |
+23:39:17.1 |
HIP 17900 |
5.08 |
| 2026-06-01 12:00 |
03:51:03.74 |
+23:42:11.0 |
HIP 18018 |
12.04 |
| 2026-06-02 00:00 |
03:52:07.56 |
+23:45:03.4 |
HIP 18018 |
17.38 |
| 2026-06-02 12:00 |
03:53:11.34 |
+23:47:54.0 |
HIP 18018 |
30.02 |
| 2026-06-03 00:00 |
03:54:15.08 |
+23:50:43.1 |
HIP 18263 |
30.98 |
| 2026-06-03 12:00 |
03:55:18.77 |
+23:53:30.5 |
HIP 18263 |
30.64 |
| 2026-06-04 00:00 |
03:56:22.43 |
+23:56:16.2 |
HIP 18559 |
28.39 |
| 2026-06-04 12:00 |
03:57:26.04 |
+23:59:00.3 |
HIP 18559 |
13.83 |
| 2026-06-05 00:00 |
03:58:29.60 |
+24:01:42.8 |
HIP 18559 |
3.73 |
| 2026-06-05 12:00 |
03:59:33.12 |
+24:04:23.7 |
HIP 18559 |
16.49 |
| 2026-06-06 00:00 |
04:00:36.59 |
+24:07:02.9 |
HIP 18559 |
31.05 |
| 2026-06-06 12:00 |
04:01:40.02 |
+24:09:40.5 |
HIP 19009 |
37.03 |
| 2026-06-07 00:00 |
04:02:43.40 |
+24:12:16.4 |
HIP 19009 |
23.18 |
| 2026-06-07 12:00 |
04:03:46.74 |
+24:14:50.8 |
HIP 19009 |
11.64 |
| 2026-06-08 00:00 |
04:04:50.02 |
+24:17:23.4 |
HIP 19009 |
12.78 |
| 2026-06-08 12:00 |
04:05:53.26 |
+24:19:54.5 |
HIP 19137 |
24.16 |
| 2026-06-09 00:00 |
04:06:56.45 |
+24:22:23.9 |
HIP 19137 |
24.54 |
| 2026-06-09 12:00 |
04:07:59.58 |
+24:24:51.7 |
HIP 19436 |
31.35 |
| 2026-06-10 00:00 |
04:09:02.67 |
+24:27:17.9 |
HIP 19436 |
24.75 |
| 2026-06-10 12:00 |
04:10:05.71 |
+24:29:42.4 |
HIP 19464 |
22.81 |
| 2026-06-11 00:00 |
04:11:08.69 |
+24:32:05.3 |
HIP 19586 |
11.53 |
| 2026-06-11 12:00 |
04:12:11.62 |
+24:34:26.6 |
HIP 19604 |
2.27 |
| 2026-06-12 00:00 |
04:13:14.50 |
+24:36:46.3 |
HIP 19604 |
16.75 |
| 2026-06-12 12:00 |
04:14:17.32 |
+24:39:04.3 |
HIP 19829 |
23.30 |
| 2026-06-13 00:00 |
04:15:20.08 |
+24:41:20.8 |
HIP 19829 |
22.95 |
| 2026-06-13 12:00 |
04:16:22.79 |
+24:43:35.6 |
HIP 20047 |
23.21 |
| 2026-06-14 00:00 |
04:17:25.44 |
+24:45:48.7 |
HIP 20047 |
13.26 |
| 2026-06-14 12:00 |
04:18:28.03 |
+24:48:00.3 |
HIP 20065 |
7.79 |
| 2026-06-15 00:00 |
04:19:30.56 |
+24:50:10.2 |
HIP 20091 |
17.42 |
| 2026-06-15 12:00 |
04:20:33.03 |
+24:52:18.6 |
HIP 20091 |
29.47 |
| 2026-06-16 00:00 |
04:21:35.44 |
+24:54:25.3 |
HIP 20491 |
39.84 |
| 2026-06-16 12:00 |
04:22:37.79 |
+24:56:30.4 |
HIP 20491 |
34.32 |
| 2026-06-17 00:00 |
04:23:40.07 |
+24:58:33.9 |
HIP 20604 |
30.10 |
| 2026-06-17 12:00 |
04:24:42.29 |
+25:00:35.7 |
HIP 20604 |
24.00 |
| 2026-06-18 00:00 |
04:25:44.44 |
+25:02:36.0 |
HIP 20812 |
24.85 |
| 2026-06-18 12:00 |
04:26:46.52 |
+25:04:34.7 |
HIP 20812 |
10.80 |
| 2026-06-19 00:00 |
04:27:48.54 |
+25:06:31.8 |
HIP 20812 |
4.34 |
| 2026-06-19 12:00 |
04:28:50.49 |
+25:08:27.2 |
HIP 20812 |
17.95 |
| 2026-06-20 00:00 |
04:29:52.37 |
+25:10:21.1 |
HIP 21103 |
20.86 |
| 2026-06-20 12:00 |
04:30:54.19 |
+25:12:13.4 |
HIP 21103 |
11.55 |
| 2026-06-21 00:00 |
04:31:55.93 |
+25:14:04.1 |
HIP 21174 |
6.55 |
| 2026-06-21 12:00 |
04:32:57.60 |
+25:15:53.2 |
HIP 21174 |
9.39 |
| 2026-06-22 00:00 |
04:33:59.20 |
+25:17:40.7 |
HIP 21174 |
22.98 |