| Parameter |
Value |
| Designation |
171P/Spahr |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2019-01-13T17:32:17.119680Z |
| Orbit solution date (soln_date, UTC) |
2026-03-07T15:25:06Z |
| Obs used |
681 |
| NEO |
- |
| M1 |
11.600 |
| K1 |
22.750 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2018-04-24.0000000 |
| e |
0.50194793 |
| q (au) |
1.772172 |
| a (au) |
3.558207 |
| i (deg) |
21.933094 |
| Ω (om, deg) |
101.699366 |
| ω (w, deg) |
347.157914 |
| M (ma, deg) |
321.125775 |
Magnitude
Scatter + Global Linear
$$
M_a = (13.725 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
13.725 |
| 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
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
13:24:22.51 |
+09:23:01.1 |
HIP 65490 |
20.56 |
| 2026-09-20 12:00 |
13:25:00.47 |
+09:18:26.3 |
HIP 65490 |
19.91 |
| 2026-09-21 00:00 |
13:25:38.42 |
+09:13:52.3 |
HIP 65490 |
24.22 |
| 2026-09-21 12:00 |
13:26:16.37 |
+09:09:19.2 |
HIP 65646 |
18.53 |
| 2026-09-22 00:00 |
13:26:54.32 |
+09:04:46.8 |
HIP 65646 |
11.55 |
| 2026-09-22 12:00 |
13:27:32.26 |
+09:00:15.3 |
HIP 65646 |
11.81 |
| 2026-09-23 00:00 |
13:28:10.19 |
+08:55:44.6 |
HIP 65686 |
5.95 |
| 2026-09-23 12:00 |
13:28:48.12 |
+08:51:14.7 |
HIP 65686 |
10.76 |
| 2026-09-24 00:00 |
13:29:26.04 |
+08:46:45.6 |
HIP 65686 |
20.30 |
| 2026-09-24 12:00 |
13:30:03.96 |
+08:42:17.3 |
HIP 65817 |
20.86 |
| 2026-09-25 00:00 |
13:30:41.87 |
+08:37:49.9 |
HIP 65817 |
22.52 |
| 2026-09-25 12:00 |
13:31:19.77 |
+08:33:23.3 |
HIP 66007 |
26.96 |
| 2026-09-26 00:00 |
13:31:57.67 |
+08:28:57.6 |
HIP 66147 |
24.31 |
| 2026-09-26 12:00 |
13:32:35.56 |
+08:24:32.6 |
HIP 66147 |
17.69 |
| 2026-09-27 00:00 |
13:33:13.45 |
+08:20:08.6 |
HIP 66147 |
15.78 |
| 2026-09-27 12:00 |
13:33:51.33 |
+08:15:45.3 |
HIP 66274 |
16.94 |
| 2026-09-28 00:00 |
13:34:29.20 |
+08:11:22.9 |
HIP 66274 |
9.62 |
| 2026-09-28 12:00 |
13:35:07.06 |
+08:07:01.4 |
HIP 66274 |
10.57 |
| 2026-09-29 00:00 |
13:35:44.92 |
+08:02:40.6 |
HIP 66345 |
14.99 |
| 2026-09-29 12:00 |
13:36:22.76 |
+07:58:20.8 |
HIP 66413 |
14.93 |
| 2026-09-30 00:00 |
13:37:00.61 |
+07:54:01.8 |
HIP 66413 |
8.00 |
| 2026-09-30 12:00 |
13:37:38.44 |
+07:49:43.6 |
HIP 66413 |
10.86 |
| 2026-10-01 00:00 |
13:38:16.26 |
+07:45:26.3 |
HIP 66413 |
19.61 |
| 2026-10-01 12:00 |
13:38:54.08 |
+07:41:09.9 |
HIP 66661 |
25.02 |
| 2026-10-02 00:00 |
13:39:31.89 |
+07:36:54.3 |
HIP 66661 |
16.57 |
| 2026-10-02 12:00 |
13:40:09.69 |
+07:32:39.6 |
HIP 66661 |
11.64 |
| 2026-10-03 00:00 |
13:40:47.48 |
+07:28:25.7 |
HIP 66788 |
11.19 |
| 2026-10-03 12:00 |
13:41:25.26 |
+07:24:12.8 |
HIP 66788 |
12.56 |
| 2026-10-04 00:00 |
13:42:03.03 |
+07:20:00.7 |
HIP 66788 |
20.02 |
| 2026-10-04 12:00 |
13:42:40.79 |
+07:15:49.5 |
HIP 66921 |
15.32 |
| 2026-10-05 00:00 |
13:43:18.55 |
+07:11:39.2 |
HIP 66921 |
12.47 |
| 2026-10-05 12:00 |
13:43:56.29 |
+07:07:29.8 |
HIP 66921 |
16.92 |
| 2026-10-06 00:00 |
13:44:34.02 |
+07:03:21.2 |
HIP 66921 |
25.05 |
| 2026-10-06 12:00 |
13:45:11.74 |
+06:59:13.6 |
HIP 67127 |
26.63 |
| 2026-10-07 00:00 |
13:45:49.46 |
+06:55:06.9 |
HIP 67127 |
30.80 |
| 2026-10-07 12:00 |
13:46:27.15 |
+06:51:01.1 |
HIP 67246 |
30.91 |
| 2026-10-08 00:00 |
13:47:04.84 |
+06:46:56.2 |
HIP 67246 |
25.96 |
| 2026-10-08 12:00 |
13:47:42.51 |
+06:42:52.2 |
HIP 67291 |
24.15 |
| 2026-10-09 00:00 |
13:48:20.18 |
+06:38:49.2 |
HIP 67430 |
15.32 |
| 2026-10-09 12:00 |
13:48:57.82 |
+06:34:47.1 |
HIP 67430 |
5.61 |
| 2026-10-10 00:00 |
13:49:35.46 |
+06:30:45.9 |
HIP 67430 |
5.97 |
| 2026-10-10 12:00 |
13:50:13.08 |
+06:26:45.6 |
HIP 67461 |
12.48 |
| 2026-10-11 00:00 |
13:50:50.68 |
+06:22:46.3 |
HIP 67653 |
12.83 |