| 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) |
| 2026-07-29 00:00 |
12:17:56.44 |
+18:32:24.9 |
HIP 59980 |
6.57 |
| 2026-07-29 12:00 |
12:18:33.17 |
+18:26:45.0 |
HIP 59980 |
6.91 |
| 2026-07-30 00:00 |
12:19:09.91 |
+18:21:05.6 |
HIP 59980 |
16.39 |
| 2026-07-30 12:00 |
12:19:46.69 |
+18:15:26.6 |
HIP 59980 |
26.56 |
| 2026-07-31 00:00 |
12:20:23.49 |
+18:09:48.0 |
HIP 60202 |
22.72 |
| 2026-07-31 12:00 |
12:21:00.32 |
+18:04:09.9 |
HIP 60202 |
17.10 |
| 2026-08-01 00:00 |
12:21:37.18 |
+17:58:32.2 |
HIP 60202 |
16.91 |
| 2026-08-01 12:00 |
12:22:14.06 |
+17:52:54.9 |
HIP 60202 |
22.30 |
| 2026-08-02 00:00 |
12:22:50.97 |
+17:47:18.1 |
HIP 60543 |
26.32 |
| 2026-08-02 12:00 |
12:23:27.90 |
+17:41:41.8 |
HIP 60543 |
19.69 |
| 2026-08-03 00:00 |
12:24:04.85 |
+17:36:05.9 |
HIP 60441 |
16.85 |
| 2026-08-03 12:00 |
12:24:41.83 |
+17:30:30.4 |
HIP 60441 |
19.27 |
| 2026-08-04 00:00 |
12:25:18.84 |
+17:24:55.4 |
HIP 60441 |
26.03 |
| 2026-08-04 12:00 |
12:25:55.87 |
+17:19:20.9 |
HIP 60441 |
34.68 |
| 2026-08-05 00:00 |
12:26:32.92 |
+17:13:46.8 |
HIP 60790 |
39.02 |
| 2026-08-05 12:00 |
12:27:10.00 |
+17:08:13.2 |
HIP 60874 |
30.19 |
| 2026-08-06 00:00 |
12:27:47.10 |
+17:02:40.1 |
HIP 60874 |
20.27 |
| 2026-08-06 12:00 |
12:28:24.23 |
+16:57:07.4 |
HIP 60874 |
11.37 |
| 2026-08-07 00:00 |
12:29:01.38 |
+16:51:35.2 |
HIP 60874 |
8.19 |
| 2026-08-07 12:00 |
12:29:38.55 |
+16:46:03.5 |
HIP 60874 |
14.99 |
| 2026-08-08 00:00 |
12:30:15.74 |
+16:40:32.3 |
HIP 61080 |
12.68 |
| 2026-08-08 12:00 |
12:30:52.96 |
+16:35:01.5 |
HIP 61080 |
3.70 |
| 2026-08-09 00:00 |
12:31:30.20 |
+16:29:31.2 |
HIP 61080 |
9.29 |
| 2026-08-09 12:00 |
12:32:07.46 |
+16:24:01.5 |
HIP 61194 |
8.79 |
| 2026-08-10 00:00 |
12:32:44.74 |
+16:18:32.2 |
HIP 61194 |
14.98 |
| 2026-08-10 12:00 |
12:33:22.04 |
+16:13:03.4 |
HIP 61194 |
24.32 |
| 2026-08-11 00:00 |
12:33:59.37 |
+16:07:35.2 |
HIP 61385 |
21.99 |
| 2026-08-11 12:00 |
12:34:36.71 |
+16:02:07.4 |
HIP 61385 |
13.79 |
| 2026-08-12 00:00 |
12:35:14.08 |
+15:56:40.2 |
HIP 61385 |
10.85 |
| 2026-08-12 12:00 |
12:35:51.46 |
+15:51:13.5 |
HIP 61450 |
13.76 |
| 2026-08-13 00:00 |
12:36:28.87 |
+15:45:47.3 |
HIP 61450 |
15.40 |
| 2026-08-13 12:00 |
12:37:06.29 |
+15:40:21.6 |
HIP 61642 |
15.83 |
| 2026-08-14 00:00 |
12:37:43.73 |
+15:34:56.5 |
HIP 61642 |
6.98 |
| 2026-08-14 12:00 |
12:38:21.19 |
+15:29:31.9 |
HIP 61642 |
8.24 |
| 2026-08-15 00:00 |
12:38:58.67 |
+15:24:07.9 |
HIP 61642 |
17.55 |
| 2026-08-15 12:00 |
12:39:36.16 |
+15:18:44.5 |
HIP 61901 |
22.11 |
| 2026-08-16 00:00 |
12:40:13.67 |
+15:13:21.6 |
HIP 61901 |
15.75 |
| 2026-08-16 12:00 |
12:40:51.20 |
+15:07:59.2 |
HIP 61901 |
15.12 |
| 2026-08-17 00:00 |
12:41:28.74 |
+15:02:37.4 |
HIP 61901 |
20.74 |
| 2026-08-17 12:00 |
12:42:06.30 |
+14:57:16.2 |
HIP 61987 |
26.17 |
| 2026-08-18 00:00 |
12:42:43.87 |
+14:51:55.6 |
HIP 61987 |
21.96 |
| 2026-08-18 12:00 |
12:43:21.46 |
+14:46:35.5 |
HIP 62116 |
21.39 |
| 2026-08-19 00:00 |
12:43:59.06 |
+14:41:16.1 |
HIP 62116 |
25.54 |