242P/Spahr
| Parameter |
Value |
| Designation |
242P/Spahr |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2025-01-10T11:19:32.064960Z |
| Orbit solution date (soln_date, UTC) |
2026-01-13T08:12:54Z |
| Obs used |
1332 |
| NEO |
- |
| M1 |
6.900 |
| K1 |
14.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2019-02-07.0000000 |
| e |
0.27759167 |
| q (au) |
3.955100 |
| a (au) |
5.474881 |
| i (deg) |
32.485109 |
| Ω (om, deg) |
180.586449 |
| ω (w, deg) |
246.458413 |
| M (ma, deg) |
193.469434 |
Magnitude
Scatter + Global Linear
$$
M_a = (5.723 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
5.723 |
| 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 |
| 2023-07-28 |
2025-01-09 |
+12.5085 |
-7.465 |
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 |
07:38:22.20 |
-14:26:14.8 |
HIP 37119 |
10.51 |
| 2026-02-03 12:00 |
07:38:07.99 |
-14:23:05.7 |
HIP 37119 |
7.82 |
| 2026-02-04 00:00 |
07:37:53.92 |
-14:19:54.7 |
HIP 37119 |
7.49 |
| 2026-02-04 12:00 |
07:37:39.98 |
-14:16:41.8 |
HIP 37119 |
9.75 |
| 2026-02-05 00:00 |
07:37:26.18 |
-14:13:26.9 |
HIP 37119 |
13.35 |
| 2026-02-05 12:00 |
07:37:12.52 |
-14:10:10.1 |
HIP 37062 |
15.59 |
| 2026-02-06 00:00 |
07:36:59.00 |
-14:06:51.5 |
HIP 37062 |
11.93 |
| 2026-02-06 12:00 |
07:36:45.63 |
-14:03:31.0 |
HIP 37062 |
9.18 |
| 2026-02-07 00:00 |
07:36:32.41 |
-14:00:08.7 |
HIP 37062 |
8.29 |
| 2026-02-07 12:00 |
07:36:19.34 |
-13:56:44.6 |
HIP 37062 |
9.79 |
| 2026-02-08 00:00 |
07:36:06.43 |
-13:53:18.8 |
HIP 36939 |
8.28 |
| 2026-02-08 12:00 |
07:35:53.67 |
-13:49:51.2 |
HIP 36939 |
4.23 |
| 2026-02-09 00:00 |
07:35:41.07 |
-13:46:22.0 |
HIP 36939 |
3.26 |
| 2026-02-09 12:00 |
07:35:28.63 |
-13:42:51.0 |
HIP 36939 |
6.82 |
| 2026-02-10 00:00 |
07:35:16.36 |
-13:39:18.5 |
HIP 36939 |
11.21 |
| 2026-02-10 12:00 |
07:35:04.26 |
-13:35:44.3 |
HIP 36939 |
15.74 |
| 2026-02-11 00:00 |
07:34:52.32 |
-13:32:08.6 |
HIP 36939 |
20.31 |
| 2026-02-11 12:00 |
07:34:40.55 |
-13:28:31.3 |
HIP 36719 |
22.55 |
| 2026-02-12 00:00 |
07:34:28.96 |
-13:24:52.5 |
HIP 36719 |
19.49 |
| 2026-02-12 12:00 |
07:34:17.55 |
-13:21:12.2 |
HIP 36719 |
17.19 |
| 2026-02-13 00:00 |
07:34:06.31 |
-13:17:30.5 |
HIP 36719 |
15.96 |
| 2026-02-13 12:00 |
07:33:55.26 |
-13:13:47.4 |
HIP 36719 |
16.06 |
| 2026-02-14 00:00 |
07:33:44.39 |
-13:10:02.9 |
HIP 36719 |
17.45 |
| 2026-02-14 12:00 |
07:33:33.70 |
-13:06:17.0 |
HIP 36719 |
19.87 |
| 2026-02-15 00:00 |
07:33:23.20 |
-13:02:29.8 |
HIP 36662 |
15.62 |
| 2026-02-15 12:00 |
07:33:12.89 |
-12:58:41.4 |
HIP 36662 |
11.35 |
| 2026-02-16 00:00 |
07:33:02.77 |
-12:54:51.6 |
HIP 36662 |
7.47 |
| 2026-02-16 12:00 |
07:32:52.84 |
-12:51:00.7 |
HIP 36662 |
4.97 |
| 2026-02-17 00:00 |
07:32:43.11 |
-12:47:08.6 |
HIP 36662 |
5.95 |
| 2026-02-17 12:00 |
07:32:33.58 |
-12:43:15.3 |
HIP 36662 |
9.36 |
| 2026-02-18 00:00 |
07:32:24.25 |
-12:39:20.9 |
HIP 36662 |
13.46 |
| 2026-02-18 12:00 |
07:32:15.12 |
-12:35:25.4 |
HIP 36662 |
17.77 |
| 2026-02-19 00:00 |
07:32:06.18 |
-12:31:28.9 |
HIP 36579 |
19.72 |
| 2026-02-19 12:00 |
07:31:57.46 |
-12:27:31.3 |
HIP 36579 |
15.23 |
| 2026-02-20 00:00 |
07:31:48.94 |
-12:23:32.8 |
HIP 36579 |
10.75 |
| 2026-02-20 12:00 |
07:31:40.63 |
-12:19:33.3 |
HIP 36579 |
6.31 |
| 2026-02-21 00:00 |
07:31:32.52 |
-12:15:32.9 |
HIP 36579 |
2.06 |
| 2026-02-21 12:00 |
07:31:24.63 |
-12:11:31.6 |
HIP 36579 |
2.95 |
| 2026-02-22 00:00 |
07:31:16.94 |
-12:07:29.5 |
HIP 36579 |
7.27 |
| 2026-02-22 12:00 |
07:31:09.47 |
-12:03:26.6 |
HIP 36579 |
11.69 |
| 2026-02-23 00:00 |
07:31:02.22 |
-11:59:22.9 |
HIP 36579 |
16.11 |
| 2026-02-23 12:00 |
07:30:55.18 |
-11:55:18.5 |
HIP 36579 |
20.53 |
| 2026-02-24 00:00 |
07:30:48.35 |
-11:51:13.3 |
HIP 36579 |
24.94 |