242P/Spahr
Metadata
| Parameter | Value |
|---|---|
| Designation | 242P/Spahr |
| Type | P |
| Perihelion (tp_cal, UTC) | 2025-01-06T19:27:53.035200Z |
| Orbit solution date (soln_date, UTC) | 2026-03-31T09:42:38Z |
| Obs used | 1500 |
| NEO | - |
| M1 | 9.300 |
| K1 | 10.250 |
| PC | 0.030 |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2019-12-08.0000000 |
| e | 0.27782165 |
| q (au) | 3.954437 |
| a (au) | 5.475707 |
| i (deg) | 32.479823 |
| Ω (om, deg) | 180.521346 |
| ω (w, deg) | 246.328749 |
| M (ma, deg) | 217.172607 |
Magnitude
Scatter + Global Linear
$$ M_a = (5.658 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 5.658 |
| n | 6.000 |
| gf | 1.000 |
| gb | -0.998 |
| 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 | 2025-01-06 | +12.5528 | -7.429 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Finding Chart
Ephemeris
| Date/Time (UTC) | RA (J2000) | Dec (J2000) | Nearest HIP | Dist from HIP (arcmin) |
|---|---|---|---|---|
| 2026-03-26 00:00 | 07:30:49.37 | -07:42:09.7 | HIP 36562 | 7.16 |
| 2026-03-26 12:00 | 07:30:56.21 | -07:38:12.3 | HIP 36562 | 8.70 |
| 2026-03-27 00:00 | 07:31:03.27 | -07:34:15.6 | HIP 36562 | 11.69 |
| 2026-03-27 12:00 | 07:31:10.55 | -07:30:19.8 | HIP 36562 | 15.31 |
| 2026-03-28 00:00 | 07:31:18.03 | -07:26:24.9 | HIP 36562 | 19.21 |
| 2026-03-28 12:00 | 07:31:25.73 | -07:22:30.8 | HIP 36688 | 21.51 |
| 2026-03-29 00:00 | 07:31:33.63 | -07:18:37.6 | HIP 36688 | 18.92 |
| 2026-03-29 12:00 | 07:31:41.74 | -07:14:45.2 | HIP 36688 | 17.01 |
| 2026-03-30 00:00 | 07:31:50.07 | -07:10:53.8 | HIP 36688 | 16.03 |
| 2026-03-30 12:00 | 07:31:58.59 | -07:07:03.3 | HIP 36688 | 16.16 |
| 2026-03-31 00:00 | 07:32:07.33 | -07:03:13.7 | HIP 36703 | 17.09 |
| 2026-03-31 12:00 | 07:32:16.27 | -06:59:25.0 | HIP 36703 | 12.98 |
| 2026-04-01 00:00 | 07:32:25.41 | -06:55:37.3 | HIP 36703 | 9.12 |
| 2026-04-01 12:00 | 07:32:34.75 | -06:51:50.5 | HIP 36703 | 6.04 |
| 2026-04-02 00:00 | 07:32:44.30 | -06:48:04.8 | HIP 36703 | 5.34 |
| 2026-04-02 12:00 | 07:32:54.05 | -06:44:20.0 | HIP 36703 | 7.73 |
| 2026-04-03 00:00 | 07:33:04.00 | -06:40:36.2 | HIP 36703 | 11.42 |
| 2026-04-03 12:00 | 07:33:14.14 | -06:36:53.4 | HIP 36703 | 15.53 |
| 2026-04-04 00:00 | 07:33:24.49 | -06:33:11.6 | HIP 36754 | 19.70 |
| 2026-04-04 12:00 | 07:33:35.03 | -06:29:30.8 | HIP 36754 | 15.90 |
| 2026-04-05 00:00 | 07:33:45.76 | -06:25:51.1 | HIP 36754 | 12.60 |
| 2026-04-05 12:00 | 07:33:56.70 | -06:22:12.5 | HIP 36754 | 10.33 |
| 2026-04-06 00:00 | 07:34:07.82 | -06:18:34.9 | HIP 36754 | 9.85 |
| 2026-04-06 12:00 | 07:34:19.14 | -06:14:58.3 | HIP 36754 | 11.40 |
| 2026-04-07 00:00 | 07:34:30.65 | -06:11:22.9 | HIP 36754 | 14.36 |
| 2026-04-07 12:00 | 07:34:42.35 | -06:07:48.5 | HIP 36754 | 18.06 |
| 2026-04-08 00:00 | 07:34:54.25 | -06:04:15.3 | HIP 36754 | 22.13 |
| 2026-04-08 12:00 | 07:35:06.33 | -06:00:43.1 | HIP 36984 | 20.46 |
| 2026-04-09 00:00 | 07:35:18.60 | -05:57:12.1 | HIP 36984 | 15.84 |
| 2026-04-09 12:00 | 07:35:31.05 | -05:53:42.2 | HIP 36984 | 11.22 |
| 2026-04-10 00:00 | 07:35:43.70 | -05:50:13.4 | HIP 36984 | 6.66 |
| 2026-04-10 12:00 | 07:35:56.53 | -05:46:45.8 | HIP 36984 | 2.53 |
| 2026-04-11 00:00 | 07:36:09.54 | -05:43:19.3 | HIP 36984 | 3.56 |
| 2026-04-11 12:00 | 07:36:22.74 | -05:39:54.0 | HIP 36984 | 7.98 |
| 2026-04-12 00:00 | 07:36:36.12 | -05:36:29.9 | HIP 36984 | 12.65 |
| 2026-04-12 12:00 | 07:36:49.68 | -05:33:06.9 | HIP 36984 | 17.38 |
| 2026-04-13 00:00 | 07:37:03.42 | -05:29:45.2 | HIP 36984 | 22.14 |
| 2026-04-13 12:00 | 07:37:17.34 | -05:26:24.6 | HIP 37233 | 23.41 |
| 2026-04-14 00:00 | 07:37:31.44 | -05:23:05.3 | HIP 37233 | 20.43 |
| 2026-04-14 12:00 | 07:37:45.71 | -05:19:47.1 | HIP 37233 | 18.21 |
| 2026-04-15 00:00 | 07:38:00.17 | -05:16:30.2 | HIP 37233 | 17.08 |
| 2026-04-15 12:00 | 07:38:14.79 | -05:13:14.5 | HIP 37220 | 15.48 |
| 2026-04-16 00:00 | 07:38:29.60 | -05:10:00.1 | HIP 37220 | 11.06 |