| Parameter |
Value |
| Designation |
121P/Shoemaker-Holt 2 |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2004-02-28T21:35:48.249600Z |
| Orbit solution date (soln_date, UTC) |
2026-05-22T14:12:30Z |
| Obs used |
772 |
| NEO |
- |
| M1 |
6.700 |
| K1 |
18.500 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2008-08-22.0000000 |
| e |
0.20402943 |
| q (au) |
3.596644 |
| a (au) |
4.518564 |
| i (deg) |
20.725153 |
| Ω (om, deg) |
95.964916 |
| ω (w, deg) |
18.015655 |
| M (ma, deg) |
167.885521 |
Magnitude
Scatter + Global Linear
$$
M_a = (16.404 + 2.723\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
16.404 |
| n |
2.723 |
| gf |
1.000 |
| gb |
-0.696 |
| k |
0.800 |
| 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 |
15:11:25.52 |
-04:27:38.6 |
HIP 74483 |
28.91 |
| 2026-07-29 12:00 |
15:11:28.93 |
-04:29:55.1 |
HIP 74483 |
27.23 |
| 2026-07-30 00:00 |
15:11:32.51 |
-04:32:12.0 |
HIP 74483 |
25.62 |
| 2026-07-30 12:00 |
15:11:36.27 |
-04:34:29.4 |
HIP 74483 |
24.11 |
| 2026-07-31 00:00 |
15:11:40.22 |
-04:36:47.3 |
HIP 74483 |
22.72 |
| 2026-07-31 12:00 |
15:11:44.34 |
-04:39:05.7 |
HIP 74483 |
21.49 |
| 2026-08-01 00:00 |
15:11:48.64 |
-04:41:24.5 |
HIP 74483 |
20.46 |
| 2026-08-01 12:00 |
15:11:53.12 |
-04:43:43.7 |
HIP 74483 |
19.66 |
| 2026-08-02 00:00 |
15:11:57.77 |
-04:46:03.4 |
HIP 74483 |
19.13 |
| 2026-08-02 12:00 |
15:12:02.60 |
-04:48:23.6 |
HIP 74483 |
18.92 |
| 2026-08-03 00:00 |
15:12:07.61 |
-04:50:44.2 |
HIP 74483 |
19.03 |
| 2026-08-03 12:00 |
15:12:12.79 |
-04:53:05.1 |
HIP 74483 |
19.49 |
| 2026-08-04 00:00 |
15:12:18.15 |
-04:55:26.6 |
HIP 74483 |
20.26 |
| 2026-08-04 12:00 |
15:12:23.69 |
-04:57:48.4 |
HIP 74483 |
21.34 |
| 2026-08-05 00:00 |
15:12:29.40 |
-05:00:10.6 |
HIP 74483 |
22.68 |
| 2026-08-05 12:00 |
15:12:35.28 |
-05:02:33.2 |
HIP 74483 |
24.26 |
| 2026-08-06 00:00 |
15:12:41.33 |
-05:04:56.2 |
HIP 74483 |
26.04 |
| 2026-08-06 12:00 |
15:12:47.56 |
-05:07:19.6 |
HIP 74353 |
26.46 |
| 2026-08-07 00:00 |
15:12:53.96 |
-05:09:43.4 |
HIP 74353 |
25.64 |
| 2026-08-07 12:00 |
15:13:00.54 |
-05:12:07.5 |
HIP 74353 |
25.16 |
| 2026-08-08 00:00 |
15:13:07.28 |
-05:14:32.0 |
HIP 74353 |
25.04 |
| 2026-08-08 12:00 |
15:13:14.20 |
-05:16:56.9 |
HIP 74353 |
25.29 |
| 2026-08-09 00:00 |
15:13:21.29 |
-05:19:22.1 |
HIP 74623 |
24.71 |
| 2026-08-09 12:00 |
15:13:28.54 |
-05:21:47.7 |
HIP 74623 |
22.07 |
| 2026-08-10 00:00 |
15:13:35.97 |
-05:24:13.5 |
HIP 74623 |
19.50 |
| 2026-08-10 12:00 |
15:13:43.57 |
-05:26:39.8 |
HIP 74623 |
17.05 |
| 2026-08-11 00:00 |
15:13:51.33 |
-05:29:06.3 |
HIP 74623 |
14.79 |
| 2026-08-11 12:00 |
15:13:59.26 |
-05:31:33.1 |
HIP 74623 |
12.85 |
| 2026-08-12 00:00 |
15:14:07.36 |
-05:34:00.3 |
HIP 74623 |
11.43 |
| 2026-08-12 12:00 |
15:14:15.63 |
-05:36:27.8 |
HIP 74623 |
10.75 |
| 2026-08-13 00:00 |
15:14:24.06 |
-05:38:55.5 |
HIP 74623 |
10.98 |
| 2026-08-13 12:00 |
15:14:32.66 |
-05:41:23.5 |
HIP 74623 |
12.09 |
| 2026-08-14 00:00 |
15:14:41.42 |
-05:43:51.9 |
HIP 74594 |
13.51 |
| 2026-08-14 12:00 |
15:14:50.35 |
-05:46:20.4 |
HIP 74594 |
11.97 |
| 2026-08-15 00:00 |
15:14:59.44 |
-05:48:49.3 |
HIP 74594 |
11.24 |
| 2026-08-15 12:00 |
15:15:08.69 |
-05:51:18.4 |
HIP 74594 |
11.53 |
| 2026-08-16 00:00 |
15:15:18.10 |
-05:53:47.7 |
HIP 74594 |
12.78 |
| 2026-08-16 12:00 |
15:15:27.67 |
-05:56:17.3 |
HIP 74594 |
14.77 |
| 2026-08-17 00:00 |
15:15:37.41 |
-05:58:47.1 |
HIP 74594 |
17.27 |
| 2026-08-17 12:00 |
15:15:47.30 |
-06:01:17.1 |
HIP 74594 |
20.10 |
| 2026-08-18 00:00 |
15:15:57.35 |
-06:03:47.4 |
HIP 74777 |
19.64 |
| 2026-08-18 12:00 |
15:16:07.56 |
-06:06:17.9 |
HIP 74679 |
18.53 |
| 2026-08-19 00:00 |
15:16:17.93 |
-06:08:48.5 |
HIP 74679 |
17.24 |