| Parameter |
Value |
| Designation |
21P/Giacobini-Zinner |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2018-09-10T06:22:53.924160Z |
| Orbit solution date (soln_date, UTC) |
2025-11-23T22:20:59Z |
| Obs used |
1993 |
| NEO |
Yes |
| M1 |
13.200 |
| K1 |
8.250 |
| PC |
- |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2017-11-13.0000000 |
| e |
0.71047048 |
| q (au) |
1.013441 |
| a (au) |
3.500303 |
| i (deg) |
32.002592 |
| Ω (om, deg) |
195.404480 |
| ω (w, deg) |
172.812482 |
| M (ma, deg) |
314.658527 |
Magnitude
Scatter + Global Linear
$$
M_a = (10.458 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
10.458 |
| n |
6.000 |
| gf |
0.983 |
| gb |
-0.641 |
| 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
Finding Chart
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
10:49:32.63 |
-08:17:11.7 |
HIP 52860 |
13.33 |
| 2026-09-20 12:00 |
10:49:57.09 |
-08:19:21.9 |
HIP 52860 |
19.44 |
| 2026-09-21 00:00 |
10:50:21.50 |
-08:21:32.4 |
HIP 52860 |
25.70 |
| 2026-09-21 12:00 |
10:50:45.87 |
-08:23:43.1 |
HIP 53090 |
23.82 |
| 2026-09-22 00:00 |
10:51:10.19 |
-08:25:54.2 |
HIP 53090 |
23.01 |
| 2026-09-22 12:00 |
10:51:34.45 |
-08:28:05.5 |
HIP 53090 |
23.95 |
| 2026-09-23 00:00 |
10:51:58.67 |
-08:30:17.1 |
HIP 53090 |
26.45 |
| 2026-09-23 12:00 |
10:52:22.83 |
-08:32:29.0 |
HIP 53027 |
29.65 |
| 2026-09-24 00:00 |
10:52:46.94 |
-08:34:41.1 |
HIP 53348 |
28.38 |
| 2026-09-24 12:00 |
10:53:11.00 |
-08:36:53.5 |
HIP 53348 |
22.07 |
| 2026-09-25 00:00 |
10:53:35.01 |
-08:39:06.1 |
HIP 53348 |
15.79 |
| 2026-09-25 12:00 |
10:53:58.96 |
-08:41:18.9 |
HIP 53348 |
9.59 |
| 2026-09-26 00:00 |
10:54:22.86 |
-08:43:32.1 |
HIP 53348 |
3.86 |
| 2026-09-26 12:00 |
10:54:46.70 |
-08:45:45.4 |
HIP 53348 |
4.16 |
| 2026-09-27 00:00 |
10:55:10.49 |
-08:47:59.0 |
HIP 53348 |
9.94 |
| 2026-09-27 12:00 |
10:55:34.23 |
-08:50:12.8 |
HIP 53348 |
16.09 |
| 2026-09-28 00:00 |
10:55:57.91 |
-08:52:26.8 |
HIP 53348 |
22.30 |
| 2026-09-28 12:00 |
10:56:21.53 |
-08:54:41.0 |
HIP 53348 |
28.53 |
| 2026-09-29 00:00 |
10:56:45.10 |
-08:56:55.5 |
HIP 53671 |
31.95 |
| 2026-09-29 12:00 |
10:57:08.61 |
-08:59:10.2 |
HIP 53671 |
26.84 |
| 2026-09-30 00:00 |
10:57:32.06 |
-09:01:25.0 |
HIP 53671 |
22.31 |
| 2026-09-30 12:00 |
10:57:55.45 |
-09:03:40.1 |
HIP 53671 |
18.79 |
| 2026-10-01 00:00 |
10:58:18.79 |
-09:05:55.3 |
HIP 53671 |
16.90 |
| 2026-10-01 12:00 |
10:58:42.06 |
-09:08:10.8 |
HIP 53671 |
17.17 |
| 2026-10-02 00:00 |
10:59:05.28 |
-09:10:26.4 |
HIP 53671 |
19.51 |
| 2026-10-02 12:00 |
10:59:28.43 |
-09:12:42.2 |
HIP 53794 |
21.50 |
| 2026-10-03 00:00 |
10:59:51.52 |
-09:14:58.2 |
HIP 53794 |
16.47 |
| 2026-10-03 12:00 |
11:00:14.55 |
-09:17:14.3 |
HIP 53794 |
12.48 |
| 2026-10-04 00:00 |
11:00:37.52 |
-09:19:30.6 |
HIP 53794 |
10.71 |
| 2026-10-04 12:00 |
11:01:00.43 |
-09:21:47.1 |
HIP 53794 |
12.16 |
| 2026-10-05 00:00 |
11:01:23.27 |
-09:24:03.7 |
HIP 53794 |
15.96 |
| 2026-10-05 12:00 |
11:01:46.04 |
-09:26:20.5 |
HIP 54002 |
17.13 |
| 2026-10-06 00:00 |
11:02:08.75 |
-09:28:37.4 |
HIP 54002 |
13.50 |
| 2026-10-06 12:00 |
11:02:31.40 |
-09:30:54.4 |
HIP 54002 |
12.03 |
| 2026-10-07 00:00 |
11:02:53.98 |
-09:33:11.6 |
HIP 54002 |
13.41 |
| 2026-10-07 12:00 |
11:03:16.49 |
-09:35:28.9 |
HIP 54002 |
16.95 |
| 2026-10-08 00:00 |
11:03:38.93 |
-09:37:46.2 |
HIP 54002 |
21.60 |
| 2026-10-08 12:00 |
11:04:01.30 |
-09:40:03.7 |
HIP 54002 |
26.78 |
| 2026-10-09 00:00 |
11:04:23.60 |
-09:42:21.3 |
HIP 54002 |
32.22 |
| 2026-10-09 12:00 |
11:04:45.83 |
-09:44:39.0 |
HIP 54195 |
33.61 |
| 2026-10-10 00:00 |
11:05:07.99 |
-09:46:56.8 |
HIP 54195 |
30.58 |
| 2026-10-10 12:00 |
11:05:30.08 |
-09:49:14.7 |
HIP 54350 |
28.42 |
| 2026-10-11 00:00 |
11:05:52.10 |
-09:51:32.6 |
HIP 54350 |
22.58 |