| 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
$$
M_a = (10.463 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
10.463 |
| n |
6.000 |
| gf |
0.882 |
| gb |
-0.912 |
| k |
1.000 |
| δ90 |
9.999 |
| 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) |
| 2026-03-26 00:00 |
08:55:18.84 |
-12:53:49.4 |
HIP 43939 |
25.03 |
| 2026-03-26 12:00 |
08:55:12.28 |
-12:48:27.9 |
HIP 43939 |
26.20 |
| 2026-03-27 00:00 |
08:55:06.03 |
-12:43:07.6 |
HIP 43939 |
28.36 |
| 2026-03-27 12:00 |
08:55:00.08 |
-12:37:48.3 |
HIP 43939 |
31.29 |
| 2026-03-28 00:00 |
08:54:54.42 |
-12:32:30.3 |
HIP 43939 |
34.79 |
| 2026-03-28 12:00 |
08:54:49.06 |
-12:27:13.5 |
HIP 43939 |
38.67 |
| 2026-03-29 00:00 |
08:54:44.00 |
-12:21:57.8 |
HIP 43939 |
42.83 |
| 2026-03-29 12:00 |
08:54:39.24 |
-12:16:43.5 |
HIP 43608 |
42.62 |
| 2026-03-30 00:00 |
08:54:34.76 |
-12:11:30.4 |
HIP 43608 |
37.90 |
| 2026-03-30 12:00 |
08:54:30.59 |
-12:06:18.6 |
HIP 43608 |
33.44 |
| 2026-03-31 00:00 |
08:54:26.70 |
-12:01:08.1 |
HIP 43608 |
29.32 |
| 2026-03-31 12:00 |
08:54:23.10 |
-11:55:59.0 |
HIP 43608 |
25.70 |
| 2026-04-01 00:00 |
08:54:19.80 |
-11:50:51.3 |
HIP 43608 |
22.79 |
| 2026-04-01 12:00 |
08:54:16.78 |
-11:45:45.0 |
HIP 43608 |
20.86 |
| 2026-04-02 00:00 |
08:54:14.05 |
-11:40:40.1 |
HIP 43746 |
18.97 |
| 2026-04-02 12:00 |
08:54:11.61 |
-11:35:36.6 |
HIP 43746 |
14.51 |
| 2026-04-03 00:00 |
08:54:09.45 |
-11:30:34.6 |
HIP 43746 |
10.62 |
| 2026-04-03 12:00 |
08:54:07.57 |
-11:25:34.1 |
HIP 43746 |
8.07 |
| 2026-04-04 00:00 |
08:54:05.98 |
-11:20:35.1 |
HIP 43746 |
8.17 |
| 2026-04-04 12:00 |
08:54:04.66 |
-11:15:37.6 |
HIP 43746 |
10.82 |
| 2026-04-05 00:00 |
08:54:03.63 |
-11:10:41.7 |
HIP 43746 |
14.66 |
| 2026-04-05 12:00 |
08:54:02.88 |
-11:05:47.4 |
HIP 43776 |
15.24 |
| 2026-04-06 00:00 |
08:54:02.40 |
-11:00:54.6 |
HIP 43776 |
13.95 |
| 2026-04-06 12:00 |
08:54:02.19 |
-10:56:03.4 |
HIP 43776 |
14.22 |
| 2026-04-07 00:00 |
08:54:02.27 |
-10:51:13.9 |
HIP 43776 |
15.96 |
| 2026-04-07 12:00 |
08:54:02.61 |
-10:46:26.0 |
HIP 43776 |
18.74 |
| 2026-04-08 00:00 |
08:54:03.23 |
-10:41:39.7 |
HIP 43776 |
22.16 |
| 2026-04-08 12:00 |
08:54:04.12 |
-10:36:55.1 |
HIP 43776 |
25.95 |
| 2026-04-09 00:00 |
08:54:05.27 |
-10:32:12.2 |
HIP 43776 |
29.96 |
| 2026-04-09 12:00 |
08:54:06.70 |
-10:27:31.0 |
HIP 43776 |
34.11 |
| 2026-04-10 00:00 |
08:54:08.39 |
-10:22:51.5 |
HIP 43818 |
33.54 |
| 2026-04-10 12:00 |
08:54:10.34 |
-10:18:13.8 |
HIP 43818 |
29.58 |
| 2026-04-11 00:00 |
08:54:12.56 |
-10:13:37.8 |
HIP 43818 |
25.82 |
| 2026-04-11 12:00 |
08:54:15.05 |
-10:09:03.6 |
HIP 43818 |
22.37 |
| 2026-04-12 00:00 |
08:54:17.79 |
-10:04:31.1 |
HIP 43818 |
19.35 |
| 2026-04-12 12:00 |
08:54:20.79 |
-10:00:00.4 |
HIP 43818 |
17.01 |
| 2026-04-13 00:00 |
08:54:24.05 |
-09:55:31.5 |
HIP 43818 |
15.61 |
| 2026-04-13 12:00 |
08:54:27.57 |
-09:51:04.5 |
HIP 43818 |
15.40 |
| 2026-04-14 00:00 |
08:54:31.34 |
-09:46:39.3 |
HIP 43818 |
16.43 |
| 2026-04-14 12:00 |
08:54:35.37 |
-09:42:15.9 |
HIP 43818 |
18.46 |
| 2026-04-15 00:00 |
08:54:39.64 |
-09:37:54.3 |
HIP 43818 |
21.20 |
| 2026-04-15 12:00 |
08:54:44.17 |
-09:33:34.6 |
HIP 43731 |
21.91 |
| 2026-04-16 00:00 |
08:54:48.95 |
-09:29:16.8 |
HIP 43731 |
18.16 |