| 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) |
| 2026-06-01 00:00 |
09:16:07.86 |
-05:12:50.6 |
HIP 45489 |
20.83 |
| 2026-06-01 12:00 |
09:16:28.60 |
-05:11:29.9 |
HIP 45489 |
20.13 |
| 2026-06-02 00:00 |
09:16:49.44 |
-05:10:10.9 |
HIP 45489 |
20.85 |
| 2026-06-02 12:00 |
09:17:10.38 |
-05:08:53.5 |
HIP 45489 |
22.88 |
| 2026-06-03 00:00 |
09:17:31.43 |
-05:07:37.9 |
HIP 45657 |
19.10 |
| 2026-06-03 12:00 |
09:17:52.57 |
-05:06:23.8 |
HIP 45657 |
14.85 |
| 2026-06-04 00:00 |
09:18:13.81 |
-05:05:11.4 |
HIP 45657 |
11.63 |
| 2026-06-04 12:00 |
09:18:35.15 |
-05:04:00.7 |
HIP 45657 |
10.46 |
| 2026-06-05 00:00 |
09:18:56.59 |
-05:02:51.6 |
HIP 45657 |
12.00 |
| 2026-06-05 12:00 |
09:19:18.12 |
-05:01:44.1 |
HIP 45657 |
15.46 |
| 2026-06-06 00:00 |
09:19:39.74 |
-05:00:38.2 |
HIP 45657 |
19.89 |
| 2026-06-06 12:00 |
09:20:01.46 |
-04:59:34.0 |
HIP 45657 |
24.78 |
| 2026-06-07 00:00 |
09:20:23.27 |
-04:58:31.3 |
HIP 45657 |
29.91 |
| 2026-06-07 12:00 |
09:20:45.17 |
-04:57:30.3 |
HIP 45998 |
31.61 |
| 2026-06-08 00:00 |
09:21:07.16 |
-04:56:30.9 |
HIP 45998 |
26.41 |
| 2026-06-08 12:00 |
09:21:29.25 |
-04:55:33.0 |
HIP 46000 |
21.20 |
| 2026-06-09 00:00 |
09:21:51.42 |
-04:54:36.7 |
HIP 46000 |
15.61 |
| 2026-06-09 12:00 |
09:22:13.67 |
-04:53:42.0 |
HIP 46000 |
10.00 |
| 2026-06-10 00:00 |
09:22:36.02 |
-04:52:48.9 |
HIP 46000 |
4.41 |
| 2026-06-10 12:00 |
09:22:58.45 |
-04:51:57.3 |
HIP 46000 |
1.61 |
| 2026-06-11 00:00 |
09:23:20.96 |
-04:51:07.3 |
HIP 46000 |
7.06 |
| 2026-06-11 12:00 |
09:23:43.56 |
-04:50:18.9 |
HIP 46000 |
12.73 |
| 2026-06-12 00:00 |
09:24:06.24 |
-04:49:32.0 |
HIP 46000 |
18.42 |
| 2026-06-12 12:00 |
09:24:29.00 |
-04:48:46.6 |
HIP 46221 |
22.84 |
| 2026-06-13 00:00 |
09:24:51.84 |
-04:48:02.8 |
HIP 46221 |
20.62 |
| 2026-06-13 12:00 |
09:25:14.76 |
-04:47:20.5 |
HIP 46221 |
19.84 |
| 2026-06-14 00:00 |
09:25:37.76 |
-04:46:39.7 |
HIP 46221 |
20.67 |
| 2026-06-14 12:00 |
09:26:00.84 |
-04:46:00.5 |
HIP 46359 |
16.94 |
| 2026-06-15 00:00 |
09:26:23.99 |
-04:45:22.7 |
HIP 46359 |
11.16 |
| 2026-06-15 12:00 |
09:26:47.22 |
-04:44:46.4 |
HIP 46359 |
5.40 |
| 2026-06-16 00:00 |
09:27:10.52 |
-04:44:11.7 |
HIP 46359 |
1.20 |
| 2026-06-16 12:00 |
09:27:33.90 |
-04:43:38.4 |
HIP 46359 |
6.48 |
| 2026-06-17 00:00 |
09:27:57.34 |
-04:43:06.6 |
HIP 46359 |
12.30 |
| 2026-06-17 12:00 |
09:28:20.86 |
-04:42:36.3 |
HIP 46378 |
16.66 |
| 2026-06-18 00:00 |
09:28:44.45 |
-04:42:07.4 |
HIP 46378 |
21.67 |
| 2026-06-18 12:00 |
09:29:08.11 |
-04:41:40.0 |
HIP 46378 |
27.06 |
| 2026-06-19 00:00 |
09:29:31.83 |
-04:41:14.0 |
HIP 46543 |
26.44 |
| 2026-06-19 12:00 |
09:29:55.62 |
-04:40:49.5 |
HIP 46543 |
26.67 |
| 2026-06-20 00:00 |
09:30:19.48 |
-04:40:26.4 |
HIP 46543 |
28.20 |
| 2026-06-20 12:00 |
09:30:43.40 |
-04:40:04.7 |
HIP 46780 |
24.65 |
| 2026-06-21 00:00 |
09:31:07.39 |
-04:39:44.4 |
HIP 46780 |
20.06 |
| 2026-06-21 12:00 |
09:31:31.43 |
-04:39:25.6 |
HIP 46780 |
16.41 |
| 2026-06-22 00:00 |
09:31:55.54 |
-04:39:08.1 |
HIP 46780 |
14.45 |