| Parameter |
Value |
| Designation |
17P/Holmes |
| Type |
P |
| Perihelion (tp_cal, UTC) |
2014-03-26T17:17:14.196480Z |
| Orbit solution date (soln_date, UTC) |
2023-10-10T13:05:23Z |
| Obs used |
2211 |
| NEO |
- |
| M1 |
9.400 |
| K1 |
14.750 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2016-10-19.0000000 |
| e |
0.43015482 |
| q (au) |
2.066329 |
| a (au) |
3.626124 |
| i (deg) |
19.070359 |
| Ω (om, deg) |
326.773810 |
| ω (w, deg) |
24.738506 |
| M (ma, deg) |
133.785581 |
Magnitude
Scatter + Global Linear
$$
M_a = (8.460 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
8.460 |
| n |
6.000 |
| gf |
1.000 |
| gb |
-0.500 |
| 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 |
| 2019-01-17 |
2021-07-29 |
-14.8750 |
+4.940 |
| 2021-07-29 |
2021-10-22 |
+35.1628 |
-14.605 |
| 2021-10-22 |
2022-01-30 |
-23.8751 |
+11.231 |
| 2022-01-30 |
2023-01-22 |
+4.5697 |
-3.280 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-05-12 00:00 |
13:21:14.60 |
-33:33:40.1 |
HIP 65097 |
10.94 |
| 2026-05-12 12:00 |
13:20:53.98 |
-33:31:16.9 |
HIP 65097 |
9.59 |
| 2026-05-13 00:00 |
13:20:33.56 |
-33:28:52.6 |
HIP 65097 |
10.62 |
| 2026-05-13 12:00 |
13:20:13.33 |
-33:26:27.3 |
HIP 65097 |
13.47 |
| 2026-05-14 00:00 |
13:19:53.30 |
-33:24:01.0 |
HIP 65097 |
17.24 |
| 2026-05-14 12:00 |
13:19:33.47 |
-33:21:33.7 |
HIP 64937 |
19.87 |
| 2026-05-15 00:00 |
13:19:13.85 |
-33:19:05.6 |
HIP 64937 |
15.58 |
| 2026-05-15 12:00 |
13:18:54.43 |
-33:16:36.5 |
HIP 64937 |
11.69 |
| 2026-05-16 00:00 |
13:18:35.22 |
-33:14:06.6 |
HIP 64937 |
8.68 |
| 2026-05-16 12:00 |
13:18:16.22 |
-33:11:36.0 |
HIP 64937 |
7.64 |
| 2026-05-17 00:00 |
13:17:57.45 |
-33:09:04.5 |
HIP 64937 |
9.21 |
| 2026-05-17 12:00 |
13:17:38.89 |
-33:06:32.3 |
HIP 64937 |
12.40 |
| 2026-05-18 00:00 |
13:17:20.56 |
-33:03:59.5 |
HIP 64937 |
16.26 |
| 2026-05-18 12:00 |
13:17:02.45 |
-33:01:25.9 |
HIP 64937 |
20.39 |
| 2026-05-19 00:00 |
13:16:44.57 |
-32:58:51.8 |
HIP 64824 |
24.01 |
| 2026-05-19 12:00 |
13:16:26.92 |
-32:56:17.1 |
HIP 64824 |
23.09 |
| 2026-05-20 00:00 |
13:16:09.51 |
-32:53:41.8 |
HIP 64824 |
22.99 |
| 2026-05-20 12:00 |
13:15:52.33 |
-32:51:06.0 |
HIP 64824 |
23.71 |
| 2026-05-21 00:00 |
13:15:35.39 |
-32:48:29.7 |
HIP 64824 |
25.16 |
| 2026-05-21 12:00 |
13:15:18.70 |
-32:45:53.0 |
HIP 64824 |
27.21 |
| 2026-05-22 00:00 |
13:15:02.24 |
-32:43:15.9 |
HIP 64824 |
29.72 |
| 2026-05-22 12:00 |
13:14:46.03 |
-32:40:38.4 |
HIP 64534 |
26.27 |
| 2026-05-23 00:00 |
13:14:30.07 |
-32:38:00.6 |
HIP 64534 |
22.29 |
| 2026-05-23 12:00 |
13:14:14.36 |
-32:35:22.5 |
HIP 64534 |
18.47 |
| 2026-05-24 00:00 |
13:13:58.90 |
-32:32:44.1 |
HIP 64534 |
14.87 |
| 2026-05-24 12:00 |
13:13:43.70 |
-32:30:05.5 |
HIP 64534 |
11.68 |
| 2026-05-25 00:00 |
13:13:28.74 |
-32:27:26.7 |
HIP 64534 |
9.28 |
| 2026-05-25 12:00 |
13:13:14.05 |
-32:24:47.7 |
HIP 64534 |
8.31 |
| 2026-05-26 00:00 |
13:12:59.61 |
-32:22:08.6 |
HIP 64534 |
9.18 |
| 2026-05-26 12:00 |
13:12:45.43 |
-32:19:29.4 |
HIP 64534 |
11.45 |
| 2026-05-27 00:00 |
13:12:31.51 |
-32:16:50.1 |
HIP 64534 |
14.44 |
| 2026-05-27 12:00 |
13:12:17.85 |
-32:14:10.8 |
HIP 64534 |
17.76 |
| 2026-05-28 00:00 |
13:12:04.46 |
-32:11:31.4 |
HIP 64459 |
20.95 |
| 2026-05-28 12:00 |
13:11:51.33 |
-32:08:52.1 |
HIP 64459 |
19.98 |
| 2026-05-29 00:00 |
13:11:38.47 |
-32:06:12.9 |
HIP 64260 |
17.71 |
| 2026-05-29 12:00 |
13:11:25.87 |
-32:03:33.7 |
HIP 64260 |
15.19 |
| 2026-05-30 00:00 |
13:11:13.54 |
-32:00:54.6 |
HIP 64260 |
13.32 |
| 2026-05-30 12:00 |
13:11:01.48 |
-31:58:15.7 |
HIP 64260 |
12.35 |
| 2026-05-31 00:00 |
13:10:49.69 |
-31:55:37.0 |
HIP 64260 |
12.48 |
| 2026-05-31 12:00 |
13:10:38.17 |
-31:52:58.4 |
HIP 64260 |
13.63 |
| 2026-06-01 00:00 |
13:10:26.93 |
-31:50:20.1 |
HIP 64260 |
15.55 |
| 2026-06-01 12:00 |
13:10:15.95 |
-31:47:42.1 |
HIP 64260 |
17.98 |
| 2026-06-02 00:00 |
13:10:05.25 |
-31:45:04.3 |
HIP 64292 |
18.09 |