| Parameter |
Value |
| Designation |
C/1998 P1 (Williams) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
1998-10-17T20:04:26.601600Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:29:57Z |
| Obs used |
403 |
| NEO |
- |
| M1 |
7.800 |
| K1 |
14.750 |
| PC |
0.030 |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
1998-12-15.0000000 |
| e |
0.99935941 |
| q (au) |
1.146154 |
| a (au) |
1789.224617 |
| i (deg) |
145.728519 |
| Ω (om, deg) |
156.373092 |
| ω (w, deg) |
294.452932 |
| M (ma, deg) |
0.000757 |
Magnitude
Scatter + Global Linear
$$
M_a = (6.727 + 4.174\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
6.727 |
| n |
4.174 |
| gf |
0.891 |
| gb |
-0.729 |
| k |
0.993 |
| δ90 |
1.273 |
| 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 |
| 1998-08-10 |
1998-08-29 |
+48.4077 |
-7.973 |
| 1998-08-29 |
1998-10-04 |
-9.7163 |
+0.414 |
| 1998-11-14 |
1998-12-30 |
-0.7986 |
+0.004 |
| 1998-12-30 |
1999-01-17 |
-4.5488 |
+1.146 |
| 1999-01-17 |
1999-02-09 |
+3.1416 |
-0.885 |
| 1999-02-09 |
1999-03-04 |
+15.9071 |
-5.048 |
| 1999-03-04 |
1999-04-13 |
-6.4456 |
+2.729 |
| 1999-04-13 |
1999-05-18 |
-16.8421 |
+7.088 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-06-01 00:00 |
02:56:37.49 |
+51:46:21.6 |
HIP 13664 |
7.56 |
| 2026-06-01 12:00 |
02:56:40.65 |
+51:46:36.4 |
HIP 13664 |
8.11 |
| 2026-06-02 00:00 |
02:56:43.79 |
+51:46:51.4 |
HIP 13664 |
8.65 |
| 2026-06-02 12:00 |
02:56:46.93 |
+51:47:06.4 |
HIP 13664 |
9.20 |
| 2026-06-03 00:00 |
02:56:50.05 |
+51:47:21.6 |
HIP 13664 |
9.74 |
| 2026-06-03 12:00 |
02:56:53.16 |
+51:47:36.9 |
HIP 13664 |
10.29 |
| 2026-06-04 00:00 |
02:56:56.26 |
+51:47:52.3 |
HIP 13664 |
10.83 |
| 2026-06-04 12:00 |
02:56:59.35 |
+51:48:07.8 |
HIP 13664 |
11.37 |
| 2026-06-05 00:00 |
02:57:02.42 |
+51:48:23.5 |
HIP 13664 |
11.91 |
| 2026-06-05 12:00 |
02:57:05.48 |
+51:48:39.2 |
HIP 13664 |
12.45 |
| 2026-06-06 00:00 |
02:57:08.53 |
+51:48:55.1 |
HIP 13664 |
12.99 |
| 2026-06-06 12:00 |
02:57:11.56 |
+51:49:11.0 |
HIP 13664 |
13.53 |
| 2026-06-07 00:00 |
02:57:14.58 |
+51:49:27.1 |
HIP 13664 |
14.07 |
| 2026-06-07 12:00 |
02:57:17.59 |
+51:49:43.3 |
HIP 13664 |
14.61 |
| 2026-06-08 00:00 |
02:57:20.58 |
+51:49:59.6 |
HIP 13664 |
15.14 |
| 2026-06-08 12:00 |
02:57:23.56 |
+51:50:16.0 |
HIP 13664 |
15.68 |
| 2026-06-09 00:00 |
02:57:26.52 |
+51:50:32.5 |
HIP 13664 |
16.21 |
| 2026-06-09 12:00 |
02:57:29.47 |
+51:50:49.1 |
HIP 13664 |
16.75 |
| 2026-06-10 00:00 |
02:57:32.40 |
+51:51:05.9 |
HIP 13664 |
17.28 |
| 2026-06-10 12:00 |
02:57:35.32 |
+51:51:22.7 |
HIP 13664 |
17.81 |
| 2026-06-11 00:00 |
02:57:38.22 |
+51:51:39.6 |
HIP 13664 |
18.34 |
| 2026-06-11 12:00 |
02:57:41.11 |
+51:51:56.6 |
HIP 13881 |
17.91 |
| 2026-06-12 00:00 |
02:57:43.98 |
+51:52:13.8 |
HIP 13881 |
17.43 |
| 2026-06-12 12:00 |
02:57:46.84 |
+51:52:31.0 |
HIP 13881 |
16.94 |
| 2026-06-13 00:00 |
02:57:49.68 |
+51:52:48.3 |
HIP 13881 |
16.46 |
| 2026-06-13 12:00 |
02:57:52.50 |
+51:53:05.7 |
HIP 13881 |
15.99 |
| 2026-06-14 00:00 |
02:57:55.31 |
+51:53:23.2 |
HIP 13881 |
15.51 |
| 2026-06-14 12:00 |
02:57:58.10 |
+51:53:40.8 |
HIP 13881 |
15.04 |
| 2026-06-15 00:00 |
02:58:00.87 |
+51:53:58.5 |
HIP 13881 |
14.57 |
| 2026-06-15 12:00 |
02:58:03.62 |
+51:54:16.3 |
HIP 13881 |
14.11 |
| 2026-06-16 00:00 |
02:58:06.36 |
+51:54:34.2 |
HIP 13881 |
13.65 |
| 2026-06-16 12:00 |
02:58:09.08 |
+51:54:52.2 |
HIP 13881 |
13.19 |
| 2026-06-17 00:00 |
02:58:11.78 |
+51:55:10.2 |
HIP 13881 |
12.74 |
| 2026-06-17 12:00 |
02:58:14.46 |
+51:55:28.4 |
HIP 13881 |
12.29 |
| 2026-06-18 00:00 |
02:58:17.13 |
+51:55:46.6 |
HIP 13881 |
11.85 |
| 2026-06-18 12:00 |
02:58:19.77 |
+51:56:04.9 |
HIP 13881 |
11.41 |
| 2026-06-19 00:00 |
02:58:22.40 |
+51:56:23.3 |
HIP 13881 |
10.98 |
| 2026-06-19 12:00 |
02:58:25.01 |
+51:56:41.8 |
HIP 13881 |
10.56 |
| 2026-06-20 00:00 |
02:58:27.60 |
+51:57:00.3 |
HIP 13881 |
10.14 |
| 2026-06-20 12:00 |
02:58:30.17 |
+51:57:18.9 |
HIP 13881 |
9.73 |
| 2026-06-21 00:00 |
02:58:32.72 |
+51:57:37.7 |
HIP 13881 |
9.33 |
| 2026-06-21 12:00 |
02:58:35.25 |
+51:57:56.4 |
HIP 13881 |
8.94 |
| 2026-06-22 00:00 |
02:58:37.76 |
+51:58:15.3 |
HIP 13881 |
8.56 |