| 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 |
-9.7164 |
+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) |
| 2026-05-12 00:00 |
02:54:23.97 |
+51:38:17.5 |
HIP 13664 |
14.84 |
| 2026-05-12 12:00 |
02:54:27.42 |
+51:38:26.8 |
HIP 13664 |
14.29 |
| 2026-05-13 00:00 |
02:54:30.87 |
+51:38:36.2 |
HIP 13664 |
13.73 |
| 2026-05-13 12:00 |
02:54:34.31 |
+51:38:45.8 |
HIP 13664 |
13.17 |
| 2026-05-14 00:00 |
02:54:37.75 |
+51:38:55.6 |
HIP 13664 |
12.61 |
| 2026-05-14 12:00 |
02:54:41.19 |
+51:39:05.5 |
HIP 13664 |
12.06 |
| 2026-05-15 00:00 |
02:54:44.62 |
+51:39:15.5 |
HIP 13664 |
11.50 |
| 2026-05-15 12:00 |
02:54:48.05 |
+51:39:25.7 |
HIP 13664 |
10.94 |
| 2026-05-16 00:00 |
02:54:51.48 |
+51:39:36.1 |
HIP 13664 |
10.38 |
| 2026-05-16 12:00 |
02:54:54.90 |
+51:39:46.6 |
HIP 13664 |
9.82 |
| 2026-05-17 00:00 |
02:54:58.31 |
+51:39:57.2 |
HIP 13664 |
9.27 |
| 2026-05-17 12:00 |
02:55:01.73 |
+51:40:08.0 |
HIP 13664 |
8.71 |
| 2026-05-18 00:00 |
02:55:05.13 |
+51:40:19.0 |
HIP 13664 |
8.15 |
| 2026-05-18 12:00 |
02:55:08.53 |
+51:40:30.1 |
HIP 13664 |
7.59 |
| 2026-05-19 00:00 |
02:55:11.93 |
+51:40:41.3 |
HIP 13664 |
7.04 |
| 2026-05-19 12:00 |
02:55:15.32 |
+51:40:52.7 |
HIP 13664 |
6.48 |
| 2026-05-20 00:00 |
02:55:18.70 |
+51:41:04.2 |
HIP 13664 |
5.93 |
| 2026-05-20 12:00 |
02:55:22.08 |
+51:41:15.9 |
HIP 13664 |
5.38 |
| 2026-05-21 00:00 |
02:55:25.45 |
+51:41:27.7 |
HIP 13664 |
4.83 |
| 2026-05-21 12:00 |
02:55:28.81 |
+51:41:39.7 |
HIP 13664 |
4.28 |
| 2026-05-22 00:00 |
02:55:32.17 |
+51:41:51.8 |
HIP 13664 |
3.73 |
| 2026-05-22 12:00 |
02:55:35.52 |
+51:42:04.0 |
HIP 13664 |
3.19 |
| 2026-05-23 00:00 |
02:55:38.86 |
+51:42:16.4 |
HIP 13664 |
2.66 |
| 2026-05-23 12:00 |
02:55:42.20 |
+51:42:28.9 |
HIP 13664 |
2.15 |
| 2026-05-24 00:00 |
02:55:45.52 |
+51:42:41.5 |
HIP 13664 |
1.66 |
| 2026-05-24 12:00 |
02:55:48.84 |
+51:42:54.3 |
HIP 13664 |
1.24 |
| 2026-05-25 00:00 |
02:55:52.15 |
+51:43:07.2 |
HIP 13664 |
0.97 |
| 2026-05-25 12:00 |
02:55:55.45 |
+51:43:20.3 |
HIP 13664 |
0.98 |
| 2026-05-26 00:00 |
02:55:58.74 |
+51:43:33.4 |
HIP 13664 |
1.27 |
| 2026-05-26 12:00 |
02:56:02.03 |
+51:43:46.8 |
HIP 13664 |
1.70 |
| 2026-05-27 00:00 |
02:56:05.30 |
+51:44:00.2 |
HIP 13664 |
2.18 |
| 2026-05-27 12:00 |
02:56:08.56 |
+51:44:13.8 |
HIP 13664 |
2.69 |
| 2026-05-28 00:00 |
02:56:11.82 |
+51:44:27.5 |
HIP 13664 |
3.22 |
| 2026-05-28 12:00 |
02:56:15.06 |
+51:44:41.3 |
HIP 13664 |
3.76 |
| 2026-05-29 00:00 |
02:56:18.30 |
+51:44:55.3 |
HIP 13664 |
4.29 |
| 2026-05-29 12:00 |
02:56:21.52 |
+51:45:09.3 |
HIP 13664 |
4.84 |
| 2026-05-30 00:00 |
02:56:24.74 |
+51:45:23.6 |
HIP 13664 |
5.38 |
| 2026-05-30 12:00 |
02:56:27.94 |
+51:45:37.9 |
HIP 13664 |
5.92 |
| 2026-05-31 00:00 |
02:56:31.13 |
+51:45:52.3 |
HIP 13664 |
6.47 |
| 2026-05-31 12:00 |
02:56:34.32 |
+51:46:06.9 |
HIP 13664 |
7.02 |
| 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 |