| Parameter |
Value |
| Designation |
C/1987 U3 (McNaught) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
1987-12-11T22:32:44.332800Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:29:36Z |
| Obs used |
106 |
| NEO |
- |
| M1 |
6.100 |
| K1 |
17.250 |
| PC |
- |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
1988-01-08.0000000 |
| e |
0.99855807 |
| q (au) |
0.841167 |
| a (au) |
583.363126 |
| i (deg) |
97.126481 |
| Ω (om, deg) |
261.341785 |
| ω (w, deg) |
17.409142 |
| M (ma, deg) |
0.001893 |
Magnitude
Scatter + Global Linear
$$
M_a = (4.978 + 3.538\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
4.978 |
| n |
3.538 |
| 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 |
| 1987-12-27 |
1988-02-01 |
-7.4131 |
+0.143 |
| 1988-02-01 |
1988-02-18 |
+3.8294 |
-0.662 |
| 1988-02-18 |
1988-03-22 |
+3.4165 |
-0.549 |
| 1988-03-22 |
1988-05-10 |
-6.7830 |
+2.088 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-07-29 00:00 |
05:23:40.95 |
+18:39:58.2 |
HIP 25204 |
4.62 |
| 2026-07-29 12:00 |
05:23:42.33 |
+18:39:57.3 |
HIP 25204 |
4.79 |
| 2026-07-30 00:00 |
05:23:43.70 |
+18:39:56.4 |
HIP 25204 |
4.98 |
| 2026-07-30 12:00 |
05:23:45.06 |
+18:39:55.5 |
HIP 25204 |
5.17 |
| 2026-07-31 00:00 |
05:23:46.40 |
+18:39:54.6 |
HIP 25204 |
5.37 |
| 2026-07-31 12:00 |
05:23:47.73 |
+18:39:53.6 |
HIP 25204 |
5.59 |
| 2026-08-01 00:00 |
05:23:49.06 |
+18:39:52.6 |
HIP 25204 |
5.81 |
| 2026-08-01 12:00 |
05:23:50.37 |
+18:39:51.6 |
HIP 25204 |
6.03 |
| 2026-08-02 00:00 |
05:23:51.67 |
+18:39:50.5 |
HIP 25204 |
6.26 |
| 2026-08-02 12:00 |
05:23:52.95 |
+18:39:49.4 |
HIP 25204 |
6.50 |
| 2026-08-03 00:00 |
05:23:54.23 |
+18:39:48.3 |
HIP 25204 |
6.74 |
| 2026-08-03 12:00 |
05:23:55.49 |
+18:39:47.2 |
HIP 25204 |
6.98 |
| 2026-08-04 00:00 |
05:23:56.74 |
+18:39:46.1 |
HIP 25204 |
7.22 |
| 2026-08-04 12:00 |
05:23:57.98 |
+18:39:44.9 |
HIP 25204 |
7.46 |
| 2026-08-05 00:00 |
05:23:59.20 |
+18:39:43.7 |
HIP 25204 |
7.71 |
| 2026-08-05 12:00 |
05:24:00.42 |
+18:39:42.5 |
HIP 25204 |
7.95 |
| 2026-08-06 00:00 |
05:24:01.62 |
+18:39:41.3 |
HIP 25204 |
8.19 |
| 2026-08-06 12:00 |
05:24:02.81 |
+18:39:40.0 |
HIP 25204 |
8.44 |
| 2026-08-07 00:00 |
05:24:03.98 |
+18:39:38.7 |
HIP 25204 |
8.68 |
| 2026-08-07 12:00 |
05:24:05.14 |
+18:39:37.4 |
HIP 25204 |
8.92 |
| 2026-08-08 00:00 |
05:24:06.29 |
+18:39:36.1 |
HIP 25204 |
9.16 |
| 2026-08-08 12:00 |
05:24:07.43 |
+18:39:34.7 |
HIP 25204 |
9.41 |
| 2026-08-09 00:00 |
05:24:08.55 |
+18:39:33.3 |
HIP 25204 |
9.64 |
| 2026-08-09 12:00 |
05:24:09.66 |
+18:39:31.9 |
HIP 25204 |
9.88 |
| 2026-08-10 00:00 |
05:24:10.76 |
+18:39:30.5 |
HIP 25204 |
10.12 |
| 2026-08-10 12:00 |
05:24:11.84 |
+18:39:29.1 |
HIP 25204 |
10.35 |
| 2026-08-11 00:00 |
05:24:12.91 |
+18:39:27.6 |
HIP 25204 |
10.58 |
| 2026-08-11 12:00 |
05:24:13.97 |
+18:39:26.1 |
HIP 25204 |
10.81 |
| 2026-08-12 00:00 |
05:24:15.01 |
+18:39:24.6 |
HIP 25204 |
11.04 |
| 2026-08-12 12:00 |
05:24:16.04 |
+18:39:23.0 |
HIP 25204 |
11.26 |
| 2026-08-13 00:00 |
05:24:17.06 |
+18:39:21.4 |
HIP 25204 |
11.48 |
| 2026-08-13 12:00 |
05:24:18.06 |
+18:39:19.9 |
HIP 25204 |
11.70 |
| 2026-08-14 00:00 |
05:24:19.04 |
+18:39:18.2 |
HIP 25204 |
11.92 |
| 2026-08-14 12:00 |
05:24:20.02 |
+18:39:16.6 |
HIP 25204 |
12.14 |
| 2026-08-15 00:00 |
05:24:20.97 |
+18:39:15.0 |
HIP 25204 |
12.35 |
| 2026-08-15 12:00 |
05:24:21.92 |
+18:39:13.3 |
HIP 25204 |
12.56 |
| 2026-08-16 00:00 |
05:24:22.85 |
+18:39:11.6 |
HIP 25204 |
12.76 |
| 2026-08-16 12:00 |
05:24:23.76 |
+18:39:09.8 |
HIP 25204 |
12.97 |
| 2026-08-17 00:00 |
05:24:24.66 |
+18:39:08.1 |
HIP 25204 |
13.17 |
| 2026-08-17 12:00 |
05:24:25.55 |
+18:39:06.3 |
HIP 25204 |
13.36 |
| 2026-08-18 00:00 |
05:24:26.42 |
+18:39:04.5 |
HIP 25204 |
13.56 |
| 2026-08-18 12:00 |
05:24:27.28 |
+18:39:02.7 |
HIP 25204 |
13.75 |
| 2026-08-19 00:00 |
05:24:28.12 |
+18:39:00.9 |
HIP 25204 |
13.94 |