1P/Halley
Metadata
| Parameter | Value |
|---|---|
| Designation | 1P/Halley |
| Type | P |
| Perihelion (tp_cal, UTC) | 1986-02-08T11:22:00.431040Z |
| Orbit solution date (soln_date, UTC) | 2025-11-21T15:57:34Z |
| Obs used | 8518 |
| NEO | Yes |
| M1 | 5.500 |
| K1 | 8.000 |
| PC | 0.030 |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 1968-01-20.0000000 |
| e | 0.96793600 |
| q (au) | 0.574864 |
| a (au) | 17.928635 |
| i (deg) | 162.190530 |
| Ω (om, deg) | 59.098947 |
| ω (w, deg) | 112.241431 |
| M (ma, deg) | 274.382337 |
Description
The first predicted periodic comet; the earliest known record appears in China’s Shiji (Records of the Grand Historian) in 240 BCE.
Magnitude
Scatter + Global Linear
$$ M_a = (3.661 + 3.876\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 3.661 |
| n | 3.876 |
| 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 |
|---|---|---|---|
| 1981-12-02 | 1985-11-05 | +6.7140 | -0.431 |
| 1985-11-05 | 1986-01-28 | +2.0298 | +0.388 |
| 1986-02-15 | 1986-07-08 | -2.7942 | -0.455 |
| 1986-07-08 | 1987-12-12 | +0.0819 | -1.319 |
| 1987-12-12 | 2003-03-08 | +3.7502 | -4.319 |
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 | 08:15:06.07 | +03:30:27.9 | HIP 40500 | 23.13 |
| 2026-07-29 12:00 | 08:15:09.12 | +03:30:17.1 | HIP 40500 | 22.77 |
| 2026-07-30 00:00 | 08:15:12.18 | +03:30:06.1 | HIP 40500 | 22.44 |
| 2026-07-30 12:00 | 08:15:15.23 | +03:29:55.1 | HIP 40500 | 22.13 |
| 2026-07-31 00:00 | 08:15:18.28 | +03:29:43.9 | HIP 40500 | 21.84 |
| 2026-07-31 12:00 | 08:15:21.32 | +03:29:32.7 | HIP 40500 | 21.58 |
| 2026-08-01 00:00 | 08:15:24.37 | +03:29:21.3 | HIP 40500 | 21.35 |
| 2026-08-01 12:00 | 08:15:27.41 | +03:29:09.8 | HIP 40500 | 21.14 |
| 2026-08-02 00:00 | 08:15:30.45 | +03:28:58.2 | HIP 40500 | 20.97 |
| 2026-08-02 12:00 | 08:15:33.48 | +03:28:46.6 | HIP 40500 | 20.83 |
| 2026-08-03 00:00 | 08:15:36.51 | +03:28:34.8 | HIP 40500 | 20.71 |
| 2026-08-03 12:00 | 08:15:39.54 | +03:28:22.9 | HIP 40500 | 20.63 |
| 2026-08-04 00:00 | 08:15:42.56 | +03:28:10.9 | HIP 40500 | 20.57 |
| 2026-08-04 12:00 | 08:15:45.58 | +03:27:58.8 | HIP 40500 | 20.55 |
| 2026-08-05 00:00 | 08:15:48.59 | +03:27:46.6 | HIP 40500 | 20.56 |
| 2026-08-05 12:00 | 08:15:51.60 | +03:27:34.3 | HIP 40500 | 20.61 |
| 2026-08-06 00:00 | 08:15:54.61 | +03:27:22.0 | HIP 40500 | 20.68 |
| 2026-08-06 12:00 | 08:15:57.61 | +03:27:09.5 | HIP 40500 | 20.78 |
| 2026-08-07 00:00 | 08:16:00.60 | +03:26:56.9 | HIP 40500 | 20.92 |
| 2026-08-07 12:00 | 08:16:03.59 | +03:26:44.2 | HIP 40500 | 21.08 |
| 2026-08-08 00:00 | 08:16:06.57 | +03:26:31.4 | HIP 40500 | 21.27 |
| 2026-08-08 12:00 | 08:16:09.55 | +03:26:18.6 | HIP 40500 | 21.49 |
| 2026-08-09 00:00 | 08:16:12.52 | +03:26:05.6 | HIP 40500 | 21.74 |
| 2026-08-09 12:00 | 08:16:15.49 | +03:25:52.5 | HIP 40500 | 22.01 |
| 2026-08-10 00:00 | 08:16:18.45 | +03:25:39.4 | HIP 40500 | 22.30 |
| 2026-08-10 12:00 | 08:16:21.40 | +03:25:26.1 | HIP 40500 | 22.62 |
| 2026-08-11 00:00 | 08:16:24.34 | +03:25:12.8 | HIP 40500 | 22.97 |
| 2026-08-11 12:00 | 08:16:27.28 | +03:24:59.4 | HIP 40500 | 23.33 |
| 2026-08-12 00:00 | 08:16:30.21 | +03:24:45.9 | HIP 40500 | 23.71 |
| 2026-08-12 12:00 | 08:16:33.13 | +03:24:32.3 | HIP 40500 | 24.12 |
| 2026-08-13 00:00 | 08:16:36.05 | +03:24:18.6 | HIP 40500 | 24.54 |
| 2026-08-13 12:00 | 08:16:38.96 | +03:24:04.8 | HIP 40500 | 24.98 |
| 2026-08-14 00:00 | 08:16:41.86 | +03:23:50.9 | HIP 40500 | 25.43 |
| 2026-08-14 12:00 | 08:16:44.75 | +03:23:37.0 | HIP 40500 | 25.90 |
| 2026-08-15 00:00 | 08:16:47.63 | +03:23:23.0 | HIP 40500 | 26.38 |
| 2026-08-15 12:00 | 08:16:50.50 | +03:23:08.9 | HIP 40500 | 26.88 |
| 2026-08-16 00:00 | 08:16:53.36 | +03:22:54.7 | HIP 40500 | 27.39 |
| 2026-08-16 12:00 | 08:16:56.22 | +03:22:40.4 | HIP 40500 | 27.91 |
| 2026-08-17 00:00 | 08:16:59.06 | +03:22:26.1 | HIP 40500 | 28.43 |
| 2026-08-17 12:00 | 08:17:01.90 | +03:22:11.7 | HIP 40500 | 28.97 |
| 2026-08-18 00:00 | 08:17:04.72 | +03:21:57.2 | HIP 40500 | 29.52 |
| 2026-08-18 12:00 | 08:17:07.54 | +03:21:42.6 | HIP 40500 | 30.08 |
| 2026-08-19 00:00 | 08:17:10.34 | +03:21:27.9 | HIP 40500 | 30.64 |