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 | +2.0297 | +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) |
|---|---|---|---|---|
| 2026-03-26 00:00 | 08:09:16.21 | +03:07:43.3 | HIP 39872 | 14.06 |
| 2026-03-26 12:00 | 08:09:14.65 | +03:08:01.9 | HIP 39872 | 14.07 |
| 2026-03-27 00:00 | 08:09:13.12 | +03:08:20.5 | HIP 39872 | 14.10 |
| 2026-03-27 12:00 | 08:09:11.61 | +03:08:39.0 | HIP 39872 | 14.15 |
| 2026-03-28 00:00 | 08:09:10.13 | +03:08:57.5 | HIP 39872 | 14.22 |
| 2026-03-28 12:00 | 08:09:08.68 | +03:09:16.0 | HIP 39872 | 14.31 |
| 2026-03-29 00:00 | 08:09:07.26 | +03:09:34.4 | HIP 39872 | 14.41 |
| 2026-03-29 12:00 | 08:09:05.86 | +03:09:52.8 | HIP 39872 | 14.54 |
| 2026-03-30 00:00 | 08:09:04.49 | +03:10:11.1 | HIP 39872 | 14.67 |
| 2026-03-30 12:00 | 08:09:03.15 | +03:10:29.4 | HIP 39872 | 14.83 |
| 2026-03-31 00:00 | 08:09:01.84 | +03:10:47.7 | HIP 39872 | 14.99 |
| 2026-03-31 12:00 | 08:09:00.55 | +03:11:05.9 | HIP 39872 | 15.17 |
| 2026-04-01 00:00 | 08:08:59.29 | +03:11:24.0 | HIP 39872 | 15.37 |
| 2026-04-01 12:00 | 08:08:58.06 | +03:11:42.1 | HIP 39872 | 15.57 |
| 2026-04-02 00:00 | 08:08:56.86 | +03:12:00.1 | HIP 39872 | 15.78 |
| 2026-04-02 12:00 | 08:08:55.68 | +03:12:18.1 | HIP 39872 | 16.00 |
| 2026-04-03 00:00 | 08:08:54.53 | +03:12:36.1 | HIP 39872 | 16.23 |
| 2026-04-03 12:00 | 08:08:53.41 | +03:12:54.0 | HIP 39872 | 16.47 |
| 2026-04-04 00:00 | 08:08:52.32 | +03:13:11.8 | HIP 39872 | 16.72 |
| 2026-04-04 12:00 | 08:08:51.25 | +03:13:29.5 | HIP 39872 | 16.97 |
| 2026-04-05 00:00 | 08:08:50.21 | +03:13:47.3 | HIP 39872 | 17.22 |
| 2026-04-05 12:00 | 08:08:49.20 | +03:14:04.9 | HIP 39872 | 17.48 |
| 2026-04-06 00:00 | 08:08:48.22 | +03:14:22.5 | HIP 39872 | 17.75 |
| 2026-04-06 12:00 | 08:08:47.27 | +03:14:40.0 | HIP 39872 | 18.02 |
| 2026-04-07 00:00 | 08:08:46.34 | +03:14:57.5 | HIP 39872 | 18.29 |
| 2026-04-07 12:00 | 08:08:45.45 | +03:15:14.9 | HIP 39872 | 18.57 |
| 2026-04-08 00:00 | 08:08:44.58 | +03:15:32.2 | HIP 39872 | 18.84 |
| 2026-04-08 12:00 | 08:08:43.74 | +03:15:49.5 | HIP 39872 | 19.12 |
| 2026-04-09 00:00 | 08:08:42.92 | +03:16:06.7 | HIP 39872 | 19.40 |
| 2026-04-09 12:00 | 08:08:42.14 | +03:16:23.8 | HIP 39872 | 19.69 |
| 2026-04-10 00:00 | 08:08:41.38 | +03:16:40.9 | HIP 39872 | 19.97 |
| 2026-04-10 12:00 | 08:08:40.66 | +03:16:57.9 | HIP 39872 | 20.25 |
| 2026-04-11 00:00 | 08:08:39.96 | +03:17:14.8 | HIP 39872 | 20.54 |
| 2026-04-11 12:00 | 08:08:39.29 | +03:17:31.6 | HIP 39872 | 20.82 |
| 2026-04-12 00:00 | 08:08:38.64 | +03:17:48.4 | HIP 39872 | 21.10 |
| 2026-04-12 12:00 | 08:08:38.03 | +03:18:05.1 | HIP 39872 | 21.39 |
| 2026-04-13 00:00 | 08:08:37.44 | +03:18:21.7 | HIP 39872 | 21.67 |
| 2026-04-13 12:00 | 08:08:36.89 | +03:18:38.3 | HIP 39872 | 21.95 |
| 2026-04-14 00:00 | 08:08:36.36 | +03:18:54.7 | HIP 39872 | 22.23 |
| 2026-04-14 12:00 | 08:08:35.86 | +03:19:11.1 | HIP 39872 | 22.51 |
| 2026-04-15 00:00 | 08:08:35.39 | +03:19:27.4 | HIP 39872 | 22.79 |
| 2026-04-15 12:00 | 08:08:34.94 | +03:19:43.6 | HIP 39872 | 23.07 |
| 2026-04-16 00:00 | 08:08:34.53 | +03:19:59.7 | HIP 39872 | 23.34 |