| Parameter |
Value |
| Designation |
C/1921 E1 (Reid) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
1921-05-10T10:47:48.370560Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:29:02Z |
| Obs used |
20 |
| NEO |
- |
| M1 |
- |
| K1 |
- |
| PC |
- |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
1921-04-10.0000000 |
| e |
1.00057570 |
| q (au) |
1.008454 |
| a (au) |
-1751.685065 |
| i (deg) |
132.188784 |
| Ω (om, deg) |
269.441203 |
| ω (w, deg) |
64.493054 |
| M (ma, deg) |
-0.000409 |
Magnitude
Scatter + Global Linear
$$
M_a = (H_0 + n\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
- |
| n |
- |
| gf |
- |
| gb |
- |
| k |
- |
| δ90 |
- |
| 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
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-05-12 00:00 |
03:38:29.13 |
-18:15:20.1 |
HIP 16877 |
29.54 |
| 2026-05-12 12:00 |
03:38:30.07 |
-18:15:16.8 |
HIP 16877 |
29.64 |
| 2026-05-13 00:00 |
03:38:31.01 |
-18:15:13.5 |
HIP 16877 |
29.75 |
| 2026-05-13 12:00 |
03:38:31.95 |
-18:15:10.2 |
HIP 16877 |
29.85 |
| 2026-05-14 00:00 |
03:38:32.89 |
-18:15:07.1 |
HIP 16877 |
29.96 |
| 2026-05-14 12:00 |
03:38:33.84 |
-18:15:04.0 |
HIP 16877 |
30.07 |
| 2026-05-15 00:00 |
03:38:34.78 |
-18:15:01.0 |
HIP 16877 |
30.18 |
| 2026-05-15 12:00 |
03:38:35.72 |
-18:14:58.1 |
HIP 16877 |
30.30 |
| 2026-05-16 00:00 |
03:38:36.67 |
-18:14:55.2 |
HIP 16877 |
30.41 |
| 2026-05-16 12:00 |
03:38:37.61 |
-18:14:52.4 |
HIP 16877 |
30.53 |
| 2026-05-17 00:00 |
03:38:38.56 |
-18:14:49.7 |
HIP 16877 |
30.65 |
| 2026-05-17 12:00 |
03:38:39.50 |
-18:14:47.0 |
HIP 16877 |
30.78 |
| 2026-05-18 00:00 |
03:38:40.45 |
-18:14:44.5 |
HIP 16877 |
30.90 |
| 2026-05-18 12:00 |
03:38:41.39 |
-18:14:41.9 |
HIP 16877 |
31.03 |
| 2026-05-19 00:00 |
03:38:42.34 |
-18:14:39.5 |
HIP 16877 |
31.16 |
| 2026-05-19 12:00 |
03:38:43.28 |
-18:14:37.2 |
HIP 16877 |
31.29 |
| 2026-05-20 00:00 |
03:38:44.23 |
-18:14:34.9 |
HIP 16877 |
31.42 |
| 2026-05-20 12:00 |
03:38:45.17 |
-18:14:32.7 |
HIP 16877 |
31.56 |
| 2026-05-21 00:00 |
03:38:46.12 |
-18:14:30.5 |
HIP 16877 |
31.69 |
| 2026-05-21 12:00 |
03:38:47.06 |
-18:14:28.5 |
HIP 16877 |
31.83 |
| 2026-05-22 00:00 |
03:38:48.00 |
-18:14:26.5 |
HIP 16877 |
31.97 |
| 2026-05-22 12:00 |
03:38:48.95 |
-18:14:24.5 |
HIP 16877 |
32.12 |
| 2026-05-23 00:00 |
03:38:49.89 |
-18:14:22.7 |
HIP 16877 |
32.26 |
| 2026-05-23 12:00 |
03:38:50.83 |
-18:14:20.9 |
HIP 16877 |
32.41 |
| 2026-05-24 00:00 |
03:38:51.77 |
-18:14:19.2 |
HIP 16877 |
32.55 |
| 2026-05-24 12:00 |
03:38:52.71 |
-18:14:17.6 |
HIP 16877 |
32.70 |
| 2026-05-25 00:00 |
03:38:53.65 |
-18:14:16.0 |
HIP 16877 |
32.85 |
| 2026-05-25 12:00 |
03:38:54.59 |
-18:14:14.6 |
HIP 16877 |
33.00 |
| 2026-05-26 00:00 |
03:38:55.52 |
-18:14:13.2 |
HIP 16877 |
33.16 |
| 2026-05-26 12:00 |
03:38:56.46 |
-18:14:11.8 |
HIP 16877 |
33.31 |
| 2026-05-27 00:00 |
03:38:57.40 |
-18:14:10.6 |
HIP 16877 |
33.47 |
| 2026-05-27 12:00 |
03:38:58.33 |
-18:14:09.4 |
HIP 16877 |
33.62 |
| 2026-05-28 00:00 |
03:38:59.26 |
-18:14:08.3 |
HIP 16877 |
33.78 |
| 2026-05-28 12:00 |
03:39:00.19 |
-18:14:07.3 |
HIP 16877 |
33.94 |
| 2026-05-29 00:00 |
03:39:01.12 |
-18:14:06.3 |
HIP 16877 |
34.10 |
| 2026-05-29 12:00 |
03:39:02.05 |
-18:14:05.4 |
HIP 16877 |
34.27 |
| 2026-05-30 00:00 |
03:39:02.98 |
-18:14:04.6 |
HIP 16877 |
34.43 |
| 2026-05-30 12:00 |
03:39:03.90 |
-18:14:03.9 |
HIP 16877 |
34.59 |
| 2026-05-31 00:00 |
03:39:04.83 |
-18:14:03.2 |
HIP 16877 |
34.76 |
| 2026-05-31 12:00 |
03:39:05.75 |
-18:14:02.6 |
HIP 16877 |
34.93 |
| 2026-06-01 00:00 |
03:39:06.67 |
-18:14:02.1 |
HIP 16877 |
35.09 |
| 2026-06-01 12:00 |
03:39:07.59 |
-18:14:01.7 |
HIP 16877 |
35.26 |
| 2026-06-02 00:00 |
03:39:08.50 |
-18:14:01.3 |
HIP 16877 |
35.43 |