| 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) |
| 2026-06-01 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 |
| 2026-06-02 12:00 |
03:39:09.42 |
-18:14:01.0 |
HIP 16877 |
35.60 |
| 2026-06-03 00:00 |
03:39:10.33 |
-18:14:00.8 |
HIP 16877 |
35.77 |
| 2026-06-03 12:00 |
03:39:11.24 |
-18:14:00.7 |
HIP 16877 |
35.95 |
| 2026-06-04 00:00 |
03:39:12.15 |
-18:14:00.6 |
HIP 16877 |
36.12 |
| 2026-06-04 12:00 |
03:39:13.06 |
-18:14:00.6 |
HIP 16877 |
36.29 |
| 2026-06-05 00:00 |
03:39:13.96 |
-18:14:00.7 |
HIP 16877 |
36.47 |
| 2026-06-05 12:00 |
03:39:14.86 |
-18:14:00.9 |
HIP 16877 |
36.64 |
| 2026-06-06 00:00 |
03:39:15.76 |
-18:14:01.1 |
HIP 16877 |
36.82 |
| 2026-06-06 12:00 |
03:39:16.66 |
-18:14:01.4 |
HIP 16877 |
37.00 |
| 2026-06-07 00:00 |
03:39:17.55 |
-18:14:01.8 |
HIP 16877 |
37.17 |
| 2026-06-07 12:00 |
03:39:18.45 |
-18:14:02.2 |
HIP 16877 |
37.35 |
| 2026-06-08 00:00 |
03:39:19.34 |
-18:14:02.8 |
HIP 16877 |
37.53 |
| 2026-06-08 12:00 |
03:39:20.22 |
-18:14:03.4 |
HIP 16877 |
37.71 |
| 2026-06-09 00:00 |
03:39:21.11 |
-18:14:04.1 |
HIP 16877 |
37.89 |
| 2026-06-09 12:00 |
03:39:21.99 |
-18:14:04.8 |
HIP 16877 |
38.07 |
| 2026-06-10 00:00 |
03:39:22.87 |
-18:14:05.7 |
HIP 16877 |
38.25 |
| 2026-06-10 12:00 |
03:39:23.74 |
-18:14:06.6 |
HIP 16877 |
38.43 |
| 2026-06-11 00:00 |
03:39:24.62 |
-18:14:07.5 |
HIP 16877 |
38.61 |
| 2026-06-11 12:00 |
03:39:25.49 |
-18:14:08.6 |
HIP 16877 |
38.79 |
| 2026-06-12 00:00 |
03:39:26.35 |
-18:14:09.7 |
HIP 16877 |
38.97 |
| 2026-06-12 12:00 |
03:39:27.22 |
-18:14:10.9 |
HIP 16877 |
39.15 |
| 2026-06-13 00:00 |
03:39:28.08 |
-18:14:12.2 |
HIP 16877 |
39.34 |
| 2026-06-13 12:00 |
03:39:28.93 |
-18:14:13.6 |
HIP 16877 |
39.52 |
| 2026-06-14 00:00 |
03:39:29.79 |
-18:14:15.0 |
HIP 16877 |
39.70 |
| 2026-06-14 12:00 |
03:39:30.64 |
-18:14:16.5 |
HIP 16877 |
39.89 |
| 2026-06-15 00:00 |
03:39:31.48 |
-18:14:18.1 |
HIP 16877 |
40.07 |
| 2026-06-15 12:00 |
03:39:32.33 |
-18:14:19.7 |
HIP 16877 |
40.25 |
| 2026-06-16 00:00 |
03:39:33.17 |
-18:14:21.5 |
HIP 16877 |
40.44 |
| 2026-06-16 12:00 |
03:39:34.00 |
-18:14:23.3 |
HIP 16877 |
40.62 |
| 2026-06-17 00:00 |
03:39:34.83 |
-18:14:25.1 |
HIP 16877 |
40.80 |
| 2026-06-17 12:00 |
03:39:35.66 |
-18:14:27.1 |
HIP 16877 |
40.99 |
| 2026-06-18 00:00 |
03:39:36.49 |
-18:14:29.1 |
HIP 16877 |
41.17 |
| 2026-06-18 12:00 |
03:39:37.31 |
-18:14:31.2 |
HIP 16877 |
41.35 |
| 2026-06-19 00:00 |
03:39:38.12 |
-18:14:33.4 |
HIP 16877 |
41.54 |
| 2026-06-19 12:00 |
03:39:38.94 |
-18:14:35.6 |
HIP 16877 |
41.72 |
| 2026-06-20 00:00 |
03:39:39.75 |
-18:14:37.9 |
HIP 16877 |
41.91 |
| 2026-06-20 12:00 |
03:39:40.55 |
-18:14:40.3 |
HIP 16877 |
42.09 |
| 2026-06-21 00:00 |
03:39:41.35 |
-18:14:42.8 |
HIP 16877 |
42.27 |
| 2026-06-21 12:00 |
03:39:42.15 |
-18:14:45.3 |
HIP 16877 |
42.46 |
| 2026-06-22 00:00 |
03:39:42.94 |
-18:14:47.9 |
HIP 16877 |
42.64 |