C/1921 E1 (Reid)
| 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) |
| 2026-02-03 00:00 |
03:36:53.79 |
-18:39:51.6 |
HIP 16799 |
11.86 |
| 2026-02-03 12:00 |
03:36:53.56 |
-18:39:43.7 |
HIP 16799 |
11.74 |
| 2026-02-04 00:00 |
03:36:53.34 |
-18:39:35.7 |
HIP 16799 |
11.62 |
| 2026-02-04 12:00 |
03:36:53.13 |
-18:39:27.7 |
HIP 16799 |
11.50 |
| 2026-02-05 00:00 |
03:36:52.93 |
-18:39:19.6 |
HIP 16799 |
11.39 |
| 2026-02-05 12:00 |
03:36:52.73 |
-18:39:11.5 |
HIP 16799 |
11.28 |
| 2026-02-06 00:00 |
03:36:52.55 |
-18:39:03.4 |
HIP 16799 |
11.17 |
| 2026-02-06 12:00 |
03:36:52.37 |
-18:38:55.3 |
HIP 16799 |
11.06 |
| 2026-02-07 00:00 |
03:36:52.20 |
-18:38:47.1 |
HIP 16799 |
10.95 |
| 2026-02-07 12:00 |
03:36:52.04 |
-18:38:38.8 |
HIP 16799 |
10.85 |
| 2026-02-08 00:00 |
03:36:51.89 |
-18:38:30.6 |
HIP 16799 |
10.74 |
| 2026-02-08 12:00 |
03:36:51.75 |
-18:38:22.3 |
HIP 16799 |
10.65 |
| 2026-02-09 00:00 |
03:36:51.61 |
-18:38:14.0 |
HIP 16799 |
10.55 |
| 2026-02-09 12:00 |
03:36:51.49 |
-18:38:05.6 |
HIP 16799 |
10.45 |
| 2026-02-10 00:00 |
03:36:51.37 |
-18:37:57.2 |
HIP 16799 |
10.36 |
| 2026-02-10 12:00 |
03:36:51.26 |
-18:37:48.8 |
HIP 16799 |
10.27 |
| 2026-02-11 00:00 |
03:36:51.16 |
-18:37:40.4 |
HIP 16799 |
10.19 |
| 2026-02-11 12:00 |
03:36:51.07 |
-18:37:31.9 |
HIP 16799 |
10.10 |
| 2026-02-12 00:00 |
03:36:50.99 |
-18:37:23.4 |
HIP 16799 |
10.02 |
| 2026-02-12 12:00 |
03:36:50.91 |
-18:37:14.9 |
HIP 16799 |
9.95 |
| 2026-02-13 00:00 |
03:36:50.85 |
-18:37:06.3 |
HIP 16799 |
9.87 |
| 2026-02-13 12:00 |
03:36:50.79 |
-18:36:57.7 |
HIP 16799 |
9.80 |
| 2026-02-14 00:00 |
03:36:50.74 |
-18:36:49.1 |
HIP 16799 |
9.73 |
| 2026-02-14 12:00 |
03:36:50.70 |
-18:36:40.5 |
HIP 16799 |
9.67 |
| 2026-02-15 00:00 |
03:36:50.67 |
-18:36:31.8 |
HIP 16799 |
9.61 |
| 2026-02-15 12:00 |
03:36:50.65 |
-18:36:23.2 |
HIP 16799 |
9.55 |
| 2026-02-16 00:00 |
03:36:50.63 |
-18:36:14.5 |
HIP 16799 |
9.50 |
| 2026-02-16 12:00 |
03:36:50.63 |
-18:36:05.7 |
HIP 16799 |
9.45 |
| 2026-02-17 00:00 |
03:36:50.63 |
-18:35:57.0 |
HIP 16799 |
9.40 |
| 2026-02-17 12:00 |
03:36:50.64 |
-18:35:48.2 |
HIP 16799 |
9.36 |
| 2026-02-18 00:00 |
03:36:50.66 |
-18:35:39.5 |
HIP 16799 |
9.32 |
| 2026-02-18 12:00 |
03:36:50.69 |
-18:35:30.7 |
HIP 16799 |
9.29 |
| 2026-02-19 00:00 |
03:36:50.73 |
-18:35:21.8 |
HIP 16799 |
9.26 |
| 2026-02-19 12:00 |
03:36:50.77 |
-18:35:13.0 |
HIP 16799 |
9.23 |
| 2026-02-20 00:00 |
03:36:50.83 |
-18:35:04.2 |
HIP 16799 |
9.21 |
| 2026-02-20 12:00 |
03:36:50.89 |
-18:34:55.3 |
HIP 16799 |
9.19 |
| 2026-02-21 00:00 |
03:36:50.96 |
-18:34:46.4 |
HIP 16799 |
9.18 |
| 2026-02-21 12:00 |
03:36:51.04 |
-18:34:37.5 |
HIP 16799 |
9.17 |
| 2026-02-22 00:00 |
03:36:51.13 |
-18:34:28.6 |
HIP 16799 |
9.17 |
| 2026-02-22 12:00 |
03:36:51.23 |
-18:34:19.7 |
HIP 16799 |
9.17 |
| 2026-02-23 00:00 |
03:36:51.33 |
-18:34:10.8 |
HIP 16799 |
9.17 |
| 2026-02-23 12:00 |
03:36:51.45 |
-18:34:01.8 |
HIP 16799 |
9.18 |
| 2026-02-24 00:00 |
03:36:51.57 |
-18:33:52.9 |
HIP 16799 |
9.19 |