| 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) |
| 2026-09-20 00:00 |
03:40:17.80 |
-18:36:18.9 |
HIP 17071 |
26.09 |
| 2026-09-20 12:00 |
03:40:17.30 |
-18:36:27.8 |
HIP 17071 |
25.90 |
| 2026-09-21 00:00 |
03:40:16.79 |
-18:36:36.7 |
HIP 17071 |
25.72 |
| 2026-09-21 12:00 |
03:40:16.28 |
-18:36:45.6 |
HIP 17071 |
25.53 |
| 2026-09-22 00:00 |
03:40:15.76 |
-18:36:54.5 |
HIP 17071 |
25.34 |
| 2026-09-22 12:00 |
03:40:15.23 |
-18:37:03.4 |
HIP 17071 |
25.16 |
| 2026-09-23 00:00 |
03:40:14.69 |
-18:37:12.2 |
HIP 17071 |
24.97 |
| 2026-09-23 12:00 |
03:40:14.15 |
-18:37:21.0 |
HIP 17071 |
24.78 |
| 2026-09-24 00:00 |
03:40:13.60 |
-18:37:29.8 |
HIP 17071 |
24.60 |
| 2026-09-24 12:00 |
03:40:13.04 |
-18:37:38.6 |
HIP 17071 |
24.41 |
| 2026-09-25 00:00 |
03:40:12.48 |
-18:37:47.4 |
HIP 17071 |
24.22 |
| 2026-09-25 12:00 |
03:40:11.91 |
-18:37:56.1 |
HIP 17071 |
24.03 |
| 2026-09-26 00:00 |
03:40:11.33 |
-18:38:04.8 |
HIP 17071 |
23.84 |
| 2026-09-26 12:00 |
03:40:10.75 |
-18:38:13.5 |
HIP 17071 |
23.66 |
| 2026-09-27 00:00 |
03:40:10.16 |
-18:38:22.1 |
HIP 17071 |
23.47 |
| 2026-09-27 12:00 |
03:40:09.56 |
-18:38:30.7 |
HIP 17071 |
23.28 |
| 2026-09-28 00:00 |
03:40:08.95 |
-18:38:39.3 |
HIP 17071 |
23.09 |
| 2026-09-28 12:00 |
03:40:08.34 |
-18:38:47.9 |
HIP 17071 |
22.90 |
| 2026-09-29 00:00 |
03:40:07.73 |
-18:38:56.5 |
HIP 17071 |
22.72 |
| 2026-09-29 12:00 |
03:40:07.10 |
-18:39:05.0 |
HIP 17071 |
22.53 |
| 2026-09-30 00:00 |
03:40:06.47 |
-18:39:13.5 |
HIP 17071 |
22.34 |
| 2026-09-30 12:00 |
03:40:05.83 |
-18:39:21.9 |
HIP 17071 |
22.15 |
| 2026-10-01 00:00 |
03:40:05.19 |
-18:39:30.4 |
HIP 17071 |
21.97 |
| 2026-10-01 12:00 |
03:40:04.54 |
-18:39:38.7 |
HIP 17071 |
21.78 |
| 2026-10-02 00:00 |
03:40:03.88 |
-18:39:47.1 |
HIP 17071 |
21.59 |
| 2026-10-02 12:00 |
03:40:03.22 |
-18:39:55.4 |
HIP 17071 |
21.41 |
| 2026-10-03 00:00 |
03:40:02.55 |
-18:40:03.7 |
HIP 17071 |
21.22 |
| 2026-10-03 12:00 |
03:40:01.87 |
-18:40:12.0 |
HIP 17071 |
21.04 |
| 2026-10-04 00:00 |
03:40:01.19 |
-18:40:20.2 |
HIP 17071 |
20.85 |
| 2026-10-04 12:00 |
03:40:00.50 |
-18:40:28.4 |
HIP 17071 |
20.67 |
| 2026-10-05 00:00 |
03:39:59.81 |
-18:40:36.6 |
HIP 17071 |
20.48 |
| 2026-10-05 12:00 |
03:39:59.11 |
-18:40:44.7 |
HIP 17071 |
20.30 |
| 2026-10-06 00:00 |
03:39:58.40 |
-18:40:52.8 |
HIP 17071 |
20.12 |
| 2026-10-06 12:00 |
03:39:57.69 |
-18:41:00.8 |
HIP 17071 |
19.94 |
| 2026-10-07 00:00 |
03:39:56.97 |
-18:41:08.9 |
HIP 17071 |
19.76 |
| 2026-10-07 12:00 |
03:39:56.25 |
-18:41:16.8 |
HIP 17071 |
19.58 |
| 2026-10-08 00:00 |
03:39:55.52 |
-18:41:24.8 |
HIP 17071 |
19.40 |
| 2026-10-08 12:00 |
03:39:54.78 |
-18:41:32.6 |
HIP 17071 |
19.22 |
| 2026-10-09 00:00 |
03:39:54.04 |
-18:41:40.5 |
HIP 17071 |
19.04 |
| 2026-10-09 12:00 |
03:39:53.29 |
-18:41:48.3 |
HIP 17071 |
18.87 |
| 2026-10-10 00:00 |
03:39:52.54 |
-18:41:56.1 |
HIP 17071 |
18.69 |
| 2026-10-10 12:00 |
03:39:51.78 |
-18:42:03.8 |
HIP 17071 |
18.52 |
| 2026-10-11 00:00 |
03:39:51.01 |
-18:42:11.5 |
HIP 17071 |
18.35 |