| Parameter |
Value |
| Designation |
C/2021 C4 (ATLAS) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2021-01-17T01:15:25.960320Z |
| Orbit solution date (soln_date, UTC) |
2025-10-28T16:12:33Z |
| Obs used |
234 |
| NEO |
- |
| M1 |
6.900 |
| K1 |
13.500 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2021-02-12T14:39:53.769600Z |
| Discovery magnitude (MPC) |
18.73 c |
| Discovery observatory (MPC) |
T05 · ATLAS-HKO, Haleakala |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2021-06-12.0000000 |
| e |
0.99919682 |
| q (au) |
4.504185 |
| a (au) |
5607.929825 |
| i (deg) |
132.842626 |
| Ω (om, deg) |
194.276215 |
| ω (w, deg) |
320.231119 |
| M (ma, deg) |
0.000343 |
Magnitude
Scatter + Global Linear
$$
M_a = (5.414 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
5.414 |
| n |
6.000 |
| gf |
0.942 |
| gb |
-0.980 |
| k |
1.000 |
| δ90 |
1.000 |
| 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
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-09-20 00:00 |
10:21:01.83 |
+56:54:20.6 |
HIP 50725 |
30.73 |
| 2026-09-20 12:00 |
10:21:11.89 |
+56:54:49.5 |
HIP 50725 |
30.13 |
| 2026-09-21 00:00 |
10:21:21.90 |
+56:55:19.1 |
HIP 50725 |
29.59 |
| 2026-09-21 12:00 |
10:21:31.88 |
+56:55:49.4 |
HIP 50725 |
29.09 |
| 2026-09-22 00:00 |
10:21:41.82 |
+56:56:20.4 |
HIP 50725 |
28.65 |
| 2026-09-22 12:00 |
10:21:51.71 |
+56:56:52.2 |
HIP 50725 |
28.26 |
| 2026-09-23 00:00 |
10:22:01.57 |
+56:57:24.6 |
HIP 50725 |
27.92 |
| 2026-09-23 12:00 |
10:22:11.38 |
+56:57:57.8 |
HIP 50725 |
27.65 |
| 2026-09-24 00:00 |
10:22:21.14 |
+56:58:31.7 |
HIP 50725 |
27.43 |
| 2026-09-24 12:00 |
10:22:30.87 |
+56:59:06.4 |
HIP 50725 |
27.27 |
| 2026-09-25 00:00 |
10:22:40.55 |
+56:59:41.7 |
HIP 50725 |
27.18 |
| 2026-09-25 12:00 |
10:22:50.18 |
+57:00:17.8 |
HIP 50725 |
27.15 |
| 2026-09-26 00:00 |
10:22:59.77 |
+57:00:54.6 |
HIP 50725 |
27.18 |
| 2026-09-26 12:00 |
10:23:09.31 |
+57:01:32.1 |
HIP 50725 |
27.27 |
| 2026-09-27 00:00 |
10:23:18.81 |
+57:02:10.4 |
HIP 50725 |
27.42 |
| 2026-09-27 12:00 |
10:23:28.26 |
+57:02:49.3 |
HIP 50725 |
27.63 |
| 2026-09-28 00:00 |
10:23:37.66 |
+57:03:29.0 |
HIP 50725 |
27.90 |
| 2026-09-28 12:00 |
10:23:47.01 |
+57:04:09.4 |
HIP 50725 |
28.23 |
| 2026-09-29 00:00 |
10:23:56.31 |
+57:04:50.6 |
HIP 50725 |
28.61 |
| 2026-09-29 12:00 |
10:24:05.56 |
+57:05:32.4 |
HIP 50725 |
29.04 |
| 2026-09-30 00:00 |
10:24:14.76 |
+57:06:15.0 |
HIP 50725 |
29.53 |
| 2026-09-30 12:00 |
10:24:23.90 |
+57:06:58.3 |
HIP 51207 |
29.53 |
| 2026-10-01 00:00 |
10:24:33.00 |
+57:07:42.3 |
HIP 51207 |
28.83 |
| 2026-10-01 12:00 |
10:24:42.04 |
+57:08:27.1 |
HIP 51207 |
28.19 |
| 2026-10-02 00:00 |
10:24:51.03 |
+57:09:12.6 |
HIP 51207 |
27.62 |
| 2026-10-02 12:00 |
10:24:59.96 |
+57:09:58.8 |
HIP 51207 |
27.14 |
| 2026-10-03 00:00 |
10:25:08.84 |
+57:10:45.7 |
HIP 51207 |
26.73 |
| 2026-10-03 12:00 |
10:25:17.66 |
+57:11:33.4 |
HIP 51207 |
26.42 |
| 2026-10-04 00:00 |
10:25:26.43 |
+57:12:21.8 |
HIP 51207 |
26.19 |
| 2026-10-04 12:00 |
10:25:35.14 |
+57:13:10.9 |
HIP 51207 |
26.06 |
| 2026-10-05 00:00 |
10:25:43.79 |
+57:14:00.7 |
HIP 51207 |
26.02 |
| 2026-10-05 12:00 |
10:25:52.38 |
+57:14:51.3 |
HIP 51207 |
26.08 |
| 2026-10-06 00:00 |
10:26:00.91 |
+57:15:42.6 |
HIP 51207 |
26.23 |
| 2026-10-06 12:00 |
10:26:09.38 |
+57:16:34.6 |
HIP 51207 |
26.47 |
| 2026-10-07 00:00 |
10:26:17.78 |
+57:17:27.4 |
HIP 51253 |
26.42 |
| 2026-10-07 12:00 |
10:26:26.13 |
+57:18:20.9 |
HIP 51253 |
25.05 |
| 2026-10-08 00:00 |
10:26:34.41 |
+57:19:15.1 |
HIP 51253 |
23.69 |
| 2026-10-08 12:00 |
10:26:42.63 |
+57:20:10.0 |
HIP 51253 |
22.32 |
| 2026-10-09 00:00 |
10:26:50.78 |
+57:21:05.7 |
HIP 51253 |
20.96 |
| 2026-10-09 12:00 |
10:26:58.87 |
+57:22:02.1 |
HIP 51253 |
19.61 |
| 2026-10-10 00:00 |
10:27:06.89 |
+57:22:59.2 |
HIP 51253 |
18.26 |
| 2026-10-10 12:00 |
10:27:14.85 |
+57:23:57.1 |
HIP 51253 |
16.92 |
| 2026-10-11 00:00 |
10:27:22.73 |
+57:24:55.6 |
HIP 51253 |
15.59 |