C/2021 C4 (ATLAS)
| 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
$$
M_a = (5.588 + 6.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
5.588 |
| n |
6.000 |
| gf |
0.904 |
| gb |
-0.582 |
| k |
0.977 |
| δ90 |
5.062 |
| 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 |
10:38:28.06 |
+59:54:58.7 |
HIP 52064 |
12.57 |
| 2026-02-03 12:00 |
10:38:09.59 |
+59:56:36.8 |
HIP 52064 |
10.96 |
| 2026-02-04 00:00 |
10:37:51.04 |
+59:58:14.0 |
HIP 52064 |
9.94 |
| 2026-02-04 12:00 |
10:37:32.41 |
+59:59:50.1 |
HIP 52064 |
9.69 |
| 2026-02-05 00:00 |
10:37:13.70 |
+60:01:25.3 |
HIP 52064 |
10.25 |
| 2026-02-05 12:00 |
10:36:54.91 |
+60:02:59.5 |
HIP 52064 |
11.51 |
| 2026-02-06 00:00 |
10:36:36.04 |
+60:04:32.8 |
HIP 52064 |
13.28 |
| 2026-02-06 12:00 |
10:36:17.10 |
+60:06:05.0 |
HIP 52064 |
15.36 |
| 2026-02-07 00:00 |
10:35:58.09 |
+60:07:36.2 |
HIP 52064 |
17.66 |
| 2026-02-07 12:00 |
10:35:39.01 |
+60:09:06.3 |
HIP 52064 |
20.09 |
| 2026-02-08 00:00 |
10:35:19.86 |
+60:10:35.5 |
HIP 52064 |
22.61 |
| 2026-02-08 12:00 |
10:35:00.64 |
+60:12:03.6 |
HIP 52064 |
25.20 |
| 2026-02-09 00:00 |
10:34:41.35 |
+60:13:30.7 |
HIP 52064 |
27.83 |
| 2026-02-09 12:00 |
10:34:22.01 |
+60:14:56.7 |
HIP 52064 |
30.49 |
| 2026-02-10 00:00 |
10:34:02.60 |
+60:16:21.6 |
HIP 52064 |
33.17 |
| 2026-02-10 12:00 |
10:33:43.13 |
+60:17:45.5 |
HIP 51378 |
33.92 |
| 2026-02-11 00:00 |
10:33:23.60 |
+60:19:08.4 |
HIP 51378 |
32.41 |
| 2026-02-11 12:00 |
10:33:04.02 |
+60:20:30.1 |
HIP 51378 |
31.06 |
| 2026-02-12 00:00 |
10:32:44.39 |
+60:21:50.8 |
HIP 51378 |
29.90 |
| 2026-02-12 12:00 |
10:32:24.70 |
+60:23:10.4 |
HIP 51378 |
28.95 |
| 2026-02-13 00:00 |
10:32:04.97 |
+60:24:28.9 |
HIP 51378 |
28.23 |
| 2026-02-13 12:00 |
10:31:45.18 |
+60:25:46.3 |
HIP 51378 |
27.75 |
| 2026-02-14 00:00 |
10:31:25.35 |
+60:27:02.6 |
HIP 51378 |
27.52 |
| 2026-02-14 12:00 |
10:31:05.48 |
+60:28:17.8 |
HIP 51378 |
27.56 |
| 2026-02-15 00:00 |
10:30:45.57 |
+60:29:31.8 |
HIP 51378 |
27.85 |
| 2026-02-15 12:00 |
10:30:25.62 |
+60:30:44.8 |
HIP 51378 |
28.39 |
| 2026-02-16 00:00 |
10:30:05.63 |
+60:31:56.6 |
HIP 51378 |
29.17 |
| 2026-02-16 12:00 |
10:29:45.61 |
+60:33:07.3 |
HIP 51160 |
26.82 |
| 2026-02-17 00:00 |
10:29:25.55 |
+60:34:16.8 |
HIP 51160 |
24.21 |
| 2026-02-17 12:00 |
10:29:05.46 |
+60:35:25.2 |
HIP 51160 |
21.65 |
| 2026-02-18 00:00 |
10:28:45.35 |
+60:36:32.5 |
HIP 51160 |
19.14 |
| 2026-02-18 12:00 |
10:28:25.21 |
+60:37:38.6 |
HIP 51160 |
16.70 |
| 2026-02-19 00:00 |
10:28:05.04 |
+60:38:43.5 |
HIP 51160 |
14.38 |
| 2026-02-19 12:00 |
10:27:44.86 |
+60:39:47.4 |
HIP 51160 |
12.22 |
| 2026-02-20 00:00 |
10:27:24.65 |
+60:40:50.0 |
HIP 51160 |
10.33 |
| 2026-02-20 12:00 |
10:27:04.43 |
+60:41:51.5 |
HIP 51160 |
8.89 |
| 2026-02-21 00:00 |
10:26:44.20 |
+60:42:51.8 |
HIP 51160 |
8.11 |
| 2026-02-21 12:00 |
10:26:23.95 |
+60:43:51.0 |
HIP 51160 |
8.19 |
| 2026-02-22 00:00 |
10:26:03.69 |
+60:44:49.0 |
HIP 51160 |
9.09 |
| 2026-02-22 12:00 |
10:25:43.42 |
+60:45:45.8 |
HIP 51160 |
10.61 |
| 2026-02-23 00:00 |
10:25:23.14 |
+60:46:41.5 |
HIP 51160 |
12.52 |
| 2026-02-23 12:00 |
10:25:02.87 |
+60:47:35.9 |
HIP 50877 |
13.46 |
| 2026-02-24 00:00 |
10:24:42.59 |
+60:48:29.2 |
HIP 50877 |
11.51 |