C/2021 P4 (ATLAS)
| Parameter |
Value |
| Designation |
C/2021 P4 (ATLAS) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2022-07-30T09:00:29.151360Z |
| Orbit solution date (soln_date, UTC) |
2024-07-30T14:57:24Z |
| Obs used |
954 |
| NEO |
- |
| M1 |
10.800 |
| K1 |
8.000 |
| PC |
0.030 |
| Discovery observation (MPC, UTC) |
2021-08-10T12:53:31.315200Z |
| Discovery magnitude (MPC) |
19.44 o |
| Discovery observatory (MPC) |
T05 · ATLAS-HKO, Haleakala |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2022-01-11.0000000 |
| e |
0.99656560 |
| q (au) |
1.080462 |
| a (au) |
314.600427 |
| i (deg) |
56.310801 |
| Ω (om, deg) |
348.094879 |
| ω (w, deg) |
175.822404 |
| M (ma, deg) |
359.964608 |
Magnitude
Scatter + Global Linear
$$
M_a = (9.844 + 3.192\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
9.844 |
| n |
3.192 |
| gf |
0.800 |
| gb |
-0.500 |
| k |
1.000 |
| δ90 |
7.364 |
| 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
Residuals (Piecewise)
$$\epsilon = a \log_{10} r_{\mathrm{au}} + b$$
| Start (UTC) |
End (UTC) |
a |
b |
| 2021-08-10 |
2022-05-06 |
+2.3133 |
-1.380 |
| 2022-05-06 |
2022-06-13 |
-2.7477 |
+0.128 |
| 2022-06-13 |
2022-07-22 |
+21.5568 |
-2.643 |
| 2023-01-02 |
2023-03-26 |
+6.5949 |
-1.180 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-02-03 00:00 |
22:30:36.92 |
-41:00:03.9 |
HIP 111283 |
23.70 |
| 2026-02-03 12:00 |
22:30:48.15 |
-40:58:40.4 |
HIP 111283 |
21.35 |
| 2026-02-04 00:00 |
22:30:59.41 |
-40:57:17.3 |
HIP 111283 |
19.05 |
| 2026-02-04 12:00 |
22:31:10.68 |
-40:55:54.7 |
HIP 111283 |
16.81 |
| 2026-02-05 00:00 |
22:31:21.97 |
-40:54:32.5 |
HIP 111283 |
14.67 |
| 2026-02-05 12:00 |
22:31:33.29 |
-40:53:10.8 |
HIP 111283 |
12.66 |
| 2026-02-06 00:00 |
22:31:44.62 |
-40:51:49.5 |
HIP 111283 |
10.87 |
| 2026-02-06 12:00 |
22:31:55.97 |
-40:50:28.7 |
HIP 111283 |
9.42 |
| 2026-02-07 00:00 |
22:32:07.34 |
-40:49:08.4 |
HIP 111283 |
8.48 |
| 2026-02-07 12:00 |
22:32:18.72 |
-40:47:48.5 |
HIP 111283 |
8.24 |
| 2026-02-08 00:00 |
22:32:30.12 |
-40:46:29.1 |
HIP 111283 |
8.74 |
| 2026-02-08 12:00 |
22:32:41.54 |
-40:45:10.2 |
HIP 111283 |
9.88 |
| 2026-02-09 00:00 |
22:32:52.97 |
-40:43:51.7 |
HIP 111283 |
11.46 |
| 2026-02-09 12:00 |
22:33:04.42 |
-40:42:33.7 |
HIP 111283 |
13.33 |
| 2026-02-10 00:00 |
22:33:15.88 |
-40:41:16.2 |
HIP 111283 |
15.39 |
| 2026-02-10 12:00 |
22:33:27.35 |
-40:39:59.2 |
HIP 111283 |
17.56 |
| 2026-02-11 00:00 |
22:33:38.84 |
-40:38:42.7 |
HIP 111283 |
19.81 |
| 2026-02-11 12:00 |
22:33:50.34 |
-40:37:26.6 |
HIP 111283 |
22.12 |
| 2026-02-12 00:00 |
22:34:01.85 |
-40:36:11.1 |
HIP 111283 |
24.46 |
| 2026-02-12 12:00 |
22:34:13.37 |
-40:34:56.0 |
HIP 111428 |
22.94 |
| 2026-02-13 00:00 |
22:34:24.90 |
-40:33:41.5 |
HIP 111428 |
21.53 |
| 2026-02-13 12:00 |
22:34:36.44 |
-40:32:27.4 |
HIP 111428 |
20.34 |
| 2026-02-14 00:00 |
22:34:47.98 |
-40:31:13.9 |
HIP 111556 |
18.57 |
| 2026-02-14 12:00 |
22:34:59.54 |
-40:30:00.8 |
HIP 111556 |
16.13 |
| 2026-02-15 00:00 |
22:35:11.10 |
-40:28:48.3 |
HIP 111556 |
13.72 |
| 2026-02-15 12:00 |
22:35:22.67 |
-40:27:36.2 |
HIP 111556 |
11.37 |
| 2026-02-16 00:00 |
22:35:34.25 |
-40:26:24.7 |
HIP 111556 |
9.10 |
| 2026-02-16 12:00 |
22:35:45.83 |
-40:25:13.8 |
HIP 111556 |
7.00 |
| 2026-02-17 00:00 |
22:35:57.42 |
-40:24:03.3 |
HIP 111556 |
5.28 |
| 2026-02-17 12:00 |
22:36:09.01 |
-40:22:53.4 |
HIP 111556 |
4.40 |
| 2026-02-18 00:00 |
22:36:20.60 |
-40:21:44.0 |
HIP 111556 |
4.83 |
| 2026-02-18 12:00 |
22:36:32.20 |
-40:20:35.1 |
HIP 111556 |
6.31 |
| 2026-02-19 00:00 |
22:36:43.80 |
-40:19:26.7 |
HIP 111556 |
8.29 |
| 2026-02-19 12:00 |
22:36:55.40 |
-40:18:18.9 |
HIP 111556 |
10.49 |
| 2026-02-20 00:00 |
22:37:07.00 |
-40:17:11.7 |
HIP 111556 |
12.79 |
| 2026-02-20 12:00 |
22:37:18.60 |
-40:16:05.0 |
HIP 111655 |
14.70 |
| 2026-02-21 00:00 |
22:37:30.20 |
-40:14:58.8 |
HIP 111655 |
16.22 |
| 2026-02-21 12:00 |
22:37:41.80 |
-40:13:53.2 |
HIP 111655 |
17.95 |
| 2026-02-22 00:00 |
22:37:53.39 |
-40:12:48.1 |
HIP 111655 |
19.82 |
| 2026-02-22 12:00 |
22:38:04.99 |
-40:11:43.6 |
HIP 111718 |
20.57 |
| 2026-02-23 00:00 |
22:38:16.58 |
-40:10:39.6 |
HIP 111718 |
20.01 |
| 2026-02-23 12:00 |
22:38:28.16 |
-40:09:36.2 |
HIP 111718 |
19.76 |
| 2026-02-24 00:00 |
22:38:39.74 |
-40:08:33.4 |
HIP 111718 |
19.81 |