C/2021 G2 (ATLAS)
Metadata
| Parameter | Value |
|---|---|
| Designation | C/2021 G2 (ATLAS) |
| Type | C |
| Perihelion (tp_cal, UTC) | 2024-09-09T03:16:28.044480Z |
| Orbit solution date (soln_date, UTC) | 2026-09-08T09:12:17Z |
| Obs used | 5087 |
| NEO | - |
| M1 | 7.200 |
| K1 | 6.250 |
| PC | 0.030 |
Osculating Elements
| Parameter | Value |
|---|---|
| Epoch (epoch_cal, TDB) | 2025-02-17.0000000 |
| e | 1.00056004 |
| q (au) | 4.982372 |
| a (au) | -8896.434144 |
| i (deg) | 48.470226 |
| Ω (om, deg) | 221.095363 |
| ω (w, deg) | 343.267752 |
| M (ma, deg) | 0.000189 |
Magnitude
Scatter + Global Linear
$$ M_a = (6.616 + 2.217\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$
Model Parameters
| Parameter | Value |
|---|---|
| H0 | 6.616 |
| n | 2.217 |
| gf | 0.897 |
| gb | -0.893 |
| k | 1.000 |
| δ90 | 4.341 |
| 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 |
|---|---|---|---|
| 2021-09-29 | 2023-08-24 | +3.0530 | -2.266 |
| 2023-08-24 | 2024-08-29 | +9.4750 | -7.015 |
| 2024-12-22 | 2026-09-26 | -1.1960 | +0.833 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Finding Chart
Ephemeris
| Date/Time (UTC) | RA (J2000) | Dec (J2000) | Nearest HIP | Dist from HIP (arcmin) |
|---|---|---|---|---|
| 2026-09-20 00:00 | 17:03:48.00 | +13:24:29.8 | HIP 83504 | 9.87 |
| 2026-09-20 12:00 | 17:03:57.35 | +13:23:05.2 | HIP 83504 | 10.98 |
| 2026-09-21 00:00 | 17:04:06.81 | +13:21:40.8 | HIP 83504 | 12.57 |
| 2026-09-21 12:00 | 17:04:16.38 | +13:20:16.6 | HIP 83504 | 14.49 |
| 2026-09-22 00:00 | 17:04:26.06 | +13:18:52.6 | HIP 83504 | 16.65 |
| 2026-09-22 12:00 | 17:04:35.85 | +13:17:29.0 | HIP 83504 | 18.96 |
| 2026-09-23 00:00 | 17:04:45.74 | +13:16:05.6 | HIP 83504 | 21.39 |
| 2026-09-23 12:00 | 17:04:55.75 | +13:14:42.4 | HIP 83504 | 23.91 |
| 2026-09-24 00:00 | 17:05:05.86 | +13:13:19.6 | HIP 83713 | 24.49 |
| 2026-09-24 12:00 | 17:05:16.08 | +13:11:57.0 | HIP 83713 | 23.26 |
| 2026-09-25 00:00 | 17:05:26.40 | +13:10:34.7 | HIP 83713 | 22.30 |
| 2026-09-25 12:00 | 17:05:36.82 | +13:09:12.8 | HIP 83713 | 21.67 |
| 2026-09-26 00:00 | 17:05:47.35 | +13:07:51.1 | HIP 83713 | 21.38 |
| 2026-09-26 12:00 | 17:05:57.99 | +13:06:29.8 | HIP 83713 | 21.47 |
| 2026-09-27 00:00 | 17:06:08.73 | +13:05:08.8 | HIP 83713 | 21.95 |
| 2026-09-27 12:00 | 17:06:19.57 | +13:03:48.1 | HIP 83793 | 20.49 |
| 2026-09-28 00:00 | 17:06:30.51 | +13:02:27.7 | HIP 83793 | 17.52 |
| 2026-09-28 12:00 | 17:06:41.55 | +13:01:07.7 | HIP 83793 | 14.55 |
| 2026-09-29 00:00 | 17:06:52.70 | +12:59:48.0 | HIP 83793 | 11.57 |
| 2026-09-29 12:00 | 17:07:03.95 | +12:58:28.7 | HIP 83793 | 8.62 |
| 2026-09-30 00:00 | 17:07:15.29 | +12:57:09.8 | HIP 83793 | 5.74 |
| 2026-09-30 12:00 | 17:07:26.74 | +12:55:51.2 | HIP 83793 | 3.22 |
| 2026-10-01 00:00 | 17:07:38.28 | +12:54:33.0 | HIP 83793 | 2.62 |
| 2026-10-01 12:00 | 17:07:49.92 | +12:53:15.1 | HIP 83793 | 4.78 |
| 2026-10-02 00:00 | 17:08:01.66 | +12:51:57.7 | HIP 83793 | 7.66 |
| 2026-10-02 12:00 | 17:08:13.50 | +12:50:40.7 | HIP 83793 | 10.71 |
| 2026-10-03 00:00 | 17:08:25.44 | +12:49:24.0 | HIP 83908 | 12.18 |
| 2026-10-03 12:00 | 17:08:37.47 | +12:48:07.8 | HIP 83908 | 9.51 |
| 2026-10-04 00:00 | 17:08:49.60 | +12:46:51.9 | HIP 83908 | 7.27 |
| 2026-10-04 12:00 | 17:09:01.82 | +12:45:36.6 | HIP 83908 | 6.01 |
| 2026-10-05 00:00 | 17:09:14.14 | +12:44:21.6 | HIP 83908 | 6.37 |
| 2026-10-05 12:00 | 17:09:26.55 | +12:43:07.1 | HIP 83908 | 8.17 |
| 2026-10-06 00:00 | 17:09:39.06 | +12:41:53.0 | HIP 83908 | 10.71 |
| 2026-10-06 12:00 | 17:09:51.66 | +12:40:39.3 | HIP 83908 | 13.60 |
| 2026-10-07 00:00 | 17:10:04.35 | +12:39:26.2 | HIP 84036 | 15.24 |
| 2026-10-07 12:00 | 17:10:17.13 | +12:38:13.4 | HIP 84036 | 12.36 |
| 2026-10-08 00:00 | 17:10:30.01 | +12:37:01.2 | HIP 84036 | 9.78 |
| 2026-10-08 12:00 | 17:10:42.97 | +12:35:49.4 | HIP 84036 | 7.83 |
| 2026-10-09 00:00 | 17:10:56.03 | +12:34:38.2 | HIP 84036 | 7.08 |
| 2026-10-09 12:00 | 17:11:09.18 | +12:33:27.4 | HIP 84036 | 7.89 |
| 2026-10-10 00:00 | 17:11:22.41 | +12:32:17.1 | HIP 84036 | 9.92 |
| 2026-10-10 12:00 | 17:11:35.74 | +12:31:07.4 | HIP 84036 | 12.59 |
| 2026-10-11 00:00 | 17:11:49.15 | +12:29:58.1 | HIP 84036 | 15.60 |