| Parameter |
Value |
| Designation |
C/2018 W2 (Africano) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
2019-09-05T17:29:59.596800Z |
| Orbit solution date (soln_date, UTC) |
2021-08-24T14:05:51Z |
| Obs used |
1995 |
| NEO |
- |
| M1 |
13.400 |
| K1 |
4.500 |
| PC |
- |
| Discovery observation (MPC, UTC) |
2018-11-27T12:43:12.864000Z |
| Discovery magnitude (MPC) |
18.30 G |
| Discovery observatory (MPC) |
G96 · University of Arizona Mt. Lemmon Survey |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
2019-07-27.0000000 |
| e |
1.00075966 |
| q (au) |
1.454668 |
| a (au) |
-1914.899581 |
| i (deg) |
116.615771 |
| Ω (om, deg) |
181.849455 |
| ω (w, deg) |
157.972854 |
| M (ma, deg) |
-0.000479 |
Magnitude
Scatter + Global Linear
$$
M_a = (13.119 + 2.000\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
13.119 |
| n |
2.000 |
| gf |
0.994 |
| gb |
-0.500 |
| k |
0.800 |
| δ90 |
1.652 |
| 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 |
| 2018-08-24 |
2018-12-01 |
-96.0365 |
+55.664 |
| 2018-12-01 |
2019-09-05 |
+4.8869 |
-2.512 |
| 2019-09-05 |
2020-06-15 |
-2.6714 |
+0.118 |
log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)
Ephemeris
| Date/Time (UTC) |
RA (J2000) |
Dec (J2000) |
Nearest HIP |
Dist from HIP (arcmin) |
| 2026-07-29 00:00 |
12:08:28.99 |
-52:51:49.5 |
HIP 59172 |
7.62 |
| 2026-07-29 12:00 |
12:08:34.26 |
-52:50:54.8 |
HIP 59172 |
8.81 |
| 2026-07-30 00:00 |
12:08:39.57 |
-52:50:00.7 |
HIP 59172 |
10.00 |
| 2026-07-30 12:00 |
12:08:44.95 |
-52:49:07.0 |
HIP 59172 |
11.19 |
| 2026-07-31 00:00 |
12:08:50.38 |
-52:48:13.9 |
HIP 59172 |
12.39 |
| 2026-07-31 12:00 |
12:08:55.86 |
-52:47:21.4 |
HIP 59186 |
13.26 |
| 2026-08-01 00:00 |
12:09:01.40 |
-52:46:29.4 |
HIP 59186 |
12.90 |
| 2026-08-01 12:00 |
12:09:07.00 |
-52:45:37.9 |
HIP 59186 |
12.65 |
| 2026-08-02 00:00 |
12:09:12.65 |
-52:44:46.9 |
HIP 59186 |
12.53 |
| 2026-08-02 12:00 |
12:09:18.35 |
-52:43:56.5 |
HIP 59186 |
12.54 |
| 2026-08-03 00:00 |
12:09:24.11 |
-52:43:06.6 |
HIP 59186 |
12.67 |
| 2026-08-03 12:00 |
12:09:29.92 |
-52:42:17.3 |
HIP 59186 |
12.93 |
| 2026-08-04 00:00 |
12:09:35.78 |
-52:41:28.6 |
HIP 59186 |
13.31 |
| 2026-08-04 12:00 |
12:09:41.69 |
-52:40:40.3 |
HIP 59186 |
13.79 |
| 2026-08-05 00:00 |
12:09:47.66 |
-52:39:52.7 |
HIP 59186 |
14.36 |
| 2026-08-05 12:00 |
12:09:53.67 |
-52:39:05.5 |
HIP 59186 |
15.03 |
| 2026-08-06 00:00 |
12:09:59.74 |
-52:38:19.0 |
HIP 59186 |
15.76 |
| 2026-08-06 12:00 |
12:10:05.86 |
-52:37:33.0 |
HIP 59186 |
16.56 |
| 2026-08-07 00:00 |
12:10:12.03 |
-52:36:47.5 |
HIP 59186 |
17.42 |
| 2026-08-07 12:00 |
12:10:18.24 |
-52:36:02.6 |
HIP 59186 |
18.32 |
| 2026-08-08 00:00 |
12:10:24.51 |
-52:35:18.3 |
HIP 59449 |
17.42 |
| 2026-08-08 12:00 |
12:10:30.83 |
-52:34:34.5 |
HIP 59449 |
16.24 |
| 2026-08-09 00:00 |
12:10:37.19 |
-52:33:51.3 |
HIP 59449 |
15.07 |
| 2026-08-09 12:00 |
12:10:43.60 |
-52:33:08.7 |
HIP 59449 |
13.91 |
| 2026-08-10 00:00 |
12:10:50.06 |
-52:32:26.6 |
HIP 59449 |
12.76 |
| 2026-08-10 12:00 |
12:10:56.57 |
-52:31:45.1 |
HIP 59449 |
11.63 |
| 2026-08-11 00:00 |
12:11:03.12 |
-52:31:04.2 |
HIP 59449 |
10.51 |
| 2026-08-11 12:00 |
12:11:09.72 |
-52:30:23.9 |
HIP 59449 |
9.43 |
| 2026-08-12 00:00 |
12:11:16.37 |
-52:29:44.1 |
HIP 59449 |
8.38 |
| 2026-08-12 12:00 |
12:11:23.06 |
-52:29:04.9 |
HIP 59449 |
7.40 |
| 2026-08-13 00:00 |
12:11:29.80 |
-52:28:26.3 |
HIP 59449 |
6.49 |
| 2026-08-13 12:00 |
12:11:36.57 |
-52:27:48.2 |
HIP 59449 |
5.71 |
| 2026-08-14 00:00 |
12:11:43.40 |
-52:27:10.8 |
HIP 59449 |
5.12 |
| 2026-08-14 12:00 |
12:11:50.26 |
-52:26:33.9 |
HIP 59449 |
4.77 |
| 2026-08-15 00:00 |
12:11:57.17 |
-52:25:57.6 |
HIP 59449 |
4.74 |
| 2026-08-15 12:00 |
12:12:04.12 |
-52:25:21.9 |
HIP 59449 |
5.01 |
| 2026-08-16 00:00 |
12:12:11.11 |
-52:24:46.8 |
HIP 59449 |
5.56 |
| 2026-08-16 12:00 |
12:12:18.15 |
-52:24:12.3 |
HIP 59449 |
6.31 |
| 2026-08-17 00:00 |
12:12:25.22 |
-52:23:38.3 |
HIP 59449 |
7.20 |
| 2026-08-17 12:00 |
12:12:32.33 |
-52:23:05.0 |
HIP 59449 |
8.18 |
| 2026-08-18 00:00 |
12:12:39.49 |
-52:22:32.2 |
HIP 59449 |
9.22 |
| 2026-08-18 12:00 |
12:12:46.68 |
-52:22:00.0 |
HIP 59449 |
10.31 |
| 2026-08-19 00:00 |
12:12:53.91 |
-52:21:28.4 |
HIP 59449 |
11.43 |