| Parameter |
Value |
| Designation |
C/1991 A2 (Arai) |
| Type |
C |
| Perihelion (tp_cal, UTC) |
1990-12-10T21:20:14.118720Z |
| Orbit solution date (soln_date, UTC) |
2021-04-15T23:29:38Z |
| Obs used |
110 |
| NEO |
- |
| M1 |
6.400 |
| K1 |
32.000 |
| PC |
- |
Osculating Elements
| Parameter |
Value |
| Epoch (epoch_cal, TDB) |
1991-01-21.0000000 |
| e |
0.99066384 |
| q (au) |
1.434192 |
| a (au) |
153.616954 |
| i (deg) |
70.980280 |
| Ω (om, deg) |
115.522769 |
| ω (w, deg) |
337.640099 |
| M (ma, deg) |
0.021282 |
Magnitude
Scatter + Global Linear
$$
M_a = (8.566 + 5.072\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
8.566 |
| n |
5.072 |
| gf |
1.000 |
| gb |
-0.993 |
| k |
1.000 |
| δ90 |
10.000 |
| 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) |
| 2026-07-29 00:00 |
18:33:54.25 |
+13:44:57.5 |
HIP 90864 |
25.23 |
| 2026-07-29 12:00 |
18:33:52.41 |
+13:44:46.4 |
HIP 90864 |
24.78 |
| 2026-07-30 00:00 |
18:33:50.57 |
+13:44:35.2 |
HIP 90864 |
24.33 |
| 2026-07-30 12:00 |
18:33:48.74 |
+13:44:23.9 |
HIP 90864 |
23.88 |
| 2026-07-31 00:00 |
18:33:46.92 |
+13:44:12.4 |
HIP 90864 |
23.44 |
| 2026-07-31 12:00 |
18:33:45.11 |
+13:44:00.8 |
HIP 90864 |
23.00 |
| 2026-08-01 00:00 |
18:33:43.31 |
+13:43:49.1 |
HIP 90864 |
22.57 |
| 2026-08-01 12:00 |
18:33:41.51 |
+13:43:37.2 |
HIP 90864 |
22.14 |
| 2026-08-02 00:00 |
18:33:39.73 |
+13:43:25.2 |
HIP 90864 |
21.71 |
| 2026-08-02 12:00 |
18:33:37.96 |
+13:43:13.1 |
HIP 90864 |
21.29 |
| 2026-08-03 00:00 |
18:33:36.20 |
+13:43:00.9 |
HIP 90864 |
20.87 |
| 2026-08-03 12:00 |
18:33:34.44 |
+13:42:48.5 |
HIP 90864 |
20.46 |
| 2026-08-04 00:00 |
18:33:32.70 |
+13:42:36.0 |
HIP 90864 |
20.05 |
| 2026-08-04 12:00 |
18:33:30.97 |
+13:42:23.4 |
HIP 90864 |
19.65 |
| 2026-08-05 00:00 |
18:33:29.25 |
+13:42:10.7 |
HIP 90864 |
19.25 |
| 2026-08-05 12:00 |
18:33:27.54 |
+13:41:57.8 |
HIP 90864 |
18.86 |
| 2026-08-06 00:00 |
18:33:25.84 |
+13:41:44.8 |
HIP 90864 |
18.48 |
| 2026-08-06 12:00 |
18:33:24.15 |
+13:41:31.7 |
HIP 90864 |
18.11 |
| 2026-08-07 00:00 |
18:33:22.47 |
+13:41:18.5 |
HIP 90864 |
17.74 |
| 2026-08-07 12:00 |
18:33:20.80 |
+13:41:05.1 |
HIP 90864 |
17.38 |
| 2026-08-08 00:00 |
18:33:19.14 |
+13:40:51.7 |
HIP 90864 |
17.02 |
| 2026-08-08 12:00 |
18:33:17.50 |
+13:40:38.1 |
HIP 90864 |
16.68 |
| 2026-08-09 00:00 |
18:33:15.86 |
+13:40:24.4 |
HIP 90864 |
16.34 |
| 2026-08-09 12:00 |
18:33:14.24 |
+13:40:10.6 |
HIP 90864 |
16.01 |
| 2026-08-10 00:00 |
18:33:12.63 |
+13:39:56.6 |
HIP 90864 |
15.70 |
| 2026-08-10 12:00 |
18:33:11.03 |
+13:39:42.6 |
HIP 90864 |
15.39 |
| 2026-08-11 00:00 |
18:33:09.45 |
+13:39:28.4 |
HIP 90864 |
15.09 |
| 2026-08-11 12:00 |
18:33:07.87 |
+13:39:14.1 |
HIP 90864 |
14.81 |
| 2026-08-12 00:00 |
18:33:06.31 |
+13:38:59.8 |
HIP 90864 |
14.54 |
| 2026-08-12 12:00 |
18:33:04.76 |
+13:38:45.3 |
HIP 90864 |
14.27 |
| 2026-08-13 00:00 |
18:33:03.22 |
+13:38:30.7 |
HIP 90864 |
14.03 |
| 2026-08-13 12:00 |
18:33:01.70 |
+13:38:16.0 |
HIP 90864 |
13.79 |
| 2026-08-14 00:00 |
18:33:00.19 |
+13:38:01.1 |
HIP 90864 |
13.57 |
| 2026-08-14 12:00 |
18:32:58.69 |
+13:37:46.2 |
HIP 90864 |
13.36 |
| 2026-08-15 00:00 |
18:32:57.20 |
+13:37:31.2 |
HIP 90864 |
13.17 |
| 2026-08-15 12:00 |
18:32:55.73 |
+13:37:16.1 |
HIP 90864 |
13.00 |
| 2026-08-16 00:00 |
18:32:54.27 |
+13:37:00.9 |
HIP 90864 |
12.84 |
| 2026-08-16 12:00 |
18:32:52.82 |
+13:36:45.5 |
HIP 90864 |
12.70 |
| 2026-08-17 00:00 |
18:32:51.39 |
+13:36:30.1 |
HIP 90864 |
12.57 |
| 2026-08-17 12:00 |
18:32:49.97 |
+13:36:14.6 |
HIP 90864 |
12.46 |
| 2026-08-18 00:00 |
18:32:48.57 |
+13:35:59.0 |
HIP 90864 |
12.37 |
| 2026-08-18 12:00 |
18:32:47.17 |
+13:35:43.2 |
HIP 90864 |
12.30 |
| 2026-08-19 00:00 |
18:32:45.80 |
+13:35:27.4 |
HIP 90864 |
12.25 |