| 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 |
-0.998 |
| 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) |
| 2026-05-12 00:00 |
18:38:54.50 |
+13:42:52.2 |
HIP 91294 |
23.62 |
| 2026-05-12 12:00 |
18:38:53.10 |
+13:43:04.3 |
HIP 91294 |
23.29 |
| 2026-05-13 00:00 |
18:38:51.69 |
+13:43:16.3 |
HIP 91294 |
22.97 |
| 2026-05-13 12:00 |
18:38:50.27 |
+13:43:28.2 |
HIP 91294 |
22.64 |
| 2026-05-14 00:00 |
18:38:48.83 |
+13:43:39.9 |
HIP 91294 |
22.31 |
| 2026-05-14 12:00 |
18:38:47.38 |
+13:43:51.6 |
HIP 91294 |
21.98 |
| 2026-05-15 00:00 |
18:38:45.91 |
+13:44:03.1 |
HIP 91294 |
21.64 |
| 2026-05-15 12:00 |
18:38:44.43 |
+13:44:14.5 |
HIP 91294 |
21.31 |
| 2026-05-16 00:00 |
18:38:42.94 |
+13:44:25.7 |
HIP 91294 |
20.98 |
| 2026-05-16 12:00 |
18:38:41.44 |
+13:44:36.9 |
HIP 91294 |
20.64 |
| 2026-05-17 00:00 |
18:38:39.92 |
+13:44:47.9 |
HIP 91294 |
20.31 |
| 2026-05-17 12:00 |
18:38:38.39 |
+13:44:58.8 |
HIP 91294 |
19.97 |
| 2026-05-18 00:00 |
18:38:36.84 |
+13:45:09.5 |
HIP 91294 |
19.63 |
| 2026-05-18 12:00 |
18:38:35.29 |
+13:45:20.1 |
HIP 91294 |
19.30 |
| 2026-05-19 00:00 |
18:38:33.72 |
+13:45:30.6 |
HIP 91294 |
18.96 |
| 2026-05-19 12:00 |
18:38:32.14 |
+13:45:41.0 |
HIP 91294 |
18.62 |
| 2026-05-20 00:00 |
18:38:30.55 |
+13:45:51.2 |
HIP 91294 |
18.29 |
| 2026-05-20 12:00 |
18:38:28.94 |
+13:46:01.3 |
HIP 91294 |
17.95 |
| 2026-05-21 00:00 |
18:38:27.33 |
+13:46:11.3 |
HIP 91294 |
17.61 |
| 2026-05-21 12:00 |
18:38:25.70 |
+13:46:21.2 |
HIP 91294 |
17.28 |
| 2026-05-22 00:00 |
18:38:24.06 |
+13:46:30.9 |
HIP 91294 |
16.94 |
| 2026-05-22 12:00 |
18:38:22.41 |
+13:46:40.4 |
HIP 91294 |
16.61 |
| 2026-05-23 00:00 |
18:38:20.74 |
+13:46:49.9 |
HIP 91294 |
16.28 |
| 2026-05-23 12:00 |
18:38:19.07 |
+13:46:59.2 |
HIP 91294 |
15.95 |
| 2026-05-24 00:00 |
18:38:17.39 |
+13:47:08.3 |
HIP 91294 |
15.62 |
| 2026-05-24 12:00 |
18:38:15.69 |
+13:47:17.4 |
HIP 91294 |
15.29 |
| 2026-05-25 00:00 |
18:38:13.98 |
+13:47:26.3 |
HIP 91294 |
14.97 |
| 2026-05-25 12:00 |
18:38:12.27 |
+13:47:35.0 |
HIP 91294 |
14.64 |
| 2026-05-26 00:00 |
18:38:10.54 |
+13:47:43.6 |
HIP 91294 |
14.33 |
| 2026-05-26 12:00 |
18:38:08.80 |
+13:47:52.1 |
HIP 91294 |
14.01 |
| 2026-05-27 00:00 |
18:38:07.05 |
+13:48:00.4 |
HIP 91294 |
13.70 |
| 2026-05-27 12:00 |
18:38:05.29 |
+13:48:08.6 |
HIP 91294 |
13.39 |
| 2026-05-28 00:00 |
18:38:03.53 |
+13:48:16.6 |
HIP 91294 |
13.09 |
| 2026-05-28 12:00 |
18:38:01.75 |
+13:48:24.5 |
HIP 91294 |
12.79 |
| 2026-05-29 00:00 |
18:37:59.96 |
+13:48:32.3 |
HIP 91294 |
12.50 |
| 2026-05-29 12:00 |
18:37:58.16 |
+13:48:39.9 |
HIP 91294 |
12.22 |
| 2026-05-30 00:00 |
18:37:56.35 |
+13:48:47.4 |
HIP 91294 |
11.94 |
| 2026-05-30 12:00 |
18:37:54.54 |
+13:48:54.7 |
HIP 91294 |
11.67 |
| 2026-05-31 00:00 |
18:37:52.71 |
+13:49:01.9 |
HIP 91294 |
11.41 |
| 2026-05-31 12:00 |
18:37:50.88 |
+13:49:09.0 |
HIP 91294 |
11.16 |
| 2026-06-01 00:00 |
18:37:49.03 |
+13:49:15.9 |
HIP 91294 |
10.92 |
| 2026-06-01 12:00 |
18:37:47.18 |
+13:49:22.6 |
HIP 91294 |
10.69 |
| 2026-06-02 00:00 |
18:37:45.32 |
+13:49:29.2 |
HIP 91294 |
10.48 |