| 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) |
| 2026-06-01 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 |
| 2026-06-02 12:00 |
18:37:43.45 |
+13:49:35.7 |
HIP 91294 |
10.27 |
| 2026-06-03 00:00 |
18:37:41.57 |
+13:49:42.0 |
HIP 91294 |
10.08 |
| 2026-06-03 12:00 |
18:37:39.69 |
+13:49:48.1 |
HIP 91294 |
9.91 |
| 2026-06-04 00:00 |
18:37:37.79 |
+13:49:54.1 |
HIP 91294 |
9.75 |
| 2026-06-04 12:00 |
18:37:35.89 |
+13:50:00.0 |
HIP 91294 |
9.61 |
| 2026-06-05 00:00 |
18:37:33.98 |
+13:50:05.7 |
HIP 91294 |
9.49 |
| 2026-06-05 12:00 |
18:37:32.06 |
+13:50:11.3 |
HIP 91294 |
9.39 |
| 2026-06-06 00:00 |
18:37:30.13 |
+13:50:16.7 |
HIP 91294 |
9.31 |
| 2026-06-06 12:00 |
18:37:28.20 |
+13:50:21.9 |
HIP 91294 |
9.25 |
| 2026-06-07 00:00 |
18:37:26.26 |
+13:50:27.0 |
HIP 91294 |
9.21 |
| 2026-06-07 12:00 |
18:37:24.31 |
+13:50:32.0 |
HIP 91294 |
9.19 |
| 2026-06-08 00:00 |
18:37:22.36 |
+13:50:36.8 |
HIP 91294 |
9.19 |
| 2026-06-08 12:00 |
18:37:20.39 |
+13:50:41.4 |
HIP 91294 |
9.22 |
| 2026-06-09 00:00 |
18:37:18.42 |
+13:50:45.9 |
HIP 91294 |
9.27 |
| 2026-06-09 12:00 |
18:37:16.45 |
+13:50:50.2 |
HIP 91294 |
9.34 |
| 2026-06-10 00:00 |
18:37:14.47 |
+13:50:54.4 |
HIP 91294 |
9.44 |
| 2026-06-10 12:00 |
18:37:12.48 |
+13:50:58.4 |
HIP 91294 |
9.55 |
| 2026-06-11 00:00 |
18:37:10.48 |
+13:51:02.3 |
HIP 91294 |
9.69 |
| 2026-06-11 12:00 |
18:37:08.48 |
+13:51:06.0 |
HIP 91294 |
9.84 |
| 2026-06-12 00:00 |
18:37:06.48 |
+13:51:09.5 |
HIP 91294 |
10.02 |
| 2026-06-12 12:00 |
18:37:04.46 |
+13:51:12.9 |
HIP 91294 |
10.21 |
| 2026-06-13 00:00 |
18:37:02.45 |
+13:51:16.2 |
HIP 91294 |
10.43 |
| 2026-06-13 12:00 |
18:37:00.42 |
+13:51:19.3 |
HIP 91294 |
10.66 |
| 2026-06-14 00:00 |
18:36:58.39 |
+13:51:22.2 |
HIP 91294 |
10.90 |
| 2026-06-14 12:00 |
18:36:56.36 |
+13:51:24.9 |
HIP 91294 |
11.16 |
| 2026-06-15 00:00 |
18:36:54.32 |
+13:51:27.5 |
HIP 91294 |
11.43 |
| 2026-06-15 12:00 |
18:36:52.28 |
+13:51:30.0 |
HIP 91294 |
11.72 |
| 2026-06-16 00:00 |
18:36:50.23 |
+13:51:32.3 |
HIP 91294 |
12.02 |
| 2026-06-16 12:00 |
18:36:48.18 |
+13:51:34.4 |
HIP 91294 |
12.33 |
| 2026-06-17 00:00 |
18:36:46.12 |
+13:51:36.3 |
HIP 91294 |
12.65 |
| 2026-06-17 12:00 |
18:36:44.06 |
+13:51:38.1 |
HIP 91294 |
12.98 |
| 2026-06-18 00:00 |
18:36:41.99 |
+13:51:39.8 |
HIP 91294 |
13.32 |
| 2026-06-18 12:00 |
18:36:39.93 |
+13:51:41.3 |
HIP 91294 |
13.66 |
| 2026-06-19 00:00 |
18:36:37.85 |
+13:51:42.6 |
HIP 91294 |
14.02 |
| 2026-06-19 12:00 |
18:36:35.78 |
+13:51:43.7 |
HIP 91294 |
14.38 |
| 2026-06-20 00:00 |
18:36:33.70 |
+13:51:44.7 |
HIP 91294 |
14.75 |
| 2026-06-20 12:00 |
18:36:31.62 |
+13:51:45.6 |
HIP 91294 |
15.13 |
| 2026-06-21 00:00 |
18:36:29.53 |
+13:51:46.2 |
HIP 91294 |
15.51 |
| 2026-06-21 12:00 |
18:36:27.45 |
+13:51:46.7 |
HIP 91294 |
15.90 |
| 2026-06-22 00:00 |
18:36:25.36 |
+13:51:47.1 |
HIP 91294 |
16.30 |