C/1991 A2 (Arai)
| 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
$$
M_a = (8.569 + 5.077\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta
$$
$$
\theta = 180^\circ - \alpha
$$
$$
\Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b)
$$
$$
\Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1
$$
Model Parameters
| Parameter |
Value |
| H0 |
8.569 |
| n |
5.077 |
| gf |
1.000 |
| gb |
-0.500 |
| 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) |
| 2026-02-03 00:00 |
18:38:03.36 |
+12:51:17.2 |
HIP 91233 |
22.59 |
| 2026-02-03 12:00 |
18:38:05.16 |
+12:51:28.4 |
HIP 91233 |
22.93 |
| 2026-02-04 00:00 |
18:38:06.94 |
+12:51:39.7 |
HIP 91233 |
23.28 |
| 2026-02-04 12:00 |
18:38:08.72 |
+12:51:51.2 |
HIP 91233 |
23.63 |
| 2026-02-05 00:00 |
18:38:10.48 |
+12:52:02.7 |
HIP 91233 |
23.98 |
| 2026-02-05 12:00 |
18:38:12.24 |
+12:52:14.4 |
HIP 91233 |
24.33 |
| 2026-02-06 00:00 |
18:38:13.98 |
+12:52:26.2 |
HIP 91233 |
24.68 |
| 2026-02-06 12:00 |
18:38:15.71 |
+12:52:38.2 |
HIP 91233 |
25.03 |
| 2026-02-07 00:00 |
18:38:17.43 |
+12:52:50.2 |
HIP 91233 |
25.39 |
| 2026-02-07 12:00 |
18:38:19.14 |
+12:53:02.4 |
HIP 91233 |
25.74 |
| 2026-02-08 00:00 |
18:38:20.83 |
+12:53:14.7 |
HIP 91233 |
26.09 |
| 2026-02-08 12:00 |
18:38:22.52 |
+12:53:27.1 |
HIP 91233 |
26.45 |
| 2026-02-09 00:00 |
18:38:24.19 |
+12:53:39.6 |
HIP 91233 |
26.80 |
| 2026-02-09 12:00 |
18:38:25.85 |
+12:53:52.2 |
HIP 91233 |
27.15 |
| 2026-02-10 00:00 |
18:38:27.50 |
+12:54:04.9 |
HIP 91233 |
27.51 |
| 2026-02-10 12:00 |
18:38:29.14 |
+12:54:17.8 |
HIP 91233 |
27.86 |
| 2026-02-11 00:00 |
18:38:30.76 |
+12:54:30.8 |
HIP 91233 |
28.21 |
| 2026-02-11 12:00 |
18:38:32.37 |
+12:54:43.8 |
HIP 91233 |
28.56 |
| 2026-02-12 00:00 |
18:38:33.97 |
+12:54:57.0 |
HIP 91233 |
28.91 |
| 2026-02-12 12:00 |
18:38:35.55 |
+12:55:10.3 |
HIP 91233 |
29.26 |
| 2026-02-13 00:00 |
18:38:37.13 |
+12:55:23.7 |
HIP 91233 |
29.61 |
| 2026-02-13 12:00 |
18:38:38.69 |
+12:55:37.2 |
HIP 91233 |
29.96 |
| 2026-02-14 00:00 |
18:38:40.23 |
+12:55:50.8 |
HIP 91233 |
30.31 |
| 2026-02-14 12:00 |
18:38:41.77 |
+12:56:04.5 |
HIP 91233 |
30.65 |
| 2026-02-15 00:00 |
18:38:43.28 |
+12:56:18.3 |
HIP 91233 |
31.00 |
| 2026-02-15 12:00 |
18:38:44.79 |
+12:56:32.3 |
HIP 91233 |
31.34 |
| 2026-02-16 00:00 |
18:38:46.28 |
+12:56:46.3 |
HIP 91233 |
31.69 |
| 2026-02-16 12:00 |
18:38:47.76 |
+12:57:00.4 |
HIP 91233 |
32.03 |
| 2026-02-17 00:00 |
18:38:49.23 |
+12:57:14.6 |
HIP 91233 |
32.37 |
| 2026-02-17 12:00 |
18:38:50.68 |
+12:57:28.9 |
HIP 91233 |
32.71 |
| 2026-02-18 00:00 |
18:38:52.11 |
+12:57:43.3 |
HIP 91569 |
32.82 |
| 2026-02-18 12:00 |
18:38:53.54 |
+12:57:57.8 |
HIP 91569 |
32.41 |
| 2026-02-19 00:00 |
18:38:54.94 |
+12:58:12.4 |
HIP 91569 |
32.00 |
| 2026-02-19 12:00 |
18:38:56.34 |
+12:58:27.1 |
HIP 91569 |
31.59 |
| 2026-02-20 00:00 |
18:38:57.72 |
+12:58:41.9 |
HIP 91569 |
31.18 |
| 2026-02-20 12:00 |
18:38:59.08 |
+12:58:56.7 |
HIP 91569 |
30.78 |
| 2026-02-21 00:00 |
18:39:00.43 |
+12:59:11.7 |
HIP 91569 |
30.38 |
| 2026-02-21 12:00 |
18:39:01.76 |
+12:59:26.7 |
HIP 91569 |
29.97 |
| 2026-02-22 00:00 |
18:39:03.08 |
+12:59:41.9 |
HIP 91569 |
29.57 |
| 2026-02-22 12:00 |
18:39:04.39 |
+12:59:57.1 |
HIP 91569 |
29.17 |
| 2026-02-23 00:00 |
18:39:05.68 |
+13:00:12.4 |
HIP 91569 |
28.78 |
| 2026-02-23 12:00 |
18:39:06.95 |
+13:00:27.7 |
HIP 91569 |
28.38 |
| 2026-02-24 00:00 |
18:39:08.21 |
+13:00:43.2 |
HIP 91569 |
27.99 |