Metadata

Parameter	Value
Designation	153P/Ikeya-Zhang
Type	P
Perihelion (tp_cal, UTC)	2002-03-18T23:31:25.772160Z
Orbit solution date (soln_date, UTC)	2020-06-17T10:40:41Z
Obs used	1893
NEO	-
M1	4.000
K1	15.000
PC	-

Osculating Elements

Parameter	Value
Epoch (epoch_cal, TDB)	2002-05-08.0000000
e	0.99008066
q (au)	0.507070
a (au)	51.119322
i (deg)	28.120957
Ω (om, deg)	93.369457
ω (w, deg)	34.668179
M (ma, deg)	0.134887

Magnitude

Scatter + Global Linear

$$ M_a = (6.663 + 3.285\cdot 2.5\log_{10} r) + \epsilon - 2.5\log_{10}\Phi(\theta) + 5\log_{10}\Delta $$ $$ \theta = 180^\circ - \alpha $$ $$ \Phi(\theta) = \frac{\delta_{90} D(\theta) + 1}{\delta_{90} + 1},\quad D(\theta) = k\cdot \Phi_{HG}(\theta; g_f) + (1-k)\cdot \Phi_{HG}(\theta; g_b) $$ $$ \Phi_{HG}(\theta; g) = \left(\frac{1+g^2}{1+g^2-2g\cos\theta}\right)^{3/2},\quad \Phi_{HG}(90^\circ)=1 $$

Model Parameters

Parameter	Value
H0	6.663
n	3.285
gf	0.800
gb	-0.500
k	0.926
δ90	1.000

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

Residuals (Piecewise)

$$\epsilon = a \log_{10} r_{\mathrm{au}} + b$$

Start (UTC)	End (UTC)	a	b
2001-08-25	2002-02-03	+7.8285	+1.084
2002-02-03	2002-03-18	+3.0730	+0.799
2002-03-19	2002-06-13	+0.2070	+0.282
2002-06-13	2002-10-11	+6.0428	-0.737

log10 r = log10(heliocentric distance / AU), Δ = geocentric distance (AU)

Ephemeris

Date/Time (UTC)	RA (J2000)	Dec (J2000)	Nearest HIP	Dist from HIP (arcmin)
2026-05-12 00:00	20:06:59.38	-32:06:15.7	HIP 99150	23.22
2026-05-12 12:00	20:06:58.29	-32:06:27.2	HIP 99150	23.49
2026-05-13 00:00	20:06:57.17	-32:06:38.7	HIP 99150	23.77
2026-05-13 12:00	20:06:56.03	-32:06:50.3	HIP 99150	24.05
2026-05-14 00:00	20:06:54.86	-32:07:01.9	HIP 99150	24.33
2026-05-14 12:00	20:06:53.66	-32:07:13.5	HIP 99150	24.61
2026-05-15 00:00	20:06:52.44	-32:07:25.2	HIP 99150	24.90
2026-05-15 12:00	20:06:51.19	-32:07:36.9	HIP 99150	25.20
2026-05-16 00:00	20:06:49.92	-32:07:48.7	HIP 99150	25.49
2026-05-16 12:00	20:06:48.62	-32:08:00.5	HIP 99150	25.80
2026-05-17 00:00	20:06:47.29	-32:08:12.3	HIP 99150	26.10
2026-05-17 12:00	20:06:45.94	-32:08:24.2	HIP 99150	26.41
2026-05-18 00:00	20:06:44.56	-32:08:36.1	HIP 99150	26.72
2026-05-18 12:00	20:06:43.16	-32:08:48.1	HIP 99150	27.04
2026-05-19 00:00	20:06:41.74	-32:09:00.0	HIP 99150	27.36
2026-05-19 12:00	20:06:40.28	-32:09:12.0	HIP 99150	27.69
2026-05-20 00:00	20:06:38.81	-32:09:24.1	HIP 99150	28.02
2026-05-20 12:00	20:06:37.31	-32:09:36.1	HIP 99150	28.35
2026-05-21 00:00	20:06:35.78	-32:09:48.2	HIP 99150	28.69
2026-05-21 12:00	20:06:34.23	-32:10:00.4	HIP 99150	29.03
2026-05-22 00:00	20:06:32.65	-32:10:12.5	HIP 98842	29.00
2026-05-22 12:00	20:06:31.06	-32:10:24.7	HIP 98842	28.72
2026-05-23 00:00	20:06:29.43	-32:10:36.9	HIP 98842	28.44
2026-05-23 12:00	20:06:27.78	-32:10:49.1	HIP 98842	28.15
2026-05-24 00:00	20:06:26.11	-32:11:01.4	HIP 98842	27.86
2026-05-24 12:00	20:06:24.42	-32:11:13.7	HIP 98842	27.58
2026-05-25 00:00	20:06:22.70	-32:11:25.9	HIP 98842	27.29
2026-05-25 12:00	20:06:20.96	-32:11:38.3	HIP 98842	27.00
2026-05-26 00:00	20:06:19.19	-32:11:50.6	HIP 98842	26.71
2026-05-26 12:00	20:06:17.41	-32:12:03.0	HIP 98842	26.41
2026-05-27 00:00	20:06:15.59	-32:12:15.3	HIP 98842	26.12
2026-05-27 12:00	20:06:13.76	-32:12:27.7	HIP 98842	25.83
2026-05-28 00:00	20:06:11.90	-32:12:40.1	HIP 98842	25.53
2026-05-28 12:00	20:06:10.02	-32:12:52.5	HIP 98842	25.24
2026-05-29 00:00	20:06:08.12	-32:13:05.0	HIP 98842	24.95
2026-05-29 12:00	20:06:06.20	-32:13:17.4	HIP 98842	24.65
2026-05-30 00:00	20:06:04.25	-32:13:29.9	HIP 98842	24.36
2026-05-30 12:00	20:06:02.28	-32:13:42.3	HIP 98842	24.07
2026-05-31 00:00	20:06:00.29	-32:13:54.8	HIP 98842	23.78
2026-05-31 12:00	20:05:58.28	-32:14:07.3	HIP 98842	23.50
2026-06-01 00:00	20:05:56.25	-32:14:19.8	HIP 98842	23.21
2026-06-01 12:00	20:05:54.19	-32:14:32.3	HIP 98842	22.93
2026-06-02 00:00	20:05:52.12	-32:14:44.8	HIP 98842	22.65