Export Format for Comet Orbits

This page describes the formats used for the export version of comet orbits, as used in the Extended Computer Service and in the Ephemerides and Orbital Elements publications. Orbital elements for comets are heliocentric.

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Extended Computer Service (ECS) Format

Columns	F77	Use
1–4	i4	Periodic comet number
5	a1	Orbit type (generally ‘C’, ‘P’ or ‘D’)
6–12	a7	Provisional designation (packed form)
21–24	i4	Year of perihelion passage
26–29	a5	Month of perihelion passage
30–37	f7.4	Day of perihelion passage (TT)
39–47	f9.6	Perihelion distance (AU)
50–57	f8.6	Orbital eccentricity
59–63	f5.2	Orbital period (years), if < 100
60–62	i3	Orbital period (years), if ≥ 100
66–73	f8.4	Argument of perihelion, J2000.0 (degrees)
76–83	f8.4	Longitude of ascending node, J2000.0 (degrees)
86–93	f8.4	Inclination to ecliptic, J2000.0 (degrees)
96–97	i2	Last two digits of epoch year
99–103	a5	Month of epoch
104–105	i2	Day of epoch (assumed .0 TT)
96–105	—	Blank if no epoch
107–111	i5	Number of observations in solution
112	a1	‘*’ indicates non-gravitational parameters considered
114–118	a5	Date of first observation (packed format)
120–124	a5	Date of last observation (packed format)
126	a1	Source of perturbing coordinates
128–130	a3	Brief descriptor of perturbers (blank if unperturbed)
132–135	h4	Fuller description of perturbers (‘0000’ if unperturbed)
137	i1	Number of perturbing planets (‘0’ unperturbed, ‘9’ perturbed)
143–172	a30	Name of comet
173–181	a9	Reference

There is no ambiguity in the century part of the epoch, as the epoch will be within +/- 20 days of the time of perihelion passage.

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Ephemerides and Orbital Elements Format

Columns	F77	Use
1–4	i4	Periodic comet number
5	a1	Orbit type (generally ‘C’, ‘P’ or ‘D’)
6–12	a7	Provisional designation (packed form)
15–18	i4	Year of perihelion passage
20–21	i2	Month of perihelion passage
23–29	f7.4	Day of perihelion passage (TT)
31–39	f9.6	Perihelion distance (AU)
42–49	f8.6	Orbital eccentricity
52–59	f8.4	Argument of perihelion, J2000.0 (degrees)
62–69	f8.4	Longitude of ascending node, J2000.0 (degrees)
72–79	f8.4	Inclination, J2000.0 (degrees)
82–85	i4	Year of epoch (perturbed solutions)
86–87	i2	Month of epoch (perturbed solutions)
88–89	i2	Day of epoch (perturbed solutions)
92–95	f4.1	Absolute magnitude
97–100	f4.0	Slope parameter
103–158	a56	Designation and Name
160–168	a9	Reference