Our collection of EDB catalogs

The MMT mount computer is now able to use XEphem format database files. (See the end of this page for details on the EDB format). These are most useful (at the MMT) for tracking non-sidereal objects such as planets, comets, minor planets, earth-orbiting satellites, and the like. Edb format catalogs can certainly be used for stellar objects, but most users prepare such catalogs in the MMT sidereal format.

The MMT uses (by permission) code derived from XEphem to parse these files and generate coordinates.

At the MMT, we regularly update and maintain the following catalogs in edb format.

The Lowell Observatory catalogs provide elements for the roughly 30,000 asteroids in ASTORB, and also includes some 237215 orbits from the Harvard/CFA Minor Planet Center.
These catalogs are fetched and converted daily.

The MPC catalogs are obtained from the Harvard/CFA Minor Planet circulars (MPCORB).
These catalogs are fetched and converted daily.

The following catalogs are derived from the JPL DASTCOM database, which is provided by the JPL HORIZONS System.
These catalogs are fetched and converted daily.

We obtain 5 catalogs from the Center for Astrophysics at Harvard University, amazingly they provide these in EDB format.

The following catalogs provide orbital elements for major planets and some earth orbiting satellites.
Note that orbital elements for earth orbiting satellites are unlikely to be useful unless recently updated.

The EDB File format

This document describes the format of an XEphem database file. The file name extension is .edb.
See the TLE document for files containing two-line Earth satellite elements.

General format rules

  1. month/day/year, where day may contain a fractional portion. examples: 1/1/1993 and 1/1.234/1993 . Note the format of dates in database files is always M/D/Y; or

  2. the year as real number as indicated by the presence of a decimal point, such as 1993.123.

Format Details

The first two fields are required and are always Name and Type. Remaining fields depend on Type.

Field 1
One or more object names, each separated by the Subfield separator, |. Any number of characters may be present in the file but only the first 20 characters of each name and only the first 20 names are actually used.
Field 2 Type designation. Consists of a single letter designation from the following set (case is significant):
f
fixed (or at most exhibits constant curvilinear proper motion)
e
heliocentric elliptical orbit
h
heliocentric hyperbolic orbit
p
heliocentric parabolic orbit
E
geocentric elliptical orbit, i.e., Earth satellite
P
built-in planet or natural satellite name

If Field 2 is f the object is fixed and the following fields and subfields are defined:


SubField 2A An optional SubField 2A can be added to further define an object class code, consisting of one character from the following list:
A
Cluster of galaxies
B
Star, binary. Deprecated as of version 3.6, gets turned into D internally. Use Field 2 type B if more than one position angle and separation or orbital elements are known.
C
Cluster, globular
D
Star, visual double
F
Nebula, diffuse
G
Galaxy, spiral
H
Galaxy, spherical
J
Radio
K
Nebula, dark
L
Pulsar
M
Star, multiple
N
Nebula, bright
O
Cluster, open
P
Nebula, planetary
Q
Quasar
R
Supernova remnant
S
Star
T
Stellar object
U
Cluster, with nebulosity
Y
Supernova
V
Star, variable

SubField 2B If SubField 2A is one of T, B, D, S or V, optional SubField 2B may consist of up to two spectral designation characters, typically one letter followed by one numerical subclass designator. Two examples are O and G3.


If SubField 2A is any other class code, optional SubField 2B may consist of up to two additional characters to further describe the type.
Field 3 RA position coordinate, given as H:M:S.

SubField 3A This optional subfield may specify a proper motion in RA. It is in milliarcseconds per year on the sky, i.e., ΔRA*cos(dec).
Field 4 Declination position coordinate, given as D:M:S.

SubField 4A This optional subfield may specify a proper motion in Dec. It is in milliarcseconds per year on the sky
Field 5
Magnitude of the object.
Field 6
This optional field is the reference epoch. It is assumed to be 2000 if absent


Field 7 depends on SubField 2A
If SubField 2A is G or H
Field 7
Galaxy major axis, in arcseconds

SubField 7A Galaxy minor axis, in arcseconds

SubField 7B Major axis position angle, in degrees East of North
If Subfield 2A is B or D
Field 7 star pair separation, in arcseconds

SubField 7A reserved, set to 0

SubField 7B position angle, in degrees East of North
Otherwise Field 7 is optional but if present
Field 7 size of the object, in arcseconds. It is assumed to be 0 if absent.

If Field 2 is B the object is a true binary pair and the following fields and subfields are defined.


SubField 2A An optional SubField 2A can be added to further define an binary class code, consisting of one character from the following list. This scheme is taken from the Washington Multiplicity catalog for compliance with the IAU 2003 recommendation.
a
Astrometric binary
c
Cataclysmic variable
e
Eclipsing binary
x
High-mass X-ray binary
y
Low-mass X-ray binary
o
Occultation binary
s
Spectroscopic binary
t
Single-line spectroscopic binary
u
Double-line spectroscopic binary
v
Spectrum binary
b
Visual binary
d
Visual binary with common proper motion
q
Visual binary - optical
r
Visual binary - physical
p
Exoplanet

SubField 2B Up to two characters to specify the spectral class of the primary star, typically one letter followed by one numerical subclass designator. Two examples are O and G3.

SubField 2C Up to two characters to specify the spectral class of the secondary star, typically one letter followed by one numerical subclass designator. Two examples are O and G3.
Field 3 RA position coordinate, given as H:M:S.

SubField 3A This optional subfield may specify a proper motion in RA. It is in milliarcseconds per year on the sky, i.e., ΔRA*cos(dec).
Field 4 Declination position coordinate, given as D:M:S.

SubField 4A This optional subfield may specify a proper motion in Dec. It is in milliarcseconds per year on the sky
Field 5
Magnitude of each star in the pair.

SubField 5A
Magnitude of the primary star

SubField 5B
Magnitude of the secondary star
Field 6
This optional field is the reference equinox year. It is assumed to be 2000 if absent
Field 7
This field may contain either 3 or 6 subfields (one or two triples of year/separation/position angle) or 7 subfields (orbital elements).

If 3 or 6 subfields, they define positions grouped as the following triplets:

SubField 7A/D Year of the separation and position angle given in the next two fields, decimal year or month/day/year

SubField 7B/E Separation, arc seconds

SubField 7C/F Position angle, degrees E of N, referenced to equinox in field 6

If 7 subfields, they define a true orbit:

SubField 7A
Semi-major axis, arcseconds

SubField 7B Inclination from plane of sky, degrees

SubField 7C Longitude of node, degrees

SubField 7D Eccentricity

SubField 7E Epoch of periastron, decimal year or month/day/year

SubField 7F Argument of periastron, degrees

SubField 7G Period. Units are designated by suffix y for years, d for days, or h for hours. If no designation the default is years.


If Field 2 is e the object type is elliptical heliocentric (eccentricity < 1) and the remaining fields are defined as follows:

Field 3
i = inclination, degrees
Field 4
O = longitude of ascending node, degrees
Field 5
o = argument of perihelion, degrees
Field 6
a = mean distance (aka semi-major axis), AU
Field 7
n = mean daily motion, degrees per day (computed from a**3/2 if omitted)
Field 8
e = eccentricity, must be < 1
Field 9
M = mean anomaly, i.e., degrees from perihelion
Field 10
E = epoch date, i.e., time of M

SubField 10A First date these elements are valid, optional

SubField 10B Last date these elements are valid, optional
Field 11
D = the equinox year, i.e., time of i, O and o
Field 12
First component of magnitude model, either g from (g,k) or H from (H,G). Specify which by preceding the number with a "g" or an "H". In absence of either specifier the default is (H,G) model. See Magnitude models.
Field 13
Second component of magnitude model, either k or G
Field 14
s = angular size at 1 AU, arc seconds, optional

You may have other parameters available for elliptical orbits that can be converted into these. The following relationships might be useful:

P = sqrt(a*a*a)
p = O + o
n = 0.9856076686/P
T = E - M/n
q = a*(1-e)

AU = 149,597,870 km = 92,955,621 U.S. statute miles

where

P = the orbital period, years;
p = longitude of perihelion, degrees
T = epoch of perihelion (add multiples of P for desired range)
q = perihelion distance, AU

Note that if you know T you can then set E = T and M = 0.

If Field 2 is h the object type is hyperbolic heliocentric (eccentricity > 1) and the remaining fields are defined as follows:

Field 3
T = date of the epoch of perihelion

SubField 3A First date these elements are valid, optional

SubField 3B Last date these elements are valid, optional
Field 4
i = inclination of orbital plane to ecliptic, degrees
Field 5
O = longitude of ascending node, degrees
Field 6
o = argument of perihelion, degrees
Field 7
e = eccentricity, must be > 1
Field 8
q = perihelion distance, AU
Field 9
D = the equinox year (i.e., time of i/O/o)
Field 10
g component of magnitude model. See Magnitude models.
Field 11
k component of magnitude model
Field 12
s = angular size at 1 AU, arc seconds, optional

As with elliptical elements, other parameters might be available. The relationships are generally the same, except:

q = a*(e-1)

If Field 2 is p the object type is parabolic heliocentric (eccentricity exactly equal to 1) and the remaining fields are defined as follows:

Field 3
T = date of epoch of perihelion

SubField 3A First date these elements are valid, optional

SubField 3B Last date these elements are valid, optional
Field 4
i = inclination, degrees
Field 5
o = argument of perihelion, degrees
Field 6
q = perihelion distance, AU
Field 7
O = longitude of ascending node, degrees
Field 8
D = the equinox year (i.e., time of i/O/o).
Field 9
g component of magnitude model. See Magnitude models.
Field 10
k component of magnitude model
Field 11
s = angular size at 1 AU, arc seconds, optional

If Field 2 is E (note upper case) the object type is Earth satellite and the remaining fields are defined as follows:


Field 3
Epoch of the other fields

SubField 3A First date these elements are valid, optional

SubField 3B
Last date these elements are valid, optional
Field 4
inclination, degrees
Field 5
RA of ascending node, degrees
Field 6
eccentricity, must be < 1
Field 7
argument of perigee, degrees
Field 8
mean anomaly, degrees
Field 9
mean motion, revs/day
Field 10
orbit decay rate, revolutions/day^2
Field 11
integral reference orbit number at Epoch
Field 12
drag coefficient, 1/(earth radii); optional

As an alternative to using the E format, files may be read directly, containing the venerable Two-Line-Element (TLE) format.
See the TLE document for details.

If Field 2 is P (note upper case) then Field 1 must be the name of a built-in object and no other fields are defined. The following names are recognized:

Sun
Moon
Mercury
Venus
Mars
Phobos
Deimos
Jupiter
Io
Europa
Ganymede
Callisto
Saturn
Mimas
Enceladus
Tethys
Dione
Rhea
Titan
Hyperion
Iapetus
Uranus
Ariel
Umbriel
Titania
Oberon
Miranda
Neptune
Pluto

Magnitude models

(Magnitude information is presently ignored by MMT software.)
The g,k magnitude model requires two parameters to be specified. One, the absolute magnitude, g, is the visual magnitude of the object if it were one AU from both the Sun and the Earth. The other, the luminosity index, k, characterizes the brightness change of the object as a function of its distance from the Sun. This is generally zero, or very small, for inactive objects like asteroids. The model may be expressed as:

m = g + 5*log10(D) + 2.5*k*log10(r)

where:

m = resulting visual magnitude
g = absolute visual magnitude
D = comet-earth distance, in AU
k = luminosity index
r = comet-sun distance.

The H,G model also requires two parameters. The first, H, is the magnitude of the object when one AU from the Sun and the Earth. The other, G, attempts to model the reflection characteristics of a passive surface, such as an asteroid. The model may be expressed with the following code fragment:

beta = acos((rp*rp + rho*rho - rsn*rsn)/ (2*rp*rho));
psi_t = exp(log(tan(beta/2.0))*0.63);
Psi_1 = exp(-3.33*psi_t);
psi_t = exp(log(tan(beta/2.0))*1.22);
Psi_2 = exp(-1.87*psi_t);
m = H + 5.0*log10(rp*rho) - 2.5*log10((1-G)*Psi_1 + G*Psi_2);

where:

m  = resulting visual magnitude
rp  = distance from sun to object
rho = distance from earth to object
rsn = distance from sun to earth

Note that neither model takes into account the phase angle of sun light.