EPH is a freeware program that can be used to compute ephemerides of comets
and minor and major planets.
It features full perturbations of orbits due to the major planets using
numerical integration with user
selectable integration increment. Major planet positions are computed using the
JPL planetary ephemeris,
version DE405. EPH can read the MPC database of minor planet elements, MPCORB.
OPERATION
When the program is executed, the first screen will ask if the ephemerides
screen output containing RA,
DEC, Solar and Earth distances and other variables is to be saved to a text
file. The name of a text
file can be given to the program where this information will be stored. This
file can be used later for
printing the ephemeris. If no file is needed, a <CR> should be input.
The second screen asks for the desired output format. Five options are given:
SHORT - Date: year-month-day, ET. RA: h, m (xx.xx), DEC: deg, min (xx.x),
Mv(xx.x),
Sun distance(xx.xxx), Earth distance(xx.xxx), phase(xx.x), elongation(xx.x)
LONG - Date: year-month-day, ET. RA: h, m (xx.xx), DEC: deg, min (xx.x),
Sun distance(xx.x), Earth distance(xx.xxxxxx), phase(xx.x), elongation(xx.xxxxx)
ASTRM - Date: year-month-day, UT. RA: h, m, s(xx.xx), DEC: deg, min, sec(xx.x),
Mv(xx.x)
Sun distance(x.xxx), Earth distance(xx.xxx)
MPC - Date: year-month, UT(xx.xxxxx), RA: h, m, s(xx.xx), DEC: deg, min,
sec(xx.x),
Sun distance (xx.xxx), Earth distance(xx.xxx)
A user generated file built with the accessory program IEDIT
The third screen shows selectable parameters which control program execution and
which can be changed by
the user when the program is started. These parameters are contained in four
files which can be accesed
when EPH executes, or an initialization file built and/or edited with an
accessory program IEDIT
(Initialize EDIT). These parameters are:
FORM: Format of the ephemerides output. Choices for this format are the same as
above:
SHORT
LONG
ASTRM
MPC
NPOS: Number of positions to list in the output.
YEAR: Year of the first position
MONTH: Month of the first position
DAY: Day of MONTH of first position, which may contain a decimal part of the
day.
XJINC: Interval between output dates. This will be in hours for the formats
SHORT, LONG, and ASTRM,
and in days for the format MPC.
DEL: Integration interval in days for numerical integration. Normally this is
set at 1.0 days, but
may have to be set as small as 0.01 days for near major planet approaches or
small perihelion orbits
to maintain accuracy. If 0 is entered, Kepler's equation will be used to
generate the ephemeris.
METHOD: Method used for numerical integration. The choices for METHOD are:
KEPLER: Two body solution without perturbations.
COWELL: Cowell's direct integration algorithm including perturbations.
ENCKE: Encke's integration method. See Technical Information, below.
CYEAR: Geocentric coordinate system designation. The default 2000 is for the
J2000 coordinate system.
OLAT: Observer's latitude. If greater than 90 degrees, the program will use
geocentric coordinates.
OLAN: Observer's longitude.
NPLANET: Number of major planets to use for perturbations. The default, 10, uses
all major planets,
Pluto, and the Moon. If NPLANET is set to 9 or less, the Earth-Moon barycenter
is used for planet 3.
NCENTER: Coordinate center. Normally this will be set to 3 to use the Earth as
the coordinate's
center. It may be set to any other major planet, but the coordinate system will
still be using
geocentric orientation with its center at planet NCENTER.
MPCFILE: Name of the element file for minor planets. This will be the Minor
Planet Center's file
MPCORB. The program will read current versions correctly.
PLANET: Source of major planet positions. Defaults to JPL which uses the JPL
database. The other
option is MEAN which uses mean elements. This option is available in case the
JPL database is not
available. Mean elements will have reduced accuracy. The mean elements will also
be used if the
dates extend beyond JPL limits (see below).
JPLFILE: Name of the JPL Planetary and Lunar Ephemerides file. This file is
supplied with EPH.
The JPL Ephemerides file extends from 1599 DEC 09 to 2169 MAR 31. If the program
needs to calculate
ephemerides outside this range of dates, it will use mean elements to extend the
range of major
planet positions, with reduced accuracy.
STFILE: Element file at first ephemeris listing. If this is specified, the
program will save a
file of elements at the first ephemeris position. This file can be recalled
later to compute other
positions.
ENDFIL: Element file at last ephemeris listing.
If any of these parameters need to be changed, the name of that parameter can be
entered, and the
program will prompt for a new setting. If no changes are needed, a carriage
control can be entered.
The next question will prompt for the source of elements. There are four
choices:
(1) Search the database MPCORB for a numbered minor planet.
You will need to supply the number of the desired object in the MPC database.
(2) Search the database MPCORB for a named minor planet.
You will need to supply a minor planet's name, or if unnamed, the provisional
designation, exactly as
it appears in the MPC database.
(3) Load a file of minor planet elements built by EPH using STFILE or ENDFIL or
the auxiliary program
BFILE. The program BFILE can build a file of elements for an object not in the
MPCORB database.
It can build files for both minor planets or comets.
You will need to supply the name of this element file.
(4) Use the JPL Planetary Ephemeris database to compute an ephemeris for a major
planet. It is
possible to generate an ephemeris with choices for both the target planet and
observing planet.
The ephemeris of the selected object will be generated at this point.
TECHNICAL INFORMATION
The program is written using Compaq Visual Fortran 6.6. All calculations are
done using double
precision arithmetic.
Effects of planetary aberration and parallax are corrected.
General relativistic corrections are not included.
For information on Gauss-Jackson integration see: Danby, "Fundamentals of
Celestial Mechanics"
Second edition, chapters 10 and 11. Also see Brouwer and Clemence "Methods of
Celestial Mechanics"
chapters IV and V. Backpoints for starting Gauss-Jackson integration are
generated using a seventh
order Runge-Kutta routine.
For information about Encke's integration method see Brouwer and Clemence
"Methods of Celestial
Mechanics", Chapter V. See the end of Chapter V, section 8 for a comparison of
Encke's and Cowell's
algorithms.
ACCESSORY PROGRAMS:
Along with EPH the following programs are supplied that may be useful:
BFILE
BFILE is used to build an element file that can be read by EPH. Options are
provided to build both
element files for minor planets and comets.
To build an element file for a minor planet you will need to supply the
following information:
A name or number designator
Epoch date, either in calendar or Julian day format
Magnitude
Mean anomaly
Argument of perihelion, degrees
Longitude of the ascending node, degrees
Inclination, degrees
Eccentricity
Semimajor axis, AU
Name for this file
To build an element file for a comet, you will need to supply the following
information:
Designation for this object
Source of the elements (optional)
Epoch date, either in calendar or Julian day format
Magnitude
Perihelion date, in calendar or Julian format
Argument of perihelion , degrees
Longitude of ascending node, degrees
Inclination, degrees
Eccentricity
Perihelion distance, AU
Name for this file
IEDIT
IEDIT enables you to build and/or edit initialization files. Four files are
supplied with the program, and IEDIT
can be used to change these files or build new initializing files without using
these previously built files.
You will be asked to supply the following information:
Format of output, from the choices above: Short, Long, Astrometric or MPC
Number of positions to compute
Year of first position
Month of first position
Day of month of first position
Increment in hours or days between positions
IEDIT will show the values present in your new file which can be changed at this
point.
If no changes are needed, the file will be saved.
JULIAN
JULIAN converts calendar dates to Julian days or Julian days to calendar dates.