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vsop2013

A Python implementation of the VSOP2013 Ephemeris functionality.

This module provides basic support for the VSOP2013 ephemerides which can be used to compute the heliocentric positions and velocities of the 8 planets Mercury, Venus, the Earth-Moon barycenter, Mars, Jupiter, Saturn, Uranus, Neptune and the dwarf planet Pluto (only in the period from +1500 to +3000).

The ephemerides are provided in 6 sequential text files (ASCII) and can be downloaded at:

ftp://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides

NOTE that you will likely have to use an ftp client to download the ephemerides files. For MacOSX I use the app ForkLift and have verified that the files are still available as of July 20, 2022.

The following provides the name of each file and the period that it covers:

  • VSOP2013.m4000: -4500 to -3000
  • VSOP2013.m2000: -3000 to -1500
  • VSOP2013.m1000: -1500 to 0
  • VSOP2013.p1000: 0 to +1500
  • VSOP2013.p2000: +1500 to +3000
  • VSOP2013.p4000: +3000 to +4500

While these text files could be used directly, this would have a serious impact on the performance of computing any significant number of planetary positions. Instead it is suggested that these files are parsed and stored into binary format for the platform on which they will be used. NOTE THAT THE BINARY FILE GENERATED FOR ONE PLATFORM MAY NOT BE COMPATIBLE FOR USE ON A DIFFERENT PLATFORM. Once converted to binary form the text files may be deleted to save storage space where necessary. The binary form of the files provides a much more efficient mechanism for performing large numbers of position calculations.

For reference the authors have provided the programs (written in Fortran) that they used for binary file generation and basic calculations.

These are:

VSOP2013_binfile.f : This program converts the sequential files into direct access files.

VSOP2013_compute.f : This program computes planetary coordinates from a direct access file.

The file VSOP2013_ctl.txt contains planetary coordinates computed by the program VSOP2013_compute.f and is provided as a means of validating the calculations using these ephemerides.

The file README.pdf also provides this information as well as other info that may be of interest.

This module has been developed to provide a degree of convenience for the Python user, not just a reference implementation.

TXT_FILES_ROOT is the path to the directory containing the VSOP2013 source text files. You may change this to reflect where your source text files are actually located. The default is to place the source text files into a subdirectory called "ephemerides" at the location of the vsop2013.py script. If the vsop2013.py functionality is being used by other python scripts then this variable can be changed once the module is loaded.

TXT_FILES is an array of the filenames of the VSOP2013 source text files.

BIN_FILES_ROOT is the path to the directory containing the VSOP2013 binary files. You may change this to reflect where your binary files are actually located. This variable is similar to the TXT_FILES_ROOT variable discussed previously.

BIN_FILES is an array of the filenames of the VSOP2013 binary files.

PLANET_NAMES is an array of the names of the supported planets and is used ONLY for the display of the results by the print_results function.

At the end of the source file is code that shows how to load the files, convert them to binary, and then to perform basic calculations.

===============================================================

To use this program:

  1. create a directory called 'vsop'
  2. change to directory 'vsop'
  3. create a directory called 'ephemerides'
  4. change to directory 'ephemerides'
  5. download file 'VSOP2013.m4000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  6. download file 'VSOP2013.m2000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  7. download file 'VSOP2013.m1000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  8. download file 'VSOP2013.p1000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  9. download file 'VSOP2013.p2000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  10. download file 'VSOP2013.p4000' from 'https://ftp.imcce.fr/pub/ephem/planets/vsop2013/ephemerides/'
  11. change back to directory 'vsop'
  12. download the python program 'vsop2013.py'
  13. run 'python ./vsop2013.py'

That will decompress and prepare the ephemerides. Once complete the you can use in idle or ipython as follows:

vsop2013 = VSOP2013File() r = vsop2013.calculate_for(, ) print_results(, , r)

This will output somthing like the following:

Jupiter JD2816818.5 X : -4.6312422242673 ua Y : 2.7235071301370 ua Z : 0.0885945013174 ua X': -0.0039324916289 ua/d Y': -0.0061510013748 ua/d Z': 0.0001158736935 ua/d

if was 4, was 2816818.5.