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I ask as a complete non expert in the field, please be patient: Wouldn't this require either downloading and maintaining a large database of ephemeri or connec

• d_silin 3y ago
  Good question! I use Skyfield library for my project, it does require downloading NASA ephemeris, but it is only <200MB, unless you want a very long time period and you need to do it once every few years. (DE430 got published in 2014 and most current version is DE440, released in 2021.
  • dsq 3y ago
    That's what I thought must be necessary, thank you.
  • mturmon 3y ago
    It may be worth adding that the planetary ephemeris are computed by NASA (JPL) by integrating the equations of motion forward in time numerically. Then the results (e.g. planet centroid as a function of time) are encoded in a file, as noted above. That file is then read by the ephemeris software to obtain the position at the desired time. I haven’t checked in a few years, but there used to be multiple files to choose from depending on the time range you needed to cover. It’s free — “your taxpayer dollars at work.”