[AstroPy] Dependencies on large data files

[Peter Williams]

Hi all,

(Apologies in advance if this topic has already been brought up -- I
haven't checked the archives/issues very thoroughly.)

One of the features I'd like to see in Astropy would be computation of
BJDs -- this is the kind of subtle calculation that many people could
use, and you really don't want people hand-rolling their own solutions.

The thing is, do to BJD calculations correctly, you need a solar system
ephemeris. The compiled version of the standard JPL ephemeris weighs in
at 14 MB and is not something that you want to have hanging out in the
Git repository.

Has any thought been given to having astropy depend on large data files
such as an ephemeris table? One could imagine similar dependencies on
leap second tables, earth orientation parameters, etc. These kinds of
files can be large and it's often desirable to be able to update them
out-of-band with regard to the software itself. Is there a model for how
to deal with such resources?

Cheers,

Peter

PS. I have code to compile the JPL ephemerides and perform a
low-precision BJD calculation, based on the NOVAS library:

   https://github.com/pkgw/precastro/

This library also uses NOVAS to provide various astrometric routines
that I think might also make valuable additions to AstroPy. Is there
interest in that kind of functionality?