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See Downloading and Using Data Files for an explanation of how Skyfield programs
use an instance of the Loader class described below
to download and open the data files they need in order to operate.
skyfield.iokit.Loader(directory, verbose=True, expire=True)¶A tool for downloading and opening astronomical data files.
A default Loader that saves data files to the current working
directory can be imported directly from the Skyfield API:
from skyfield.api import load
But users can also create a Loader of their own, if there is
another directory they want data files saved to, or if they want to
specify different options. The directory is created automatically
if it does not yet exist:
from skyfield.api import Loader
load = Loader('~/skyfield-data')
The options are:
verbose — if set to False, then the loader will not print
a progress bar to the screen each time it downloads a file. (If
the standard output is not a TTY, then no progress bar is printed
in any case.)expire — if set to False, then Skyfield will always use an
existing file on disk, instead of expiring files that are out of
date and replacing them with newly downloaded copies.directory¶The directory where this loader looks when trying to open a file, and where it downloads files that have not been downloaded yet.
path_of(filename)¶Return the path to filename in this loader’s directory.
timescale(delta_t=None)¶Open or download three time scale files, returning a Timescale.
This method is how most Skyfield users build a Timescale
object, which is necessary for building specific Time objects
that name specific moments.
This will open or download the three files that Skyfield needs
to measure time. UT1 is tabulated by the United States Naval
Observatory files deltat.data and deltat.preds, while
UTC is defined by Leap_Second.dat from the International
Earth Rotation Service.