Parameters which are not entered specifically for a new source are taken from
the previously entered source (or from .DEFAULT). This allows one to
specify parameters which are then valid for all subsequently entered sources.
For instance, in order to enter a list of stars with J1900.0 coordinates,
one would only have to type: EQ J1900
SO STAR R 12 34 56 D 12 34 56
and the equinox of all following entries will be J1900 until changed.