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For moving objects such as asteroids, comets, or planets,
it is useful to include ephemeris information, both to provide predicted
coordinates for planning observations,
and to allow accurate airmass calculations
in the reductions.
Each such object requires several positions, each associated with a time.
These times can be given either as Modified Julian Dates
MJD = JD - 2400000.5),
or as ordinary date strings like 1995 Jan 23.0.
To allow good interpolation, include two ephemeris entries before and two after
the interval of observations.
The tabular interval need not be one day, but can have any constant value from
one table entry to the next.