pub const J1900_OFFSET: f64
J1900_OFFSET determines the offset in julian days between 01 Jan 1900 at midnight and the
Modified Julian Day at 17 November 1858.
NOTE: Julian days "start" at noon so that astronomical observations throughout the night
happen at the same Julian day. Note however that the Modified Julian Date (MJD) starts at
midnight, not noon, cf. http://tycho.usno.navy.mil/mjd.html.