Function datetime_to_mjd 

pub fn datetime_to_mjd(dt: PrimitiveDateTime) -> f64

Modified Julian Date of a timezone-naive instant (taken as UTC). Inverse of mjd_to_datetime.

use skymath::datetime_to_mjd;
use time::macros::datetime;

// J2000.0 = MJD 51544.5.
assert_eq!(datetime_to_mjd(datetime!(2000-01-01 12:00)), 51_544.5);