code: public static final float toJulian(Date date) {
  
          Calendar c = Calendar.getInstance();
          c.setTime(date);
  
          return toJulian(c);
      }
docs: 暂时不用 Return a Julian date based on the input parameter. This is based
  from calculations found at <a
  href="http://quasar.as.utexas.edu/BillInfo/JulianDatesG.html">Julian Day
  Calculations (Gregorian Calendar)</a>, provided by Bill Jeffrys.
  
  @param date
  @return the julian day number