sidereal.py: Internal maintenance specification

This test has two parts; the second part is the reverse conversion from the first part.

#!/usr/bin/env python
#================================================================
# test24: Convert from right ascension to hour angle and back.
# For documentation, see:
#   http://www.nmt.edu/tcc/help/lang/python/examples/sidereal/ims/
#----------------------------------------------------------------

import sys
from math import *
import datetime
import sidereal

First we convert the value of α to radians. For the conversion of mixed units to degrees, see Section 10.2, “MixedUnits.mixToSingle(): Convert to a single value”; radians() is from Python's math module and converts degrees to radians. Next we convert 64° to radians. Then we make a datetime.datetime instance for the given time.

# - - -   m a i n

def main():
    """Main program.
    """
    global dmsUnits

    #-- 1 --
    # [ dmsUnits  :=  a MixedUnits instance for factor list (60,60) ]
    dmsUnits  =  sidereal.MixedUnits ( (60, 60) )

    #-- 2 --
    # [ ra  :=  (18h 32m 21s) in radians
    #   eLong  :=  64 degrees as radians
    #   dt  :=  14h 36m 51.67s GMT as a datetime.datetime ]
    raHours  =  dmsUnits.mixToSingle((18,32,21))
    ra  =  sidereal.hoursToRadians(raHours)
    eLong  =  radians(-64.0)
    dt  =  datetime.datetime ( 1980, 4, 22, 14, 36, 51, 670000 )
    print "Right ascension:", radHMS(ra)
    print "Longitude:", radDMS(eLong)
    print "UTC:", dt

The function Section 9.3, “hourAngleToRA(): Convert an hour angle to right ascension” returns the hour angle in radians; we'll format it in degrees, minutes, and second for display.

    #-- 3 --
    # [ hRadians  :=  hour angle in radians for right ascension (ra),
    #       time (dt), and longitude (eLong) ]
    hRadians  =  sidereal.raToHourAngle ( ra, dt, eLong )

    #-- 4 --
    # [ sys.stdout  +:=  hRadians displayed as deg/min/sec ]
    print "Hour angle:", radHMS(hRadians)

Now, the inverse test.

    #-- 5 --
    # [ check  :=  right ascension for hour angle (hRadians),
    #       time (dt), and longitude (eLong) ]
    checkRadians  =  sidereal.hourAngleToRA ( hRadians, dt, eLong )

    #-- 6 --
    # [ sys.stdout  +:=  checkRadians displayed as d/m/s ]
    raDec  =  radHMS ( checkRadians )
    print "Check RA:", radHMS ( checkRadians )

This subroutine is used to display radians as degrees, minutes, and seconds.

# - - -   r a d D M S

def radDMS(rad):
    """Display radians as degrees, minutes, and seconds.
    """
    valueList  =  dmsUnits.format (
        dmsUnits.singleToMix(degrees(rad)), lz=True, decimals=3 )
    return "%sd %s' %s\"" % tuple(valueList)

This subroutine displays radians as hours, minutes, and seconds.

# - - -   r a d H M S

def radHMS(rad):
    """Display radians as hours, minutes, and seconds.
    """
    valueList  =  dmsUnits.format (
        dmsUnits.singleToMix ( sidereal.radiansToHours(rad) ),
                               lz=True, decimals=3 )
    return "%sh %sm %ss" % tuple(valueList)


#================================================================
# Epilogue
#----------------------------------------------------------------

if  __name__ == "__main__":
    main()