• atAirmassFind
  • atAirmassFromZd
  • atMeridianAirmassFind
  • atAirmassFindHaDec
  • atZdDec2Ha
  • atAirmass

      Routines to calculate airmass
    
    
    
    

    atAirmassFind

    DESCRIPTION:
    
    This routine will calculate the airmass given a UT time in a TSTAMP struct, and the RA and DEC in degrees at the current epoch.

    The routine uses Hardie's (1962) polynomial fit to Bemporad's data for the relative air mass, X, in units of the thickness at the zenith as tabulated by Schoenberg (1929). This is adequate as it is accurate to better than 0.1% up to X=6.8. Bemporad's tabulated values are unlikely to be trustworthy to such accuracy because of variations in density pressure, and other conditions of the atmosphere assumed in his work

    RETURN VALUES:
    
    Returns the airmass
    SIGNATURE:
      
      RET_CODE atAirmassFind(
      		       TSTAMP *time, 
      		       double degra, 
      		       double degdec, 
      		       double *airmass
      		       )
    

    atAirmassFromZd

    DESCRIPTION:
    
    Nothing but a wrapper to sla_Airmas which takes a zenith distance. This is specifically for use when one might be tempted to simply use sec(z), which will incur 0.25% errors at the Survey limit without any real good reason for doing so.

    The routine uses Hardie's (1962) polynomial fit to Bemporad's data for the relative air mass, X, in units of the thickness at the zenith as tabulated by Schoenberg (1929). This is adequate as it is accurate to better than 0.1% up to X=6.8. Bemporad's tabulated values are unlikely to be trustworthy to such accuracy because of variations in density pressure, and other conditions of the atmosphere assumed in his work

    RETURN VALUES:
    
    Returns the airmass
    SIGNATURE:
      
      double atAirmassFromZd(
      		       double degzd 
      		       ) 
    

    atMeridianAirmassFind

    DESCRIPTION:
    
    Simply finds the airmass with respect to the 2.5m at APO at the meridian given the DEC. Everything is as for atAirmassFind above.

    RETURN VALUES:
    
    Returns the airmass at the meridian (at APO 2.5m).
    SIGNATURE:
      
      double atMeridianAirmassFind(
      			     double degdec    /*IN: DEC (degrees)*/
      			     ) 
    

    atAirmassFindHaDec

    DESCRIPTION:
    
    Simply finds the airmass with respect to the 2.5m at APO given the HA and DEC. Everything is as for atAirmassFind above.

    RETURN VALUES:
    
    Returns the airmass for a given HA and DEC (at APO 2.5m).
    SIGNATURE:
      
      double atAirmassFindHaDec(
      			  double hahrs,     /*IN: HA (hours)*/
      			  double degdec    /*IN: DEC (degrees)*/
      			  ) 
    

    atZdDec2Ha

    DESCRIPTION:
    
    Takes a zenith distance (deg) and DEC (degrees) and converts it to an Hour Angle (hours).

    RETURN VALUES:
    
    Return HA (hours) given zenith distance (deg) and DEC (deg).
    SIGNATURE:
      
      double atZdDec2Ha(
      		  double zddeg,       /*IN: ZD (degrees)*/
      		  double decdeg       /*IN: DEC (degrees)*/
      		  )