Note
This is an old version of the documentation. See http://docs.astropy.org/en/stable for the latest version.
Bases: astropy.coordinates.BaseCoordinateFrame
A coordinate or frame in the AltitudeAzimuth system (Horizontal coordinates). Azimuth is oriented East of North (i.e., N=0, E=90 degrees).
This frame is assumed to include refraction effects if the pressure frame attribute is nonzero.
This frame has the following frame attributes, which are necessary for transforming from AltAz to some other system:
The time at which the observation is taken. Used for determining the position and orientation of the Earth.
The location on the Earth. This can be specified either as an EarthLocation object or as anything that can be transformed to an ITRS frame.
The atmospheric pressure as an Quantity with pressure units. This is necessary for performing refraction corrections. Setting this to 0 (the default) will disable refraction calculations when transforming to/from this frame.
The groundlevel temperature as an Quantity in deg C. This is necessary for performing refraction corrections.
The relative humidity as a number from 0 to 1. This is necessary for performing refraction corrections.
with length units. This is necessary for performing refraction corrections.
Parameters:  representation : BaseRepresentation or None
az : Angle, optional, must be keyword
alt : Angle, optional, must be keyword
distance : Quantity, optional, must be keyword


Notes
The refraction model is based on that implemented in ERFA, which is fast but becomes inaccurate for altitudes below about 5 degrees. Near and below altitudes of 0, it can even give meaningless answers, and in this case transforming to AltAz and back to another frame can give highly discrepent results. For much better numerical stability, leaving the pressure at 0 (the default), disabling the refraction correction (yielding “topocentric” horizontal coordinates).
Attributes Summary
default_representation  
frame_specific_representation_info  
location  
name  str(object=’‘) > string 
obstime  
obswl  A Quantity represents a number with some associated unit. 
pressure  A Quantity represents a number with some associated unit. 
relative_humidity  int(x=0) > int or long 
secz  Secant if the zenith angle for this coordinate, a common estimate of the airmass. 
temperature  A Quantity represents a number with some associated unit. 
zen  The zenith angle for this coordinate 
Attributes Documentation
Secant if the zenith angle for this coordinate, a common estimate of the airmass.
The zenith angle for this coordinate