AltAz¶
-
class
astropy.coordinates.
AltAz
(*args, **kwargs)[source] [edit on github]¶ Bases:
astropy.coordinates.BaseCoordinateFrame
A coordinate or frame in the Altitude-Azimuth 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 non-zero.This frame has the following frame attributes, which are necessary for transforming from AltAz to some other system:
obstime
The time at which the observation is taken. Used for determining the position and orientation of the Earth.
location
The location on the Earth. This can be specified either as an
EarthLocation
object or as anything that can be transformed to anITRS
frame.
pressure
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.
temperature
The ground-level temperature as an
Quantity
in deg C. This is necessary for performing refraction corrections.
relative_humidity
The relative humidity as a number from 0 to 1. This is necessary for performing refraction corrections.
obswl
- The average wavelength of observations as an
Quantity
with length units. This is necessary for performing refraction corrections.
- The average wavelength of observations as an
Parameters: representation :
BaseRepresentation
or NoneA representation object or None to have no data (or use the other keywords)
az :
Angle
, optional, must be keywordThe Azimuth for this object (
alt
must also be given andrepresentation
must be None).alt :
Angle
, optional, must be keywordThe Altitude for this object (
az
must also be given andrepresentation
must be None).distance :
Quantity
, optional, must be keywordThe Distance for this object along the line-of-sight.
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
at0
(the default), disabling the refraction correction (yielding “topocentric” horizontal coordinates).Attributes Summary
default_representation
frame_attributes
frame_specific_representation_info
location
name
obstime
obswl
pressure
relative_humidity
secz
Secant if the zenith angle for this coordinate, a common estimate of the airmass. temperature
zen
The zenith angle for this coordinate Attributes Documentation
-
default_representation
¶
-
frame_attributes
= OrderedDict([('obstime', <astropy.coordinates.baseframe.TimeFrameAttribute object at 0x7ff5256c6a90>), ('location', <astropy.coordinates.baseframe.EarthLocationAttribute object at 0x7ff5256c6e50>), ('pressure', <astropy.coordinates.baseframe.QuantityFrameAttribute object at 0x7ff5256c6e90>), ('temperature', <astropy.coordinates.baseframe.QuantityFrameAttribute object at 0x7ff5256c6ed0>), ('relative_humidity', <astropy.coordinates.baseframe.FrameAttribute object at 0x7ff5256c6f10>), ('obswl', <astropy.coordinates.baseframe.QuantityFrameAttribute object at 0x7ff5256c6f50>)])¶
-
frame_specific_representation_info
¶
-
location
= None¶
-
name
= 'altaz'¶
-
obstime
= None¶
-
obswl
= <Quantity 1.0 micron>¶
-
pressure
= <Quantity 0.0 hPa>¶
-
relative_humidity
= 0¶
-
secz
¶ Secant if the zenith angle for this coordinate, a common estimate of the airmass.
-
temperature
= <Quantity 0.0 deg_C>¶
-
zen
¶ The zenith angle for this coordinate