# TETE¶

class astropy.coordinates.TETE(*args, copy=True, representation_type=None, differential_type=None, **kwargs)[source]

An equatorial coordinate or frame using the True Equator and True Equinox (TETE).

Equatorial coordinate frames measure RA with respect to the equinox and declination with with respect to the equator. The location of the equinox and equator vary due the gravitational torques on the oblate Earth. This variation is split into precession and nutation, although really they are two aspects of a single phenomena. The smooth, long term variation is known as precession, whilst smaller, periodic components are called nutation.

Calculation of the true equator and equinox involves the application of both precession and nutation, whilst only applying precession gives a mean equator and equinox.

TETE coordinates are often referred to as “apparent” coordinates, or “apparent place”. TETE is the apparent coordinate system used by JPL Horizons and is the correct coordinate system to use when combining the right ascension with local apparent sidereal time to calculate the hour angle.

For more background on TETE, see the references provided in the See Also section of the documentation. Of particular note are Sections 5 and 6 of USNO Circular 179) and especially the diagram at the top of page 57.

This frame also includes frames that are defined relative to the Earth, but that are offset (in both position and velocity) from the Earth. You may see such non-geocentric coordinates referred to as “topocentric”.

The frame attributes are listed under Other Parameters.

Parameters
dataBaseRepresentation subclass instance

A representation object or None to have no data (or use the coordinate component arguments, see below).

raAngle, optional, must be keyword

The RA for this object (dec must also be given and representation must be None).

decAngle, optional, must be keyword

The Declination for this object (ra must also be given and representation must be None).

distanceQuantity, optional, must be keyword

The Distance for this object along the line-of-sight. (representation must be None).

pm_ra_cosdecQuantity, optional, must be keyword

The proper motion in Right Ascension (including the cos(dec) factor) for this object (pm_dec must also be given).

pm_decQuantity, optional, must be keyword

The proper motion in Declination for this object (pm_ra_cosdec must also be given).

radial_velocityQuantity, optional, must be keyword

The radial velocity of this object.

representation_typeBaseRepresentation subclass, str, optional

A representation class or string name of a representation class. This sets the expected input representation class, thereby changing the expected keyword arguments for the data passed in. For example, passing representation_type='cartesian' will make the classes expect position data with cartesian names, i.e. x, y, z in most cases unless overriden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

differential_typeBaseDifferential subclass, str, dict, optional

A differential class or dictionary of differential classes (currently only a velocity differential with key ‘s’ is supported). This sets the expected input differential class, thereby changing the expected keyword arguments of the data passed in. For example, passing differential_type='cartesian' will make the classes expect velocity data with the argument names v_x, v_y, v_z unless overriden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

copybool, optional

If True (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument.

Other Parameters
obstimeTime

The time at which the observation is taken. Used for determining the position of the Earth.

locationEarthLocation

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 default is the centre of the Earth.

Attributes Summary

Attributes Documentation

default_differential
default_representation
frame_attributes = {'location': <astropy.coordinates.attributes.EarthLocationAttribute object>, 'obstime': <astropy.coordinates.attributes.TimeAttribute object>}
frame_specific_representation_info
location = <EarthLocation (0., 0., 0.) km>
name = 'tete'
obstime = <Time object: scale='tt' format='jyear_str' value=J2000.000>