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# TETE

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

  Bases: `BaseRADecFrame`

  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 apparent (TIRS) 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 center of the Earth, but that are offset (in both position and velocity) from the center of the Earth. You may see such non-geocentric coordinates referred to as “topocentric”.

  The frame attributes are listed under Other Parameters.

  Parameters:
    data `BaseRepresentation` subclass instance

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

    ra `Angle`, optional, keyword-only

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

    dec `Angle`, optional, keyword-only

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

    distance `Quantity` [:ref: ‘length’], optional, keyword-only

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

    pm_ra_cosdec `Quantity` [:ref: ‘angular speed’], optional, keyword-only

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

    pm_dec `Quantity` [:ref: ‘angular speed’], optional, keyword-only

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

    radial_velocity `Quantity` [:ref: ‘speed’], optional, keyword-only

      The radial velocity of this object.

    representation_type `BaseRepresentation` subclass, `python: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 overridden via `frame_specific_representation_info`. To see this frame’s names, check out `<this frame>().representation_info`.

    differential_type `BaseDifferential` subclass, `python:str`, `python: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 overridden via `frame_specific_representation_info`. To see this frame’s names, check out `<this frame>().representation_info`.

    copy bool, optional

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

  Other Parameters:
    obstime `Time`

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

    location `EarthLocation`

      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

  `default_differential` | Default representation for differential data (e.g., velocity)
  `default_representation` | Default representation for position data
  `frame_attributes` |
  `frame_specific_representation_info` | Mapping for frame-specific component names
  `location` | The location on Earth of the observer
  `name` |
  `obstime` | The reference time (e.g., time of observation)

  Attributes Documentation

  default_differential

    Default representation for differential data (e.g., velocity)

  default_representation

    Default representation for position data

  frame_attributes = {'location': <astropy.coordinates.attributes.EarthLocationAttribute object>, 'obstime': <astropy.coordinates.attributes.TimeAttribute object>}
  frame_specific_representation_info

    Mapping for frame-specific component names

  location

    The location on Earth of the observer

    Default: (0.0, 0.0, 0.0) km

  name = 'tete'
  obstime

    The reference time (e.g., time of observation)

    Default: J2000.000