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- SkyCoord

# SkyCoord

class astropy.coordinates.SkyCoord(*args, copy=True, **kwargs)

  Bases: `ShapedLikeNDArray`

  High-level object providing a flexible interface for celestial coordinate representation, manipulation, and transformation between systems.

  The `SkyCoord` class accepts a wide variety of inputs for initialization. At a minimum these must provide one or more celestial coordinate values with unambiguous units. Inputs may be scalars or lists/tuples/arrays, yielding scalar or array coordinates (can be checked via `SkyCoord.isscalar`). Typically one also specifies the coordinate frame, though this is not required. The general pattern for spherical representations is:

      SkyCoord(COORD, [FRAME], keyword_args ...)
      SkyCoord(LON, LAT, [FRAME], keyword_args ...)
      SkyCoord(LON, LAT, [DISTANCE], frame=FRAME, unit=UNIT, keyword_args ...)
      SkyCoord([FRAME], <lon_attr>=LON, <lat_attr>=LAT, keyword_args ...)

  It is also possible to input coordinate values in other representations such as cartesian or cylindrical. In this case one includes the keyword argument `representation_type='cartesian'` (for example) along with data in `x`, `y`, and `z`.

  See also: https://docs.astropy.org/en/stable/coordinates/

  Parameters:
    frame `BaseCoordinateFrame` class or `python:str`, optional

      Type of coordinate frame this `SkyCoord` should represent. Defaults to to ICRS if not given or given as None.

    unit `Unit`, `python:str`, or `python:tuple` of `Unit` or `python:str`, optional

      Units for supplied coordinate values. If only one unit is supplied then it applies to all values. Note that passing only one unit might lead to unit conversion errors if the coordinate values are expected to have mixed physical meanings (e.g., angles and distances).

    obstime astropy:time-like, optional

      Time(s) of observation.

    equinox astropy:time-like, optional

      Coordinate frame equinox time.

    representation_type `python:str` or `BaseRepresentation` class

      Specifies the representation, e.g. ‘spherical’, ‘cartesian’, or ‘cylindrical’. This affects the positional args and other keyword args which must correspond to the given representation.

    copy bool, optional

      If `True` (default), a copy of any coordinate data is made. This argument can only be passed in as a keyword argument.

    **keyword_args

      Other keyword arguments as applicable for user-defined coordinate frames. Common options include:

      ra, decangle-like, optional

        RA and Dec for frames where `ra` and `dec` are keys in the frame’s `representation_component_names`, including `ICRS`, `FK5`, `FK4`, and `FK4NoETerms`.

      pm_ra_cosdec, pm_dec`Quantity` [‘angular speed’], optional

        Proper motion components, in angle per time units.

      l, bangle-like, optional

        Galactic `l` and `b` for for frames where `l` and `b` are keys in the frame’s `representation_component_names`, including the `Galactic` frame.

      pm_l_cosb, pm_b`Quantity` [‘angular speed’], optional

        Proper motion components in the `Galactic` frame, in angle per time units.

      x, y, zfloat or `Quantity` [‘length’], optional

        Cartesian coordinates values

      u, v, wfloat or `Quantity` [‘length’], optional

        Cartesian coordinates values for the Galactic frame.

      radial_velocity`Quantity` [‘speed’], optional

        The component of the velocity along the line-of-sight (i.e., the radial direction), in velocity units.

  Examples

  The examples below illustrate common ways of initializing a `SkyCoord` object. For a complete description of the allowed syntax see the full coordinates documentation. First some imports:

      >>> from astropy.coordinates import SkyCoord  # High-level coordinates
      >>> from astropy.coordinates import ICRS, Galactic, FK4, FK5  # Low-level frames
      >>> from astropy.coordinates import Angle, Latitude, Longitude  # Angles
      >>> import astropy.units as u

  The coordinate values and frame specification can now be provided using positional and keyword arguments:

      >>> c = SkyCoord(10, 20, unit="deg")  # defaults to ICRS frame
      >>> c = SkyCoord([1, 2, 3], [-30, 45, 8], frame="icrs", unit="deg")  # 3 coords

      >>> coords = ["1:12:43.2 +31:12:43", "1 12 43.2 +31 12 43"]
      >>> c = SkyCoord(coords, frame=FK4, unit=(u.hourangle, u.deg), obstime="J1992.21")

      >>> c = SkyCoord("1h12m43.2s +1d12m43s", frame=Galactic)  # Units from string
      >>> c = SkyCoord(frame="galactic", l="1h12m43.2s", b="+1d12m43s")

      >>> ra = Longitude([1, 2, 3], unit=u.deg)  # Could also use Angle
      >>> dec = np.array([4.5, 5.2, 6.3]) * u.deg  # Astropy Quantity
      >>> c = SkyCoord(ra, dec, frame='icrs')
      >>> c = SkyCoord(frame=ICRS, ra=ra, dec=dec, obstime='2001-01-02T12:34:56')

      >>> c = FK4(1 * u.deg, 2 * u.deg)  # Uses defaults for obstime, equinox
      >>> c = SkyCoord(c, obstime='J2010.11', equinox='B1965')  # Override defaults

      >>> c = SkyCoord(w=0, u=1, v=2, unit='kpc', frame='galactic',
      ...              representation_type='cartesian')

      >>> c = SkyCoord([ICRS(ra=1*u.deg, dec=2*u.deg), ICRS(ra=3*u.deg, dec=4*u.deg)])

  Velocity components (proper motions or radial velocities) can also be provided in a similar manner:

      >>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, radial_velocity=10*u.km/u.s)

      >>> c = SkyCoord(ra=1*u.deg, dec=2*u.deg, pm_ra_cosdec=2*u.mas/u.yr, pm_dec=1*u.mas/u.yr)

  As shown, the frame can be a `BaseCoordinateFrame` class or the corresponding string alias – lower-case versions of the class name that allow for creating a `SkyCoord` object and transforming frames without explicitly importing the frame classes.

  Attributes Summary

  `frame` |
  `info` | Container for meta information like name, description, format.
  `representation` |
  `representation_type` |
  `shape` | The shape of the underlying data.

  Methods Summary

  `apply_space_motion`([new_obstime, dt]) | Compute the position of the source represented by this coordinate object to a new time using the velocities stored in this object and assuming linear space motion (including relativistic corrections).
  `contained_by`(wcs[, image]) | Determines if the SkyCoord is contained in the given wcs footprint.
  `directional_offset_by`(position_angle, separation) | Computes coordinates at the given offset from this coordinate.
  `from_name`(name[, frame, parse, cache]) | Given a name, query the CDS name resolver to attempt to retrieve coordinate information for that object.
  `from_pixel`(xp, yp, wcs[, origin, mode]) | Create a new SkyCoord from pixel coordinates using a World Coordinate System.
  `get_constellation`([short_name, ...]) | Determines the constellation(s) of the coordinates this SkyCoord contains.
  `guess_from_table`(table, **coord_kwargs) | A convenience method to create and return a new SkyCoord from the data in an astropy Table.
  `insert`(obj, values[, axis]) | Insert coordinate values before the given indices in the object and return a new Frame object.
  `is_equivalent_frame`(other) | Checks if this object's frame as the same as that of the `other` object.
  `is_transformable_to`(new_frame) | Determines if this coordinate frame can be transformed to another given frame.
  `match_to_catalog_3d`(catalogcoord[, nthneighbor]) | Finds the nearest 3-dimensional matches of this coordinate to a set of catalog coordinates.
  `match_to_catalog_sky`(catalogcoord[, nthneighbor]) | Finds the nearest on-sky matches of this coordinate in a set of catalog coordinates.
  `position_angle`(other) | Computes the on-sky position angle (East of North) between this SkyCoord and another.
  `radial_velocity_correction`([kind, obstime, ...]) | Compute the correction required to convert a radial velocity at a given time and place on the Earth's Surface to a barycentric or heliocentric velocity.
  `search_around_3d`(searcharoundcoords, distlimit) | Searches for all coordinates in this object around a supplied set of points within a given 3D radius.
  `search_around_sky`(searcharoundcoords, seplimit) | Searches for all coordinates in this object around a supplied set of points within a given on-sky separation.
  `separation`(other) | Computes on-sky separation between this coordinate and another.
  `separation_3d`(other) | Computes three dimensional separation between this coordinate and another.
  `skyoffset_frame`([rotation]) | Returns the sky offset frame with this SkyCoord at the origin.
  `spherical_offsets_by`(d_lon, d_lat) | Computes the coordinate that is a specified pair of angular offsets away from this coordinate.
  `spherical_offsets_to`(tocoord) | Computes angular offsets to go from this coordinate to another.
  `to_pixel`(wcs[, origin, mode]) | Convert this coordinate to pixel coordinates using a `WCS` object.
  `to_string`([style]) | A string representation of the coordinates.
  `to_table`() | Convert this `SkyCoord` to a `QTable`.
  `transform_to`(frame[, merge_attributes]) | Transform this coordinate to a new frame.

  Attributes Documentation

  frame
  info

    Container for meta information like name, description, format. This is required when the object is used as a mixin column within a table, but can be used as a general way to store meta information.

  representation
  representation_type
  shape

  Methods Documentation

  apply_space_motion(new_obstime=None, dt=None)

    Compute the position of the source represented by this coordinate object to a new time using the velocities stored in this object and assuming linear space motion (including relativistic corrections). This is sometimes referred to as an “epoch transformation.”

    The initial time before the evolution is taken from the `obstime` attribute of this coordinate. Note that this method currently does not support evolving coordinates where the frame has an `obstime` frame attribute, so the `obstime` is only used for storing the before and after times, not actually as an attribute of the frame. Alternatively, if `dt` is given, an `obstime` need not be provided at all.

    Parameters:
      new_obstime `Time`, optional

        The time at which to evolve the position to. Requires that the `obstime` attribute be present on this frame.

      dt `Quantity`, `TimeDelta`, optional

        An amount of time to evolve the position of the source. Cannot be given at the same time as `new_obstime`.

    Returns:
      new_coord `SkyCoord`

        A new coordinate object with the evolved location of this coordinate at the new time. `obstime` will be set on this object to the new time only if `self` also has `obstime`.

  contained_by(wcs, image=None, **kwargs)

    Determines if the SkyCoord is contained in the given wcs footprint.

    Parameters:
      wcs `WCS`

        The coordinate to check if it is within the wcs coordinate.

      image `array`

        Optional. The image associated with the wcs object that the cooordinate is being checked against. If not given the naxis keywords will be used to determine if the coordinate falls within the wcs footprint.

      **kwargs

        Additional arguments to pass to `to_pixel`

    Returns:
      response bool

        True means the WCS footprint contains the coordinate, False means it does not.

  directional_offset_by(position_angle, separation)

    Computes coordinates at the given offset from this coordinate.

    Parameters:
      position_angle `Angle`

        position_angle of offset

      separation `Angle`

        offset angular separation

    Returns:
      newpoints `SkyCoord`

        The coordinates for the location that corresponds to offsetting by the given `position_angle` and `separation`.

    See also

    `position_angle`

      inverse operation for the `position_angle` component

    `separation`

      inverse operation for the `separation` component

    Notes

    Returned SkyCoord frame retains only the frame attributes that are for the resulting frame type. (e.g. if the input frame is `ICRS`, an `equinox` value will be retained, but an `obstime` will not.)

    For a more complete set of transform offsets, use `WCS`. `skyoffset_frame()` can also be used to create a spherical frame with (lat=0, lon=0) at a reference point, approximating an xy cartesian system for small offsets. This method is distinct in that it is accurate on the sphere.

  classmethod from_name(name, frame='icrs', parse=False, cache=True)

    Given a name, query the CDS name resolver to attempt to retrieve coordinate information for that object. The search database, sesame url, and query timeout can be set through configuration items in `astropy.coordinates.name_resolve` – see docstring for `get_icrs_coordinates` for more information.

    Parameters:
      name `python:str`

        The name of the object to get coordinates for, e.g. `'M42'`.

      frame `python:str` or `BaseCoordinateFrame` class or instance

        The frame to transform the object to.

      parse bool

        Whether to attempt extracting the coordinates from the name by parsing with a regex. For objects catalog names that have J-coordinates embedded in their names, e.g., ‘CRTS SSS100805 J194428-420209’, this may be much faster than a Sesame query for the same object name. The coordinates extracted in this way may differ from the database coordinates by a few deci-arcseconds, so only use this option if you do not need sub-arcsecond accuracy for coordinates.

      cache bool, optional

        Determines whether to cache the results or not. To update or overwrite an existing value, pass `cache='update'`.

    Returns:
      coord `SkyCoord`

        Instance of the SkyCoord class.

  classmethod from_pixel(xp, yp, wcs, origin=0, mode='all')

    Create a new SkyCoord from pixel coordinates using a World Coordinate System.

    Parameters:
      xp, yp `python:float` or `ndarray`

        The coordinates to convert.

      wcs `WCS`

        The WCS to use for convert

      origin `python:int`

        Whether to return 0 or 1-based pixel coordinates.

      mode‘all’ or ‘wcs’

        Whether to do the transformation including distortions (`'all'`) or only including only the core WCS transformation (`'wcs'`).

    Returns:
      coord `SkyCoord`

        A new object with sky coordinates corresponding to the input `xp` and `yp`.

    See also

    `to_pixel`

      to do the inverse operation

    `astropy.wcs.utils.pixel_to_skycoord`

      the implementation of this method

  get_constellation(short_name=False, constellation_list='iau')

    Determines the constellation(s) of the coordinates this SkyCoord contains.

    Parameters:
      short_name bool

        If True, the returned names are the IAU-sanctioned abbreviated names. Otherwise, full names for the constellations are used.

      constellation_list `python:str`

        The set of constellations to use. Currently only `'iau'` is supported, meaning the 88 “modern” constellations endorsed by the IAU.

    Returns:
      constellation `python:str` or `python:str` `array`

        If this is a scalar coordinate, returns the name of the constellation. If it is an array `SkyCoord`, it returns an array of names.

    See also

    `astropy.coordinates.get_constellation`

    Notes

    To determine which constellation a point on the sky is in, this first precesses to B1875, and then uses the Delporte boundaries of the 88 modern constellations, as tabulated by Roman 1987.

  classmethod guess_from_table(table, **coord_kwargs)

    A convenience method to create and return a new SkyCoord from the data in an astropy Table.

    This method matches table columns that start with the case-insensitive names of the the components of the requested frames (including differentials), if they are also followed by a non-alphanumeric character. It will also match columns that end with the component name if a non-alphanumeric character is before it.

    For example, the first rule means columns with names like `'RA[J2000]'` or `'ra'` will be interpreted as `ra` attributes for `ICRS` frames, but `'RAJ2000'` or `'radius'` are not. Similarly, the second rule applied to the `Galactic` frame means that a column named `'gal_l'` will be used as the the `l` component, but `gall` or `'fill'` will not.

    The definition of alphanumeric here is based on Unicode’s definition of alphanumeric, except without `_` (which is normally considered alphanumeric). So for ASCII, this means the non-alphanumeric characters are `<space>_!"#$%&'()*+,-./\:;<=>?@[]^`{|}~`).

    Parameters:
      table `Table` or subclass

        The table to load data from.

      **coord_kwargs

        Any additional keyword arguments are passed directly to this class’s constructor.

    Returns:
      newsc `SkyCoord` or subclass

        The new instance.

    Raises:
      `ValueError`

        If more than one match is found in the table for a component, unless the additional matches are also valid frame component names. If a “coord_kwargs” is provided for a value also found in the table.

  insert(obj, values, axis=0)

    Insert coordinate values before the given indices in the object and return a new Frame object.

    The values to be inserted must conform to the rules for in-place setting of `SkyCoord` objects.

    The API signature matches the `np.insert` API, but is more limited. The specification of insert index `obj` must be a single integer, and the `axis` must be `0` for simple insertion before the index.

    Parameters:
      obj `python:int`

        Integer index before which `values` is inserted.

      values numpy:array_like

        Value(s) to insert. If the type of `values` is different from that of quantity, `values` is converted to the matching type.

      axis `python:int`, optional

        Axis along which to insert `values`. Default is 0, which is the only allowed value and will insert a row.

    Returns:
      out `SkyCoord` instance

        New coordinate object with inserted value(s)

  is_equivalent_frame(other)

    Checks if this object’s frame as the same as that of the `other` object.

    To be the same frame, two objects must be the same frame class and have the same frame attributes. For two `SkyCoord` objects, all of the frame attributes have to match, not just those relevant for the object’s frame.

    Parameters:
      other `SkyCoord` or `BaseCoordinateFrame`

        The other object to check.

    Returns:
      isequiv bool

        True if the frames are the same, False if not.

    Raises:
      `TypeError`

        If `other` isn’t a `SkyCoord` or a subclass of `BaseCoordinateFrame`.

  is_transformable_to(new_frame)

    Determines if this coordinate frame can be transformed to another given frame.

    Parameters:
      new_frame `frame` class, `frame` `object`, or `python:str`

        The proposed frame to transform into.

    Returns:
      transformable bool or `python:str`

        `True` if this can be transformed to `new_frame`, `False` if not, or the string ‘same’ if `new_frame` is the same system as this object but no transformation is defined.

    Notes

    A return value of ‘same’ means the transformation will work, but it will just give back a copy of this object. The intended usage is:

        if coord.is_transformable_to(some_unknown_frame):
            coord2 = coord.transform_to(some_unknown_frame)

    This will work even if `some_unknown_frame` turns out to be the same frame class as `coord`. This is intended for cases where the frame is the same regardless of the frame attributes (e.g. ICRS), but be aware that it might also indicate that someone forgot to define the transformation between two objects of the same frame class but with different attributes.

  match_to_catalog_3d(catalogcoord, nthneighbor=1)

    Finds the nearest 3-dimensional matches of this coordinate to a set of catalog coordinates.

    This finds the 3-dimensional closest neighbor, which is only different from the on-sky distance if `distance` is set in this object or the `catalogcoord` object.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      catalogcoord `SkyCoord` or `BaseCoordinateFrame`

        The base catalog in which to search for matches. Typically this will be a coordinate object that is an array (i.e., `catalogcoord.isscalar == False`)

      nthneighbor `python:int`, optional

        Which closest neighbor to search for. Typically `1` is desired here, as that is correct for matching one set of coordinates to another. The next likely use case is `2`, for matching a coordinate catalog against itself (`1` is inappropriate because each point will find itself as the closest match).

    Returns:
      idx `python:int` `array`

        Indices into `catalogcoord` to get the matched points for each of this object’s coordinates. Shape matches this object.

      sep2d `Angle`

        The on-sky separation between the closest match for each element in this object in `catalogcoord`. Shape matches this object.

      dist3d `Quantity` [:ref: ‘length’]

        The 3D distance between the closest match for each element in this object in `catalogcoord`. Shape matches this object.

    See also

    `astropy.coordinates.match_coordinates_3d`
    `SkyCoord.match_to_catalog_sky`

    Notes

    This method requires SciPy to be installed or it will fail.

  match_to_catalog_sky(catalogcoord, nthneighbor=1)

    Finds the nearest on-sky matches of this coordinate in a set of catalog coordinates.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      catalogcoord `SkyCoord` or `BaseCoordinateFrame`

        The base catalog in which to search for matches. Typically this will be a coordinate object that is an array (i.e., `catalogcoord.isscalar == False`)

      nthneighbor `python:int`, optional

        Which closest neighbor to search for. Typically `1` is desired here, as that is correct for matching one set of coordinates to another. The next likely use case is `2`, for matching a coordinate catalog against itself (`1` is inappropriate because each point will find itself as the closest match).

    Returns:
      idx `python:int` `array`

        Indices into `catalogcoord` to get the matched points for each of this object’s coordinates. Shape matches this object.

      sep2d `Angle`

        The on-sky separation between the closest match for each element in this object in `catalogcoord`. Shape matches this object.

      dist3d `Quantity` [:ref: ‘length’]

        The 3D distance between the closest match for each element in this object in `catalogcoord`. Shape matches this object. Unless both this and `catalogcoord` have associated distances, this quantity assumes that all sources are at a distance of 1 (dimensionless).

    See also

    `astropy.coordinates.match_coordinates_sky`
    `SkyCoord.match_to_catalog_3d`

    Notes

    This method requires SciPy to be installed or it will fail.

  position_angle(other)

    Computes the on-sky position angle (East of North) between this SkyCoord and another.

    Parameters:
      other `SkyCoord`

        The other coordinate to compute the position angle to. It is treated as the “head” of the vector of the position angle.

    Returns:
      pa `Angle`

        The (positive) position angle of the vector pointing from `self` to `other`. If either `self` or `other` contain arrays, this will be an array following the appropriate `numpy` broadcasting rules.

    Examples

        >>> c1 = SkyCoord(0*u.deg, 0*u.deg)
        >>> c2 = SkyCoord(1*u.deg, 0*u.deg)
        >>> c1.position_angle(c2).degree
        90.0
        >>> c3 = SkyCoord(1*u.deg, 1*u.deg)
        >>> c1.position_angle(c3).degree
        44.995636455344844

  radial_velocity_correction(kind='barycentric', obstime=None, location=None)

    Compute the correction required to convert a radial velocity at a given time and place on the Earth’s Surface to a barycentric or heliocentric velocity.

    Parameters:
      kind `python:str`

        The kind of velocity correction. Must be ‘barycentric’ or ‘heliocentric’.

      obstime `Time` or `python:None`, optional

        The time at which to compute the correction. If `None`, the `obstime` frame attribute on the `SkyCoord` will be used.

      location `EarthLocation` or `python:None`, optional

        The observer location at which to compute the correction. If `None`, the `location` frame attribute on the passed-in `obstime` will be used, and if that is None, the `location` frame attribute on the `SkyCoord` will be used.

    Returns:
      vcorr `Quantity` [:ref: ‘speed’]

        The correction with a positive sign. I.e., add this to an observed radial velocity to get the barycentric (or heliocentric) velocity. If m/s precision or better is needed, see the notes below.

    Raises:
      `ValueError`

        If either `obstime` or `location` are passed in (not `None`) when the frame attribute is already set on this `SkyCoord`.

      `TypeError`

        If `obstime` or `location` aren’t provided, either as arguments or as frame attributes.

    Notes

    The barycentric correction is calculated to higher precision than the heliocentric correction and includes additional physics (e.g time dilation). Use barycentric corrections if m/s precision is required.

    The algorithm here is sufficient to perform corrections at the mm/s level, but care is needed in application. The barycentric correction returned uses the optical approximation v = z * c. Strictly speaking, the barycentric correction is multiplicative and should be applied as:

        >>> from astropy.time import Time
        >>> from astropy.coordinates import SkyCoord, EarthLocation
        >>> from astropy.constants import c
        >>> t = Time(56370.5, format='mjd', scale='utc')
        >>> loc = EarthLocation('149d33m00.5s','-30d18m46.385s',236.87*u.m)
        >>> sc = SkyCoord(1*u.deg, 2*u.deg)
        >>> vcorr = sc.radial_velocity_correction(kind='barycentric', obstime=t, location=loc)
        >>> rv = rv + vcorr + rv * vcorr / c

    Also note that this method returns the correction velocity in the so-called optical convention:

        >>> vcorr = zb * c

    where `zb` is the barycentric correction redshift as defined in section 3 of Wright & Eastman (2014). The application formula given above follows from their equation (11) under assumption that the radial velocity `rv` has also been defined using the same optical convention. Note, this can be regarded as a matter of velocity definition and does not by itself imply any loss of accuracy, provided sufficient care has been taken during interpretation of the results. If you need the barycentric correction expressed as the full relativistic velocity (e.g., to provide it as the input to another software which performs the application), the following recipe can be used:

        >>> zb = vcorr / c
        >>> zb_plus_one_squared = (zb + 1) ** 2
        >>> vcorr_rel = c * (zb_plus_one_squared - 1) / (zb_plus_one_squared + 1)

    or alternatively using just equivalencies:

        >>> vcorr_rel = vcorr.to(u.Hz, u.doppler_optical(1*u.Hz)).to(vcorr.unit, u.doppler_relativistic(1*u.Hz))

    See also `doppler_optical`, `doppler_radio`, and `doppler_relativistic` for more information on the velocity conventions.

    The default is for this method to use the builtin ephemeris for computing the sun and earth location. Other ephemerides can be chosen by setting the `solar_system_ephemeris` variable, either directly or via `with` statement. For example, to use the JPL ephemeris, do:

        >>> from astropy.coordinates import solar_system_ephemeris
        >>> sc = SkyCoord(1*u.deg, 2*u.deg)
        >>> with solar_system_ephemeris.set('jpl'):
        ...     rv += sc.radial_velocity_correction(obstime=t, location=loc)

  search_around_3d(searcharoundcoords, distlimit)

    Searches for all coordinates in this object around a supplied set of points within a given 3D radius.

    This is intended for use on `SkyCoord` objects with coordinate arrays, rather than a scalar coordinate. For a scalar coordinate, it is better to use `separation_3d`.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      searcharoundcoords `SkyCoord` or `BaseCoordinateFrame`

        The coordinates to search around to try to find matching points in this `SkyCoord`. This should be an object with array coordinates, not a scalar coordinate object.

      distlimit `Quantity` [:ref: ‘length’]

        The physical radius to search within.

    Returns:
      idxsearcharound `python:int` `array`

        Indices into `searcharoundcoords` that match the corresponding elements of `idxself`. Shape matches `idxself`.

      idxself `python:int` `array`

        Indices into `self` that match the corresponding elements of `idxsearcharound`. Shape matches `idxsearcharound`.

      sep2d `Angle`

        The on-sky separation between the coordinates. Shape matches `idxsearcharound` and `idxself`.

      dist3d `Quantity` [:ref: ‘length’]

        The 3D distance between the coordinates. Shape matches `idxsearcharound` and `idxself`.

    See also

    `astropy.coordinates.search_around_3d`
    `SkyCoord.search_around_sky`

    Notes

    This method requires SciPy to be installed or it will fail.

    In the current implementation, the return values are always sorted in the same order as the `searcharoundcoords` (so `idxsearcharound` is in ascending order). This is considered an implementation detail, though, so it could change in a future release.

  search_around_sky(searcharoundcoords, seplimit)

    Searches for all coordinates in this object around a supplied set of points within a given on-sky separation.

    This is intended for use on `SkyCoord` objects with coordinate arrays, rather than a scalar coordinate. For a scalar coordinate, it is better to use `separation`.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      searcharoundcoords astropy:coordinate-like

        The coordinates to search around to try to find matching points in this `SkyCoord`. This should be an object with array coordinates, not a scalar coordinate object.

      seplimit `Quantity` [:ref: ‘angle’]

        The on-sky separation to search within.

    Returns:
      idxsearcharound `python:int` `array`

        Indices into `searcharoundcoords` that match the corresponding elements of `idxself`. Shape matches `idxself`.

      idxself `python:int` `array`

        Indices into `self` that match the corresponding elements of `idxsearcharound`. Shape matches `idxsearcharound`.

      sep2d `Angle`

        The on-sky separation between the coordinates. Shape matches `idxsearcharound` and `idxself`.

      dist3d `Quantity` [:ref: ‘length’]

        The 3D distance between the coordinates. Shape matches `idxsearcharound` and `idxself`.

    See also

    `astropy.coordinates.search_around_sky`
    `SkyCoord.search_around_3d`

    Notes

    This method requires SciPy to be installed or it will fail.

    In the current implementation, the return values are always sorted in the same order as the `searcharoundcoords` (so `idxsearcharound` is in ascending order). This is considered an implementation detail, though, so it could change in a future release.

  separation(other)

    Computes on-sky separation between this coordinate and another.

    Note

    If the `other` coordinate object is in a different frame, it is first transformed to the frame of this object. This can lead to unintuitive behavior if not accounted for. Particularly of note is that `self.separation(other)` and `other.separation(self)` may not give the same answer in this case.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      other `SkyCoord` or `BaseCoordinateFrame`

        The coordinate to get the separation to.

    Returns:
      sep `Angle`

        The on-sky separation between this and the `other` coordinate.

    Notes

    The separation is calculated using the Vincenty formula, which is stable at all locations, including poles and antipodes [1].

    [1]

    https://en.wikipedia.org/wiki/Great-circle_distance

  separation_3d(other)

    Computes three dimensional separation between this coordinate and another.

    For more on how to use this (and related) functionality, see the examples in Separations, Offsets, Catalog Matching, and Related Functionality.

    Parameters:
      other `SkyCoord` or `BaseCoordinateFrame`

        The coordinate to get the separation to.

    Returns:
      sep `Distance`

        The real-space distance between these two coordinates.

    Raises:
      `ValueError`

        If this or the other coordinate do not have distances.

  skyoffset_frame(rotation=None)

    Returns the sky offset frame with this SkyCoord at the origin.

    Parameters:
      rotation astropy:angle-like

        The final rotation of the frame about the `origin`. The sign of the rotation is the left-hand rule. That is, an object at a particular position angle in the un-rotated system will be sent to the positive latitude (z) direction in the final frame.

    Returns:
      astrframe `SkyOffsetFrame`

        A sky offset frame of the same type as this `SkyCoord` (e.g., if this object has an ICRS coordinate, the resulting frame is SkyOffsetICRS, with the origin set to this object)

  spherical_offsets_by(d_lon, d_lat)

    Computes the coordinate that is a specified pair of angular offsets away from this coordinate.

    Parameters:
      d_lon astropy:angle-like

        The angular offset in the longitude direction. The definition of “longitude” depends on this coordinate’s frame (e.g., RA for equatorial coordinates).

      d_lat astropy:angle-like

        The angular offset in the latitude direction. The definition of “latitude” depends on this coordinate’s frame (e.g., Dec for equatorial coordinates).

    Returns:
      newcoord `SkyCoord`

        The coordinates for the location that corresponds to offsetting by `d_lat` in the latitude direction and `d_lon` in the longitude direction.

    See also

    `spherical_offsets_to`

      compute the angular offsets to another coordinate

    `directional_offset_by`

      offset a coordinate by an angle in a direction

    Notes

    This internally uses `SkyOffsetFrame` to do the transformation. For a more complete set of transform offsets, use `SkyOffsetFrame` or `WCS` manually. This specific method can be reproduced by doing `SkyCoord(SkyOffsetFrame(d_lon, d_lat, origin=self.frame).transform_to(self))`.

  spherical_offsets_to(tocoord)

    Computes angular offsets to go from this coordinate to another.

    Parameters:
      tocoord `BaseCoordinateFrame`

        The coordinate to find the offset to.

    Returns:
      lon_offset `Angle`

        The angular offset in the longitude direction. The definition of “longitude” depends on this coordinate’s frame (e.g., RA for equatorial coordinates).

      lat_offset `Angle`

        The angular offset in the latitude direction. The definition of “latitude” depends on this coordinate’s frame (e.g., Dec for equatorial coordinates).

    Raises:
      `ValueError`

        If the `tocoord` is not in the same frame as this one. This is different from the behavior of the `separation`/`separation_3d` methods because the offset components depend critically on the specific choice of frame.

    See also

    `separation`

      for the total angular offset (not broken out into components).

    `position_angle`

      for the direction of the offset.

    Notes

    This uses the sky offset frame machinery, and hence will produce a new sky offset frame if one does not already exist for this object’s frame class.

  to_pixel(wcs, origin=0, mode='all')

    Convert this coordinate to pixel coordinates using a `WCS` object.

    Parameters:
      wcs `WCS`

        The WCS to use for convert

      origin `python:int`

        Whether to return 0 or 1-based pixel coordinates.

      mode‘all’ or ‘wcs’

        Whether to do the transformation including distortions (`'all'`) or only including only the core WCS transformation (`'wcs'`).

    Returns:
      xp, yp `numpy.ndarray`

        The pixel coordinates

    See also

    `astropy.wcs.utils.skycoord_to_pixel`

      the implementation of this method

  to_string(style='decimal', **kwargs)

    A string representation of the coordinates.

    The default styles definitions are:

        'decimal': 'lat': {'decimal': True, 'unit': "deg"}
                   'lon': {'decimal': True, 'unit': "deg"}
        'dms': 'lat': {'unit': "deg"}
               'lon': {'unit': "deg"}
        'hmsdms': 'lat': {'alwayssign': True, 'pad': True, 'unit': "deg"}
                  'lon': {'pad': True, 'unit': "hour"}

    See `to_string()` for details and keyword arguments (the two angles forming the coordinates are are both `Angle` instances). Keyword arguments have precedence over the style defaults and are passed to `to_string()`.

    Parameters:
      style{‘hmsdms’, ‘dms’, ‘decimal’}

        The formatting specification to use. These encode the three most common ways to represent coordinates. The default is `decimal`.

      **kwargs

        Keyword args passed to `to_string()`.

  to_table()

    Convert this `SkyCoord` to a `QTable`.

    Any attributes that have the same length as the `SkyCoord` will be converted to columns of the `QTable`. All other attributes will be recorded as metadata.

    Returns:
      `QTable`

        A `QTable` containing the data of this `SkyCoord`.

    Examples

        >>> sc = SkyCoord(ra=[40, 70]*u.deg, dec=[0, -20]*u.deg,
        ...               obstime=Time([2000, 2010], format='jyear'))
        >>> t =  sc.to_table()
        >>> t
        <QTable length=2>
           ra     dec   obstime
          deg     deg
        float64 float64   Time
        ------- ------- -------
           40.0     0.0  2000.0
           70.0   -20.0  2010.0
        >>> t.meta
        {'representation_type': 'spherical', 'frame': 'icrs'}

  transform_to(frame, merge_attributes=True)

    Transform this coordinate to a new frame.

    The precise frame transformed to depends on `merge_attributes`. If `False`, the destination frame is used exactly as passed in. But this is often not quite what one wants. E.g., suppose one wants to transform an ICRS coordinate that has an obstime attribute to FK4; in this case, one likely would want to use this information. Thus, the default for `merge_attributes` is `True`, in which the precedence is as follows: (1) explicitly set (i.e., non-default) values in the destination frame; (2) explicitly set values in the source; (3) default value in the destination frame.

    Note that in either case, any explicitly set attributes on the source `SkyCoord` that are not part of the destination frame’s definition are kept (stored on the resulting `SkyCoord`), and thus one can round-trip (e.g., from FK4 to ICRS to FK4 without losing obstime).

    Parameters:
      frame `python:str`, `BaseCoordinateFrame` class or instance, or `SkyCoord` instance

        The frame to transform this coordinate into. If a `SkyCoord`, the underlying frame is extracted, and all other information ignored.

      merge_attributes bool, optional

        Whether the default attributes in the destination frame are allowed to be overridden by explicitly set attributes in the source (see note above; default: `True`).

    Returns:
      coord `SkyCoord`

        A new object with this coordinate represented in the `frame` frame.

    Raises:
      `ValueError`

        If there is no possible transformation route.