astropycoordinates

Astropy coordinates is a subpackage of the Astropy project that provides tools for representing and transforming astronomical coordinates. It supports a wide range of celestial and local reference frames and a flexible transformation framework, enabling consistent handling of positions, motions, and distances.

Representations and frames: The package defines multiple coordinate representations, such as spherical and Cartesian forms, which can optionally include a distance. It provides a diverse set of reference frames, including ICRS, FK5, FK4, Galactic, Ecliptic, AltAz, and ITRS, among others. The high-level SkyCoord class combines a coordinate with its frame and can store associated quantities like distance, proper motion, and radial velocity, facilitating convenient manipulation and transformation.

Transformations: Coordinates can be transformed between frames with a single call to transform_to or by switching to a target frame. Transformations are implemented through a graph that accounts for relevant astrometric effects, such as precession, nutation, aberration, and light deflection. Time (Time) and observer information (EarthLocation) influence transforms, particularly for observer-centric frames like AltAz.

Usage and integration: The module integrates with NumPy arrays, astropy.units, and astropy.time, enabling vectorized operations on coordinate data. Users can create SkyCoord objects from various input formats, convert between frames, and access components such as right ascension, declination, Galactic longitude and latitude, distance, proper motions, and radial velocity. The interface is designed for consistency and ease of use across coordinate types.

Applications and ecosystem: Astropy coordinates is widely used for catalog cross-matching, plotting, orbit calculations, and observational planning within the Astropy ecosystem. It benefits from comprehensive documentation, tests, and ongoing development as part of the broader Astropy project.