Astropy Astronomy Library

Astropy is a community-developed core Python package for astronomy and astrophysics, providing essential tools for celestial coordinate calculations, time conversion, FITS file handling, cosmological computations, and data analysis. Initiated in 2011 by the Astropy Project coordination committee, with over 4,000 stars as of 2026 and contributions from hundreds of astronomers worldwide, Astropy serves as the foundation for most Python-based astronomy research. Key features include: units and quantities (physical units with automatic dimensional analysis, unit conversion, and equivalencies for spectral, temperature, and angular conversions), sky coordinates (coordinate systems including ICRS, FK5, FK4, Galactic, AltAz, and Heliocentric with proper motion, parallax, and radial velocity handling), time (precise time representation with UTC, TAI, TDB, and TT scales, leap second handling, and Besselian and Julian epoch conversions), FITS I/O (FITS file reading and writing with header manipulation, image and table data access, and memory-mapped file support), WCS (World Coordinate System transformations between pixel and sky coordinates for astronomical images), tables (flexible tabular data structure with heterogeneous column types, unit handling, masking, and joining), modeling (model fitting framework with over 50 built-in models including polynomials, Gaussian, Lorentzian, and custom compound models), cosmology (cosmological distance calculations for LambdaCDM, wCDM models with luminosity distance, angular diameter distance, and lookback time), and visualization (astronomy-specific plotting with WCS axes, image normalization, and physical quantity plotting).