Process astronomical data with Python coordinate transforms

Astropy supports Python astronomy analysis through physical units, celestial coordinates, FITS files, cosmological models, time scales, tables, and image coordinate systems. This skill maps common research tasks to the corresponding modules and highlights assumptions that affect scientific interpretation and reproducibility.

Units and quantities support conversions, dimensional arithmetic, spectral or Doppler equivalencies, parallax, and logarithmic units. SkyCoord represents positions in frames such as ICRS, Galactic, FK5, and AltAz, with transformations, angular separations, distance, proper motion, radial velocity, and catalog matching. Cosmology tools provide standard or custom models for luminosity, comoving and angular-diameter distance, age, lookback time, Hubble parameters, density, volumes, and inverse distance-to-redshift calculations.

Use for celestial-coordinate conversion, unit-bearing calculations, FITS image or table analysis, catalog operations, cosmological calculations, precise timestamps, and pixel-to-world transformations. Choose the cosmology and coordinate frame appropriate to the analysis, and specify time scales rather than relying on ambiguity.

Nearest-neighbor cross-matches do not confirm physical identity and may be many-to-one. Review epochs, proper motion, uncertainty, units, and the matching policy. Do not attach degrees a second time to columns that already carry units. Validate WCS information before applying its transformations.

Inputs can be quantities, celestial positions, observing time and location, redshifts, image headers, or catalogs. Outputs include transformed coordinates, converted units, cosmological distances or times, manipulated tables, and image-to-sky mappings. A supplied unit-conversion excerpt is:

import astropy.units as u
from astropy.coordinates import SkyCoord
from astropy.time import Time
from astropy.io import fits
from astropy.table import Table
from astropy.cosmology import Planck18

# Units and quantities
distance = 100 * u.pc
distance_km = distance.to(u.km)

FITS operations access named or indexed HDUs, headers, NumPy image arrays, binary or ASCII tables, and multi-extension files. Context managers close files reliably; memory mapping supports large inputs. Table operations cover format I/O, filtering, sorting, joins, grouping, stacking, and missing-value masks. QTable retains unit-aware columns.

Time supports ISO, JD, MJD, Unix, and scales such as UTC, TAI, TT, and TDB, plus TimeDelta arithmetic, sidereal time, and light-travel corrections. WCS reads transformations from FITS headers and exposes footprints, reference pixels, projections, and scales.

Additional modules include NDData and CCDData containers for uncertainty, masks, metadata, and WCS; model fitting; astronomical visualization; physical constants; convolution kernels; and robust statistics such as sigma clipping. Prefer array operations for many coordinates or times and cache expensive repeated calculations where appropriate.

AltAz and precise-time transformations may download IERS Earth-orientation updates. Offline reproducibility needs auto_download=False with a reviewed local table and recorded coverage and accuracy limits. Named-object lookups and remote FITS access are network operations requiring task-appropriate authorization.

The seven referenced local files are short pointers or placeholders, not comprehensive procedures. Use the official Astropy documentation when detailed module guidance is needed rather than claiming it is bundled.