astropy

Astropy - Astronomy & Astrophysics

Astropy is more than a library; it's a community standard. It ensures that astronomical calculations are reproducible and physically consistent by linking numerical arrays with physical units and celestial reference frames.

When to Use

• Handling physical units and constants in calculations.
• Working with celestial coordinates (Right Ascension, Declination) and frame transformations.
• Reading/writing FITS (Flexible Image Transport System), ASDF, and VO (Virtual Observatory) files.
• Managing astronomical time scales (UTC, TAI, TDB, Julian Dates).
• World Coordinate System (WCS) mapping (pixels to sky coordinates).
• Cosmological calculations (distances, ages, Hubble parameters).
• Tabular data with attached units and metadata (astropy.table).

Reference Documentation

Official docs: https://docs.astropy.org/
Learn Astropy: https://learn.astropy.org/
Search patterns: astropy.units.Quantity, astropy.coordinates.SkyCoord, astropy.io.fits, astropy.time.Time

Core Principles

Units and Quantities

Everything in Astropy should be a Quantity — a number or array paired with a Unit. This prevents errors like adding meters to feet.

Celestial Coordinates

Coordinates are represented by SkyCoord objects, which handle the complex math of spherical trigonometry and frame precession automatically.

Tables with Units

While Pandas is great for dataframes, astropy.table.QTable is superior for physics because it preserves units during operations.

Quick Reference

Installation

pip install astropy

Standard Imports

import numpy as np
from astropy import units as u
from astropy import constants as const
from astropy.coordinates import SkyCoord
from astropy.time import Time
from astropy.table import QTable
from astropy.io import fits
from astropy.wcs import WCS

Basic Pattern - Physical Calculation

# Calculate Schwarzschild radius of the Sun
mass_sun = 1.0 * u.M_sun
rs = (2 * const.G * mass_sun) / (const.c**2)

print(f"Radius: {rs.to(u.km):.2f}")
# Output: Radius: 2.95 km