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astrometry-basics

Precision position measurement — proper motions, parallaxes, reference frames, and working with Gaia data.

skills/astrometry-basics/SKILL.md

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## Overview

Astrometry measures where things are and how they move: positions,
proper motions, and parallaxes. The Gaia mission revolutionized the
field with microarcsecond precision for billions of stars. This skill
covers the astrometric observables, reference frames (ICRS), working
with Gaia catalog data correctly, and deriving distances and kinematics.

## When to use

- Querying Gaia for parallaxes, proper motions, and photometry of a sample
- Converting parallax to distance (correctly — it's not 1/π for noisy data)
- Computing space velocities (U, V, W) and Galactic orbits
- Cross-matching catalogs with proper-motion propagation to a common epoch