Deep Field

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Deep Field
29 September 2026 2518 stories tracked

Glossary · Telescopes & Instruments

Astrometry

Measuring exactly where things are, and how that position changes.

Positions sound less interesting than spectra until you notice that distance, motion and mass all come out of them. Parallax — the tiny shift in a star's position as Earth moves round its orbit — is the only direct distance measurement in astronomy and the foundation everything else is calibrated against. Gaia measured nearly two billion of them to microarcsecond precision, which is the angle a coin subtends on the Moon, and rebuilt the map of the galaxy in the process.

Related terms

Lagrange point Five places where two bodies' gravity lets a third sit still relative to both. Adaptive optics Bending a mirror hundreds of times a second to cancel out the atmosphere. Interferometry Combining separate telescopes so they resolve detail like one enormous dish. First light The night a new telescope is pointed at the sky and actually works.

Questions

What is Astrometry?

Measuring exactly where things are, and how that position changes.

Why does it matter?

Parallax — the tiny shift in a star's position as Earth moves round its orbit — is the only direct distance measurement in astronomy and the foundation everything else is calibrated against. Gaia measured nearly two billion of them to microarcsecond precision, which is the angle a coin subtends on the Moon, and rebuilt the map of the galaxy in the process.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.