Which star catalog was compiled to support Hubble's guide-star targeting?

The Guide Star Catalog was compiled to support Hubble’s guide-star targeting. Hubble’s Fine Guidance Sensors lock onto selected stars so the telescope can maintain extremely accurate pointing while its scientific instruments observe a target.

The catalog was created specifically for the operational needs of the Space Telescope. It supplied positions and brightness information for potential guide stars across the sky, allowing flight planners to identify suitable stars near each observation target before commands were sent to Hubble.

The first Guide Star Catalog was completed in 1989, shortly before Hubble launched. Its original catalog contained nearly 19 million objects brighter than approximately 16th magnitude, including more than 15 million objects classified as stars. Later versions improved the astrometry and expanded the available data.

Gaia, Tycho, and Hipparcos are important astronomical catalogs, but they were not the canonical answer to this Hubble-specific question. The catalog’s full name is often written Space Telescope Guide Star Catalog, while “Guide Star Catalog” is the standard short form.