Guide Star Catalog II: All-Sky Optical Catalog for Telescope Operations

The Guide Star Catalog II (GSC-II) is an all-sky optical catalog based on 1" resolution scans of photographic Sky Survey plates from the Palomar and UK Schmidt telescopes. It contains positions, proper motions, classifications, and magnitudes for nearly a billion objects down to approximately Jpg=21, Fpg=20. The catalog is maintained by the National Aeronautics and Space Administration and is used for Hubble Space Telescope operations and will support the James Webb Space Telescope.

Use Cases

• Calibrate telescope pointing systems based on precise celestial object positions.
• Implement bright object protection for space telescopes based on object classifications and magnitudes.
• Support astronomical research and observation planning based on an all-sky catalog of nearly a billion objects.
• Develop future guide star catalogs for next-generation telescopes like JWST based on the GSC-II foundation.

Strengths

• All-sky coverage from scans of photographic plates at two epochs and three bandpasses.
• Contains data for nearly a billion celestial objects down to specific magnitude limits.
• Used operationally for Hubble Space Telescope pointing and bright object protection.
• Constructed in collaboration with major ground-based observatories (GEMINI, VLT, GALILEO).

Limitations

• Column-level documentation is absent; field semantics must be inferred after download.
• Row count is unknown, which may limit suitability assessment.
• Data is stored in a BIN format, which may require specialized tools for access.

Provenance

Source

National Aeronautics and Space Administration

Collection Method

Constructed from 1" resolution scans of photographic Sky Survey plates from Palomar and UK Schmidt telescopes.

Time Range

Based on plates from two epochs, but specific dates are not provided.

Freshness

Last updated 2026-03-13 18:09:24.494527; freshness should be verified.

Geography

All-sky (global celestial sphere).