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About FGS

Enabling Precision Astrometry

The Fine Guidance Sensors, in addition to being an integral part of the HST Pointing Control System (PCS), provide HST observers with the capability of precision astrometry and milliarcsecond resolution over a wide range of magnitudes (3 < V < 16.8). Its two observing modes — Position Mode and Transfer Mode — have been used to determine the parallax and proper motion of astrometric targets to a precision of 0.2 mas, and to detect duplicity or structure around targets as close as 8 mas (visual orbits can be determined for binaries as close as 12 mas).

Current FGS Status

FGS is operating nominally.

Program Information

FGS Instrument Resources


HST Help Desk 

Please contact the HST Help Desk with any questions.