The Gemini facility Calibration unit (GCal)
03 May 2011



The Gemini Facility Calibration Unit (GCal)




GCAL is the calibration unit for each of the Gemini telescopes. Calibration is an unglamorous but vital aspect of observational astronomy. Without good calibration observational data is almost useless as it is impossible to extract accurate numerical values to test theory.

The Gemini calibration units fulfil two vital functions. They can provide very evenly illuminated but otherwise featureless images so that the response of all the different parts of the detectors within each instrument can be determined (Flat Fielding). Using arc lamps it can introduce very well defined spectral lines into the instruments for accurate wavelength calibration of spectrometers.

Though this calibration unit is certainly the least complicated of any of the Gemini facility instruments, it is expected to have the longest lifetime because of the flexible nature of its design, which can accommodate many different types of calibrators in the future. It will play a key role in essentially all data recorded with the Gemini telescopes.

GCAL N was commissioned and accepted in autumn 2000 and GCAL S in summer 2001. Further technical information about GCAL is available on the Gemini website (link opens in a new window).