Editing Cosmic Background Explorer (section)

==== Far Infrared Absolute Spectrophotometer (FIRAS) ====
The Far Infrared Absolute Spectrophotometer (FIRAS) is a cryogenically cooled polarizing [[Michelson interferometer]] used as a [[Fourier transform]] spectrometer. The instrument points along the spin axis and has a 7° field of view. This device measures the spectrum to a precision of 1/1000 of the peak flux at {{cvt|1.7|mm}} for each 7° field of view on the sky (over the range 0.1 to {{cvt|10|mm}}). The FIRAS uses a special flared trumpet horn flux collector having very low sidelobe levels and an external calibrator covering the entire beam; precise temperature regulation and calibration are required. The instrument has a differential input to compare the sky with an internal reference at 3 K. This feature provides immunity from systematic errors in the spectrometer and contributes significantly to the ability to detect small deviations from a blackbody spectrum. The instrument weighs {{cvt|60|kg}}, uses 84 watts and has a data rate of 1200 bit/s.<ref name="Experiment1">{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1989-089A-01 |title=Experiment: Far Infrared Absolute Spectrophotometer (FIRAS) |publisher=NASA |date=28 October 2021 |access-date=27 November 2021}} {{PD-notice}}</ref>