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(instrument measuring brightness)

A photometer is an instrument measuring brightness, used in observing stars, etc., i.e., determining their magnitude.

A CCD is essentially a grid of photometers, and a photometer in modern astronomy may be a CCD, aiming to catch all the photons from a star. The apparent brightness of a star is found by adding the count of all the photons received in the Airy disk of the star in question.

(EMR,visible light,instrument type)

Referenced by:
Large Altazimuth Telescope (BTA-6)
Hubble Space Telescope (HST)
Mercator Telescope
Spitzer Space Telescope (SST)
2dF Galaxy Redshift Survey (2dFGRS)