Methods
The methods used to perform photometry depend on the wavelength regime under study. At its most basic, photometry is conducted by gathering radiation in a telescope, perhaps passing it through specialized optical filters, and then capturing and recording the light energy with a photosensitive instrument. The set of passbands (filters) is called a photometric system.
Historically, photometry in the near infrared through long-wavelength ultra-violet was done with a photoelectric photometer, an instrument that measured the light intensity of a single object by directing its light on to a photosensitive cell. They have largely been replaced with CCD cameras which can simultaneously image multiple objects, though photoelectric photometers are still used in special situations, such as where high time resolution is required.
Read more about this topic: Photometry (astronomy)
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