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photometry
In optics: 1) the measurement of the intensity, distribution, color, absorption factor, and spectral distribution of visible light, and occasionally of near-ultraviolet and near-infrared light; 2) the science of making such measurements. In astronomy: the use of photometric instruments and techniques to make a precise measurement of the amount of electromagnetic energy that is received from a celestial object.
It can be applied, for example, to the detection and characterization of extrasolar planets, since planets in transit cause tiny periodic variations in the apparent light output of their host stars. From the period and depth of the transits, the orbit and size of the planetary companions can be calculated: the smaller the planet, the smaller the photometric effect. Transits by Earth-class planets, for example, are expected to produce only a tiny drop in stellar brightness of between 0.005 and 0.04 percent, and lasting for 4 to 16 hours. See also Kepler mission.
Related category
• OPTICS AND OPTICAL PHENOMENA
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