Photometry

Photometry is the measurement of light received from astronomical sources, usually expressed as flux or magnitude. It quantifies brightness across specified wavelength bands.

Astronomical magnitude: A logarithmic scale for expressing the brightness of astronomical objects. Photometric measurements are commonly reported as magnitudes rather than linear fluxes.
Variable star: A star whose observed brightness changes over time. Repeated photometric measurements reveal its brightness cycle and variability.
Radiant flux: The rate at which electromagnetic energy is emitted, transmitted, or received. Astronomical flux measures the energy arriving from a source per area and time.
Spectrophotometry: The measurement of light intensity as a function of wavelength. Unlike band-limited photometry, it resolves how flux varies across a spectrum.
Photometric filter: An optical filter that selects a wavelength range for measuring astronomical light. A filter defines which part of a source’s spectrum a photometric measurement samples.
Transit photometry: A method for detecting an orbiting body by measuring the periodic dimming it causes when crossing a star. Small dips in stellar flux can reveal transiting exoplanets.
Apparent magnitude: A logarithmic measure of how bright an astronomical object appears from Earth. It expresses observed brightness while depending on distance and intervening effects.
Astrometry: The measurement of celestial positions and motions. It measures where sources are, while photometry measures how bright they appear.
Charge-coupled device: A light-sensitive semiconductor detector that converts incident photons into electrical charge. CCD images provide pixel values from which stellar fluxes are extracted.
Light curve: A graph of an object's measured brightness over time. It is the standard way to inspect photometric variability and transits.

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