Atmospheric extinction

Atmospheric extinction is the reduction of astronomical light as it travels through Earth's atmosphere, chiefly through absorption and scattering. It dims celestial objects and can alter their measured colors.

Beer–Lambert law: A law relating light attenuation in a material to its absorption coefficient and the distance traveled. It describes the exponential loss of direct starlight along an atmospheric path.
Airmass correction: An observational correction that accounts for atmospheric attenuation along a line of sight. It adjusts brightness measurements for the longer atmospheric path away from the zenith.
Apparent magnitude: A logarithmic measure of how bright an astronomical object appears from Earth. Extinction makes an object's apparent magnitude numerically larger.
Interstellar extinction: The dimming and reddening of starlight by dust and gas between stars. It resembles atmospheric extinction observationally but occurs beyond Earth's atmosphere.
Rayleigh scattering: The scattering of light by particles much smaller than its wavelength, with stronger scattering at shorter wavelengths. Air molecules scatter blue light more strongly, contributing to wavelength-dependent extinction.
Photometric calibration: The process of converting astronomical detector measurements into standardized brightness measurements. Extinction corrections connect observed instrumental magnitudes to calibrated magnitudes.
Optical depth: A dimensionless measure of attenuation along a path through absorbing or scattering material. It provides a direct measure of the atmosphere's total light-blocking effect.
Atmospheric seeing: The blurring of astronomical images caused by turbulence in Earth's atmosphere. Seeing distorts image sharpness, whereas extinction reduces received flux.
Mie scattering: The scattering of light by particles comparable to or larger than its wavelength. Aerosols and dust produce this scattering, often adding nearly wavelength-independent dimming.
Standard star: A star with established photometric properties used to calibrate astronomical observations. Observations of standard stars help determine extinction during a night.

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