thirdbrightest

Thirdbrightest is a term used in astronomy and data analysis to denote the object that ranks third in brightness within a specified sample, field, or catalog. Brightness is usually expressed as apparent magnitude, a logarithmic scale where smaller numbers indicate brighter objects. The third-brightest object is the one with the third-lowest magnitude in the chosen dataset, and the label is dependent on the chosen wavelength band and observational conditions.

In practice, thirdbrightest is not a fixed celestial object; its identity can vary with the wavelength (for example optical vs infrared), time (for variable stars), distance and extinction, and the subset of objects considered. Catalogs and star charts may label the third-brightest star in a constellation, a field, or a survey strip, assisting observers in orientation or analysis.

Ranking considerations: Magnitude scales, photometric errors, and selection criteria influence ordering; variable stars can move in ranking; extinction by interstellar dust can dim objects differently; deep surveys may reveal faint third-brightest objects not visible in shallower catalogs.

See also: Brightest star, Apparent magnitude, Absolute magnitude, Photometry, Variable star, Astronomical catalogs.