n. (Astron.) The determination of the brightness of stars, and also of the sun, moon, and planets. -- As`tro*pho`to*met"ric*al a. [Webster 1913 Suppl.]
n. 1. The art of comparing, photometrically, the brightness of two spectra, wave length by wave length; the use of the spectrophotometer. [ Webster 1913 Suppl. ]
2. (Chem., Physics) the art or process of measuring the degree of absorption of light at different wavelengths by a chemical substance, by means of a spectrometer or spectrophotometer. It is a technique for chemical analysis. [ PJC ]
-- Spec`tro*pho`to*met"ric a. [Webster 1913 Suppl.]