The accurate determination of the magnitudes of stars, or other astronomical objects, within specified wavelength bands. Photometric measurements can be used to deduce broad physical characteristics of stars, without the need for detailed study of their spectra. Several photometric systems are used for this purpose, most commonly UBV photometry and uvby photometry. Photometric measurements are also important for determining the light curves of variable stars. Photometry is carried out using photoelectric measurements; it is very difficult to determine magnitudes accurately from photographs or visually. Photoelectric measurements also allow monitoring of light intensity changes over very short timescales.