The astronomical 'B' and 'V' filters pass electromagnetic radiation with wavelengths centered at 4400 Angstroms ( B) and 5500 Angstroms (V). These 'Standard 3-color' filters have carefully standardized widths of 980 and 890 Angstroms respectively. Astronomers use them to separate the shorter wavelength 'blue' light from the 'visual' light near the center of the optical spectrum. This helps us measure interstellar extinction by dust grains, and estimate from the 'blue-visual' brightness difference the temperature of the star. These filters can also be used to enhance the contrast of various photographic features on planets and in various astronomical objects where the 'blue' light traces young massive stars, and 'visual' light traces older stellar populations.