Transcript: Apparent magnitude or apparent brightness must be specified at a particular wavelength. Stars have different colors or different energy distributions, so the apparent brightness depends on the wavelength of observation. Traditionally, astronomy is done by eye, and the detector was the visual detector which is the wavelength sensitivity of the human eye peaking somewhere in the green part of the visual spectrum. This is called visual apparent brightness or visual magnitude. Professional astronomers have, however, more carefully defined the wavelength scales that they use when measuring astronomical objects. They’ve used filters to isolate relatively small ranges of wavelengths, and they define magnitudes or apparent brightness in terms of those narrow wavelength ranges.