The photometric system called UBV (from Ultraviolet, Blue, Visual), also called the Johnson system (or Johnson-Morgan system), is a wide central band of the electromagnetic spectrum, and usually employed for classifying stars according to their colors. It has been the first known standardized photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are measured for a star; two subtractions are then performed in a specific order to classify it in the more technical, formulaic values given by this system. It thereby can focus on the less apparent, when unmodified for viewing, first two groups of these wavelengths to the human eye. This in turn provides maximal contrast with other readings (values) of apparent (or when adjusted for distance) absolu