  Planck's law describes the radiation of black bodies. The study of its
properties is of special interest, as black bodies are a good description for
the behavior of many phenomena. In this work a new mathematical study of
Planck's law is performed and new properties of this old acquaintance are
obtained. As a result, the exact form for the locus in a color-color diagrams
has been deduced, and an analytical formula to determine with precision the
black body temperature of an object from any pair of measurements has been
developed. Thus, using two images of the same field obtained with different
filters, one can compute a fast estimation of black body temperatures for every
pixel in the image, that is, a new image of the black body temperatures for all
the objects in the field. Once these temperatures are obtained, the method
allows, as a consequence, a quick estimation of their emission in other
frequencies, assuming a black body behavior. These results provide new tools
for data analysis.
