45 million years ago, one star of a close pair exploded in a galaxy called NGC 3972, seen from Earth in the bowl of the big dipper. The light from the explosion just arrived in April. Although too faint to be seen in binoculars, you can follow the luminosity in photographs and charts in this pdf. 

The red, green, and blue dots in the graph represent the respective luminosities in red, green, and blue light. Note how the overall color of the expanding fireball has become increasingly more red, as it expands and cools. 

SN2011by.pdf   (Posted 2011-06-10)