U Gem - The Classic Dwarf Nova

This cataclysmic variable is the prototype of the class of dwarf novae having occasional flare-ups in brightness of several magnitudes. it is also an eclipsing system, where the red main sequence star, a little dimmer than the sun, orbits about the white dwarf and its attendant disk of gaseous matter. The eclipse is evident in the light curves of the star. It is a CBA target star so that the eclipses can be used to analyze the changes in the shape of the disk during the period of time between oputbursts.
The comparison star (labeled "123") is indicated as such on the AAVSO chart, meaning it is magnitude 12.3. The other AAVSO magnitudes are shown for the 13.3 magnitude star (which was used as the comparison star for the first part of the first night's data) and the 14.5 magnitude check star.

This light curve was collected on December 3, 1999 (UT).