Discovered in 1908 by L. Ceraski of Moscow, the variable SU Ursae Majoris is located
near the tip of the nose of the Great Bear constellation of Ursa Major, about 3 degrees
northwest of the bright star omicron Ursae Majoris. SU UMa belongs to the dwarf nova
class of cataclysmic variable stars (CVs), being similar to U Geminorum, SS Cygni,
and Z Camelopardalis subtypes in terms of the physical system. Variables of this sort
are composed of a compact binary pair with a solar-type secondary star, a white dwarf
primary star, and an accretion disk around the primary component. The observed
outbursts are believed to be the result of interactions within the disk that circles the
white dwarf. However, in addition to exhibiting normal dwarf nova outbursts
(which consist of a rise from quiescence of 2-6 magnitudes and 1-3 day durations)
SU UMa also displays bouts of superoutbursts.

Superoutbursts occur less frequently than normal outbursts (may occur every 3-10 cycles),
last for 10-18 days, and may rise in brightness by at least an additional magnitude. Thus,
as the name implies, superoutbursts are longer in duration and brighter in magnitude than
the normal outburst. The rise to superoutburst cannot be distinguished from the rise to a
normal outburst and while in superoutburst, a small periodic fluctuation of several tenths
of a magnitude known as a superhump is observed at maximum. The unique aspect of
superhumps is that the period of fluctuation is 2-3% longer than the orbital period of the system.
Therefore, by observing the superhumps, one can obtain the orbital period of the system.
SU UMa-type stars have been found (in almost all cases) to have orbital periods of less than 2 hours!

SU UMa is the prototype for variables belonging to this subtype of dwarf novae.