{{astrobox begin2}} {{star listings}} {{astrobox end}} '''U Geminorum''', in the Constellation Gemini, is an archetypal example of a Dwarf_nova. The Binary_star system consists of a White_dwarf closely orbiting a Red_dwarf. Roughly every 100 days it undergoes an outburst that greatly increases its brightness. Discovered by J.R._Hind in 1855 during one of its outbursts, it has been continuously observed since. The U Geminorum binary has a very short orbital period of 4 hours and 11 minutes; this orbit alone makes the system variable, as the components transit and eclipse each other with each revolution. Normally, the combined Apparent_magnitude varies between 14.0 and 15.1; during an outburst however, the star can brighten a hundredfold, to 9th magnitude. Though the average interval is 100 days, the period is in fact highly irregular, varying from as little as 62 days to as long as 257. As is the case with dwarf novae, the outbursts are theorized results of a periodic surge of influx from the white dwarf's Accretion_disk, caused by instability in the disk itself. ==See also== *SS_Cygni ==References== *AAVSO: "U Gem: February 1999 Variable Star of the Month." (Accessed 5/19/06) *Burnham, Robert. ''Burnham's Celestial Handbook.'' New York: Dover Publications, Inc., 1978. ISBN 0-486-23568-8 pp. 925-34. Category:Red_dwarfs Category:White_dwarfs Category:Binary_stars Category:Dwarf_novae Category:Gemini_constellation Geminorum, U {{astronomy-stub}} {{star-system-stub}} == External Links == * animation * data