) ▁is ▁a ▁multiple ▁star ▁system ▁in ▁the ▁const ell ation ▁Or ion , ▁consisting ▁of ▁the ▁bright est ▁members ▁of ▁a ▁young ▁open ▁cluster . ▁ ▁It ▁is ▁found ▁at ▁the ▁eastern ▁end ▁of ▁the ▁bel t , ▁south ▁west ▁of ▁Al nit ak ▁and ▁west ▁of ▁the ▁Hor se head ▁Neb ula ▁which ▁it ▁partially ▁ill umin ates . ▁ ▁The ▁total ▁bright ness ▁of ▁the ▁component ▁stars ▁is ▁magnitude ▁ 3 . 8 0 . ▁ ▁History ▁▁ σ ▁Or ion is ▁is ▁a ▁n aked ▁eye ▁star ▁at ▁the ▁eastern ▁end ▁of ▁Or ion ' s ▁B elt , ▁and ▁has ▁been ▁known ▁since ▁anti qu ity , ▁but ▁it ▁was ▁not ▁included ▁in ▁P to le my ' s ▁Al mag est . ▁ ▁It ▁was ▁referred ▁to ▁by ▁Al ▁S uf i , ▁but ▁not ▁formally ▁listed ▁in ▁his ▁catalog ue . ▁ ▁In ▁more ▁modern ▁times , ▁it ▁was ▁measured ▁by ▁Ty cho ▁Bra he ▁and ▁included ▁in ▁his ▁catalog ue . ▁ ▁In ▁Ke pler ' s ▁extension ▁it ▁is ▁described ▁as ▁" Qu ae ▁ult im am ▁bal tei ▁pra ec edit ▁ad ▁a ustr ." ▁( pre ced ing ▁the ▁outer most ▁of ▁the ▁bel t , ▁to ▁the ▁south ). ▁ ▁It ▁was ▁then ▁recorded ▁by ▁Johann ▁Bayer ▁in ▁his ▁U ran omet ria ▁as ▁a ▁single ▁star ▁with ▁the ▁Greek ▁letter ▁ σ ▁( sigma ). ▁ ▁He ▁described ▁it ▁as ▁" in ▁en ſ e , ▁prima " ▁( in