▁Cap ella . ▁A ▁ro cket ▁flight ▁on ▁that ▁date ▁briefly ▁cal ibr ated ▁its ▁attitude ▁control ▁system ▁when ▁a ▁star ▁sensor ▁pointed ▁the ▁payload ▁axis ▁at ▁Cap ella ▁( α ▁Aur ). ▁During ▁this ▁period , ▁X - ray s ▁in ▁the ▁range ▁ 0 . 2 – 1 . 6 ▁ke V ▁were ▁detected ▁by ▁an ▁X - ray ▁reflect or ▁system ▁co - aligned ▁with ▁the ▁star ▁sensor . ▁The ▁X - ray ▁lum inos ity ▁of ▁L x ▁= ▁ 1 0 3 1 ▁erg · s − 1 ▁( 1 0 2 4 ▁W ) ▁is ▁four ▁orders ▁of ▁magnitude ▁above ▁the ▁Sun ' s ▁X - ray ▁lum inos ity . ▁ ▁St ell ar ▁cor ona e ▁Cor onal ▁stars , ▁or ▁stars ▁within ▁a ▁cor onal ▁cloud , ▁are ▁u bi quit ous ▁among ▁the ▁stars ▁in ▁the ▁cool ▁half ▁of ▁the ▁H ert z spr ung - Russ ell ▁diagram . ▁Exper iments ▁with ▁instruments ▁ab o ard ▁Sk yl ab ▁and ▁Cop ern icus ▁have ▁been ▁used ▁to ▁search ▁for ▁soft ▁X - ray ▁emission ▁in ▁the ▁energy ▁range ▁~ 0 . 1 4 – 0 . 2 8 4 ▁ke V ▁from ▁stell ar ▁cor ona e . ▁The ▁experiments ▁ab o ard ▁A NS ▁succeeded ▁in ▁finding ▁X - ray ▁signals ▁from ▁Cap ella ▁and ▁Si ri us ▁( α ▁C Ma ). ▁X - ray ▁emission ▁from ▁an ▁en hanced ▁solar - like ▁cor ona ▁was ▁proposed ▁for ▁the ▁first