▁plane . ▁Therefore , ▁ 9 0 ° ▁is ▁added ▁to ▁both ▁scatter ing ▁angles ▁in ▁order ▁to ▁find ▁the ▁polar ization ▁angles . ▁From ▁this ▁the ▁Q ▁and ▁U ▁Sto kes ▁parameters ▁are ▁determined : ▁ ▁and ▁ ▁The ▁scatter ing ▁angle , ▁derived ▁from ▁the ▁law ▁of ▁cos ines ▁is ▁with ▁respect ▁to ▁the ▁sun . ▁ ▁The ▁polar ization ▁angle ▁is ▁the ▁angle ▁with ▁respect ▁to ▁the ▁z en ith , ▁or ▁positive ▁alt itude . ▁ ▁There ▁is ▁a ▁line ▁of ▁symmetry ▁defined ▁by ▁the ▁sun ▁and ▁the ▁z en ith . ▁It ▁is ▁drawn ▁from ▁the ▁sun ▁through ▁the ▁z en ith ▁to ▁the ▁other ▁side ▁of ▁the ▁cel est ial ▁sphere ▁where ▁the ▁" anti - sun " ▁would ▁be . ▁This ▁is ▁also ▁the ▁effective ▁East - Z en ith - West ▁plane . ▁ ▁The ▁first ▁image ▁to ▁the ▁right ▁represents ▁the ▁q ▁input ▁mapped ▁onto ▁the ▁cel est ial ▁sphere . ▁It ▁is ▁symmetric ▁about ▁the ▁line ▁defined ▁by ▁the ▁sun - zen ith - anti - sun . ▁ ▁At ▁tw il ight , ▁in ▁the ▁North - Z en ith - S outh ▁plane ▁it ▁is ▁negative ▁because ▁it ▁is ▁vertical ▁with ▁the ▁degree ▁of ▁polar ization . ▁ ▁It ▁is ▁horizontal , ▁or ▁positive ▁in ▁the ▁East - Z en ith - West ▁plane . ▁ ▁In ▁other ▁words , ▁it ▁is ▁positive ▁in ▁the ▁▁ ± alt itude ▁direction ▁and ▁negative ▁in ▁the ▁ ± az im uth ▁direction .