▁sun ▁moves ▁across ▁the ▁sky ▁the ▁angle ▁is ▁both ▁zero ▁and ▁high ▁along ▁the ▁line ▁defined ▁by ▁the ▁sun , ▁the ▁z en ith , ▁and ▁the ▁anti - sun . ▁ ▁It ▁is ▁lower ▁South ▁of ▁this ▁line ▁and ▁higher ▁North ▁of ▁this ▁line . ▁When ▁the ▁sun ▁is ▁at ▁the ▁z en ith , ▁the ▁angle ▁is ▁either ▁fully ▁positive ▁or ▁ 0 . ▁ ▁These ▁two ▁values ▁rotate ▁toward ▁the ▁west . ▁The ▁video ▁then ▁repe ats ▁a ▁similar ▁fashion ▁when ▁the ▁sun ▁sets ▁in ▁the ▁West . ▁ ▁Q ▁and ▁U ▁Sto kes ▁parameters ▁ ▁The ▁angle ▁of ▁polar ization ▁can ▁be ▁unw ra pped ▁into ▁the ▁Q ▁and ▁U ▁Sto kes ▁parameters . ▁ ▁Q ▁and ▁U ▁are ▁defined ▁as ▁the ▁linear ly ▁polar ized ▁intens ities ▁along ▁the ▁position ▁angles ▁ 0 ° ▁and ▁ 4 5 ° ▁respectively ; ▁- Q ▁and ▁- U ▁are ▁along ▁the ▁position ▁angles ▁ 9 0 ° ▁and ▁− 4 5 ° . ▁ ▁If ▁the ▁sun ▁is ▁located ▁on ▁the ▁horizon ▁due ▁west , ▁the ▁degree ▁of ▁polar ization ▁is ▁then ▁along ▁the ▁North - Z en ith - S outh ▁plane . ▁If ▁the ▁observer ▁faces ▁West ▁and ▁looks ▁at ▁the ▁z en ith , ▁the ▁polar ization ▁is ▁horizontal ▁with ▁the ▁observer . ▁ ▁At ▁this ▁direction ▁Q ▁is ▁ 1 ▁and ▁U ▁is ▁ 0 . ▁ ▁If ▁the ▁observer ▁is ▁still ▁facing ▁West ▁but ▁looking ▁North ▁instead ▁then ▁the ▁polar ization ▁is ▁vertical ▁with ▁him