ong ▁the ▁horizon , ▁at ▁an ▁alt itude ▁of ▁ 0 ° ▁it ▁is ▁highest ▁in ▁the ▁North ▁and ▁South , ▁and ▁lowest ▁in ▁the ▁East ▁and ▁West . ▁Then ▁as ▁alt itude ▁increases ▁approaching ▁the ▁z en ith ▁( or ▁the ▁plane ▁of ▁maximum ▁polar ization ) ▁the ▁polar ization ▁remains ▁high ▁in ▁the ▁North ▁and ▁South ▁and ▁increases ▁until ▁it ▁is ▁again ▁maximum ▁at ▁ 9 0 ° ▁in ▁the ▁East ▁and ▁West , ▁where ▁it ▁is ▁then ▁at ▁the ▁z en ith ▁and ▁within ▁the ▁plane ▁of ▁polar ization . ▁ ▁Click ▁on ▁the ▁adjacent ▁image ▁to ▁view ▁an ▁animation ▁that ▁represents ▁the ▁degree ▁of ▁polar ization ▁as ▁shown ▁on ▁the ▁cel est ial ▁sphere . ▁ ▁Black ▁represents ▁areas ▁where ▁the ▁degree ▁of ▁polar ization ▁is ▁zero , ▁whereas ▁red ▁represents ▁areas ▁where ▁the ▁degree ▁of ▁polar ization ▁is ▁much ▁larger . ▁It ▁is ▁approximately ▁ 8 0 %, ▁which ▁is ▁a ▁real istic ▁maximum ▁for ▁the ▁clear ▁Ray le igh ▁sky ▁during ▁day ▁time . ▁ ▁The ▁video ▁thus ▁begins ▁when ▁the ▁sun ▁is ▁slightly ▁above ▁the ▁horizon ▁and ▁at ▁an ▁az im uth ▁of ▁ 1 2 0 ° . ▁The ▁sky ▁is ▁highly ▁polar ized ▁in ▁the ▁effective ▁North - Z en ith - S outh ▁plane . ▁This ▁is ▁slightly ▁offset ▁because ▁the ▁sun ' s ▁az im uth ▁is ▁not ▁due ▁East . ▁ ▁The ▁sun ▁moves ▁across ▁the ▁sky ▁with ▁clear ▁circular ▁polar ization ▁patterns ▁surrounding ▁it . ▁ ▁When ▁the ▁sun ▁is