ight ▁( when ▁the ▁sun ▁is ▁ 1 8 ° ▁below ▁the ▁horizon ) ▁and ▁sun r ise , ▁or ▁sun set ▁and ▁the ▁end ▁of ▁astronom ical ▁tw il ight . ▁The ▁duration ▁of ▁astronom ical ▁tw il ight ▁depends ▁on ▁the ▁length ▁of ▁the ▁path ▁taken ▁by ▁the ▁sun ▁below ▁the ▁horizon . ▁Thus ▁it ▁depends ▁on ▁the ▁time ▁of ▁year ▁as ▁well ▁as ▁the ▁location , ▁but ▁it ▁can ▁last ▁for ▁as ▁long ▁as ▁ 1 . 5 ▁hours . ▁ ▁The ▁polar ization ▁pattern ▁caused ▁by ▁tw il ight ▁remains ▁fairly ▁consistent ▁throughout ▁this ▁time ▁period . ▁ ▁This ▁is ▁because ▁the ▁sun ▁is ▁moving ▁below ▁the ▁horizon ▁nearly ▁per pend icular ▁to ▁it , ▁and ▁its ▁az im uth ▁therefore ▁changes ▁very ▁slowly ▁throughout ▁this ▁time ▁period . ▁ ▁At ▁tw il ight , ▁scattered ▁polar ized ▁light ▁origin ates ▁in ▁the ▁upper ▁atmosphere ▁and ▁then ▁travers es ▁the ▁entire ▁lower ▁atmosphere ▁before ▁reaching ▁the ▁observer . ▁ ▁This ▁provides ▁multiple ▁scatter ing ▁opportun ities ▁and ▁causes ▁dep olar ization . ▁It ▁has ▁been ▁seen ▁that ▁polar ization ▁increases ▁by ▁about ▁ 1 0 % ▁from ▁the ▁on set ▁of ▁tw il ight ▁to ▁dawn . ▁Therefore , ▁the ▁pattern ▁remains ▁consistent ▁while ▁the ▁degree ▁changes ▁slightly . ▁ ▁Not ▁only ▁do ▁polar ization ▁patterns ▁remain ▁consistent ▁as ▁the ▁sun ▁moves ▁across ▁the ▁sky , ▁but ▁also ▁as ▁the ▁moon ▁moves ▁across ▁the ▁sky ▁at ▁night . ▁The ▁moon ▁creates ▁the ▁same ▁polar ization ▁pattern . ▁Thus ▁it