▁of ▁the ▁eyes . ▁ ▁In ▁conditions ▁with ▁poor ▁visual ▁c ues ▁accompanied ▁by ▁a ▁single ▁source ▁of ▁light , ▁these ▁eye ▁movements ▁are ▁interpreted ▁by ▁the ▁brain ▁as ▁movement ▁of ▁the ▁object ▁being ▁viewed . ▁ ▁This ▁ill usion ▁can ▁cause ▁a ▁mis per ception ▁that ▁such ▁a ▁light ▁is ▁on ▁a ▁collision ▁course ▁with ▁the ▁aircraft . ▁ ▁Plan ets ▁or ▁stars ▁in ▁the ▁night ▁sky ▁can ▁often ▁cause ▁the ▁ill usion ▁to ▁occur . ▁ ▁O ften ▁these ▁bright ▁stars ▁or ▁plan ets ▁have ▁been ▁mistaken ▁for ▁landing ▁lights ▁of ▁on coming ▁aircraft , ▁sat ell ites , ▁or ▁even ▁U FO s . ▁ ▁An ▁example ▁of ▁a ▁star ▁that ▁commonly ▁causes ▁this ▁ill usion ▁is ▁Si ri us , ▁which ▁is ▁the ▁bright est ▁star ▁in ▁the ▁northern ▁hem is phere ▁and ▁in ▁winter ▁appears ▁over ▁the ▁entire ▁contin ental ▁United ▁States ▁at ▁one ▁to ▁three ▁f ist - width s ▁above ▁the ▁horizon . ▁ ▁At ▁d usk , ▁the ▁planet ▁Ven us ▁can ▁cause ▁this ▁ill usion ▁to ▁occur ▁and ▁many ▁pil ots ▁have ▁mistaken ▁it ▁as ▁lights ▁coming ▁from ▁other ▁aircraft ▁ ▁False ▁visual ▁reference ▁▁ ▁False ▁visual ▁reference ▁ill us ions ▁may ▁cause ▁the ▁pilot ▁to ▁orient ▁the ▁aircraft ▁in ▁relation ▁to ▁a ▁false ▁horizon ; ▁these ▁ill us ions ▁can ▁be ▁caused ▁by ▁flying ▁over ▁a ▁bank ed ▁cloud , ▁night ▁flying ▁over ▁feature less ▁terrain ▁with ▁ground ▁lights ▁that ▁are ▁ind ist ingu ish able ▁from ▁a ▁dark ▁sky ▁with ▁stars ,