▁the ▁signs ▁from ▁the ▁theory ▁of ▁pro gn ost ic ation , ▁or ▁impossible ▁to ▁avoid ▁error ▁in ▁then ▁retain ing ▁and ▁making ▁use ▁of ▁them ; ▁as ▁the ▁regular ity ▁of ▁their ▁spaces ▁and ▁distances , ▁upon ▁which ▁their ▁influence ▁depends , ▁would ▁then ▁be ▁inv aded ▁and ▁broken ▁in ▁upon . ▁ ▁In ▁modern ▁astronom y ▁▁ ▁Astronom ically , ▁the ▁z od iac ▁defines ▁a ▁bel t ▁of ▁space ▁extending ▁ 9 ° ▁either ▁side ▁of ▁the ▁e cli ptic , ▁within ▁which ▁the ▁or bits ▁of ▁the ▁Moon ▁and ▁the ▁principal ▁plan ets ▁remain . ▁It ▁is ▁a ▁feature ▁of ▁a ▁cel est ial ▁coordinate ▁system ▁centered ▁upon ▁the ▁e cli ptic , ▁( the ▁plane ▁of ▁the ▁Earth ' s ▁orbit ▁and ▁the ▁Sun ' s ▁apparent ▁path ), ▁by ▁which ▁cel est ial ▁longitude ▁is ▁measured ▁in ▁degrees ▁east ▁of ▁the ▁v ernal ▁equ ino x ▁( the ▁asc ending ▁intersection ▁of ▁the ▁e cli ptic ▁and ▁equ ator ). ▁Stars ▁within ▁the ▁z od iac ▁are ▁subject ▁to ▁occ ult ations ▁by ▁the ▁Moon ▁and ▁other ▁solar ▁system ▁bodies . ▁These ▁events ▁can ▁be ▁useful , ▁for ▁example , ▁to ▁estimate ▁the ▁cross - section al ▁dimensions ▁of ▁a ▁minor ▁planet , ▁or ▁check ▁a ▁star ▁for ▁a ▁close ▁companion . ▁ ▁The ▁Sun ' s ▁pla cement ▁upon ▁the ▁v ernal ▁equ ino x , ▁which ▁occurs ▁ann ually ▁around ▁ 2 1 ▁March , ▁defines ▁the ▁starting ▁point ▁for ▁measurement , ▁the ▁first ▁degree