ids ) ▁among ▁the ▁twelve ▁signs . ▁ ▁Us age ▁▁ ▁The ▁z od iac ▁was ▁in ▁use ▁by ▁the ▁Roman ▁era , ▁based ▁on ▁concepts ▁inherited ▁by ▁H ellen istic ▁astronom y ▁from ▁Bab yl onian ▁astronom y ▁of ▁the ▁Chal de an ▁period ▁( mid - 1 st ▁mill en ni um ▁BC ), ▁which , ▁in ▁turn , ▁derived ▁from ▁an ▁earlier ▁system ▁of ▁lists ▁of ▁stars ▁along ▁the ▁e cli ptic . ▁The ▁construction ▁of ▁the ▁z od iac ▁is ▁described ▁in ▁P to le my ' s ▁vast ▁ 2 nd ▁century ▁AD ▁work , ▁the ▁Al mag est . ▁ ▁Although ▁the ▁z od iac ▁remains ▁the ▁basis ▁of ▁the ▁e cli ptic ▁coordinate ▁system ▁in ▁use ▁in ▁astronom y ▁besides ▁the ▁equ atorial ▁one , ▁the ▁term ▁and ▁the ▁names ▁of ▁the ▁twelve ▁signs ▁are ▁today ▁mostly ▁associated ▁with ▁hor os cop ic ▁ast ro log y . ▁The ▁term ▁" z od iac " ▁may ▁also ▁refer ▁to ▁the ▁region ▁of ▁the ▁cel est ial ▁sphere ▁en comp ass ing ▁the ▁paths ▁of ▁the ▁plan ets ▁corresponding ▁to ▁the ▁band ▁of ▁about ▁ 8 ▁arc ▁degrees ▁above ▁and ▁below ▁the ▁e cli ptic . ▁The ▁z od iac ▁of ▁a ▁given ▁planet ▁is ▁the ▁band ▁that ▁contains ▁the ▁path ▁of ▁that ▁particular ▁body ; ▁e . g ., ▁the ▁" z od iac ▁of ▁the ▁Moon " ▁is ▁the ▁band ▁of ▁ 5 ° ▁above ▁and ▁below ▁the ▁e cli ptic . ▁By ▁extension ,