▁By z antine ▁writers ▁Category : By z antine ▁the olog ians ▁Category : Arch im and rit es ▁Category : A bb ots ▁of ▁the ▁St oud ios ▁Mon aster y ▁Category : 1 4 th - century ▁Eastern ▁Orth odox ▁the olog ians <0x0A> </s> ▁The ▁full ▁moon ▁is ▁the ▁lun ar ▁phase ▁when ▁the ▁Moon ▁appears ▁fully ▁ill umin ated ▁from ▁Earth ' s ▁perspective . ▁This ▁occurs ▁when ▁Earth ▁is ▁located ▁between ▁the ▁Sun ▁and ▁the ▁Moon ▁( more ▁exactly , ▁when ▁the ▁e cli ptic ▁long itudes ▁of ▁the ▁Sun ▁and ▁Moon ▁differ ▁by ▁ 1 8 0 ° ). ▁This ▁means ▁that ▁the ▁lun ar ▁hem is phere ▁facing ▁Earth ▁– ▁the ▁near ▁side ▁– ▁is ▁completely ▁sun lit ▁and ▁appears ▁as ▁a ▁circular ▁disk . ▁The ▁full ▁moon ▁occurs ▁roughly ▁once ▁a ▁month . ▁ ▁The ▁time ▁interval ▁between ▁a ▁full ▁( or ▁new ) ▁moon ▁and ▁the ▁next ▁repet ition ▁of ▁the ▁same ▁phase , ▁a ▁syn od ic ▁month , ▁aver ages ▁about ▁ 2 9 . 5 3 ▁days . ▁Therefore , ▁in ▁those ▁lun ar ▁cal end ars ▁in ▁which ▁each ▁month ▁begins ▁on ▁the ▁day ▁of ▁the ▁new ▁moon , ▁the ▁full ▁moon ▁falls ▁on ▁either ▁the ▁ 1 4 th ▁or ▁ 1 5 th ▁day ▁of ▁the ▁lun ar ▁month . ▁Because ▁a ▁calendar ▁month ▁consists ▁of ▁a ▁whole ▁number ▁of ▁days , ▁a ▁month ▁in ▁a ▁lun ar ▁calendar ▁may ▁be ▁either ▁ 2 9 ▁or ▁ 3