▁background , ▁or ▁as ▁tropical , ▁with ▁the ▁signs ▁fixed ▁to ▁the ▁point ▁( vector ▁of ▁the ▁Sun ) ▁at ▁the ▁March ▁equ ino x . ▁ ▁Western ▁ast ro log y ▁takes ▁the ▁tropical ▁approach , ▁whereas ▁H indu ▁ast ro log y ▁takes ▁the ▁sid ere al ▁one . ▁This ▁results ▁in ▁the ▁originally ▁un ified ▁z odia cal ▁coordinate ▁system ▁dr ifting ▁apart ▁gradually , ▁with ▁a ▁clock wise ▁( west ward ) ▁pre cess ion ▁of ▁ 1 . 4 ▁degrees ▁per ▁century . ▁ ▁For ▁the ▁tropical ▁z od iac ▁used ▁in ▁Western ▁astronom y ▁and ▁ast ro log y , ▁this ▁means ▁that ▁the ▁tropical ▁sign ▁of ▁A ries ▁currently ▁lies ▁somewhere ▁within ▁the ▁const ell ation ▁P is ces ▁(" Age ▁of ▁P is ces "). ▁ ▁The ▁sid ere al ▁coordinate ▁system ▁takes ▁into ▁account ▁the ▁a yan ams a , ▁a yan ▁meaning ▁trans it ▁or ▁movement , ▁and ▁am sa ▁meaning ▁small ▁part , ▁i . e . ▁movement ▁of ▁equ ino xes ▁in ▁small ▁parts . ▁It ▁is ▁unclear ▁when ▁Indians ▁became ▁aware ▁of ▁the ▁pre cess ion ▁of ▁the ▁equ ino xes , ▁but ▁Bh ask ara ▁ 2 ' s ▁ 1 2 th - century ▁treat ise ▁S idd h anta ▁Sh ir oman i ▁gives ▁equations ▁for ▁measurement ▁of ▁pre cess ion ▁of ▁equ ino xes , ▁and ▁says ▁his ▁equations ▁are ▁based ▁on ▁some ▁lost ▁equations ▁of ▁S ury as idd h anta ▁plus ▁the ▁equation ▁of