It has been shown by Aveny (1981) that the development of indigenous astronomical systems in tropical cultures, whether the motive was religious or practical, centered toward a reference system consisting of zenith and nadir as poles and the horizon as a fundamental reference circle. Such a reference system differs remarkably to the celestial pole-equator (or ecliptic) systems employed by civilizations in temperate zones (also see Brennand, 1896; Stencel, et.al., 1976).
In order to obtain more insight of the view expounded by Aveny (1981) the authors undertook a test case study of the astronomically related time-keeping practice in Java. “Pranotomongso” has been chosen as it is well documented since 1855. According to Daldjoeni (1984) the “pranotomongso” (literaly means the arrangements of seasons) functions well as a practical guide for agricultural activities for the rural peasants in Central Java.