Brahma Siddhanta, also known as Paitamaha Siddhanta, is a treatise on astronomy. It is named after Brahma, often referred to as Pitamaha (grandfather). This system of Hindu astronomy is one of the five parts of Varahamihira’s Pancha Siddhantika (505 CE). The other four parts are Vasishtha, Saura, Romaka and Paulisha. Varaha’s Brahma Siddhanta has to be distinguished from three others with the same title – that which forms part of the Vishnudharmottara Purana, Brahma (sphuta) Siddhanta of Brahmagupta and Brahma (Sakalya) Siddhanta.
Brahma Siddhanta of Varaha (628 CE) is a portrayal of Hindu
astronomy free from foreign influences. The text speaks of yuga (an eon), cycle
of five solar years consisting of five revolutions of the Sun, 67 revolutions
of the Moon, 60 solar months, 62 synodic months, two adhikamas (intercalary),
1830 savana (civil) days, and 1960 tithis (lunar days). The cycle of yuga
begins with the conjunction of the sun and the moon at the first point of the Dhanishta
star. The durations of the longest and the shortest days, in the ration 3:2,
are also given.