“Varahamihira was one of the most famous astrologers in Indian history. The most famous work by him is the Panschsiddhanta(The Five Astronomical Canons). The work is a treatise on mathematical astronomy and it summarises five earlier astronomical treatises, namely the Surya, Romaka, Paulisa, Vasistha and Paitamaha siddhantas.
His work Brihatsamhita (The Great Compilation) discusses topics such as Descriptions of heavenly bodies, their movements and conjunctions, meteorological phenomena, indications of the omens these movements, conjunctions and phenomena represent, what action to take and operations to accomplish, sign to look for in humans, animals, precious stones, etc. Varahamihira made some important mathematical discoveries. Among these are certain trigonometric formulas which translated into our present day notation correspond to
sin x = cos(p/2 – x),
sin2x + cos2x = 1, and
(1 – cos 2x)/2 = sin2x.
Another important contribution to trigonometry was his sine tables where he improved those of Aryabhata I giving more accurate values. It should be emphasised that accuracy was very important for these Indian mathematicians since they were computing sine tables for applications to astronomy and astrology. This motivated much of the improved accuracy they achieved by developing new interpolation methods.”