Islamic Scientific Heritage (@IslamicSH_)

Nearly five centuries before Johannes Werner, the Egyptian astronomer Ibn Yunus used a trigonometric identity equivalent to {𝟮𝗰𝗼𝘀(𝗮)𝗰𝗼𝘀(𝗯)=𝗰𝗼𝘀(𝗮+𝗯)+𝗰𝗼𝘀(𝗮-𝗯)} in astronomical calculations for determining time from the altitude of the Sun and stars. Ibn Yunus (1009 CE) was an Egyptian Muslim mathemat...