Comparative religion is the branch of the study of religions with the systematic comparison of the doctrines and practices, themes and impacts (including migration) of the world's religions. In general the comparative study of religion yields a deeper understanding of the fundamental philosophical concerns of religion such as ethics, metaphysics and the nature and forms of salvation. It also considers and compares the origins and similarities shared between the various religions of the world. Studying such material facilitates a broadened and more sophisticated understanding of human beliefs and practices regarding the sacred, numinous, spiritual and divine. In the field of comparative religion, a common geographical classification of the main world religions distinguishes groups such as Middle Eastern religions (including Iranian religions), Indian religions, East Asian religions, African religions, American religions, Oceanic religions, and classical Hellenistic religions. There also exist various sociological classifications of religious movements. Al-Biruni (973 – c.1050) and Ibn Hazm (994 – 1064), both of the Islamic Golden Age and considered as the "fathers of comparative religion", compared the study of religious pluralism and their works have been significant in the fields of theology and philosophy. The Persian Al-Biruni discussed his idea of history in The Remaining Signs of Past Centuries (c.1000 AD) which was translated by Eduard Sachau in 19th century. It is a comparative study of calendars of different cultures and civilizations, interlaced with mathematical, astronomical, and historical information, exploring the customs and religions of different peoples. Social scientists in the 19th century took a strong interest in comparative and "primitive" religion through the work of Max Müller, Edward Burnett Tylor, William Robertson Smith, James George Frazer, Émile Durkheim, Max Weber, and Rudolf Otto.