…the chemical element of atomic number 18, an inert gaseous element of the noble gas group. Argon is the most common noble gas, making up nearly one percent of the earth’s atmosphere…
…(763–809), fifth Abbasid caliph of Baghdad 786–809…
…(1207–73), Persian poet and Sufi mystic; founder of the order of whirling dervishes; also called Mawlana…
…a city in northeastern Iran, close to the border with Turkmenistan; population 2,427,316 (2006). The burial place in ad 809 of the Abbasid caliph Harun ar-Rashid and in 818 of the Shiite leader Ali ar-Rida, it is a holy city of the Shiite Muslims. It is the second largest city in Iran…
