Iran, the land of Aryans officially known as the Islamic Republic of Iran, is a Middle Eastern country located in southwest Asia. As a land and a nation, Iran is one of the most historic and ancient countries in the world. Its capital is Tehran. The term “Iran” is derived from the hypothetical word “-Aryānām Xšaθra”, which meant “the land of Aryans” in Old Persian and gradually changed to "Iran" over time. During the Achaemenid rule, this country was called Pars by ancient Greeks and Persian (English) or Perse (French) by Europeans. In 1934, Reza Shah Pahlavi announced that all foreign states shall use the term “Iran” to refer to the country he was ruling at the time. With an area of 1,648,195 km2 and a population of 79,926,270, Iran is the world’s 17th largest and 18th populous country.   Iranians and the Persian Empire are considered the first nation and empire in history. Founded by the Achaemenid dynasty and ended with the Pahlavi dynasty, the Persian Empire consisted of a set of Iranian or Persian-speaking dynasties that ruled the Iranian Plateau, the motherland of Iranians, west, south, and central Asia, and the Caucasus. The Persian Empire reached its peak during the Achaemenid rule, when Darius the Great and Xerxes the Great established a united kingdom in the present-day Fras Province of Iran. Known as the Persian Empire, the Achaemenid Empire was closer to our definition of the concept of world domination than any other empire throughout human history. In fact, the Achaemenid Empire dominated 44.48% of the earth's inhabitants during its peak of authority and glory, only 6% less than half of the world's population at the time. In other words, one out of two people on the earth was under the rule of Iranians in 480 B.C. Unlike other empires, the Achaemenid Empire was highly close to ruling the entire planet.   Iran is one of the most unique countries in terms of weather. It is known as a four-season country because of a temperature difference of 50°C between the warmest and coldest points during the winter; whilst the temperature in Shahrekord reaches -30°C during some winter nights, the weather in Ahwaz may look like the summer days at the same time with a temperature of 50°C. In addition, the highest air temperature on the earth was measured in some points of the Lut Desert in 2004 and 2005. Iran is a semi-arid and dry country in terms of precipitation. The precipitation rate varies widely in different regions of Iran, as it exceeds 2,113 mm in the north (Rasht, Guilan Province) while it is about 15 mm in desert areas. The mean annual precipitation is about 500 mm in northwest and west areas, South Alborz, and northeast areas and almost 200 mm in other areas of Iran. The weather is warm and humid in the summer and temperate during the winter in the north of Iran (southern coasts of the Caspian Sea). Additionally, people in the northwest and west of Iran usually experience mild summers and cold winters whereas those in southern areas have hot summers and mild winters.