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By rising the urbanization, human approach to time - acquainting was increased, because he needed to study about the origin of phenomena and their inveteracy, and assess two events with each other and relations of past with future. Making the early chronometer sets and advanced tools of sight and astrolabe and then creating chronology demonstrates the same needs. Although all nations considers 12 month in a year in their calendar, to some of them counting years was solar and to the other was lunar. The less number of the lunar year from solar year leads to dissimilation in the circulation of the both and made the estimates messy and difficult. To end these disorders Babelians made leap year to unify the number of both lunar and solar year and to accompany the
circulation of the both .This way was accepted by the other nations including Arabs. To make identical their lunar year with solar year of
the neighboring countries they added one month (without any name) to the end of each year, after three years and this made it 13 months. Since to begin the New year would be delayed by this modification, they named it Nasi (means to postpone) i.e. postponing to displace the lunar months because every month in 3 years from 36 years would not settle in its place. Since a number of religious awards such as Haj, Feast, holly
war were integrated with certain months, this replacement caused to frustrate them .Therefore the prophet (PBUH) in the tenth year
prohibited the use of Nasi for ever. This writing tries to attain the real meaning of the Nasi. First we deal with the origin of chronology and
their characteristics in some countries in the world to be aware of its background. Then we study its place among Arabs and its unfair outcomes