Question

why we called Japan is land of the rising Sun

Answer 1

Both Nippon and Nihon literally mean "the sun's origin", that is, where the sunoriginates, and are often translated as the Land of the Rising Sun. This nomenclature comes from Imperial correspondence with the Chinese Sui Dynasty and refers to Japan's eastern position relative to China.

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Answer 2

we call Japan as the land of rising sun as the earth rotates from west to east direction and hence eastern part receives the sun before and also Japan is in the east