Answers

2015-08-05T22:05:59+05:30
It cannot defined in words as it is more than that example sending spaceships & statillite etc . check  more on internet

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2015-08-06T00:40:47+05:30
They take so much efforts but we can't say it in few words . the know about the earth with the help of satilites and by looking stars and planets through telescop etc...
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