Question

what would happened if the International Date Line passed through Greenwich

Answer 1

The International Date Line (180 degrees longitude) actually is half a world away from Greenwich, a borough and suburb of London, England. Greenwich is situated at 0 degrees longitude on the Prime Meridian, the companion opposite of the IDL. For this reason, and for its long maritime history and the observatory situated there, the town was used to name Greenwich Mean Time (GMT). The term was derived from the mean solar time designated at the Royal Observatory in Greenwich. The International Date Line is actually an imaginary line that runs opposite the Prime Meridian; the IDL does not run a totally straight course, however. It diverts around many Pacific islands and territories.