takahmamash
As I understand it
There are lines of longetude imaginary vertically line over the earth, they somewhat correspond with time zones (although not exactly) the starting time zone accepted by the world is Grenwich mean time which is zero longetude and that is in London. The international date line is supposed to be 180 degrees from London (Its approximatly with some zig zagging because some places wanted to be in a certain time zone like the Aleutian islands of Alaska , some are past 180 Degrees but wanted to be part of the rest of Alaska)
Some Poskim hold that London is NOT where the time zones should start, but rather Jerusalem is where it should start. If you move Greenwich mean time from London to Jerusalem which is east then the international date line moves east as well and the 180 degree point is west of Hawaii and Alaska which now it is east