I googled it: Image

Anything between lines of longitude 0° - 180° (0° is britain GMT, 180° is opposite side of earth) is EAST.

Anything between 180° to 0 (AKA 360°) is WEST.

Thus you have a western hemisphere, which i guess is just tthe americas and british Isles, and an eastern hemisphere, which i guess is most of afroeurasia and australia. This is just about the only way it could’ve worked, but as for where 0 and 180 went, it’s just arbitrary.

I would’ve defined the Levant as the boundary between east and west hemisphere, instead.