IPA: /ˈhɛmɪsfɪə/
KK: /ˈhɛmɪˌsfɪr/
A part of a sphere that is divided into two equal halves, often used to refer to the Earth or other spherical objects.
The Earth is divided into two hemispheres: the Northern Hemisphere and the Southern Hemisphere.
Hemisphere → It is formed from "hemi-" (from Greek "hēmi-", meaning half) and "sphaira" (from Greek, meaning sphere). The word "hemisphere" refers to half of a sphere, typically used to describe half of the Earth or a celestial body.
Think of 'half' ('hemi-') of a 'sphere' ('sphaira') — that's why a hemisphere is a half of a sphere.