Which of the following is NOT one of the earth's hemispheres?

a. Northern Hemisphere

b. Eastern Hemisphere

c. Southern Hemisphere

d. Southwestern Hemisphere

Heisphere means "half a sphere".

We can divide the Earth into two vertically, giving us Northern and Southern Hemisphere or Horizontally - Eastern and Western Hemisphere.

Since we have all the four hemipsheres (Northern and Southern Hemisphere and Eastern and Western Hemisphere) we know which one isn't a hemisphere: d. Southwestern Hemisphere