I know it's a silly question, but it really bothers me since the word hemisphere derives from Greek ημί- (i.e. hemi-) which cannot be further expanded, while the English equivalent semi- can be further expanded to quarter-.

So, my question has three parts:

  • Firstly, does the choice of "hemi-" instead of "semi-" only from geology or is it used as such in mathematics in the same manner?
  • If the Earth were instead flat, would we refer to a hemicircle or semicircle?
  • If I want to refer to the northwestern part of Earth, what's the correct word, since hemisphere is obviously wrong?

Thank you in advance

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    $\begingroup$ (1) The English term for half of a sphere is hemisphere, but for half of a circle is semicircle. That's English for you. This first question is about English rather than Earth Science. (2) and (3) The Earth isn't flat, so these two questions also are not about Earth Science. $\endgroup$ Jun 1, 2018 at 10:23
  • 1
    $\begingroup$ Thank you for your answer. The third question is not related with Flat Earth. I ask if there is any terminology splitting Earth to 4 parts instead of 2. $\endgroup$ Jun 1, 2018 at 10:41
  • 1
    $\begingroup$ "If the Earth was flat, would we refer to a hemicircle or semicircle?" think we might actually use something like the breakdown into quadrants, like in Star Trek (as the universe is in a complex mind-bending sense flat). Although it'd probably be a term developed historically, so who knows what it'd be called really :-p $\endgroup$ Jun 1, 2018 at 14:41
  • $\begingroup$ See also Word for half-hemisphere / quarter-sphere at English SE. Doesn't look like there's a great term :-/ $\endgroup$ Jun 1, 2018 at 14:45

1 Answer 1


Not, IMO an ES question, but depending on what level of division, and if you are talking about the surface only or a partition of the sphere extending to the core, terms such as spherical sector, spherical cap, and quadrant would be fairly common descriptive terms for parts of a sphere.

Cap would be the portion of the sphere cut by a plain passing though the sphere. The Hemispheres are caps cut by the plane passing through either the equator or the poles. Normally a cap would describe an area formed by cutting the plane parallel to the equator, as in the lines of latitude.

A sector would be a cone centered and the center of the sphere and extended to the surface. Think of a cone capped by a cap as described above.

A quadrant would typically be a wedge, think of an orange wedge, or a part of one.

I do not think any of there really are especially common to use in relationship to Earth though they are valid descriptors. Lines of longitude and latitude are the common differentiation that describe these divisions, and phrases such as above/below the 45th parallel to describe the halves of the Northern Hemisphere.


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