Although the figure of Earth is not perfectly spherical, terms borrowed from geography are convenient to apply to the sphere. A particular line passing through its center defines an axis (as in Earth's axis of rotation). The sphere-axis intersection defines two antipodal poles (north pole and south pole). The great circle equidistant to the poles is called the equator. Great circles through the poles are called lines of longitude or meridians. Small circles on the sphere that are parallel to the equator are circles of latitude (or parallels). In geometry unrelated to astronomical bodies, geocentric terminology should be used only for illustration and noted as such, unless there is no chance of misunderstanding.
Although the figure of Earth is not perfectly spherical, terms borrowed from geography are convenient to apply to the sphere. A particular line passing through its center defines an axis (as in Earth's axis ?of rotation). The sphere-axis intersection defines two antipodal poles (north pole and south pole). The great circle equidistant to the poles is called the equator. Great circles through? the poles a,re called lines of longitude or meridians. Small circles on the sphere that are parallel to the equator are circles of latitude (or parallels). In geometry unrelated to astronomical bodies, geocentric terminology should be used only for illustration and noted as such, unless there is no chance of misunder?standing.