The phrase "a perfect sphere" is correct and usable in written English.
It can be used in contexts discussing geometry, physics, or any situation where the concept of a flawless spherical shape is relevant.
Example: "In mathematics, a perfect sphere is defined as a three-dimensional object where every point on its surface is equidistant from its center."
Alternatives: "an ideal sphere" or "a flawless sphere".
Given enough mass to work on, for example, gravity will fashion it into a perfect sphere.
If the debris flies out evenly in every direction you get a perfect sphere.
The friction with other precipitation deforms a hailstone from a perfect sphere, making its velocity hard to calculate when it does become heavy enough to fall to earth.
Because the Earth rotates and is not a perfect sphere, the geocentric zenith is slightly different from the geographic zenith except at the Equator and the poles.
When would-be master builders audition for Lego, they are given a pile of bricks and asked to make a perfect sphere.
Because Earth is not a perfect sphere -- squashed in slightly at the poles and squished outward at the Equator -- it wobbles like the Frisbee.
Each is a little more than a foot wide, weighs nearly ninety pounds, and is polished to within a hundred-millionth of an inch of a perfect sphere.
Earth is wider around its Equator than a perfect sphere, but recently it has become even more oblate or pumpkinlike, researchers said.
Because Earth is not a perfect sphere, it wobbles very slightly as it rotates, too little to physically matter but enough for scientists to measure.
Celestial objects were exempt from dynamical decay because they moved in a higher stratum whereby a perfect sphere was the natural shape of heavenly bodies and uniform rotation in circles was the natural state of their motion.
In an imperfect lens, however, because of the presence of aberrations, the emerging wave is not a perfect sphere, and the optical paths from the wave to the image point are then not all equal.
