A spherical shell refers to a hollow object that is shaped like a ball. It has an outer surface that forms a perfect sphere, but it is empty on the inside. Full definition
The result is an object having two distinct parts: a well - defined core of mostly carbon ash (a white dwarf star; see below End states of stars) and a swollen spherical shell of cooler and thinner matter spread over a volume roughly the size of the solar system. (britannica.com)
New observations with the Atacama Large Millimeter / submillimeter Array (ALMA) reveal a remarkably thin spherical shell surrounding this star. (public.nrao.edu)
Nowhere else have I seen a passage that so effectively describes the workings of the «spherical shell which surrounds our planet,» as the author puts it. (dotearth.blogs.nytimes.com)