  Using the covariant electromagnetic Casimir effect (previously introduced for
real conducting cylindrical shells [1]), the Casimir force experienced by a
spherical shell, under Dirichlet boundary condition, is calculated. The
renormalization procedure is based on the plasma cut-off frequency for real
conductors. The real case of a gold (silver) sphere is considered and the
corresponding electromagnetic Casimir force is computed. In the covariant
approach, there isn't any decomposition of fields to TE and TM modes; thus, we
do not need to consider the Neumann boundary condition in parallel to the
Dirichlet problem and then add their corresponding results.
