An analytic theory is developed for both the steady state and the time-dependent electric and magnetic fields inside the moon and its downstream cavity for interplanetary electromagnetic field fluctuations incident at arbitrary angles to the cavity axis. The moon model has an electrical conductivity, electrical permittivity, and magnetic permeability which vary arbitrarily with radius. The cavity downstream of the moon in the solar wind is assumed to be an infinitely long nonconducting cylinder. If the interplanetary field fluctuations propagate parallel to the cavity, the far cavity field is a single cylindrical transverse electric mode propagating downstream with the same frequency, wavelength, and phase velocity as the interplanetary field. The far cavity field is the result of a forced surface wave on the cylindrical boundary of the void. When the interplanetary fluctuations are incident at an arbitrary angle to the cavity axis, the far cavity field is a superposition of an infinite number of cylindrical TE (transverse electric) and TM (transverse magnetic) modes. Each of these modes is a surface wave with the same frequency and downstream phase velocity (the ratio of the angular frequency to the magnitude of the component of the interplanetary wave vector parallel to the cavity axis) as the incident interplanetary field. If the magnetic perturbation vector of the incident wave is normal to the cavity axis, the far cavity field is a linear combination of cylindrical TE and TM modes for arbitrary angles of incidence. However, if the interplanetary electric field fluctuation is normal to the axis of the void, the far cavity field is pure TE independent of the incidence angle. Resonances can occur in the far cavity TE and TM forced surface waves if the apparent velocity of the interplanetary wave parallel to the void axis, i.e., the downstream phase velocity, coincides with one of the characteristic TE or TM wave guide speeds of the circular cylindrical void for waves of the same frequency as the interplanetary radiation. When the interplanetary waves travel parallel to the void axis, their downstream and actual phase velocities coincide; these phase speeds are smaller than the velocity of light in vacuum, c, so that no resonances in the far cavity field are possible, since characteristic wave guide phase velocities are greater than c. Particular TE and TM modes may be absent from the far cavity field for certain incidence angles and frequencies of the interplanetary radiation. At normal incidence the far cavity behaves as a forced electromagnetic oscillator. At frequencies greater than 50 and 105 Hz, for the TE and TM modes, respectively, the cavity is a cylindrical wave guide for electromagnetic field perturbations associated with the moon. For frequencies less than 50 Hz the cavity fieldperturbations due to the presence of the moon are attenuated downstream of the moon.