2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188019We give a solution of the wave equation for massless, or massive spin-2 particles propagating in a gravitational background. The solution is covariant, gauge-invariant and exact to first order in the background gravitational field. The background contribution is confined to a phase factor from which geometrical and physical optics can be derived. The phase also describes Mashhoon's spin-rotation coupling and, in general, the spin-gravity interaction.8 pages, 1 figureGeneral Relativity and Quantum Cosmologytext