an obscuring of the light from one celestial body by the passage of another between it and the observer or between it and its source of illumination

an eclipse of the sun

a phase during which the distinctive markings of a bird (especially a male duck) are obscured by moulting of the breeding plumage

eclipse plumage

(of a celestial body) obscure the light from or to (another celestial body)

Jupiter was eclipsed by the Moon