It's a mosaic so they're not blacked-out, they're sections where there is no image data. Presumably they either haven't taken pictures of those parts of the vis

It's a mosaic so they're not blacked-out, they're sections where there is no image data. Presumably they either haven't taken pictures of those parts of the visual field, or the pictures aren't available or are unusable for some reason. Either that or, you know, maybe a bird drifted into shot ;-)