It also could be all of the other things already discussed, and the other things unknown and not discussed. It could even be not true and merely subjective perception.
it could be that the sun bombards earth with far more than light and warmth, and when sufficiently beyond the horizon everything known and that unknown could be it, if it even does exist. And an interesting derivative in language is, that any word that abstractly equates to “may be”, “could be”, creates an inference of may NOT be, or could NOT be, otherwise descriptives such as ABSOLUTELY would be used.