I'm fairly sure that Tolkien himself states that orcs and goblins are two words for the same thing. The Orcs (or goblins) that can travel in sunlight were specially bred to do so (the Uruk-Hai); it's not that orcs are foul creatures that can move during the day and goblins are restricted to the night.
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But of bliss and glad life there is little to be said, before it ends; as works fair and wonderful, while still they endure for eyes to see, are their own record, and only when they are in peril or broken for ever do they pass into song.
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