A blessed Nativity / Theophany season to all!
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In Crucifixion icons, I haven't seen angels "represent" the sun and moon. I've seen anthropomorphized suns and moons, but the angels are just angels doing as brion posted; or at the sides of Jesus with chalice and cloth, as seen in this example.
But, this is only my experience from what I have seen.
Edit: I think I have seen more icons of Extreme Humility without angels than with.