What does "sometime too hot the eye of heaven shines" from Sonnet 18 mean?
It's from Sonnet 18, and all it means is that sometimes the sun ("the eye of heaven") shines with too much heat.
Here's the passage:
Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm'd;
And every fair from fair sometime declines,
By chance or nature's changing course untrimm'd;
But thy eternal summer shall not fade...
So the sense is this: sometimes the sun shines too hot, often you can't see the sun's gold colour, and sometimes everything beautiful looks not-quite-as-beautiful, whether that's because of chance, or just natural change. BUT, the beauty of the beloved (her "eternal summer") will not change.
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