The prohibition on the government against enacting anything "respecting an establishment of religion" is explicit. You may argue about how and when it ought apply, but that argument has not a thing to do with penumbras or their emanations.
The hell it doesn't. The term "seperation of church and state" emanated from a letter sent by a sitting President to a Danbury Baptist minister. The penumbral effect of that emanation is well documented. But thanks for the advice, the advice bin was a little low.