I stand corrected regarding the word used for the timing of a festival but that doesn't affect the general point I was trying to make. And, yes, I understand that a normal occurrence can be a sign. Another example would be circumcision. But what I was trying to say is that the word "sign" can have two basic meanings, one for a normal occurrence, which is more like a token, and one for an extraordinary occurrence, like a miracle.
When a sign is related to a normal occurrence, then the message from God is more of a token or reminder. And when a sign is related to some extraordinary occurrence, then the message from God has a special meaning, like a proof or a warning. But I see no evidence that a normal occurrence conveys some special message from God. So I don't consider an eclipse or some alignment of planets and stars is used by God to send a special message or to give people or nations a warning of future events.
How do you rightly divide or draw a line separating two areas when they overlap? You seem to be saying that some kind of Biblical astrology could be valid as long as it regards nations and isn't some personal prediction for individuals. But doesn't a prediction regarding a nation necessarily affect the individual people of that nation personally?
But the Babylonians made no distinction between astronomy and astrology (and they aren't alone in that regard). They didn't understand the actual science involved in astronomy but only based their predictions on repeating patterns over many years and I imagine they did the same for their astrology. They couldn't distinguish the difference because even their astronomy predictions were not certain and had some probability associated with them (they had no knowledge of the orbits of heavenly bodies). So they couldn't tell that their astronomy predictions were any different fundamentally than their astrology predictions.
If there had been schools for prophets I see no evidence that they involved training in some body of knowledge in how to predict the future or how to interpret signs. Prophets were spokesmen for God and obtained the message they were to proclaim directly from God, not from knowledge they obtained in school.
I think you discount the evidence in Scripture against using any type of astrology, even some type of what could be called Biblical astrology used to tell of future events for nations. Consider the following verses:
Jer 10:2 Thus says the LORD, “Do not learn the way of the nations, and do not be dismayed at the signs of the sky; for the nations are dismayed at them.God didn't write the future in the stars. Does God give miraculous and extraordinary signs in the heavens as warnings of future events? Occasionally, yes, but as far as I can tell they are never based on an interpretation of some regular occurrence in the heavens.Isa 44:24 Thus says the LORD, your Redeemer, and he who formed you from the womb: “I am the LORD, who makes all things; who alone stretches out the heavens; who spreads out the earth by myself;
Isa 44:25 who foils the omens of the empty talkers, and makes fools of diviners; who turns wise men back, and makes their knowledge foolish;