This is one of the translations of TAMIM TIHYEH IM HASHEM ELOKECHA - the summary statement/command in Parshat Shoftim in the portion that teaches us what and on whom we should rely (G-d, Torah, the Navi, Sanhedrin) and on what and whom we may not rely.
The list includes divination, astrologers, omens, sorcery, conjuring, necromancy... and other occult arts. Before we continue, let's put all this in perspective of Parshat Chayei Sara.
The gemara says, and the Rambam echoes, that Eliezer was guilty of relying on omens. When he found himself at the well/spring in Avraham's hometown, he was uncertain as to how to go about finding a suitable wife for his master's son, Yitzchak.
He turned to G-d (that's good) and announced that the girl who would offer him a drink and also offer to water his camels would be the one. It is debated by commentaries as to whether this is really relying on a sign or an omen, or did this constitute a reasonable test of suitability as a shidduch for Yitzchak.
The gemara takes what we might call a middle position on this question by stating that Eliezer was one of three people in Tanach who did not ask properly, with two of them (Eliezer and King Shaul) being answered by G-d well in spite of the problematic way the request was posed, and one was not answered well (Yiftach).
Eliezer is faulted because it could have been an inappropriate girl who made the right offers, but it was Rivka Imeinu who actually did - obviously, the right girl. But the point is, Eliezer's "sign" was flawed. This is still a far cry from Omens (according to most sources), which is akin to Avoda Zara, idolatry.
Let's focus on the topic of omens and then transit to a sub-topic of NICHUSH - astrology. It is clearly forbidden according to Jewish Law to act upon an omen, a sign that has nothing to do with the action one will or will not take. If one says, "Because a crow flew overhead, I will not do such-and-such today."
"Because my piece of bread fell from my mouth, then I won't do something I planned to do during the day." These are forbidden. And all similar things. How about what Eliezer did? He gave a sign, but - it could be argued - it wasn't an unrelated kind of sign. Commentaries debate that issue.
What about Astrology? If a person is told by an astrologer or by his horoscope that a particular day is not good for business transactions, or something like that - may the person postpone his scheduled deal? The acting upon a sign in the stars (as this would be) is one of the things forbidden by the Torah. Is there "anything" to astrology? Do the stars and constellations have anything to say to people about what will or will not happen?
The Rambam school of thought seems to be that there is no truth in the readings of the stars, and that is why it is forbidden to us. As nonsense, all it would do is divert us from our proper straightforward relationship with G-d. Many others feel that Astrology is real. That G-d does indicate with the heavenly bodies the fate and destiny of people.
But to rely on that would be to deny that Torah Jews are not bound by what is predicted for them. That we can rise above our mazal (as the expression goes). And to act upon a horoscope would be to deny G-d's ability to run the world as He sees fit. It would deny our ability to take our destiny into our own hands. And that would damage our relationship with G-d.
Either way, we have a TAMIM TIHYEH problem. Anything in astrology we can accept? Perhaps the indicators of personality traits. Then we are on our own to channel them positively. We must avoid all that might distance us from G-d.
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