JON - Why is astrology frowned upon? when the wise men new of christ birth because of a star.

JOEL - The reasons why we should avoid believing in astrology are found at this page.

The star the wise men saw had nothing to do with astrology involving the arrangement or movement of the constellations in space; it was simply a new star that they believed had been prophesied to appear to attend the birth of the new king of the Jews.
In his book "Mortal Messiah" Bruce R. McConkie states:

"As to the star, there is nothing mysterious about it. The Magi, if so they are to be designated, were not reading portents in the skies nor divining the destinies of men by the movement of celestial bodies in the sidereal heavens. The new star was simply a new star of the sort we are familiar with. No doubt it exhibited an unusual brilliance, so as to attract special attention and so as to give guidance to those who walked in its light, but it was, nonetheless, a star. There was among the Jews of that day a prophecy that such a star would arise at the time of Messiah's coming, and these men who came to Jerusalem in search of that Holy Person had seen and identified the star by the spirit of inspiration. Edersheim quotes from the ancient Jewish writings relative to the prophetic knowledge then had as to such a Messianic star. One such writing says: "A star shall come out of Jacob. . . . The star shall shine forth from the East, and this is the Star of the Messiah." Another said that "a Star in the East was to appear two years before the birth of the Messiah." (Edersheim, "The Life and Times of Jesus the Messiah" 1:211-12.)