Our forefather Abraham was an expert astrologist; he gazed up at the stars, and saw that he would never be a father.
Hashem told Abraham that his reading was accurate, but that he must put the astrology aside. By virtue of Abraham's clinging to Hashem, he raised himself to a status where he was above the stars - the zodiacs no longer had an influence on him, and he became a father to great nations.
Astrology is a true discipline, but those who cling to Hashem in faith and in loving obedience to the Torah's commandments are surely above the stars.
Nature, teaches The Ramcha'l in chapter 7 of Derech Hashem, is certainly influenced by the stars, for that is the way of Hashem's creation. But, Hashem gives us the opportunity to transcend nature, and to live above the stars' influence. Therefore, anyone can change fate or a stroke of bad luck by making Teshuva and clinging to Hashem. As such, the Gemara declares (tractate Shabbos 156b), Ayn mazal leYisroel, in other words, the stars have no influence over Israel, the loyal ones who cling to Hashem.
Rebbe Nachman of Breslev adds that for those who live above the stars' influence, miracles are natural. Just ask Esther and Mordechai... Happy Adar!