Avrahom was an expert in the wisdom of astrology

Medrish Talpiyot At Alef
-Know that everything in the spiritual worlds manifest on the physical.
-By gazing at the stars while in a meditative state one can learn many things. 
-This wisdom of astrology was known to the ancients.
-Avrahom was a master in the wisdom of astrology.
-When gazing at his own horoscope it showed he could not have children.
-G-d revealed to Avrahom how to transcend above the constrictions of destiny as he saw them in the wisdom of astrology.