Astronomers have made predictions based on the study of astrological signs as well as movement of planets and stars and their influence on Earth, and have argued it according to astronomy. This science was initially the exclusive domain of astronomers, but gradually expanded to the field of medicine and treating the patients. The subjects related to the well-known astrological signs (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces) in the zodiac and planets (Saturn, Jupiter, Mars, Sun, Venus, Mercury, and Moon) in the solar system have a special effect according to Persian Medicine. The most important applications included recognizing the suitable moment for medical affairs, including determining the time of symptom onset in patients, composing drugs, prescribing pharmaceutical drugs, medicine consumption at the suitable moment, and finally restoring patient health. Astrological concepts that are more prominent in handwritten texts of three great Iranian sages, Abu Rayhan Biruni, Sayyid Isma‘il Jurjani, and Aqili Shirazi, are those related to predicting auspicious (sa'd) and infelicitous (nahs) moments for medical affairs.