The author of this book is one of the largest and most accurate astronomers in its astronomical referrals that he conducted from the Mokattam Observatory in Egypt, and he is the true inventor of the pendulum or the dance of the clock, and he is the founder of modern astronomy, and has the most accurate table of timing differences, and his name was given to one of the invasive surface areas of the moon; It is the Muslim astronomer, Abu Al -Hassan bin Yunus Al -Sadafi, the Egyptian.