At the beginning of this course, we will take a trip back in time and start our journey of the stars with the first greek astronomers. We will pay respect to Eratosthenes and Aristarchus for their brilliant intuition and mathematical genius in discovering that our planet is a sphere and not at the center of the universe, more than 2000 years before Galileo and Copernicus. We will explore the first methods for finding a position using stars and how celestial objects locations in the celestial sphere were recorded in almanacs. On the way to modern times, we will salute Sumner and St Hilaire for giving us, back in the mid 19 th century, the 2 main methods used for sight reductions today.