‎"EULER, LEONHARD. - THE RETROGRADE MOVEMENTS OF THE PLANETS.‎
‎Mémoire sur la plus grande Équation des Planetes. (Memoir on the Maximum Value of an Equation of the Planets).‎

‎(Berlin, Haude et Spener, 1748). 4to. No wrappers as issued in ""Memoires de l'Academie Royale des Sciences et Belles Lettres"". tome II, 1746. Pp. 225-248.‎

Reference : 46593

‎First apperance of Euler's mathematical treatment of the retrograde motions of the planets. He discusses the fact that planets observed from the earth exhibit a very irregular motion. In general, they move from west to east along the ecliptic. At times however, the motion slows to a stop and the planet even appears to reverse direction and move from east to west. We call this retrograde motion. After some time the planet stops again and resumes its west to east journey. However, if we observe the planet from the stand point of an observer on the sun, this retrograde motion will not occur, and only a west to east path of the planet is seen. These facts Euler treats mathematically.‎