Euler’s Forgotten Equation of the Center

In a 1778 publication in Latin, titled Nova Methodvs Motvm Planetarvm Determinandi (New method to determine the motion of planets), Euler derives an equation of the center, which, apparently, has been forgotten. In the present work, the developments that led to Euler’s equation of the center are revisited, and applied to three planets of the Solar System. These are then compared with results obtained from an equation of center that has been proposed, showing good agreement for planets with not so high eccentricities. Nonetheless, Euler’s derivation was not influential, and since then, the resulting equation of the center has been neglected by scholars and by specialized publications alike.