The 'eccentric anomaly' E is useful to compute the position of a point moving in a Keplerian orbit. As for instance, if the body passes the periastron at coordinates x = a ( 1 − − e ) , y = 0 , at time t = t 0 , then to find out the position of the body at any time, you first calculate the mean anomaly M from the time and the mean motion n by the formula M = n ( t − − t 0 ) , then solve the Kepler equation above to get E , then get the coordinates from: