Thus celestial mechanics may be said to have begun with Newton's Principia.
The purpose of the present article is to convey a general idea of the methods by which the results of celestial mechanics are reached, without entering into those technical details which can be followed only by a trained mathematician.
In the actual problems of celestial mechanics three co-ordinates necessarily enter, leading to three differential equations and six equations of solution.
In the problems of celestial mechanics the angles within the parentheses are represented by sums or differences of multiples of the mean longitudes of the planets as they move round their orbits.
The modern methods of celestial mechanics may be considered to begin with Joseph Louis Lagrange, whose theory of the variation of elements is developed in his Mecanique analytique.
