Using analytic geometry in the limit of small Δθ , the sum of the areas of the triangles in Figure 25.9 is given by The period of revolution T of a planet about the sun is related to the semi-major ax...Using analytic geometry in the limit of small Δθ , the sum of the areas of the triangles in Figure 25.9 is given by The period of revolution T of a planet about the sun is related to the semi-major axis a of the ellipse by \(T^{2}=k a^{3}\) where k is the same for all planets. Using Equation (25.2.1) for reduced mass, the square of the period of the orbit is proportional to the semi-major axis cubed,
