Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

According to Newton's law of gravitation, the two objects exert equal forces on each other. Therefore, the sun exerts a gravitational force of $F = \frac{G~M_s~M_e}{R^2}$ on the earth. Also, the earth exerts a gravitational force of $F = \frac{G~M_s~M_e}{R^2}$ on the sun. Therefore, the earth's gravitational force on the sun is equal to the sun's gravitational force on the earth.