dynamic equilibrium. Let's apply some maths to see how it works!

Dynamic Equillibrium

Earth revolves around the Sun in a dynamic equillibrium (see diagram overleaf). For the sake of simplicity we left the Moon out, the orbit is assumed circular instead of elliptical and, well, there are no other objects or planets in the sky that could influence the system gravitationally. Thinking why the Sun is revolving at all? Well let's look at the physics then:

Let {M_⊕}, {v_⊕} be the mass and velocity of Earth (in blue) where ⊕ is the symbol for Earth, let M_☉, v_☉ be the mass and velocity of Sun (in yellow) where ☉ is the symbol for Sun and let 'O' be the point of Center of Mass (C.O.M) for the Sun-Earth system.

Centripetal force exerted on Earth:

F_c=\tfrac{M_⊕ \times v_⊕^2}{R_⊕}