In what ways is it useful to explain orbits of planets as circular orbits and why do we sometimes need to be more specific and use elliptical orbits? What can elliptical orbits help explain?

When you see distant streetlights through smog, they look dimmer and redder than they do normally. but when you see the same streetlights through fog or falling snow, they look dimmer but not redder. use your knowledge of the interstellar medium to discuss the relative sizes of the particles in smog, fog, and snowstorms compared to the wavelength of light.