Planets move around the sun in nearly circular orbits. Fig. 2-9 The solar system. The planets revolve around the sun in nearly circular orbits. Their orbital planes lie almost on the same plane. They do not emit light, they shine by reflecting sunlight. Their orbits lie in nearly the same plane as the earth? (Fig. 2-9). planets appear to move near the ecliptic they move within the Zodiac, a band of width 18° centered on the ecliptic Planets closer to the sun move faster and have shorter orbital periods. e.g., period of the earth = 1 yr.; period of Mars: ~ 1.9 yr.; period of Saturn ~ 29 yr. Inner planets (Venus and Mercury) are closer to the sun than the earth. they always appear close to the sun they can be observed for a short time just after sunset as evening stars above the western horizon, or just before sunrise as morning stars above the eastern horizon.