Why do planets change position in the night sky? The planets appear to change position against the "fixed" stars in the night sky because of the relative motion of both Earth and the planets as we all move along in our orbits around the Sun. The swift-moving inner planets Venus and Mercury can move from morning to evening appearances and back again in as little as a few months. The giant outer planets such as Jupiter or Saturn, with orbits taking decades to complete, appear to move more slowly against the background of stars. »FAQs about StarDate Online
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