JUPITER IS MOVING BACKWARD ACROSS THE NIGHT SKY — or at least, that's what it looks like from Earth. Over the past weeks, Jupiter has been drifting westward relative to the background stars in Gemini, a phenomenon astronomers call "retrograde motion." But this apparent backward motion is entirely an optical illusion caused by Earth's faster orbital speed overtaking Jupiter's slower path around the Sun. Imagine two cars on a highway: you're in the faster inside lane passing a slower car in the ou