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Why did Galileo think Saturn looked like three objects?
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Saturn
Saturn and its spectacular rings, in a natural-color composite of 126 images taken by the Cassini spacecraft on October 6, 2004. The view is directed toward Saturn's southern hemisphere, which is tipped toward the Sun. Shadows cast by the rings are visible against the bluish northern hemisphere, while the planet's shadow is projected on the rings to the left.
In 1610, when Galileo first observed Saturn through his primitive telescope, the instrument's low resolution prevented him from discerning the true nature of the planet's ring system.
Because he could not resolve the rings, he reported that Saturn appeared to be a composite of three objects: a large central body flanked by two smaller ones that seemed to touch it. He noted that these objects were arranged in a row and appeared stationary relative to one another. Two years later, he was perplexed to find that the "lateral appendages" had disappeared, an effect caused by Earth crossing the ring plane, which made the rings appear edge-on. Galileo never deduced that these features were actually a disk encircling the planet.12