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Comet of 1647. Illustration from Cometographia (1668), by the Polish astronomer Johannes Hevelius, showing a comet observed from Marienburg, Prussia (now in Poland) in 1647. Over the period of a week the comet was observed moving through the Bootes region. The comet was described as having a tail shaped like a spear, that was 12 degrees in length. Comets are bodies of rock and ice that orbit the Sun on elongated orbits lasting hundreds or thousands of years. When they pass into the inner solar system, the Sun heats them up and the ice melts, creating long tails of ice and dust that glow in the light from the Sun.
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