ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Types of comets. Artwork published in 1668 by the Polish astronomer Johannes Hevelius (1611-1687), showing different types of comets. 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. Hevelius used a crude telescope to observe the comet of 1661. These observations were published in his book Cometographia (1668), and this is figure K from that book. The Latin labels refer to bifurcated tails and pyramidal comets. The artworks also show the variations Hevelius had seen in the structure of cometary heads (nuclei).
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