ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Ferguson's planetary phases diagram. This diagram was published in 1756 by the Scottish astronomer and instrument maker James Ferguson (1710-1776), in his book Astronomy explained upon Sir Isaac Newton's Principles. The main diagram (left) shows the Earth orbiting the Sun, showing how the axial tilt causes the seasons. The outer circle is labeled with the signs of the zodiac, and the inner with the months. The same situation is shown in the diagram at upper right. The diagram at far right shows Jupiter and its four moons. The diagram at lower right shows the tilt of Saturn's ring system relative to the ecliptic.
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