JUPITER, the giant planet of our system, is nearly eleven times as large in diameter as the earth. So very far away is it that the earth's orbit shrinks almost into insignificance by com parison. it follows that there is never any sensi ble foreshortening in our view of Jupiter, nor does it exhibit any phases like the moon or closer planets. Jupiter has no less than five satellites. Your of these are of quite conspicuous magni tude, and visible easily in the smallest telescope. indeed, they were discovered, as we have already seen. by Galileo. the first time he ever turned to the heavens the telescope he had invented. The fifth is a very tiny one, so close to the planet that it can be distinguished only with the greatest difficulty. It was discovered by Barnard in 1892 at the Lick Observatory. These satellites present a great variety of interesting phenomena. At
times one or another is eclipsed, on account of the planet being between the satellite and the sun. They then rather suddenly disappear from our view. At other times, they become invisible by going behind the planet as seen from the earth. Again, sometimes they pass between the planet and the sun, so that we can see quite plainly the satellite's shadow projected as a black dot on the planet's visible disk. In the telescope, Jupiter shows truly astonishing surface mark ings. It would appear as though it possesses a great atmosphere with floating clouds of varying shapes and colors. It has an axial rotation which is completed once in about ten hours, so that the rotation alone is rapid enough to give ever changeable views of the visible surface to the observer.