If observation be conducted at or near the full, the conditions will be found to have entirely changed. There are now very few ruggednesses visible on the edge of the disc, which now presents an almost smooth circular outline, nor are there any shadows traceable on the surface. The circular depressions, formerly so conspicuous, have now almost entirely vanished, though the positions and outlines of a few of them may still be traced by their contrast in colour with the surrounding regions. The observer's attention is now claimed by the extraordinary brilliance and variety of the tones which diversify the sphere, and particularly by the curious systems of bright streaks radiating from certain well-marked centres, one of which, the system originating near Tycho, a prominent crater not very far from the South Pole, is so conspicuous as to give the full moon very much the appearance of a badly-peeled orange (Plate XII.). [Illustration: PLATE XII. The Moon, November 13, 1902. Paris Observatory.] As soon as the moon has passed the full, the ruggedness of its margin begins once more to become apparent, but this time on the opposite side; and the observer, if he have the patience to work late at night or early in the morning, has the opportunity of seeing again all the features which he saw on the waxing moon, but this time with the shadows thrown the reverse way--under evening instead of under morning illumination. In fact the character of any formation cannot be truly appreciated until it has been carefully studied under the setting as well as under the rising and meridian sun. We must now turn our attention to the various types of formation which are to be found upon the moon. These may be roughly summarized as follows: (1) The great grey plains, commonly known as Maria, or seas; (2) the circular or approximately circular formations, known generally as the lunar craters, but divided by astronomers into a number of classes to which reference will be made later; (3) the mountain ranges, corresponding with more or less closeness to similar features on our own globe; (4) the clefts or rills; (5) the systems of bright rays, to which allusion has already been made.