Fig. 40.—The Full Moon.
The adjoining picture ([Fig. 40]) gives a fair idea of what the full moon looks like when viewed through a small telescope. I do not, however, say that the lunar objects can then be observed under favorable conditions; for when the moon is full is the very worst time for making observations of our satellite. In fact, at this phase you can hardly see anything except slight differences between the colors of different parts. The best time for observing the moon is at the first quarter; but even then you can only observe satisfactorily those objects which happen to lie along the border between light and shade. To study the moon properly you must, therefore, watch it during several different phases, from the time when it presents a thin and delicate crescent (just after new moon) until it has again waned to a thin and delicate crescent (just before the next new moon). We want the relief given by shadows to bring out the full beauty of lunar scenery.
On the map you will first notice the large dark-colored patches which are so conspicuous on the moon’s face. They are, apparently, the empty basins which great seas once filled. But if water was ever there it has at all events now quite disappeared. These dark parts are, no doubt, a good deal smoother than the rest of the surface; but we can see many little irregularities which tell us that we are not looking at oceans. The chief features I want you to observe are the curious rings which you see in the figure; there is a very well-marked one a little below the centre, and in the upper part many rings—large and small—are crowded together. We call them lunar craters. You will see what they are like from the model, of which a picture is shown in [Fig. 42]. But to realize from this picture the proper scale of the object, you should imagine it to be some miles in width. The cliffs which rise all round to form the wall, as well as the mountain which adorns the centre, are quite as high as any of the mountains in Great Britain.
Fig. 41.—View on the Moon.
(By Lœwy and Puiseux, Paris Observatory.)
The large central crater is Hipparchus and above it is Albategnius.
Fig. 42.—Our Model of a Lunar Crater.