Fig. 108.—Apple Cut to Show Crescent.
The different aspects we get of the Moon as it revolves round the Earth are called the Moon’s phases; and each phase has a name, as the new moon; the first quarter; the full moon, and the last quarter.
Between the new Moon and the first quarter, and between the last quarter and the new Moon only a crescent, or sickle-like edge of the Moon, can be seen; while between the full Moon and last quarter the Moon is gibbous (pronounced gib´-us and meaning swelled, or shaped like a football).
If you will look at the picture, [Fig. 108], and the diagrams, [Figs. 109] and [110], and do the experiment which follows, the way the phases of the Moon are made will be perfectly clear.
The picture, [Fig. 108], shows an apple from which a thin sector or slice has been cut. The lower picture shows the stem end of the apple and from this point of view the part where the slice was cut out looks wedge-shaped. This is the view of the Moon shown in [Fig. 109], if we could look down on it.
Fig. 109.—Diagram Showing How the Moon’s Phases Are Made.
Now turn the apple on its side and the place where the slice was cut out can be seen from the stem to the blossom end of the apple when it takes on a crescent form. This is the view of the Moon we really get between new Moon and its first quarter, as shown in [Fig. 110].
The diagrams, [Figs. 109] and [110], show the Earth in the center of the Moon’s orbit and the Moon is pictured in eight positions, as it moves round the Earth, one for each phase, while the sunlight falling upon the Earth and the Moon is shown by streamers of light from the Sun above.
The diagram, [Fig. 110], shows how the sunlight falls on the Moon, but you must always keep in mind that only that part of the Moon which is in the sunlight and which is also inside of the line of its orbit can be seen from the Earth.