=How to Tell Time by the Moon.=—After having learned how to tell the hour of the day by the Sun you should learn to tell the hour of the night by the Moon. On some nights this is a very simple thing to do, for when the Moon is full it is due south at exactly 12 o’clock midnight, as shown in Fig. 118. Every night before the Moon is full you will find it due south 55 minutes earlier, so that you must subtract 55 minutes from 12 o’clock for each day; that is, one day before full Moon it is due south at 11:05 P. M.; two days before full Moon it is due south at 10:10 P. M.; three days before full Moon it is due south at 9:15 P. M., and so on. After the Moon is full it will be due south 55 minutes later every night and then you must add 55 minutes to 12 o’clock; that is, one day after full Moon it is due south at 12:55 A. M.; two days after full Moon it is due south at 1:50 A. M.; three days after full Moon it is due south at 2:45 A. M., and so on. The Moon’s day is 27½ of our days long. The Moon’s year is 27½ of our days long. The Moon’s diameter is 2,160 miles. The distance from the Moon to the Earth is 240,000 miles. CHAPTER VII OTHER THINGS IN THE SKY =Seeing an Eclipse.=—The word _eclipse_ is taken from the Greek and means to fail to appear. In starcraft, when the Earth passes across the Sun, and the Moon is hidden in its shadow, we say that it is an eclipse of the Moon; or when the Moon passes across the Sun and covers it we say that there has been an eclipse of the Sun. How eclipses of the Sun and of the Moon are caused can be shown by a very simple experiment and you ought to make it. =An Eclipse of the Moon.=—First let us suppose it is the Moon which is eclipsed by the Earth. All that is needed to show how this is done is a lighted lamp on a table and an apple with a knitting needle through its center. Let the flame of the lamp represent the Sun, your head the Earth and the apple the Moon. [Illustration: FIG. 119.—ECLIPSE OF THE MOON BY THE EARTH (EXPERIMENT).] Hold the apple by the knitting needle in a line between your eyes and the flame and turn round just as you did in the experiment showing the phases of the Moon. When you have turned halfway round the apple will be in the shadow of your head, when the apple is eclipsed, as shown in Fig. 119. This is just what happens when the Earth gets between the Sun and the Moon and all these bodies are in a straight line, as shown in Fig. 120; the Moon will then be in the shadow of the Earth, and thus it is that the Moon is eclipsed. [Illustration: FIG. 120.—MOON ECLIPSED BY THE EARTH (DIAGRAM).]