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HOW THE MOON THROWS ITS SHADOW ON THE EARTH, SHUTTING OFF THE LIGHT OF THE SUN

HOW THE MOON COMES BETWEEN THE EARTH AND SUN, CAUSING THE SHADOW SHOWN ABOVE

HOW THE EARTH THROWS ITS SHADOW ACROSS THE MOON

On its way through space the moon passes sometimes between the sun and the earth, shutting off the sunlight from the earth, as shown in the top picture. The drawing in the middle shows us that the moon does not hide the sunlight from the whole of the earth, but only from a part of it. But in the part from which the sun is hid the moon’s shadow makes day so dark that we can see the stars. We call this an eclipse of the sun. Sometimes, too, the earth passes between the moon and the sun so as to cut off all sunlight from the moon, as shown in the bottom picture. We call this an eclipse of the moon.

Solar Eclipses. The shadow cast by the moon is also conical, and extends over a slightly varying distance of about a quarter of a million miles from the moon’s surface. This being the approximate distance of the moon from the earth, it is seen that when the moon is between the earth and the sun the shadow may reach the earth. The extreme limit of the shadow may range from twenty-three thousand miles short of the earth, in which case an entire eclipse of the sun is impossible, to fifteen thousand miles beyond the earth. In the latter case a circular shadow will be projected on the surface of the globe, travelling onwards slowly in the direction of the motion of the moon. Within this shadow or umbra the body of the sun cannot be observed, and a total eclipse prevails. A circular region exists round this shadow, in which only part of the sun is visible; this region is therefore partly in shadow, and is called the penumbra. Outside the penumbra the whole sun may be viewed; the moon’s shadow is not nearly large enough to render a solar eclipse co-existent over all parts of the earth’s face towards the sun.