Popular Scientific Recreations / in Natural Philosphy, Astronomy, Geology, Chemistry, etc., etc., etc.

by Gaston Tissandier

Fig. 570.—New Moon.

The moon revolves round the earth in a changeable elliptical orbit, intersecting the ecliptic at certain points called Nodes. When the moon is nearest to the Earth she is said to be in perigee when farthest from us she is in apogee (the line uniting these points is the line of apsides), the difference in distance being about 4,000 miles. She passes the sun periodically, and so if the moon moved in the plane of the ecliptic there would be eclipses of the sun and moon twice a month; but as the orbit is inclined a little, she escapes by moving north or south. We will now endeavour to explain this theory.

Eclipses.

We have briefly considered the Sun and Earth and the Moon separately. We are now about to regard the effects produced by them when they come in each other’s way and cause Eclipses, which are observed with so much interest. There are eclipses of the sun and of the moon. The former occur at the time of new moon, and the latter at full moon; and this will be at once understood when we remember that the sun is eclipsed by the moon passing between us and the sun; and the moon is eclipsed because the shadow of the earth falls upon her when she is opposite the sun, and therefore “full.”

Fig. 571.—Solar eclipse with corona.

Readers of the voyages of Columbus will remember that he managed to obtain supplies from negatively hostile Jamaica savages by pretending to cause an eclipse of the moon, which he knew was about to take place, and to the ancients eclipses were of dire portent. Even in enlightened Rome, to ascribe an eclipse to the causes of nature was a crime. The Chinese have an idea that great dragons are devouring the moon when she is eclipsed.

There are total, partial, and annular eclipses. The former terms speak for themselves; the latter name is derived from “annulus,” a ring; for a ring of light is left around the dark portion eclipsed, and is only seen in solar eclipses. In one sense the eclipse of the sun is really an eclipse of the earth, because it is caused by the shadow of the moon falling upon the earth.