ECLIPSES
Reading edition
The total eclipse of the Sun, January 24, 1925, brought the subject of eclipses to the public attention as never before, and many thousands of persons watched that beautiful and impressive sight through smoked glasses or strips of film.
When we speak of eclipses, we usually mean an eclipse of either the Sun or the Moon. How are such eclipses caused?
A total or partial eclipse of the sun is caused by the moon passing between the earth and the sun, the three celestial bodies forming, as it were, a straight line. The sun is then shut-off from the vision of the inhabitants of our globe over a certain, limited area of its surface. The shadow cast by the moon falls across the earth.
But how is the moon eclipsed? Certainly the sun does not pass between the moon and the earth, on such occasions! What causes the moon to be eclipsed?
The answer is as follows: Inasmuch as both the earth and the moon are illuminated by the sun, they both cast long shadows into space, as any solid body does, when held in front of a strong light. The earth’s shadow trails away for thousands of miles into space. Into this shadow the moon enters, and when it does so, it becomes eclipsed—totally or partially, as the case may be. Total eclipses are instances when the whole surface of the celestial body is apparently covered; partial eclipses are those in which only a portion of the body is dark—the remainder being still visible.
In addition to eclipses, two other astronomical phenomena of interest should here be mentioned: Transits, and Occultations. By “transit” is meant the passage of some other heavenly body between ourselves and the sun. Thus, Mercury and Venus, both lying nearer the sun than the earth, occasionally pass in front of it. We then have a transit of Venus, or a transit of Mercury, as the case may be.
By “Occultation” is meant the hiding of one heavenly body by another—as when the moon hides some other planet or star, or one planet hides another planet or star. The three bodies are then “in line” as before. Of course, all eclipses represent instances of Occultation.