Stars and Planets.
Upon inquiry, I have found the answer to the question, "Why does a star twinkle while a planet shines clear and steady?" to be as follows:
A planet is an appreciable disk, generally of considerable magnitude; it is owing to the large size of the body that we behold its reflected light clear and steady. A star, on the other hand, no matter how large it may appear, is nothing more than a self-luminous point—a point, you understand; therefore, any object floating in the air between it and the earth will intercept its light for an instant, and thereby cause a "twinkle." Again, on its way to us the light of a star passes through media of varying densities; it is refracted—bent out of its course—and turned aside for an instant from our eyes. This occurring many, many times per minute makes the star appear to twinkle to an observer on the earth. There are many other ways of explaining the phenomenon, the majority of which, however, are hypothetical and involved. One of the more commonly accepted theories is that storms occurring in the atmosphere of the star cause its photosphere, or luminous envelope, to transmit to us light of varying intensity.
Our knowledge concerning the stars, as a professor of chemistry in our college recently informed his class, has resulted in the following revision of the old nursery rhyme:
"Twinkle, twinkle, little star,
I know exactly what you are,
For with my spectroscopic ken
I know you're naught but hydrogen;
Twinkling there so very bright,
In the distant realms of light."
Simon Theodore Stern.
New York City.