The Earth might "roll
upon this ring like
a ball upon a road."
(Aspects of Saturn's
Rings.) From Comstock's
"Textbook on Astronomy,"
by permission of publishers,
D. Appleton & Co.
Seen edgewise through the 40-inch Yerkes telescope, it is scarcely more than a streak of light "like a pair of illuminated needles piercing the ball on opposite sides." This is because all of these tiny moons which fly about Saturn are moving in the same plane. We obtained this edgewise view in 1907; in 1915 the ring was opened at its widest extent while in 1921 it was again almost invisible.
The reason that this ring may be observed at so many angles is because it is inclined about 27 degrees to the plane of the planet's orbit and about 28 degrees to the plane of the ecliptic. In the course of the earth's journey and Saturn's journey around the sun, we sometimes look up at this ring and sometimes down upon it, but when the earth lies exactly in the same plane, we look only on the edge which is so thin that it becomes almost invisible. The thickness of the ring is, indeed, scarcely anything at all in comparison to its width for, although the distance from one side to the other of the entire ring is about 172,000 miles, its edge is estimated as only about 62 miles.
When the rings are open, the dark shadow of Saturn's planet may be seen against the light of these rings.
"While Saturn whirls, his steadfast shade
Sleeps on his luminous ring."
—Tennyson.
This shadow proves that the dull, yellowish glow on the planet is reflected sunlight, and that the planet does not shine with its own light, as a star.
THE MOONS OF SATURN
Besides all the tiny moonlets in the beautiful ring, ten large moons whirl about the planet Saturn. These give Saturn a system with a radius of 8 million miles, which is quite extensive compared to the earth and moon system which has a radius of 240,000 miles.
The moons of Saturn range in size from about 200 miles to nearly 300 miles in diameter but being so far away only Titan, the largest, can be seen except in a large telescope. These satellites were given the names of the brothers and sisters of the God of Time and are called Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyperion, Japetus, Phœbe and Themis.