The little rings with wings

If the Sun is bright and the temperature too low for comfortable outdoor observations, you can still give a splendid demonstration by casting the projection onto a piece of white cardboard set at right angles to the telescope in an otherwise darkened room.

In such projections the only visible portion of the Sun is the disc, known to astronomers as the "photosphere." Around this disc is the "chromosphere" which forms a band five thousand miles wide. In a general way these two correspond to the Earth and its atmosphere. Surrounding the chromosphere is the much larger "corona," the beautiful phenomenon which becomes visible only when the Sun is totally eclipsed.

Sunspot disturbances in the innermost parts of the Sun seem to affect even the outer portions. When sunspots are most prevalent, the corona appears to surround the Sun with a perfect ring; when there are few sunspots the corona takes an entirely different form. Great lines of light, sometimes several diameters of the Sun in length, sprout from the Sun's equator; little rays project from the polar zones at right angles to the axis.

An eclipse during a sunspot minimum offers a perfect solution of the little "rings with wings" found throughout Chaldea, Babylonia and Egypt. Their prevalence is no longer a puzzle. Such an eclipse might easily have been visible in the whole territory, either at one time or on several occasions. The great streamers of light took wings, and the little man with the kilt, or the little kilt without the man, showed a pleating that almost exactly reproduced the pleats in the polar rays. Eclipses were always recorded as spectacular phenomena, and a sight like this could not fail to call forth all the innate powers of imagery in a primitive artistic mind. Of course the symbol may have been a coincidence, but if so there is no more remarkable coincidence in history.

Because the corona could never be seen except when the Sun itself was darkened, it used to be responsible for the long trips which astronomers took to see an eclipse. Today, however, a picture of the corona can be taken on any clear day, due to the ingenuity of a French astronomer, Dr. B. Lyot. His instrument, "the coronograph" creates an artificial solar eclipse within itself, photographs the corona and the solar prominences, both with still shots and movies.

The photosphere is the most obviously visible part of the Sun. It gives the continuous spectrum of an incandescent solid. The chromosphere is gaseous and it absorbs some particular colors. This absorption causes the dark Fraunhofer lines which tell us the composition of the Sun. Sometimes enormous excresences of hydrogen gas project from the chromosphere and continue to change and elongate until they are several hundred thousand miles in length. Astronomers have been able to photograph them for a number of years now by means of the "spectroheliograph" which takes their portraits in monochrome light. This instrument has its prisms between two slits. While the Sun's image passes across one slit, the plate is made to traverse behind the other at a corresponding speed in order that the picture may be sharp.

The composition of the photosphere confronts astronomers with a serious problem. This inner disc appears to be dense, heavier than water, and about one-quarter the density of Earth, whereas at high temperatures such gases should be very light. Since we cannot reach the Sun's temperature in any laboratory on Earth, we cannot study similar conditions at close range. We know the individual physical features of the Sun, but we cannot imagine how they are combined.

Most of the necessary factual data is complete. The temperature of the Sun's surface is established at 6,000° C. The diameter of the Sun is 109 times the diameter of the Earth. We know the materials of which the Sun is composed; but there our knowledge ceases. How these characteristics are combined in one body is a puzzle that has not yet been solved. Even the most plausible solutions offered are far from satisfactory.

The same puzzle exists in the stars. Some stars are incredibly light, others unbelievably heavy, far heavier than any materials known on Earth. Steady progress in astrophysics has led to some knowledge, but it is still in a state of complexity and doubt.

The relative sizes of the Earth, Moon and Sun were very effectively shown by the late Professor H. H. Turner of Oxford, in a lecture entitled, "A Journey in Space." He produced a lady's hatpin stuck into the end of a twenty-four-inch rod, on the end of which was a marble three-fourths of an inch in diameter. He explained that this was a model of the Earth and Moon on a scale of ten thousand miles to the inch. He then opened the largest commercial sized umbrella (the type that used to be called a "carriage umbrella," now used as ornaments at Palm Beach or La Jolla) and told us that this was a part of the Sun on the same scale. Holding his Earth-Moon model close to the handle of the umbrella, he demonstrated how the Moon could revolve around the Earth within the space occupied by the Sun.

In any terrestrial scale of proportions this makes the Sun seem fairly large but, as stars go, it is quite ordinary. We tend to rate it highly because it has the good taste to stay near to us, and we are attracted by it. As a matter of fact that is its great claim to importance. We can study the Sun as we can study no other star. We have one neighbor from whom we can receive communications in eight minutes, and a host of acquaintances whose messages take three years or more in transit. Everyone who has ever lived on a rural telephone line knows that it is vastly easier to know the affairs of a near neighbor than of all the other acquaintances put together, though they may be much more interesting people and more worth knowing.

Comparison from a neutral standpoint is very difficult and it is only in fairly recent years that the proper place of the Sun among the stars has been estimated. In all star tables for size, density, luminosity and all other qualities, there is nothing in which our Sun excels. There are a great many larger and heavier stars, and plenty of less significant ones. In fact, taken all together, this remarkable body around which all the movement, life and civilization of our Earth revolves is just about average.