Star-land: Being Talks With Young People About the Wonders of the Heavens

by Robert S. Ball

Fig. 23.—The Changes of the Sun with the Seasons.

I have as yet only been speaking of the daily movements by which the sun appears to go across the heavens between morning and evening. We next consider the annual movements which give rise to the changes of the seasons. It is now Christmastide, when the days are short and dark, while six months ago the days were long and glorious in the warmth and brightness of summer. A similar recurrence of the seasons takes place every year, and thus we learn that some great changes alter the relation between the earth and the sun year after year. We must try and explain this. Why is it that we enjoy warmth at one season, and suffer from frost and snow at another?

Note first a great difference between the sun in summer and the sun in winter. I will ask you to look out at noon any day when the clouds are absent, and you will then find the sun at the highest point it reaches during the day. All the morning the sun has been gradually climbing from the east; all the afternoon it will be gradually sinking down to the west. Let us make the same observation at different parts of the year. Suppose we take the shortest day in December. You will look out about twelve o’clock from some situation which affords a view towards the south, and there, as shown in the adjoining sketch ([Fig. 23]), is the midwinter sun.

But now the spring approaches, and the days begin to lengthen. If you watch the sun you will see it pass higher and higher every noon until Midsummer Day is reached, and then the sun at noon is found quite high up in the sky. As autumn draws near, the sun at noon creeps downwards again until, when the next shortest day has come round, we find that it passes just where it did at the previous midwinter. With unceasing regularity year after year the sun goes through these changes. When he is high at noon we have days both long and warm; when he is low at noon we have days both short and cold.

Vulcan with his golden boat was naturally expected to give an explanation of this. As the summer drew on, each day Vulcan shot out the sun with a stronger impulse, so that it should ascend higher and higher. His greatest effort was made on Midsummer Day, when, after rowing but a little way round from the north towards the east, he drove off the sun with a terrific effort. The sun soared aloft to the utmost height it could reach, and in the meantime Vulcan returned to the west to be ready to catch the sun as it descended. On the other hand, in midwinter, he came round much further through the east to the south, and then shot up the sun with his feeblest effort, and had to paddle as hard as ever he could so as to complete his long return voyage during the brief day.

Fig. 24.—How the Stars are to be seen in broad Daylight.

It is evident that there are two quite distinct kinds of motion of the sun. There is first the daily rising and setting, for which we have accounted by showing that it is merely an appearance produced by the fact that the earth is turning round. But now we have been considering quite a different motion by which the sun seems to creep up and down in the heavens, and this takes a whole year to go through its changes.

There is still another point which we must consider before we can understand all these puzzling movements of the sun. We shall ask the stars to help us by their familiar constellations. You know, perhaps, the Great Bear, or the Plough as it is often called, and Orion. There are also Aries the Ram, Taurus the Bull, and other fancifully named systems. These constellations have been known for countless ages, and for our present purposes we may think of them as permanent groups in the heavens, which do not alter either their own shapes or their positions relatively to each other. These groups of stars extend all around the sky. They are not only over our heads and on all sides down to the horizon, but if we could dig a deep hole through the earth, coming out somewhere near New Zealand, and if we then looked through, we should see that there was another vault of stars beneath us. We stand on our comparatively little earth in what seems the centre of this great universe of stars all around. It is true we do not often see the stars in broad daylight, but they are there nevertheless. The blaze of sunlight makes them invisible. A good telescope will always show the stars, and even without a telescope they can sometimes be seen in daylight in rather an odd way. If you can obtain a glimpse of the blue sky on a fine day from the bottom of a coal pit, stars are often visible. The top of the shaft is, however, generally obstructed by the machinery for hoisting up the coal, but the stars may be seen occasionally through the tall chimney attached to a manufactory when an opportune disuse of the chimney permits of the observation being made ([Fig. 24]). The fact is that the long tube has the effect of completely screening from the eye the direct light of the sun. The eye thus becomes more sensitive, and the feeble light from the stars can make its impression, and produce vision. From all these various lines of reasoning we see that there can be no doubt of the continuous presence of stars above and around us, and below us, on every side, and at all times.