The Beauties of Nature, and the Wonders of the World We Live In

by Sir John Lubbock

The past history of the Leonids, which Le Verrier has traced out with great probability, if not proved, is very interesting. They did not, he considers, approach the Sun until 126 a.d., when, in their career through the heavens, they chanced to come near to Uranus. But for the influence of that planet they would have passed round the Sun, and then departed again for ever. By his attraction, however, their course was altered, and they will now continue to revolve round the Sun.

There is a remarkable connection between star showers and comets, which, however, is not yet thoroughly understood. Several star showers follow paths which are also those of comets, and the conclusion appears almost irresistible that these comets are made up of Shooting Stars.

We are told, indeed, that 150,000,000 of meteors, including only those visible with a moderate telescope, fall on the earth annually. At any rate, there can be no doubt that every year millions of them are captured by the earth, thus constituting an appreciable, and in the course of ages a constantly increasing, part of the solid substance of the globe.

THE STARS

We have been dealing in the earlier part of this chapter with figures and distances so enormous that it is quite impossible for us to realise them; and yet we have still others to consider compared with which even the solar system is insignificant.

In the first place, the number of the Stars is enormous. When we look at the sky at night they seem, indeed, almost innumerable; so that, like the sands of the sea, the Stars of heaven have ever been used as effective symbols of number. The total number visible to the naked eye is, however, in reality only about 3000, while that shown by the telescope is about 100,000,000. Photography, however, has revealed to us the existence of others which no telescope can show. We cannot by looking long at the heavens see more than at first; in fact, the first glance is the keenest. In photography, on the contrary, no light which falls on the plate, however faint, is lost; it is taken in and stored up. In an hour the effect is 3600 times as great as in a second. By exposing the photographic plate, therefore, for some hours, and even on successive nights, the effect of the light is as it were accumulated, and stars are rendered visible, the light of which is too feeble to be shown by any telescope.

The distances and magnitudes of the Stars are as astonishing as their numbers, Sirius, for instance, being about twenty times as heavy as the Sun itself, 50 times as bright, and no less than 1,000,000 times as far away; while, though like other stars it seems to us stationary, it is in reality sweeping through the heavens at the rate of 1000 miles a minute; Maia, Electra, and Alcyone, three of the Pleiades, are considered to be respectively 400, 480, and 1000 times as brilliant as the Sun, Canopus 2500 times, and Arcturus, incredible as it may seem, even 8000 times, so that, in fact, the Sun is by no means one of the largest Stars. Even the minute Stars not separately visible to the naked eye, and the millions which make up the Milky Way, are considered to be on an average fully equal to the Sun in lustre.

Arcturus is, so far as we know at present, the swiftest, brightest, and largest of all. Its speed is over 300 miles a second, it is said to be 8000 times as bright as the Sun, and 80 times as large, while its distance is so great that its light takes 200 years in reaching us.

The distances of the heavenly bodies are ascertained by what is known as "parallax." Suppose the ellipse (Fig. 54), marked Jan., Apr., July, Oct., represents the course of the Earth round the Sun, and that A B are two stars. If in January we look at the star A, we see it projected against the front of the sky marked 1. Three months later it would appear to be at 2, and thus as we move round our orbit the star itself appears to move in the ellipse 1, 2, 3, 4. The more distant star B also appears to move in a similar, but smaller, ellipse; the difference arising from the greater distance. The size of the ellipse is inversely proportional to the distance, and hence as we know the magnitude of the earth's orbit we can calculate the distance of the star. The difficulty is that the apparent ellipses are so minute that it is in very few cases possible to measure them.