Through Magic Glasses and Other Lectures — An Evening among the Stars, Part 2

And now, if your eyes are not weary, let us go back to the Pole-star and draw a line from it straight down the horizon due north.

Shortly before we arrive there you will see a very brilliant bluish-white star a little to the east of this line.

This is Vega, one of the brightest stars in the heavens except Sirius.

It had not risen in the earlier part of the evening, but now it is well up and will appear to go on, steadily mounting as it circles round the Pole-star, till at four o'clock to-morrow morning it will be right overhead towards the south.

But beautiful as Vega is, a still more interesting star lies close to it (see Fig. 58).

This small star, called [Greek: e] Lyrae by astronomers, looks a little longer in one direction than in the other, and even with the naked eye some people can see a division in the middle dividing it into two stars.

Your telescopes will show them easily, and a powerful telescope tells a wonderful story, for it reveals that each of these two stars is again composed of two stars, so that [Greek: e] Lyrae (Fig. 62) is really a double-double star.

There is no doubt that each pair is a binary star, that is, the two stars move round each other very slowly, and possibly both pairs may also revolve round a common centre.

There are at least 10,000 double stars in the heavens; though, as we have seen, they are not all binary.

The list of binary stars, however, increases every year as they are carefully examined, and probably about one star in three over the whole sky is made up of more than one sun.

[Illustration: Fig. 62. [Greek: e] Lyrae.

A double-binary star.

Each couple revolves, and the couples probably also revolve round each other.

(After Chambers.

)] Let us turn the telescope for a short time upon a few of the double stars and we shall have a great treat, for one of the most interesting facts about them is that both stars are rarely of the same colour.

It seems strange at first to speak of stars as coloured, but they do not by any means all give out the same kind of light.

Our sun is yellow, and so are the Pole-star and Pollux; but Sirius, Vega, and Regulus are dazzling white or bluish-white, Arcturus is a yellowish-white, Aldebaran is a bright yellow-red, Betelgeux a deep orange-red, as you may see now in the telescope, for he is full in view; while Antares, a star in the constellation of the Scorpion, which at this time of year cannot be seen till four in the morning, is an intense ruby red.

[Illustration: _Plate II.

_] COLOURED DOUBLE STARS.

[Illustration: [Greek: g] _Andromedae_.

] [Illustration: [Greek: e] _Booetis_.

] [Illustration: [Greek: d] _Geminorum_.

] [Illustration: [Greek: a] _Herculis_.

] [Illustration: [Greek: b] _Cygni_.

] [Illustration: [Greek: e] _Cassiopeiae_.

] It appears to be almost a rule with double stars to be of two colours.

Look up at Almach ([Greek: g] Andromedae), a bright star standing next to Algol the Variable in the sweep of four bright stars behind Cassiopeia (see Fig. 58).

Even to the naked eye he appears to flash in a strange way, and in the telescope he appears as two lovely stars, one a deep orange and the other a pale green, while in powerful telescopes the green one splits again into two (Plate II.

) Then again, [Greek: e] Cassiopeae, the sixth star lying between the two large ones in the second V of Cassiopeia, divides into a yellow star and a small rich purple one, and [Greek: d] Geminorum, a bright star not far from Pollux in the constellation Gemini, is composed of a large green star and a small purple one.

Another very famous double star ([Greek: b] Cygni), which rises only a little later in the evening, lies below Vega a little to the left.

It is composed of two lovely stars; one an orange yellow and the other blue; while [Greek: e] Booetis, just visible above the horizon, is composed of a large yellow star and a very small green one.

[1] [1] The plate of coloured stars has been most kindly drawn to scale and coloured for me by Mr. Arthur Cottam, F. R.

A.

S.

There are many other stars of two colours even among the few constellations we have picked out to-night, as, for example, the star at the top of the tailboard of Charles's Waggon and the second horse Mizar.

Rigel in Orion, and the two outer stars of the belt, [Greek: a] Herculis, which will rise later in the evening, and the beautiful triple star ([Greek: z] Cancer) near the Beehive (see Fig. 54), are all composed of two or more stars of different colours.

Why do these suns give out such beautiful coloured light?

The telescope cannot tell us, but the spectroscope again reveals the secrets so long hidden from us.

By a series of very delicate experiments, Dr. Huggins has shown that the light of all stars is sifted before it comes to us, just as the light of our sun is; and those rays which are least cut off play most strongly on our eyes, and give the colour to the star.

The question is a difficult one but I will try to give you some idea of it, that you may form some picture in your mind of what happens.

We learnt in our last lecture (p. 131) that the light from our sun passes through the great atmosphere of vapours surrounding him before it goes out into space, and that many rays are in this way cut off; so that when we spread out his light in a long spectrum there are dark lines or spaces where no light falls.

[1] Now in sunlight these dark lines are scattered pretty evenly over the spectrum, so that about as much light is cut off in one part as in another, and no one colour is stronger than the rest.

[1] See No. 1 in Table of Spectra, Plate I. Dr. Huggins found, however, that in coloured stars the dark spaces are often crowded into particular parts of the long band of colour forming the spectrum; showing that many of those light-rays have been cut off in the atmosphere round the star, and thus their particular colours are dimmed, leaving the other colour or colours more vivid.

In red stars, for example, the yellow, blue, and green parts of the spectrum are much lined while the red end is strong and clear.

With blue stars it is just the opposite, and the violet end is most free from dark lines.

So there are really brilliantly coloured suns shining in the heavens, and in many cases two or more of these revolve round each other.

And now I have kept your attention and strained your eyes long enough, and you have objects to study for many a long evening before you will learn to see them plainly.

You must not expect to find them every night, for the lightest cloud or the faintest moonlight will hide many of them from view; and, moreover, though you may learn to use the telescope fairly, you will often not know how to get a clear view with it.

Still, you may learn a great deal, and before we go in I want to put a thought into your minds which will make astronomy still more interesting.

We have seen that the stronger our telescopes the more stars, star-clusters, and nebulae we see, and we cannot doubt that there are still countless heavenly bodies quite unknown to us.

Some years ago Bessel the astronomer found that Sirius, in its real motion through the heavens, moves irregularly, travelling sometimes a little more slowly than at other times, and he suggested that some unseen companion must be pulling at him.

Twenty-eight years later, in 1862, two celebrated opticians, father and son, both named Alvan Clark, were trying a new telescope at Chicago University, when suddenly the son, who was looking at Sirius, exclaimed, "Why, father, the star has a companion!"

And so it was.

The powerful telescope showed what Bessel had foretold, and proved Sirius to be a "binary" star--that is, as we have seen, a star which has another moving round it.

It has since been proved that this companion is twenty-eight times farther from Sirius than we are from our sun, and moves round him in about forty-nine years.

It is seven times as heavy as our sun, and yet gives out so little light that only the keenest telescopes can bring it into view.

Now if such a large body as this can give so very faint a light that we can scarcely see it, though Sirius, which is close to it, shines brightest of any star in the heavens, how many more bodies must there be which we shall never see, even among those which give out light, while how many there are dark like our earth, who can tell?

Now that we know each of the stars to be a brilliant sun, many of them far, far brighter than ours, yet so like in their nature and laws, we can scarcely help speculating whether round these glorious suns, worlds of some kind may not be moving.

If so, and there are people in them, what a strange effect those double coloured suns must produce with red daylight one day and blue daylight another!

Surely, as we look up at the myriads of stars bespangling the sky, and remember that our star-sun has seven planets moving round it of which one at least--our own earth--is full of living beings, we must picture these glorious suns as the centres of unseen systems, so that those twinkling specks become as suggestive as the faint lights of a great fleet far out at sea, which tell us of mighty ships, together with frigates and gunboats, full of living beings, though we cannot see them, nor even guess what they may be like.

How insignificant we feel when we look upon that starlit sky and remember that the whole of our solar system would be but a tiny speck of light if seen as far off as we see the stars!

If our little earth and our short life upon it were all we could boast of we should be mites indeed.

But our very study to-night lifts us above these and reminds us that there is a spirit within us which even now can travel beyond the narrow bounds of our globe, measure the vast distances between us and the stars, gauge their brightness, estimate their weight, and discern their movements.

As we gaze into the depths of the starlit sky, and travel onwards and onwards in imagination to those distant stars which photography alone reveals to us, do not our hearts leap at the thought of a day which must surely come when, fettered and bound no longer to earth, this spirit shall wander forth and penetrate some of the mystery of those mighty suns at which we now gaze in silent awe.

CHAPTER VIII LITTLE BEINGS FROM A MINIATURE OCEAN