A STARRY UNIVERSE.
I wonder how many of the Stars you know by sight, so as to be able
to point them out one by one, and say, “That is Sirius,” or “That is
Arcturus,” or “That is Capella,” or “That is the Pole-star.”
We are not now thinking of Planets, but of Stars; not of Worlds, but
of Suns; not of our little Solar System, but of the great _Stellar
System_, or Universe of Stars.
Our Sun and all his worlds belong to that Starry Universe. And no doubt
countless other worlds, as well as countless other suns, belong to it
also.
In long-past days the name of “fixed stars” was given to the greater
number of shining points in the sky. They are called “fixed” to make
a difference between them and the planets, which are seen to be _not_
fixed.
Of course all the stars, like all the planets, seem to travel each
night across the sky. We have explained this already, and you know
quite well now that their nightly journey from east to west is only a
seeming journey--only caused by our Earth’s spinning from west to east.
But even thus the stars are “fixed” as they go; for all move in the
same direction and at the same speed. One star does not travel here and
another there, in opposite ways. All travel the same way. Each group
of stars keeps always its own shape. Each star has its own particular
place among other stars. It is as if the whole sky moved round in one
piece.
The planets behave quite differently. A planet is seen to change its
place from day to day, from month to month, _among_ the stars. Now it
is in this group, and now it is in that group. Now it goes forward, and
now it seems to travel backward; or again it appears to stop, and then
starts off anew.
These movements of the planets are a mixture of real movements and of
seeming movements. They are partly brought about by our Earth’s own
journeying.
With the stars no such changes are seen. They remain always the same,
always fixed in the same groups. These groups are commonly called
“_Constellations_.”
The Little Bear’s tail-tip never wanders away from the Little Bear’s
body. The four chief body-stars of the Great Bear never part company.
Orion’s sword never breaks up, and his belt is always made of three
stars in a row, and his feet keep ever at the same distance from his
head. Therefore the stars are called “fixed.”
And yet they are not fixed.
So far as we can tell, every single Star in the sky, like every Planet,
has its own movement. Stars as well as worlds are on the rush. Although
we cannot actually _see_ all to be moving, we may safely say that all
do move.
It seems to us, indeed, as impossible for the stars to be at rest as it
is for the planets to be at rest.
You remember why the planets have to be always hastening along their
pathways round the Sun. If one of the worlds came to a stop it would at
once begin to fall towards the Sun, drawn by the Sun’s great pull; and
perhaps it might end by dropping into the crimson fiery sea.
And it is much the same with the stars.
Just as the Sun and planets all pull or attract one another, so
the stars all pull or attract one another. Each star draws all his
neighbor-stars and is drawn by them.
If there were nothing to meet this perpetual _pull_ of every star for
every other star, then all the stars in the universe would surely in
time rush together and become one enormous heap of Suns.
But there is something to meet and overcome this pull. The stars, too,
are in motion. Each radiant Sun, by his own swift rush through the sky,
so overcomes the pull of other stars that he can keep apart from them
as he journeys.
Some go only a few miles each second, like the planets Jupiter and
Saturn. Some go as fast as Mars or the Earth. Some rival the flight of
Mercury. Others far surpass any of the worlds in speed. There are stars
hastening through the sky at a rate of over one hundred, and over two
hundred, and even over three hundred miles each second.
Yet, despite all these journeyings, the stars remain fixed. Century
after century we see them overhead in changeless groups.
How can it be so? If each star is taking its own onward journey along
its own separate pathway at a rate of at least tens of thousands of
miles every day, surely we ought to see them moving. Surely a star
ought to get nearer to its neighbor on one side, and farther from its
neighbor on the other side. How can it be otherwise if all the stars
move, and if no two move at just the same speed?
That is exactly what the stars are doing. Each star gets daily nearer
or farther away from each of its neighbor stars.
And yet they seem to us to remain fixed. The star-groups are still the
same in shape as when our forefathers looked upon them.
No: we cannot see such changes commonly. And I will tell you why we
cannot. It is because our lives are not long enough.
Think once more about the movement of clouds as seen from the ground. A
small cloud, low down, will appear to hurry across the sky at a great
pace. But you may look for perhaps half-an-hour at far-away clouds,
very high up, and notice no change in them.
This does not mean that the clouds high up do not stir. They may be
actually moving quite as fast as the little cloud down below. Only,
they are so far distant that the movement seems very slow--too slow to
be seen at all, it may be, in one short half-hour.
The stars are enormously more distant than the very highest cloud ever
seen. However fast they really move those movements are very small,
very tiny, as watched from the Earth; so small and tiny that the lives
of many men, one after another, are, all together, too short a time for
the seeing of star-journeyings from the Earth. Only a very few can be
found out thus, by most careful watching.
Among the hosts of travelling stars is our own Sun.
We have spoken so far of the Sun as if he were fixed in one place,
always at rest in the midst of his worlds.
And so far as he has to do with the planets he is at rest. That is to
say, he is always in one place _for them_. He is always about the same
distance from Mercury, from the Earth, from Jupiter, and from Neptune.
He is always just in the middle of the Solar System.
Yet he is not really at rest. He too travels as the other stars travel.
He too is on the move--going somewhere in the skies; where, I cannot
tell you.
And as he speeds onward he carries with him all his company of worlds
and moons, of comets and meteors. They are no trouble at all to him. He
carries them in the strong grasp of his attraction as easily as you in
walking might bear along with you a muff or a hand-bag.
If you were asked how many stars can be seen any clear night in the
sky, you would very likely say--“Oh, thousands and thousands!” You
might even reply, “Millions!”
But nobody ever yet saw a million stars without the help of a
telescope. Commonly we see at most only two or three thousand stars;
and not often so many at once.
For convenience the stars are arranged in Classes, first, second,
third, and so on, like the classes in a school.
These Classes are spoken of as Magnitudes, which means “Sizes.” But the
stars really are put into Classes according to their _brightnesses_:
not according to their sizes.
We know very little as yet about the true sizes of the stars. They all
look to us, in even the biggest telescopes, as mere bright points,
showing no size at all. Some of the brighter stars may be much smaller
than others which seem to us more dim.
The shining of a star in our sky depends upon two things. It depends
partly on the size and brightness of the star. It depends partly on the
nearness of that star to the Earth.
All we are able to do is to arrange them in classes according to their
_brightness_ as seen from the Earth.
Those which shine the most are called Stars of the First Magnitude;
those which come next in brightness are called Stars of the Second
Magnitude; and so on.
In the whole sky all around the Earth there are only about twenty Stars
of the First Magnitude. Those twenty stars are mere bright points in
the sky; none of them so bright as Venus and Jupiter look to us.
Yet they are all Suns; radiant globes of heat and light more or less
like our own great Sun; not like a mere planet.
QUESTIONS.
1. What is meant by the Stellar System?
The Universe of Stars to which our Sun belongs.
2. How are Planets known from Stars?
The Stars remain fixed in groups, while Planets are always changing
their places among the Stars.
3. What is meant by “Fixed Stars?”
The Stars are so called because of their fixity in certain groups.
4. Tell me the name commonly given to groups of Stars.
They are called Constellations.
5. Name two or three Constellations mentioned in this chapter.
The Little Bear; the Great Bear; Orion.
6. Are the Stars really fixed?
No; they are believed to be all moving.
7. If the Stars are moving why do we not see it?
Because of their immense distance from us. Our lives are not long
enough for us to see most of the Stars change their places in our sky.
8. Is the Sun at rest?
Our Sun journeys like other stars through the sky.
9. Does he ever leave his planets behind?
No; he carries them all with him.
10. How does he do so?
By means of his powerful attraction.
11. What is the meaning of “Magnitude?”
The word “Magnitude” means “Size.”
12. What is meant by Star-Magnitudes?
The Stars are divided into different classes, called Magnitudes--such
as Stars of the First Magnitude, Stars of the Second Magnitude.
13. Are all Stars of the First Magnitude larger than all other Stars?
No; it is a question of brightness, and not of size.
14. What do we really mean by Stars of the First Magnitude?
We mean those stars in our sky which shine more brightly, as seen from
the Earth, than any other stars.
15. Does not brighter shining show greater size?
It may sometimes show greater size, or it may only show greater
nearness to the Earth.
16. How many Stars of the First Magnitude are there?
About twenty altogether, round the whole sky.