There are a hundred million to choose from, and we
shall begin with the brightest. It is often called
the Dog Star, but astronomers know it better as Sirius.
Let us see where it is to be placed on our map.
Sirius is beyond Neptune, so it must be outside somewhere.
Indeed, it is a good deal further off than Neptune;
so I try at the edge of the drawing-board; I have
got a method of making a little calculation that I
do not intend to trouble you with, but I can assure
you that the results it leads me to are quite correct;
they show me that this board is not big enough.
But could a board which was big enough fit into this
lecture theatre? Here, again, I make my little
calculations, and I find that there would not be room
for a board sufficiently great; in fact, if I put
the sun here at one end, with its planets around it?
Sirius would be too near on the same scale if it were
at the further corner. The board would have to
go out through the wall of the theatre, out through
London. Indeed, big as London is, it would not
be large enough to contain the drawing-board that
I should require. It would have to stretch about
twenty miles from where we are now assembled.
We may therefore dismiss any hope of making a practical
map of our system on this scale if Sirius is to have
its proper place. Let us, then, take some other
star. We shall naturally try with the nearest
of all. It is one that we do not know in this
part of the world, but those that live in the southern
hemisphere are well acquainted with it. The name
of this star is Alpha Centauri. Even for this
star we should require a drawing three or four miles
long if the distance from the earth to the sun is
to be taken as one inch. You see what an isolated
position our sun and his planets occupy. The members
of the family are all close together, and the nearest
neighbors are situated at enormous distances.
There is a good reason for this separation. The
stars are very pretty and perfectly harmless to us
where they are at present situated. They might
be very troublesome neighbors if they were very much
closer to our system. It is therefore well they
are so far off; they would be constantly making disturbances
in the sun’s family if they were near at hand.
Sometimes they would be dragging us into unpleasantly
great heat by bringing us too close to the sun, or
producing a coolness by pulling us away from the sun,
which would be quite as disagreeable.
The Stars are Suns.
We are about to discuss one of the grandest truths
in the whole of nature. We have had occasion
to see that this sun of ours is a magnificent globe
immensely larger than the greatest of his planets,
while the greatest of these planets is immensely larger
than this earth; but now we are to learn that our
sun is, indeed, only a star not nearly so bright as
many of those which shine over our heads every night.
We are comparatively close to the sun, so that we are
able to enjoy his beautiful light and cheering heat.