LONG-TAILED COMETS.
A good deal has been said about empty gaps in the sky between and
around the pathways of the worlds. But those gaps are at least not
always quite empty.
Comets, with long bright tails, flash through the darkness by hundreds,
perhaps thousands. Meteors travel in vast swarms, by millions of
millions. Each comet gives forth a radiant shining, and each little
meteor is bright in the sunlight. I am going to tell you about Comets
first, and then about Meteors.
The word “comet” means “a hairy star.”
But comets are not stars really, though they have often been mistaken
for stars, especially when first seen without any tail.
There may be any number of comets as far away as the stars, millions of
them in each direction. But those we cannot possibly see. We only see
such comets as belong to our Sun and travel about in his kingdom, or
else those which come to pay him a visit from far away.
No comet that is outside the Solar System can be visible to us on the
Earth. The distance becomes too great. For the light of a comet is
not like the light of a star, and it cannot reach through billions of
miles, as the light of a star can.
Once in a while a splendid comet makes its appearance, with a tail
reaching half across our sky. But this is not at all common. Most of
those seen are small and faint, and the greater number can only be seen
at all in telescopes.
Almost every year some fresh ones are found in the sky, and hardly a
day passes in which at least one may not be noticed, in some part of
the heavens, with a good telescope.
Each comet, like each world, has its own pathway in the sky round
the Sun. But a comet-pathway is much more oval in shape than a
planet-pathway. Sometimes it is a very long and very narrow oval
indeed, with the Sun almost close to one end of the long oval.
To get round such a pathway as this takes a good while. At one part
the comet gets quite near to the Sun, and then rushes at a tremendous
speed. After which he wanders far away from the Sun, and creeps along
more and more slowly.
There are comets belonging to the Solar System which draw closer to the
Sun than Mercury and go farther away than Neptune.
Comet-pathways do not keep to the level of the chief planet-pathways.
They slope about in all manner of ways, like the paths of the little
Planetoids.
Very many comets belong to the Sun’s kingdom. They journey round and
round the Sun, and appear again and again from time to time. Some take
only a few years for their journey, while others come back only once in
the life of a man; and others again may be hundreds of years absent.
And some comets never return. They do not belong to our Sun, but only
pay him a single visit. These are strangers to our kingdom of worlds,
travelling from the kingdom of some other far-off sun, perhaps one of
the twinkling stars in our sky.
A stranger comet comes, like other comets, slowly from the distance,
quickening his speed day by day as he gets nearer to the Sun. Then he
rushes at a mad rate round the Sun and flies off in a new direction, to
quite another part of the heavens.
What wonderful stories these bright visitors might tell us, if they
could speak, of the skies from which they arrive!
A comet is made of three parts: the _nucleus_, or the thickest portion
of the head; the _coma_, or the bright fog round the nucleus; and the
_train_ or _tail_.
Sometimes there is no nucleus, and sometimes there is no tail; but
there is always a coma--a soft hazy cloud of light, perhaps small
enough to look like a dim star at first.
But a comet watched from the Earth can never be so far off as the
stars. Even the very largest comets are seldom to be seen farther away
than Jupiter.
There are comets of all sizes, from the huge to the tiny. Perhaps one
would find as much difference between comets in the sky as between a
whale and a minnow in water.
Under a certain size they are hidden from us; but tinier comets than we
can see may float in the sky by myriads.
Of those which we can see, the thickest and heaviest part of the
whole--the “nucleus”--may be only about fifty or a hundred miles
through, or it may be some thousands of miles. The coma, or bright
fog surrounding this thickest part of the comet, is generally as much
as ten thousand miles across; and sometimes it is a hundred thousand
miles. As for the bright train, it is, when fully formed, seldom less
than ten millions of miles long, and sometimes it is a hundred millions
of miles. Such a tail as this would reach the whole way from our Earth
to the Sun.
Yet a comet is not heavy. Its make is most wonderfully light; far more
so than the very lightest world in the Sun’s kingdom. Saturn is not so
solid or so heavy as water; but a comet really almost seems to be less
solid and heavy than a mist.
Very faint stars can be seen shining through thousands of miles of
comet-thickness; while it does not take much of an earth-mist to hide
the light of even the brightest star.
Not long ago people were much frightened at comets. If a big one
appeared in the sky it was thought to be a sign of something dreadful
about to happen. Nobody then had any idea what immense numbers of
comets are always in the sky.
It was feared that, if a comet should run against our Earth, the whole
world would be destroyed. Nobody knew how very light and delicate in
its make a comet is.
If such a thing ever did happen, which is most unlikely, one cannot
say that no harm would be done; but certainly our Earth would not be
destroyed.
These comets seem to shine partly in the sunlight, and partly by their
own brightness.
You must not think that a comet always has a tail. More often, when one
is first seen in the distance, it is only as a little hazy patch, or
like a dim star, with no train of light at all.
But as it comes hastening out of cold and darkness into the warmth and
glare of the Sun great changes take place in its shape.
The nucleus very often gets a little smaller; and why this should be I
cannot tell you. But the coma gets larger, and takes to throwing out
bright jets. Then the tail begins to grow; and day by day it becomes
larger and larger.
A comet drawing nearer to the Sun travels head-foremost, with the tail
following after the head. This is only what one would expect.
But as the comet swings round the Sun with a mighty rush its tail is
sent round also in a great outward sweep, pointing all the time away
from the Sun.
Lastly, as the comet on the other side of its pathway goes away from
the Sun, its tail travels first, end-foremost, and the head follows
after the tail.
So the head of a comet always points towards the Sun, and the tail of a
comet always points away from the Sun.
We know little as to the true nature of comets. They are, however,
believed to be made partly of shining gases, and partly perhaps of
small masses or lumps of more solid substance--in short, of little
meteors.
_Biela’s Comet_ was once a comet belonging to the Sun’s kingdom;
but its story is rather curious. In 1846 it broke into two separate
comets. These two kept company for a while, and then parted. One went
ahead, and one dropped behind. After this both vanished, and in their
stead our Earth in her journeying came across a shower of meteors. So
perhaps the meteors are the remains of those two comets--the broken up
bits, if one may so speak.
_The Great Comet of_ 1882 was often to be seen in full daylight.
When passing away, after its rapid whirl round the Sun, it could be
perceived in telescopes at a distance greater than that of Jupiter--a
very unusual thing.
In the picture of a Sun-Eclipse you will notice a tiny comet quite
near the Sun. This little comet had been hidden by the Sun’s glare and
nobody knew it to be there at all. But when the moon glided between,
hiding the Sun’s great brightness, and a photograph was taken--then the
tiny comet had its picture taken also, side by side with the dark body
of the Moon and the light edge of the Sun, with the fiery sea and sharp
mountains.
QUESTIONS.
1. What does the word “comet” mean?
It means “a hairy star.”
2. What is a comet like?
A star-like body, with a hazy kind of fog round it, and a long tail.
3. Do comets always have tails?
No; the tail generally appears when the comet comes near to the Sun.
4. Tell me the three parts of a comet.
The Nucleus, or thickest part; the Coma, or hazy part round the
Nucleus; and the long Tail or Train.
5. Which of these is always found in a comet?
Only the coma. The nucleus and tail may be wanting.
6. What shape is a comet’s pathway?
A long oval: sometimes very long and narrow indeed, with the Sun close
to one end of it.
7. How long is a comet’s year?
All lengths, from three or four of our years up to hundreds of our
years.
8. Do all comets belong to the Solar System?
No; only a certain number seem to do so.
9. Where do others come from?
They seem to come from far-distant stars, paying one visit to our Sun,
and then going off, never to return.
10. How does a comet carry its tail?
Always pointing away from the Sun.
11. Which goes first, head or tail?
When a comet is coming towards the Sun its head journeys first. But
when a comet is going away from the Sun, its tail journeys first.
12. What is a comet made of?
It is believed to be made partly of gases, and perhaps partly of
meteors.
13. Is a comet heavy, or light?
Very light indeed, compared with its great size.