THE HEAD OF OUR FAMILY.
People began very early in the history of the world to pay close
attention to the sun. And no wonder. We owe so much to his heat and
light that the marvel would be if men had not thought much about him.
Was the sun really any larger than he looked, and if so, how much
larger was he? And what was his distance from the earth? These were two
of the questions which puzzled our ancestors the longest. If once they
could have settled exactly how far off the sun really was, they could
easily have calculated his exact size; but this was just what they
could not do.
So one man supposed that the sun must be quite near, and very little
larger than he looked. Another thought he might be seventy-five miles
in diameter. A third ventured to believe that he was larger than the
country of Greece. A fourth was so bold as to imagine that he might
even outweigh the earth herself.
After a while many attempts were made to measure the distance of the
sun; and a great many different answers to this difficult question
were given by different men, most of them very wide of the mark. It
is only of late years that the matter has been clearly settled. And,
indeed, it was found quite lately that a mistake of no less than three
millions of miles had been made, notwithstanding all the care and all
the attention given. But though three millions of miles sounds a great
deal, yet it is really very little--only a tiny portion of the whole.
For the distance of the sun from the earth is no less than about
NINETY-THREE MILLIONS OF MILES. Ninety-three millions of miles! Can
you picture that to yourself? Try to think what is meant by a thousand
miles. Our earth is eight thousand miles in diameter. In other words,
if you were to thrust a gigantic knitting-needle through her body,
from the North Pole to the South Pole, it would have to be about eight
thousand miles long.
To reach the thought of one million, you must picture _one thousand
times one thousand_. Our earth is about twenty-five thousand miles
round. If you were to start from the mouth of the River Amazon, in
South America, and journey straight round the whole earth on the
equator, till you came back to the same point, you would have traveled
about twenty-five thousand miles. But that would be a long way off from
a million miles. You would have gone only once round the earth. Now a
cord one million miles in length could be wrapped, not once only, but
_forty times_, round and round the earth. And when you have managed
to reach up to the thought of one million miles, you have then to
remember that the sun’s distance is ninety-three times as much again.
So, to picture clearly to ourselves the actual meaning of “ninety-three
millions of miles” is not so easy.
Suppose it were possible to lay a railroad from here to the sun. If
you could journey thither in a perfectly straight line, at the rate
of thirty miles an hour, never pausing for one single minute, night or
day, you would reach the sun in about three hundred and forty-six years.
Thirty miles an hour is a slow train. Suppose we double the speed, and
make it an express train, rushing along at the pace of sixty miles
an hour. Then you might hope to reach the end of your journey in one
hundred and seventy-three years. If you had quitted this earth early in
the eighteenth century, never stopping on your way, you would be, just
about now, near the end of the nineteenth, arriving at the sun.
So much for the sun’s distance from us. Now as to his size.
I have already mentioned that our earth’s diameter--that is, her
_through measure_, as, for instance, the line drawn straight from
England through her center to New Zealand--is about eight thousand
miles. This sounds a good deal. But what do you think of the diameter
of the sun being no less than _eight hundred and fifty-eight thousand
miles_? The one is eight thousand miles, the other over eight hundred
thousand!
Suppose you had a long slender pole which would pass through the middle
of the earth, one end just showing at the North Pole and the other at
the South Pole. You would need more than a hundred and eight of such
poles, all joined together, to show the diameter of the sun.
The sun seems not to be made of nearly such heavy materials as the
earth. He is what astronomers call less “dense,” less close and compact
in his make, just as wood is less dense and heavy than iron. Still,
his size is so enormous, that if you could have a pair of gigantic
scales, and put the sun into one scale and the earth with every one of
her brother and sister planets into the other, the sun’s side would go
down like lightning. He would be found to weigh seven hundred and fifty
times as much as all the rest put together. And, it would take more
than twelve hundred thousand little earths like ours, rolled into one
huge ball, to make a globe as large as the sun.
In the beginning of the seventeenth century a man named Fabricius was
startled by the sight of a certain black spot upon the face of the
sun. He watched till too dazzled to look any longer, supposing it to
be a small cloud, yet anxious to learn more. Next day the spot was
there still, but it seemed to have moved on a little way. Morning after
morning this movement was found to continue, and soon a second spot,
and then a third spot, were observed creeping in like manner across
the sun. After a while they vanished, one at a time, round his edge,
as it were; but after some days of patient waiting on the part of the
lookers-on, they appeared again at the opposite edge, and once more
began their journey across.
Fabricius seems to have been the first, but he was not the last, to
watch sun-spots. Many astronomers have given close attention to them.
Modern telescopes, and the modern plan of looking at the sun through
darkened glass, have made this possible in a way that was not possible
two or three hundred years ago.
The first important discovery made through the spots on the sun, was
that the sun turns round upon his axis, just in the same manner that
the earth turns round upon hers. Instead of doing so once in the course
of each twenty-four hours, like the earth, he turns once in the course
of about twenty-five days.
It must not be supposed that the spots seen now upon the sun are the
same spots that Fabricius saw so long ago. There is perpetual change
going on; new spots forming, old spots vanishing; one spot breaking
into two, two spots joining into one, and so on. Even in a single hour
great alterations are sometimes seen to take place.
Still, many of the spots do remain long enough and keep their shapes
closely enough to be watched from day to day, and to be known again as
old friends when they reappear, after being about twelve days hidden on
the other side of the sun. So that the turning of the sun upon his axis
has become, after long and careful examination, a certain known fact.
For more than thirty years one astronomer kept close watch over the
spots on every day that it was possible to see the sun. Much has been
learned from his resolute perseverance.
Now what are these spots?
One thing seems pretty sure, and that is that they are caused by some
kind of tremendous storms or cyclones taking place on the surface of
that huge ball of fire.
[Illustration: SUN SPOTS.]
The first attentive observer of the sun, Scheiner, at first regarded
the spots as satellites--an indefensible opinion, which, however,
some have attempted to revive. Galileo attributed them to clouds or
vapors floating in the solar atmosphere; this was the best conclusion
which could be drawn from the observations of that epoch. This opinion
met for a long time with general approval; it has even been renewed
in our day. Some astronomers, and among them Lalande, believed, on
the contrary, that they were mountains, of which the flanks, more
or less steep, might produce the aspect of the penumbra--an opinion
irreconcilable with the proper motion which the spots sometimes possess
in a very marked manner. It is not usual, in fact, to see mountains
traveling. Derham attributed them to the smoke issuing from the
volcanic craters of the sun, an opinion revived and maintained in
recent times by Chacornac. Several _savants_, regarding the sun as a
liquid and incandescent mass, have also explained the spots by immense
cinders floating on this ocean of fire. But a century had scarcely
elapsed after the epoch when the spots were observed for the first
time, when an English astronomer, Wilson, showed with certainty that
the spots are hollow.
We do not know with any certainty whether the sun is through and
through one mass of glowing molten heat, or whether he may have a solid
and even cool body within the blazing covering. Some have thought the
one, and some the other. We only know that he is a mighty furnace of
heat and flame, beyond anything that we can possibly imagine on our
quiet little earth.
It seems very sure that no such thing as “quietness” is to be found on
the surface of the sun. The wildest and fiercest turmoil of rushing
wind and roaring flame there prevails. The cyclones or hurricanes which
take place are sometimes so rapid and so tremendous in extent, tearing
open the blazing envelope of the sun, and showing glimpses of fiery
though darker depths below, that we, on our far-distant earth, can
actually watch their progress.
Astronomers speak of the “quivering fringe of fire” all around the edge
of the sun, visible through telescopes. But the sun is perpetually
turning on his axis, so that each hour fresh portions of his surface
thus pass the edge, showing the same appearance. What conclusion
can we come to but that the whole enormous surface of the sun is one
restless, billowy sea of fire and flame?
It sounds to us both grand and startling to hear of the mighty
outbreaks from Mount Vesuvius, or to read of glowing lava from a
volcano in Hawaii pouring in one unbroken stream for miles.
But what shall be thought of rosy flames mounting to a height of fifty
or a hundred thousand miles above the edge of the sun? What shall be
thought of a tongue of fire long enough to fold three or four times
round our solid earth? What shall be thought of the awful rush of
burning gases, sometimes seen, borne along at the rate of one or two or
even three hundred miles in a single second across the sun’s surface?
What shall be thought of the huge dark rents in this raging fiery
ocean, rents commonly from fifty to one hundred thousand miles across,
and not seldom more?
Fifty thousand miles! A mere speck, scarcely visible without a
telescope; yet large enough to hold seven earths like ours flung in
together. The largest spot measured was so enormous that eighteen
earths might have been arranged in a row across the breadth of it, like
huge boulders of rock in a mountain cavern; and to have filled up the
entire hole about one hundred earths would have been needed.
It is well to grow familiar with certain names given by astronomers to
certain parts of the sun.
The round shining disk or flat surface, seen by all of us, is called
the _photosphere_, or “light-sphere.” It has a tolerably well-defined
edge or “limb,” and dazzles the eye with its intense brightness.
Across the photosphere the spots move, sometimes many, sometimes
few, in number. Besides the dark spots, there are spots of extreme
brilliancy, standing out on even that dazzling surface, which causes
a piece of white-hot iron to look black and cold by contrast. These
extra-radiant spots which come and go, and at times change with great
rapidity, are named _faculæ_--a Latin word meaning “torches.”
At the edge of the photosphere astronomers see what has been already
mentioned, that which is sometimes called the _chromotosphere_, which
one has named “the _sierra_,” and which another has described as “a
quivering fringe of fire.” The waves of the sea, on a stormy day, seen
in the distance rising and breaking the horizon-line, may serve as an
illustration; only in the sun the waves are of fire, not water. What
must their height be, to be thus visible at a distance of ninety-three
millions of miles?
Outside the _sierra_ are seen, at certain seasons, bright,
“rose-colored prominences” or flames of enormous height. During an
eclipse, when the dark body of the moon comes between the sun and us,
exactly covering the photosphere, these red tips stand out distinctly
beyond the edge of sun and moon. Their changes have been watched, and
their height repeatedly measured. Some are so lofty that ten little
earths such as ours might be heaped up, one upon another, without
reaching to their top. Whether they are in character at all like the
outbursts from our own volcanoes it is hard to say. To compare the
two would be rather like comparing a small kitchen fire with a mighty
iron-smelting furnace. The faculæ, the sierra, and the prominences are
visible only through a telescope.
Outside these red flames or “prominences” is the corona, commonly
divided into the inner and outer coronas.
Many different explanations have been offered of this beautiful crown
of light round the sun, plainly visible to the naked eye during an
eclipse. But here again we know little, and must be content to watch
and wait.