Sidelights on Astronomy and Kindred Fields of Popular Science | Page 9

details of its surface have been
mapped by several observers, using the best telescopes under the most
favorable conditions of air and climate. And yet it must be confessed
that the result of this labor is not altogether satisfactory. It seems
certain that the so-called seas are really land and not water. When it
comes to comparing Mars with the earth, we cannot be certain of more
than a single point of resemblance. This is that during the Martian
winter a white cap, as of snow, is formed over the pole, which partially
melts away during the summer. The conclusion that there are oceans
whose evaporation forms clouds which give rise to this snow seems
plausible. But the telescope shows no clouds, and nothing to make it
certain that there is an atmosphere to sustain them. There is no certainty
that the white deposit is what we call snow; perhaps it is not formed of
water at all. The most careful studies of the surface of this planet, under
the best conditions, are those made at the Lowell Observatory at
Flagstaff, Arizona. Especially wonderful is the system of so-called
canals, first seen by Schiaparelli, but mapped in great detail at Flagstaff.
But the nature and meaning of these mysterious lines are still to be
discovered. The result is that the question of the real nature of the
surface of Mars and of what we should see around us could we land
upon it and travel over it are still among the unsolved problems of
astronomy.

If this is the case with the nearest planets that we can study, how is it
with more distant ones? Jupiter is the only one of these of the condition
of whose surface we can claim to have definite knowledge. But even
this knowledge is meagre. The substance of what we know is that its
surface is surrounded by layers of what look like dense clouds, through
which nothing can certainly be seen.
I have already spoken of the heat of the sun and its probable origin. But
the question of its heat, though the most important, is not the only one
that the sun offers us. What is the sun? When we say that it is a very
hot globe, more than a million times as large as the earth, and hotter
than any furnace that man can make, so that literally "the elements melt
with fervent heat" even at its surface, while inside they are all
vaporized, we have told the most that we know as to what the sun
really is. Of course we know a great deal about the spots, the rotation of
the sun on its axis, the materials of which it is composed, and how its
surroundings look during a total eclipse. But all this does not answer
our question. There are several mysteries which ingenious men have
tried to explain, but they cannot prove their explanations to be correct.
One is the cause and nature of the spots. Another is that the shining
surface of the sun, the "photosphere," as it is technically called, seems
so calm and quiet while forces are acting within it of a magnitude quite
beyond our conception. Flames in which our earth and everything on it
would be engulfed like a boy's marble in a blacksmith's forge are
continually shooting up to a height of tens of thousands of miles. One
would suppose that internal forces capable of doing this would break
the surface up into billows of fire a thousand miles high; but we see
nothing of the kind. The surface of the sun seems almost as placid as a
lake.
Yet another mystery is the corona of the sun. This is something we
should never have known to exist if the sun were not sometimes totally
eclipsed by the dark body of the moon. On these rare occasions the sun
is seen to be surrounded by a halo of soft, white light, sending out rays
in various directions to great distances. This halo is called the corona,
and has been most industriously studied and photographed during
nearly every total eclipse for thirty years. Thus we have learned much

about how it looks and what its shape is. It has a fibrous, woolly
structure, a little like the loose end of a much-worn hempen rope. A
certain resemblance has been seen between the form of these seeming
fibres and that of the lines in which iron filings arrange themselves
when sprinkled on paper over a magnet. It has hence been inferred that
the sun has magnetic properties, a conclusion which, in a general way,
is supported by many other facts. Yet the corona itself remains no less
an unexplained phenomenon.
[Illustration with caption: PHOTOGRAPH OF THE CORONA OF
THE SUN, TAKEN IN TRIPOLI DURING