We Resume Our Voyage-the Sun And The Sky As Seen From Space
:
To Mars Via The Moon
All the time the Areonal had been near the moon some of our machines
were storing up fresh power, and we had accumulated a supply amply
sufficient to meet any extra requirements in the event of our arrival
upon Mars being unduly delayed.
We now turned and looked back at the earth; and, as the moon was so near
to it at that time, the earth's disc appeared very nearly two degrees in
diameter, or near
y four times the usual apparent diameter of the full
moon as seen from the earth. The crescent of light on its right-hand
side was rather wider than when we last looked at it; but so many clouds
hung over it, that we could not see what countries were comprised in the
lighted portion of its surface. Owing to the light of the stars behind
the earth being diffused by the dense atmosphere-in the same way as it
would be diffused by a large lens-there was a ring of brilliant light
like a halo all round the earth's disc.
Having passed away from the moon, I now gave M'Allister the necessary
directions in order to keep the Areonal on a course which would enable
us to head off the planet Mars at, as near as I could reckon, the point
it would reach in fifty days' time. The course having been set,
M'Allister was free to join us again, as the machinery required very
little attention.
When he did so, M'Allister at once asked me a question. "Professor, can
you tell me when it's going to be daylight? The sun has been shining for
hours and hours, yet it's still night; the sky is blacker than the
blackest night I ever saw, and the stars are all out!"
John laughed heartily, and said, "M'Allister, this is daylight! and all
the daylight you will get until we reach Mars."
M'Allister turned to me with a perplexed look on his face and asked, "Is
that right, Professor, or is he trying to pull my leg, as he said he
would?"
"Oh yes! It's quite right, M'Allister," I replied. "It is now full
daylight, and we shall have no more night until we reach Mars. That, as
you know, will be seven weeks from the present time."
"Well, Professor," he exclaimed, "then how is it the sky is so densely
black and the stars all shining so brightly? I never saw the stars in
the daytime before, yet these are shining brighter than they do on the
earth at night."
"Simply," I said, "because upon the earth we were surrounded by a dense
atmosphere, which so diffused the sun's light that the whole sky
appeared bright. The stars were there all the time, but their light was
so overpowered by the brilliancy of the atmosphere that they were quite
invisible to us.
"Now, we are out in space where there is no atmosphere at all, so the
sky appears a very dense black; and the stars, having nothing to obscure
their light, shine out more brilliantly than they do on the earth. They
appear as bright points of light, and even the sun does not shed a
general light over the sky, there being no atmosphere to diffuse it."
"Yes," he persisted, "but you said we should have no more night until we
got to Mars!"
"Certainly," I answered. "Surely, M'Allister, you must have forgotten
that night is brought about by the earth's rotation on its axis, and
that the part which is turned away from the sun is in darkness because
its light is hidden by the solid body of the earth, while the earth's
shadow darkens all the sky. When, by the earth's rotation, that part is
again turned to the sun then it becomes daylight. Remember we are not
now on the earth, but out in space!"
"Of course I did know all that, Professor," he exclaimed, "but, just for
the time, I had forgotten."
"Never mind, M'Allister, we all forget such matters sometimes, and this
is quite a new experience for you. But just take a good look at the
sun-have you noticed any difference in its appearance?"
"Yes, Professor, it doesn't look the same colour as when we saw it from
the earth; it seems to have a violet tinge, like some of the electric
lights in our streets. There are also long streamers of light around it,
and coloured fringes close to the sun!"
"Yes, that is so," I said; "and we can see all those things now because
there is no atmosphere. No doubt you have noticed that on the earth the
sun appeared red when low down in the sky, and during a fog it appeared
redder and duskier still."
"Oh yes, I've often noticed that," he answered.
"That was caused by our atmosphere which, when thick, absorbs all but
the red rays of light. On a clear day the sun appears an extremely pale
yellow, or very nearly white; still the atmosphere absorbs some of the
light rays, so we cannot see its true colour as we do now. Those
coloured fringes round the edges can only be seen from the earth by the
aid of a special instrument, and then they do not show all their true
colours.
"That pearly light all round the sun, and the long streamers that give
it the appearance of an enormous star with six long points, form what is
termed the solar corona, and this can only be seen from our earth during
the very few minutes when an eclipse of the sun is at its totality. It
is to see the corona and other surroundings of the sun, in order to
study them, that astronomers go such very long distances-often
thousands of miles-when there is a total eclipse expected, and not
merely to see the eclipse itself. They hope, in time, to learn much from
such observations; but if it happens that the sky is over-clouded during
the period of total eclipse, then all their expense, and the time spent
in preparations and rehearsals of their procedure, are, unfortunately,
entirely wasted.
"Now, M'Allister, if you will take my glass you will be able to look at
the sun and examine it without any risk to your eyesight, for it is
provided with a dark glass to shut out all the dangerous glare. You will
then see what the fringes and inner and outer coronas really are like."
He took the glass and looked for a long time at the sun, and, judging
from his exclamations of surprise and astonishment, he was extremely
interested and delighted with what he saw. John was also examining it at
the same time through his own glass.
Presently the latter turned to me saying, "Professor, I no longer
wonder that astronomers are prepared to travel long distances, and to
risk a great deal of discomfort, and even hardship, in order to view and
study the sun's surroundings. Of course to them it is not merely a sight
to be seen, but the only means by which they can acquire a knowledge of
solar physics. Merely as a sight, however, it is most wonderful. At many
places all round the edge of the sun's disc I can see what look like
coloured flames-pink, pea-green, carmine, orange, or yellow, all in
incessant movement-shooting out at times, or waving and shimmering in a
manner that is indescribable. The changes in form and colour are as
sudden, yet as definite, as the changes produced by turning a
kaleidoscope; while the intermingling of the various colours frequently
produces an effect which I can only compare to the iridescent colours on
mother o' pearl. Then all around and beyond the coloured fringe there is
the light of the pearly inner corona; beyond that are pearly and
violet-tinged rays curling away in both directions from the poles,
whilst outside all are the long, pearly, and violet-tinted streamers
which assume the shape of a large many-pointed star; and even these do
not seem at rest. Though astronomers cannot see all that we do now,
there must be sufficient visible to them to afford opportunity for a
most interesting study."
"That is indeed the case, John," I replied. "Those coloured flames, for
instance, form a study in themselves, which some observers make their
particular hobby. As seen from the earth, they all appear some tint of
red; and, normally, according to measurements, they seem to extend a
distance of some 20,000 miles above the sun. They shift their position
very rapidly indeed; movements at the rate of 100 miles a second are
quite moderate compared with some which have been noted, yet one can
scarcely realise such rapidity of motion. Frequently, however, these
flames are seen to rise in immense masses to tremendous heights above
the sun's surface, evidently driven upwards by explosions of the most
intense energy. In 1888, for instance, one was observed which, in the
course of two hours, rose to a height of 350,000 miles before it broke
up; that is, at the rate of 50 miles a second all the time; but, as the
force would become less and less as the distance increased, at the
earlier part of the time the movement must have been far more rapid.
When the impetus derived from the explosive force is quite exhausted,
the top part of the mass of flame often spreads out like the top of a
tree, then breaks up and falls back into the sun in large flakes of
flame.
"It is supposed that these violent explosions are the cause of the spots
we so often see on the sun when observing it with our telescopes; and,
when looking at them in their earliest stage, we are probably looking at
a mass of flame end on, instead of seeing it in profile, as is the
case when the explosion occurs near the edge of the disc. The flames, as
examined by the spectroscope, appear to be largely composed of hydrogen
gas; and no doubt many other gases-some quite unknown to us-enter into
their composition. They are termed flames, but are more probably immense
volumes of incandescent gases. The corona itself is never seen twice
alike; its shape and size vary at every eclipse, but the variation runs
in a regular cycle from maximum to minimum.
"You will also observe that all around the corona, and extending a vast
distance beyond it on both sides, is a fainter pearly light. This is
what is termed the zodiacal light, and is believed to be the thinner
portion of the sun's atmosphere. We can see it from the earth
occasionally after the sun has set, extending far up into the sky in the
form of a semi-ellipse, the base of which is over the place where the
sun is."
M'Allister here asked me to tell him "What was supposed to be the actual
size of our sun, and how far it was away from the earth?"
I answered that "The sun is about 865,000 miles in diameter; and that he
would have some idea of what an immense body it is if he remembered that
it would require 64,000,000 globes the size of the moon to make one
globe the size of the sun! Yet, notwithstanding this immense size, our
sun is quite a small body as compared with some of the fixed stars,
which, as perhaps you may know, are really suns at an inconceivable
distance from us. The bright star Sirius, which is visible during our
winter time, is not only very much brighter in reality than our sun, but
must be many times larger; and there are others known to be very much
larger than Sirius. It has been computed that Arcturus is in mass
500,000 times as large as our sun!
"The sun revolves on its axis in a little over twenty-five days, but the
exact period of its revolution is difficult to determine. The mean
distance of the sun from the earth is about 92,800,000 miles. When we
are farthest from it its distance is 94,600,000 miles, and when nearest,
91,000,000 miles-these differences, of course, arising from the
eccentricity of the earth's orbit.
"The sun's density is only about one-fifth of the earth's density; so it
is evidently mainly gaseous-at all events in the outer envelopes.
"The spots upon the sun often cover such an immense area, that if our
earth were dropped into the cavity, it would be like placing a pea in a
teacup! Some of the spots entirely close up in a short time, but others
last for weeks."
We now turned from the sun and looked at the stars. Such a multitude
were visible as we had never seen from the earth; for small stars, which
there required a telescope to bring them into view, could now be plainly
seen without any such aid, and their various colours were seen much more
clearly. They all shone with a clear and steady light; the twinkling and
scintillation of the stars, as seen from the earth, being caused by the
vibrations and movements in our own atmosphere. We also saw many nebulae
without using a glass.
The Milky Way was a most gorgeous spectacle, and its beauty utterly
beyond description, as such an immense number of its component stars,
and their different colours, were visible to the unaided eye; besides,
we could trace wisps and branches of it to regions of the sky far beyond
the limits within which it is seen from the earth.
We noted that the planets were also much more clearly seen; and the
orange-red disc of Mars, of course, received our particular attention.
We had spent very many hours in viewing the moon, and a long time in
examining the sun and stars; so we now sat down to a hearty meal, and,
after a short time spent in conversation, we made our arrangements for
taking turns in attending to the machinery, and then retired to bed.
Planets between the 3rd of August and the 24th of September, 1909: and
the Course taken by the "Areonal" on the Voyage to Mars.
The dotted line joining the Earth to Mars shows the course taken.
The dotted Circles show the Orbits of the Planets. The thick arrows
show the distances travelled by the respective planets during the period
covered by the Voyage: the line at the back end of the Arrow being the
planet's position on the 3rd August, and the points of the Arrows the
position reached on the 24th September.
The Orbits of Mercury, Venus, the Earth and Mars are drawn
approximately to scale, but those of the outer planets are not. On the
same scale, the radii of the Orbits of the outer Planets would,
approximately, be as stated below. These figures will afford some idea
of the enormous distances separating those planets.
Jupiter 3 Inches
Saturn 5-3/8 "
Uranus 10-7/8 "
Neptune 17 "
Drawn by M. Wicks
Plate V]