Celestial Phenomena Seen From Mars-m'allister Receives A Practical Lesson In Gravitation
From: To Mars Via The Moon
Mars is really an ideal world for an astronomer to live in, its skies
being so clear, the air so thin and pure, and the stars shining so
Besides these advantages, the rapid movements of the two satellites of
the planet result in a constant succession of celestial phenomena which
afford very frequent opportunities for most interesting observations.
Changes in the phases of the two moons, eclipses, occultations,
transits, &c., are constantly occurring, so there is nearly always
something to attract our attention to the Martian sky.
We have already seen several of these phenomena, and I will now describe
what we have observed.
Early one evening when we were out with Merna, we looked up at the sky
and saw the two moons a considerable distance apart, but approaching
each other from opposite directions, Phobos appearing to move very
rapidly. Both were near the full phase, Deimos being more nearly full
than Phobos; and we watched them drawing closer and closer together till
Phobos passed right in front of Deimos so as to hide it entirely. This
is termed an occultation; and both the satellites had become full when
the occultation occurred; but when they were again clear of each other
both were beginning to wane.
This sight may be seen anywhere near the Martian equator about every ten
The movements of Phobos seemed very peculiar to us who had lived upon
the earth and seen all the celestial bodies appearing to move in the
I have already alluded to the fact that Phobos is only 3700 miles above
the surface of Mars, and moves so rapidly that it makes more than three
complete revolutions round the planet whilst the latter is turning only
once on its axis.
The effect of this very rapid revolution of the satellite, which has no
counterpart, so far as we know, in our Solar system is that, instead of
rising in the east and setting in the west as all the other heavenly
bodies appear to do, Phobos appears to rise in the west, cross the sky,
and set in the east.
The moon and planets all actually move from west to east; the apparent
reverse of this being caused by the more rapid movement of the earth on
its axis, giving the other bodies the appearance of moving from east to
west. If, however, our moon is closely watched, and its position with
regard to a fixed star carefully noted, it will be found that in the
course of a short time its real movement has been eastward, and that its
position with regard to the fixed star has changed, although the
revolution of the earth has appeared to carry both westward.
Phobos is 36 miles in diameter. Its actual period of revolution round
the planet is 7 hours and 39 minutes, but, owing to the movement of Mars
on its axis in the same direction, it appears to take a few minutes
over 11 hours to complete one revolution.
Near the equator, Phobos is seen above the horizon for about 4-1/4
hours, and is below it about 6-3/4 hours. According as the place from
which it is viewed is farther from the equator so will the time of
visibility of Phobos be decreased, until when latitude 69 deg. is reached
in either hemisphere, it will cease to become visible at all. This is
owing to its nearness to the planet; and, Mars being small, the curve
of its sphere is sharp, so that the horizon is more limited than on the
earth, and the satellite is shut out from view anywhere above latitude
69 deg. by the body of the planet.
Another peculiarity is that, when in the zenith, Phobos appears twice as
large in area as it does when near the horizon, and notwithstanding its
very small size, Phobos appears rather larger than our moon, because it
is so near to the planet.
The length of the Martian "night" is about 12 hours and 20 minutes, and
during this very short time Phobos may be seen to rise in the west, set
in the east, and rise again once more in the west. Consequently it will
be evident that it must travel very rapidly across the sky. It really
moves over a space of 32-1/2 deg. in a single hour-a great contrast to
the slow and stately movement of our moon, which only passes over half a
degree in an hour.
Moreover, Phobos may be seen to rise as a new moon, pass through its
phases to the full, wane, and again become new, all in the course of a
single Martian night; or it may be seen twice full and once new during
the same time.
Even this does not exhaust the list of phenomena, for, being so close
to Mars, Phobos is very frequently eclipsed by the shadow of the planet.
On the other hand, the sun may be eclipsed by Phobos something like
fourteen hundred times in the course of a Martian year; and, as already
mentioned, the other satellite is often occulted by Phobos-sometimes
when both may be only at the half full phase, and these occultations
look very peculiar.
Deimos, being only 10 miles in diameter and about 12,500 miles from the
surface of the planet, does not give rise to so many phenomena as the
nearer satellite: still they are very numerous.
It revolves round the planet in 30-1/4 hours, but appears to take
131-1/2 hours to do so, being above the horizon about 60 hours, and
below it nearly 72 hours. These are the times as seen from the equator;
but, as in the case of Phobos, the farther the place is from the equator
the shorter is the period that Deimos is seen above the horizon, until,
when latitude 82 deg. is reached in either hemisphere, it ceases to
become visible at all.
Our moon, being so very much more distant from our earth, could be seen
from both the poles.
Deimos also passes nearly twice through all its phases whilst it is
above the horizon, viz. during about 60 hours, and may be seen twice
full and twice new in that time.
Eclipses of Deimos by the planet and occultations of it by the other
satellite are very frequent. Being so small, it can never cause an
eclipse of the sun, but it transits the sun as a dark spot about one
hundred and twenty times during the Martian year.
This is really a very inadequate list of the phenomena connected with
the satellites, but it will be seen that the number is enormous
compared with the few eclipses of the sun or moon seen on the earth
during the course of one year. Certainly Mars is an astronomer's world!
Merna heard my statements respecting these movements and phenomena as I
explained them to my two friends; and when I had finished, he remarked,
"You seem to be fairly well posted in these matters, sir?"
"Yes," I said; "thanks to our astronomers, both professional and
amateur, all these things have been very carefully calculated; and, with
the exception of a few doubtful points, we probably know nearly as much
about them as the Martians themselves do."
M'Allister then turned to me and said, "Professor, you told us that the
two satellites of Mars revolved round the planet in a certain time, but
in each case you afterwards said they appeared to take a much longer
time to do so. I'm rather puzzled to understand how that can be."
"It's really a simple matter, M'Allister," I answered, "and I think I
can make it clear to you. While the satellite is making one revolution
round the planet the latter is turning on its axis in the same direction
as the satellite is moving, following it up in fact; and you will I
think understand that in these circumstances the people on that part of
the planet where the moon is visible must necessarily keep it in view
for a longer period than would be the case if the planet were not
revolving in the same direction.
"You have been used to being on board a ship; so suppose your vessel was
steaming twelve miles an hour and there was another vessel at anchor
just twelve miles ahead of you, you would reach it in just one hour,
would you not?"
"Yes, certainly I should," replied M'Allister.
"Now," I continued, "suppose that the other vessel, instead of being at
rest, was moving away from you at the rate of six miles an hour; after
you had steamed one hour it would still be six miles ahead of you, and
it would take you exactly another hour to catch it up. So you would be
just double the time reaching it when moving as compared with the time
required to do so when it was at anchor. This is very similar to the
cases of the satellites of Mars, and much the same thing happens in
regard to Mars and the earth. If they are opposite to each other at a
certain point, Mars will have taken much more than one revolution round
its orbit before they will be opposite to each other again, because they
are both moving in the same direction. Do you see it now?" I asked.
"Yes, Professor," he replied. "I know now, because you have cleared it
all up. It's simple enough when one understands it."
Merna then asked me if I would like to see some of their astronomical
instruments, and, on my replying that I should very much like to do so,
he took us to an observatory where Corontus was at work.
I was at once struck by the small size of the telescopes; and, on
inquiring about them, Corontus told me that very large instruments had
long become obsolete, for these small ones could be used for all the
purposes for which a large one had been required, and gave better
I examined one of them and found, to my surprise, that it embodied the
very ideas that I had long been trying to carry into effect. With this
view I had made many experiments, as it seemed to me that it ought to be
possible to construct an instrument of moderate and convenient
dimensions which would show as much as our monsters will show, and yet
be capable of being used with low powers when occasion required. I had
endeavoured to attain this result by the aid of electricity, but failed
to do so. Evidently I had missed something, but here was the thing
itself in successful working, as I found upon testing it.
On looking at some drawings of Saturn, which were hanging up in the
observatory, I noticed that this planet was depicted with two faint
outer rings which do not appear on our drawings of the planet. One of
these rings has, however, been discovered by M. Jarry-Desloges, but the
outermost ring is still unknown to our observers. This ring is a very
broad one, its particles being widely scattered, hence its extreme
The Martians have also discovered two planets far beyond the orbit of
Neptune, and their knowledge of the other planets and also of the sun
and the stars is far ahead of ours.
I was also shown a comet which had recently become visible through their
telescopes, and found from its position that it was undoubtedly Halley's
comet, for which our astronomers were so eagerly watching. I wondered
whether any of them had been fortunate enough to discover it early in
August, as the Martian astronomers did. Its last appearance was in the
John remarked that "He thought Halley's comet might be termed 'Britain's
Comet,' for several of its appearances had coincided with the
occurrence of very important events and turning-points in our national
history, such as the Battle of Hastings, the Reformation, &c.," and he
added, "as it will be a conspicuous object in our skies in 1910, I
wonder whether any important event will occur in our country? In 1835,
when it last appeared, we had a political crisis!"
"Well, John," I replied, "I do not attach much importance to comets as
affecting mundane affairs; we have got rather beyond such beliefs as
that. Besides, when we left England early in August things were going on
all right in our political world, and there was no indication of any
"Still," said John, "it would be rather curious if we did have a crisis
next year; and I should not be surprised!"
As we were walking home next day, M'Allister suddenly tripped over some
little projection and fell prone to the ground. John ran to his
assistance and raised him up, at the same time asking "If he were hurt?"
"No, not at all," said M'Allister; "I seemed to fall so lightly that I
scarcely felt it when I touched the ground."
"Ah, M'Allister!" I exclaimed, "if you had fallen like that upon our
earth, I think you would not have come off quite scatheless. You see,
upon Mars the gravitation is much less than on the earth, being only
three-eighths of what it is there, so one does not fall so swiftly, nor
so heavily, as on the earth.
"You can prove that very easily. Just take up a stone and hold it out
higher than your head, and let it fall; at the same time note, by the
second hand of your watch, how long it takes for the stone to reach the
He did so, and said that "As near as he could tell, the stone was just
about one second of time in passing from his hand to the ground."
"Just so," I replied. "On Mars a falling body only moves through a space
of about six feet in the first second of time. On the earth, however,
the gravitation is so much greater that a falling body passes through a
space of a little over sixteen feet during the first second.
"In addition to that, although you weighed twelve stones when on the
earth, you only weigh about four and a half stones here upon Mars. Now
you can understand why it was you seemed to fall so lightly."
"Yes, Professor," he replied, "and I'm glad I fell here, and not upon
Then, picking up the stone again and throwing it high in the air, he
watched its fall, and turning to me, remarked, "Professor, you were
quite right; that stone seemed to be quite a long time coming down
again, much longer than it would have been on our own world."
"Well, M'Allister," I replied, "now you know for certain that upon a
small planet gravitation really is much less than upon a larger planet
of the same kind.
"That's another little wrinkle for you, and you have found it all out
through tripping over a stone!"
"Losh, mon," replied he, "I seem to have learnt something almost every
day since I have been here; even a tumble down teaches me something!"
I then drew his attention to the birds flying near us, and pointed out
that they had a much wider spread of wing than our birds have, and that
this was owing to the fact that the air being so thin a wide spread of
wing was absolutely necessary to support them in the air and enable them
to fly. I further explained that, if the gravitation upon Mars were as
great as upon the earth, the birds' wings must necessarily have been
still larger, as the pull of the planet would have been so much the
greater, and would thus have prevented the birds from flying at all in
such thin air if their wings had been small.
"M'Allister," I then remarked, "you will, no doubt, have noticed the
same thing with regard to those large and beautiful butterflies we have
seen. Why, the outspread wings of the largest must have measured ten or
twelve inches across, and many of the smaller varieties were more than
six inches across. I wonder what our naturalists would say if they could
see some specimens of these large and splendidly coloured insects!"
"Well, Professor," he answered, "I never saw such large butterflies
anywhere else, not even when I was in the tropics on our own world. It
had never occurred to me that gravitation, or even the density of the
air, had anything to do with their size. Even now I do not understand
how it is the small insects are able to fly, for they are heavy for
their size, and do not possess very large wings, yet they can move very
"Let me explain then," I answered. "Large birds can only move their
wings with comparative slowness, and it is therefore necessary that
their wings should be large to enable them to keep their balance and be
able to fly. Their wings are somewhat in the nature of aeroplanes, and
they shift them to different angles to take advantage of the varying
currents of air.
"In the case of humming-birds and small insects, the wings are capable
of intensely rapid vibrations, so rapid indeed that, when flying, the
wings are almost, if not quite, invisible. This intensely rapid movement
enables them to fly, and is somewhat analogous to the rapid movements of
the vertical spiral screws, which you have seen on some of the Martian
air-ships that screw their way up into the air.
"Such rapid movements would not be suited to larger creatures, because
their muscular powers would have to be so enormously great that their
bodies would require to be larger and heavier in proportion. They would
thus be very unwieldy."
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