Celestial Phenomena Seen From Mars-m'allister Receives A Practical Lesson In Gravitation

: 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

brilliantly.



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

hours.



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

same direction.



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

results.



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

faintness.



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

year 1835.



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

serious crisis."



"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

ground."



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

the earth!"



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

swiftly."



"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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