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“From Earth to the Moon ” :
Jules Verne and the big Lunar Telescope
by Paolo Morini
Introduction
Jules Verne is a well-known writer who doesn't need particular presentations, and one of
the reasons of his celebrity is due to the prophetic aspect of some of his stories.
From this point of view one of the most famous is "From Earth to the Moon".
The story
The story takes place initially in the city of Baltimore in the State of Maryland.
During the War of the Rebellion, a new and influential club was established in this city: the
Gun Club.
The only condition imposed upon every candidate for admission into the Club was the
condition of having designed, or perfected a cannon, or, at least, a firearm of some kind.
The cannon, howitzers, and mortars of English, French, and Prussians were mere pocketpistols compared with the formidable engines of the American artillery: "the Yankees, the
first mechanicians in the world, are engineers-- just as the Italians are musicians and the
Germans metaphysicians".
But one day - a sad and melancholy day for the Gun Club members - peace was signed
between the survivors of the war; the thunder of the guns gradually ceased, and the Gun
Club was relegated to profound inactivity.
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Consequently, the clubrooms became deserted, sounds of snoring came from dark
corners, and the members of the Gun Club were reduced to silence.
"This is horrible!" said Tom Hunter "nothing to do! nothing to look forward to! what a
loathsome existence! When again shall the guns arouse us in the morning with their
delightful reports?"
"Those days are gone by," said jolly Bilsby "It was delightful once upon a time! One
invented a gun, and hardly was it cast, when one hastened to try it in the face of the
enemy! Then one returned to camp with a word of encouragement from Sherman or a
friendly shake of the hand from McClellan. But now the generals are gone back to their
counters; and in place of projectiles, they despatch bales of cotton. By Jove, the future of
gunnery in America is lost!"
"Ay! and no war in prospect!" continued the famous James T. Maston "Not a cloud on the
horizon!"
But one day arrived at the Club a letter from Impey Barbicane, the President:
BALTIMORE, October 3.
The president of the Gun Club has the honor to inform his colleagues that, at the meeting
of the 5th instant, he will bring before them a communication of an extremely interesting
nature. He requests, therefore, that they will make it convenient to attend in accordance
with the present invitation.
Very cordially,
IMPEY BARBICANE, P.G.C.
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During the meeting President Barbicane told to the members of the Club that "the moon
has been carefully studied, her mass, density, and weight; her constitution, motions,
distance, as well as her place in the solar system, have all been exactly determined.
Selenographic charts have been constructed with a perfection which equals, if it does not
even surpass, that of our terrestrial maps. Photography has given us proofs of the
incomparable beauty of our satellite; all is known regarding the moon which mathematical
science, astronomy, geology, and optics can learn about her. But up to the present
moment no direct communication has been established with her
…..I have looked at the question in all its bearings, I have resolutely attacked it, and by
incontrovertible calculations I find that a projectile endowed with an initial velocity of
12,000 yards per second, and aimed at the moon, must necessarily reach it. I have the
honor, my brave colleagues, to propose a trial of this little experiment."
The effect produced by the word of the honorable president was incredible: all the
members shouted and clapped their president.
Soon it was formed a scientific and technical committee to study the problem from every
point of view.
All the calculations were made and the main dimensions of the gun were fixed: as the gun
was enormous in size, the gun itself wouldn't have any mount.
It was necessary to cast the barrel directly in the ground and pointing toward zenith.
The staff of the Cambridge Observatory performed all the astronomical calculations and
gave the location (latitude) of the gun and the firing date.
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The location was in Florida and the engineering enterprise started.
When the construction of the gun was over a strange guy, Michelle Ardan, asked to
Barbicane to sit inside the projectile and to go to the Moon: this eccentric traveler wanted
to be the first man on the Moon.
After a moment of thinking, Barbicane organized the construction of a new cannon ball
suited to host people inside. Michelle Ardan convinced everyone about the importance of
his travel. Not only, he persuaded Barbicane and Captain Nicholl, who adversed the entire
project, to sit with him and to resolve practically their ballistic disputations.
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The story ends with the firing of the gun and the starting of the travel toward the outer
space of our three heroes.
Verne continued the story in a following book, "Around the Moon".
Here our three astronauts are not able to reach the surface of our satellite because of a
wrong calculation, and their spaceship becomes an artificial satellite of the Moon.
Thinking about a solution, they decide to fire the auxiliary rockets intended to decrease the
speed near the landing point on the Moon.
But, speaking in modern language, the Murphy's Law strikes again.
They make a bad evaluation of the position and the thrust of the rockets put the projectile
out of his orbit, but toward the Earth.
They return to Earth and they land on the sea (the first splashdown), and is a triumph for
our three heroes.
Verne's biographers tells us that the writer, before his death (24 th March 1905), gave the
manuscript of "From Earth to the Moon" to his nephew and told him to preserve it with the
greatest care, as he will be witnessed the arrival of Man on the Moon.
Truly, a century in advance, Verne made a good provision of the flight plan of Apollo 8
mission (which took place in the month of December 1968).
He foresaw exactly the nation that will have organized the first launch toward the Moon
(United States of America), the month of the firing (December), the number of men
onboard (three), the landing system (the splash down) and the location of the splash down
(Pacific Ocean).
Finally, the location in which was built the gun, in Florida, is at a distance of one hundred
km from the location in which today we found Cape Kennedy, from which Apollo missions
were fired.
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The Gun Club Telescope
In the first part of the book, when nobody realizes that what is beginning is the human
exploration of the space, the technical staff of the Gun Club studies all the problem of the
enterprise.
The first argument is about the cannon ball to be sent on the Moon.
Secretary Club J.T.Maston observe that "the shot must be big enough to attract the
attention of the inhabitants of the moon, if there are any"
President Barbicane agrees about this consideration, "and for another reason more
important still…It is not enough to discharge a projectile, and then take no further notice of
it; we must follow it throughout its course, up to the moment when it shall reach its goal, or
our experiment would produce no result."
"But then," replied Major Elphiston "you will have to give this projectile enormous
dimensions."
"No! Be so good as to listen. You know that optical instruments have acquired great
perfection; with certain instruments we have succeeded in obtaining enlargements of
6,000 times and reducing the moon to within forty miles' distance. Now, at this distance,
any objects sixty feet square would be perfectly visible.
If, then, the penetrative power of telescopes has not been further increased, it is because
that power detracts from their light; and the moon, which is but a reflecting mirror, does not
give back sufficient light to enable us to perceive objects of lesser magnitude."
"Well, then, what do you propose to do?" asked the general "Would you give your
projectile a diameter of sixty feet?"
"Not so."
"Do you intend, then, to increase the luminous power of the moon?"
"Exactly so. If I can succeed in diminishing the density of the atmosphere through which
the moon's light has to travel I shall have rendered her light more intense. To effect that
object it will be enough to establish a telescope on some elevated mountain. That is what
we will do."
"And what enlargement do you expect to obtain in this way?"
"One of 48,000 times, which should bring the moon within an apparent distance of five
miles; and, in order to be visible, objects need not have a diameter of more than nine
feet."
"So, then," cried J. T. Maston, "our projectile need not be more than nine feet in diameter."
To amateur astronomer like us, even if our scope has an aperture of 10 or 20 cm and we
can't use telescopes of some meter of diameter, these values of the enlarging power
(6000x or 48000x) sound very strange.
We are used to think at the power of a scope in terms of a magnification two or three
times the number of the diameter expressed in millimeters.
A very well rule tells us that is not very useful to go over twice this number; in the best
conditions we can use something more with a refractor, something less with a reflector or
Schmidt-Cassegrain, so we think, for example, at a 100 mm refractor, we think to a power
of 200x.
President Barbicane states that with some telescopes that can offer a power of 6000x, we
observe the Moon like if it was at a distance of 40 miles.
Thinking that a terrestrial mile is equal to 1609.344 meters, we calculate an effective
Earth-Moon distance of
40  6000  1..609344  386243 km
a value near to the mean distance between the two celestial objects (384400 km).
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First of all, is it possible, with a power of 6000x, to glimpse an object with a dimension of
60 feet (1 foot = 0.3048 m, so 60 feet = 18.3 m) ?
An object of this dimension, put at a distance of 384400 km, offer us an apparent
dimension of 0.0098", and looking with a power of 6000x, its apparent dimension to the
eye would be 58.9”.
This is represented by the apparent diameter of a middle-sized coin seen with unaided
eye at a distance of about 90 m (something like the observing Venus near inferior
conjunction).
We can remember again that the apparent diameter of Jupiter at opposition is something
like 40”, and its observation with a 200x telescope gives us an apparent diameter of 133’,
more than four times the diameter of full Moon observed with unaided eye.
Italian astronomer Walter Ferreri, in his book “Il libro dei telescopi”, write that generally the
human eye has a resolving power of 1’ (60"). But Ferreri tells us that this is true in
particular conditions, and not in every situation.
In fact we can try to observe a double star with a separation of 1” (using a scope with an
equal or better resolving power) and with a power of 60x.
The apparent distance between the components is 60", but with this power we can't split
the star.
We need a power of 180-240x to see the two components.
This is for two main reasons:
 the resolving power of the human eye has not really the value of 60": we can trust of a
resolving power of 75-80”
 the resolving power of 80” is reached with a pupil diameter of 2 mm; if the pupil is
larger, the power is drastically reduced to the value of 2-3’ (with subject at the limit of
the perception only 12’)
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But if the subject is well illuminated and has a high contrast, the resolving power of the eye
can catch very thin features, even if their apparent dimension is of about 20” or less (is
remembered the case of aerial cables in a well lit landscape).
So it seems possible to see a cannon ball of 60 feet in diameter at the distance of the
Moon through a 6000x scope.
And with a power eight time larger (48000x) it should be possible to see a cannon ball 8
times inferior in diameter (7.5 feet).
Barbicane is right when he decides for a diameter of 9 feet for the Big Gun but, obviously,
the power of the telescope is useful only if the lens or mirror is able itself to reveal the
features we want to see.
Amateur astronomers know that observing double stars the lens or mirror diameter is a
very important factor to know if we can split a particular double star.
Upon the diameter of our scope, we know which doubles can be split and which of them
are out of our possibilities: this can be done calculating the resolving power.
A mean value of resolving power, expressed in second of arc, is given by the formula:
12
PR =
D[cm]
( D[cm] is the diameter of the lens or mirror in cm).
This value, suitable for the biggest part of the possible observing conditions, can be
multiplied by 0.4 to calculate the minimal angular dimension of the smallest details we can
see (like to say, for example, that with a 12 cm lens, with a resolving power of 1”, we can
perceive details of 0.4”).
The 6000x telescope which shows us an object 18.3 m (60 ft) wide at a distance of
384400 km has to perform a minimum resolving power of 0.0098”, with a diameter of
12  0.4
D
 490 cm
0.0098
like the 5 meter reflecting telescope at Mount Palomar.
The 9 feet cannon ball is seen through an angle 6.7 times smaller, and the telescope has
to be 6.7 times larger in diameter.
So we obtain for the diameter of the Barbicane's scope, working at 48000x, a value of 33
meters!
Barbicane, about the possibility to obtain high powers with a telescope, tells us that the
only problem is that the more your power is high, the more the image is dim.
The solution is found immediately: we have only to diminish the thickness of the air
through which we look at the Moon to have a more intense light, and putting the scope on
a mountain peak is the only and simple thing to do.
In a chapter dedicated to the Big Scope, we know that Barbicane chooses the Long’s
Peak, in the Rocky Mountains (3210 m high) to set up the telescope.
The optical design is of the Herschelian type, to avoid the loss of light due to the
secondary mirror.
The mirror has a diameter of 16 ft (4877 mm, almost like Mount Palomar's telescope who
was built many decades later: Jules Verne strikes again!), and a focal length of 280 ft
(85.34 m), with a f/ratio of 17.5 : you need only a Vixen Lanthanium eyepiece of 2.5 mm
focal length and you are cranked up to 34136x !
In the same chapter of the book are remembered the major telescopes of the time, the
reflector of Herschel, 4.5 ft diameter (1372 mm) and 36 ft of focal length (10.97 m), and
the famous Leviathan of Birrcastle, in Ireland, owned by Lord Rosse, 6 ft diameter (1829
mm) and 48 ft of focal length (14.6 m).
These telescopes are credited, respectively, of an operating power of 6000x e 6400x.
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Effective power on a big scope
We have established the fact that the telescope on the Rocky Mountains was not the right
instrument to follow the travel of the 9-ft cannon ball toward the Moon.
It was out of the possibilities of the instrument to see such a little object, notwithstanding
the tremendous enlarging power employed.
About the power on a particular scope, we have seen that the power can bring the object
that can be resolved by the lens or mirror to the level of the resolving power of our eye.
Walter Ferreri in his book gives us (for a 500 cm diameter objective, the same dimension
of the Barbicane's scope) the following powers:
 a minimum power of 714x, which offers an exit pupil of 7 mm in diameter
 a resolving power of 2500x: objects with an angular dimension equal to the resolving
power of the telescope (0.024”) are seen by the observer at the eyepiece with an
apparent extension of 60 ", the resolving power of the human eye
 a maximum theoretical power of 8333x: the most subtle details revealed by the
objective (0.4 times the resolving power, in this case 0.0096”) are seen under an angle
of 80”, the resolving power of the human eye in most conditions
 a maximum practical power of 1564x, derived from purely empirical considerations.
Without considering the particular situation of double star observing (we can use
powers up to three times the diameter in mm of the lens), Walter Ferreri tells us that
nobody among the great visual observers of the past have found useful a power greater
than this.
On the “Il libro dei telescopi” we read that planetary observer Gerard Kuiper used a
maximum power of 900x with the 208 cm reflector of the McDonald Observatory.
Audoin Dollfus, observing Mars and Saturn, used powers of 900x e 1000x with the 60 cm
refractor of Pic du Midi, and Ferreri itself state that on double stars he can use a power of
1000x with the 42 cm refractor of the observatory of Torino (Italy).
Again, Kuiper found useful 1200x for an evaluation of Pluto's dimension at the 5 m
reflector at Mount Palomar, Antoniadi pushed up at 2500x the 83 cm refractor of Meudon
for studying Jupiter's satellites, and R.G. Aitken, in very particular conditions, cranked up
the power at 3000x with the 91 cm refractor of the Lick Observatory, and only on double
stars work.
We must also remember that between our telescope and the star or planet there is a thick
layer of air, and the "boiling" images it causes make impossible for us to appreciate the
subtle features that our scope could show us.
Because of air turbulence, and respecting the ratio between power and diameter, it is not
the same thing to observe through a 10 cm scope at 200x or through a 1 meter scope at
2000x.
When the turbulence of the air make possible to glimpse details of a dimension from 1" to
2", a very common value, Walter Ferreri tells us that it is not possible to use powers
greater than 300-400x with any instrument.
So, the biggest overestimation of Barbicane was not about his gun, but about his scope !
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