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Reading
on: The universe according to Copernicus
Nicholas
Copernicus quoted in Danielson, Dennis R., Editor
The Book of the Cosmos, Perseus Publishing, Cambridge,
MA, 2000 [abridged — 1900 words]
Source:
Translated from De Revolutionibus Orbium Carlestium,
Nuremberg, 1543, in consultation with Nikolaus Kopernikus
Gesamtausgabe, vol. 2, Munich: Oldenbourg, 1949.
THE UNIVERSE IS SPHERICAL
The first thing for us to realize is that the universe
is spherical. This is so either because, of all forms,
the sphere is the most perfect, requiring no joins,
and being an integrated whole; or because it is the
most capacious of all forms, and so best fitted to enclose
and preserve all things—or also because the most
perfected parts of the universe such as the sun, the
moon, and the stars display this shape; or because all
things strive to be bounded thus, as we observe in drops
of water and other liquids when they seek to be bounded
within themselves. There can be no doubt, then, about
the rightness of ascribing this shape to the heavenly
bodies.
THE
EARTH TOO IS SPHERICAL
The earth also has the shape of a globe, because all
of its parts tend towards its center. We do not immediately
perceive it as a perfect sphere because the mountains
are so high and the valleys so deep, and yet these hardly
affect the overall sphericity of the earth. This is
clear from the fact that if one travels northward, the
pole of the diurnal rotation gradually rises, while
the opposite pole sinks accordingly, and more stars
in the northern sky seem never to set, while some in
the south seem never to rise… Conversely, as one
travels southward, such stars rise higher, while those
which appear high to us sink lower…
Seafarers
know that the waters too conform to this shape, for
land that is not visible from the ship is observed from
the top of the mast. And if a bright light is placed
at the top of the mast, then to those remaining on the
shore it appears gradually to sink as the ship moves
farther off from land. Finally, the light as it were
sets and disappears…
THE
MOTION OF THE HEAVENLY BODIES IS UNIFORM, PERPETUAL,
AND CIRCULAR, OR MADE UP OF CIRCULAR MOTIONS
…the sun metes out our year and the moon our month,
these being the other most common measures of time.
In this way too each of the five planets completes its
circuit. Yet there are differences among their various
motions. First, these do not turn about the same axis
as the primary motion but take a slantwise course through
the zodiac. Secondly, they are not observed moving uniformly
in their orbits. For we see that the sun and moon in
their courses sometimes move slowly and sometimes more
quickly.
As
for the other five planets, as we observe, sometimes
they even come to a stop and retrace their steps. And
while the sun always keeps strictly to its own pathway,
these others wander in various ways, sometimes towards
the south, sometimes towards the north—which is
why they are called planets [from Greek planetes, “wanderer”].
Moreover, sometimes they are nearer the earth and said
to be “in perigee”; at other times they are
farther off and said to be “in apogee.”
We
must admit, nonetheless, that their motions are circular,
or made up of several circles, because these nonuniformities
conform to a consistent law and to the fact that the
planets return to where they began, which could not
be the case unless the motions were circular, for only
a circle can replicate what has already taken place…
For example, by a motion made up of circles the sun
causes for us a repetition of unequal days and nights
and of the four seasons. In this cycle we discern several
motions, since no simple heavenly body can move irregularly
in a single sphere. For such irregularity would have
to result either from an inconstancy in the force of
movement, whether arising internally or externally,
or from some irregularity in the revolving body. But
either alternative is abhorrent to reason. We must not
ascribe any such indignity to things framed and governed
optimally.
We
must conclude, then, that their uniform motions appear
to us as irregular either because they take place around
different axes, or else because the earth is not at
the center of their circles of revolution…
Admittedly,
virtually everyone has been taught, and believes, that
the earth is the center of the universe. However, anyone
who denies that the earth occupies the center or midpoint
may still assert that its distance from the center is
negligible by comparison with that of the sphere of
the fixed stars, yet noticeable and noteworthy relative
to the spheres of the sun and other planets. He may
consider that this is why their motions appear nonuniform,
and that they are regular relative to some center other
than that of the earth. In this way, perhaps, he can
offer a not-so-inept explanation for the appearance
of irregular motion. For the fact that we observe the
planets sometimes nearer the earth and sometimes farther
away is logical proof that the center of the earth is
not the center of their orbits…
And
yet the question of earth’s location remains uncertain…
Even though it is not in the center of the universe,
its distance from the center is nevertheless inconsiderable
when compared to the distance of the sphere of the fixed
stars…
[If
the heaven of fixed stars moved about the earth would
not their] swiftness of motion be that much greater
in proportion as the heavens are greater than the earth?
Or are the heavens so immense precisely because the
ineffable force of their motion impels them away from
the center? Would they otherwise collapse if they did
stand still? If this reasoning were sound, then surely
the magnitude of the heavens must expand to infinity.
For the higher they are impelled by the force of their
motion, the faster their motion will be on account of
the continuously expanding circumference which has to
make its revolution every twenty-four hours. In turn,
as the motion increased, so would the immensity of the
heavens—speed thus increasing size, and size increasing
speed, ad infinitum. Yet according to that axiom of
physics, nothing that is infinite can be traversed nor
moved by any means, and so the heavens are necessarily
at rest…
Why,
then, do we still hesitate to accept the earth’s
movement in keeping with the nature of its form instead
of attributing motion to the whole universe, whose bounds
are unknown and unknowable. As regards the daily rotation,
why not grant that in the heavens is the appearance
but in the earth is the reality? For when a ship glides
along smoothly, its passengers see its motion reflected
by everything outside of the ship and, by contrast,
suppose themselves and everything else on board to be
motionless. No wonder, then, that the movement of the
earth makes us think the whole universe is turning round.
CAN
THE EARTH BE SAID TO MOVE IN MORE WAYS THAN ONE? WHERE
IS THE CENTER OF THE UNIVERSE?
Since therefore nothing precludes the earth’s movement,
I propose we now consider whether it may be thought
to move in more than one way: can it be regarded as
one of the planets?
For
earth is not the center of all the revolutions. This
claim is demonstrated by the apparently nonuniform motion
of the planets and by their variable distances from
the earth, which cannot be conceived as implying circles
concentric to the earth. Therefore, there being numerous
centers, it is worth asking whether the center of the
universe, or some other, is the center of earthly gravity.
In my view gravity is nothing but a certain natural
desire which by divine providence the Creator of all
has infused into the parts, whereby they draw themselves
into a unity and an integrity in the form of a globe.
The same desire may be credibly predicated also of the
sun, the moon, and the other luminous planets; by its
efficacy they persist in the rounded shape in which
we behold them, although they pursue their own various
orbits.
Therefore,
if the earth too moves in other ways—about a center,
for example—then this must similarly be reflected
in many external things. Among them, it would seem,
is the annual revolution. For if, granting immobility
to the sun, we exchange earthly movement for solar movement,
then the risings and settings of the constellations
and the fixed stars which accompany morning and evening
will appear just as they do. Furthermore, the stations
as well as both the backward and forward motions of
the planets will be seen not as their own motions but
as earthly motion transmuted into apparent planetary
motions. Finally, it will be accepted that the sun occupies
the center of the universe.
We
learn all these things by discerning the order whereby
the planets follow one another and by the harmony of
the entire universe-if only we examine these matters
(as they say) with both eyes open.
THE
ORDER OF THE HEAVENLY SPHERES
We should not be ashamed to admit that this whole domain
encircled by the moon, with the center of the earth,
traverses this great orbit amidst the other planets
in an annual revolution around the sun, and that near
the sun is the center of the universe; and moreover
that, since the sun stands still, whatever motion the
sun appears to have is instead actually attributable
to the motion of the earth. Furthermore, although the
distance between the earth and the sun is quite noticeable
relative to the size of the other planetary orbits,
it is imperceptible as compared with the sphere of the
fixed stars—so great indeed is the size of the
universe. I think it is a lot easier to accept this
than to drive our minds to distraction multiplying spheres
almost ad infinitum, as has been the compulsion of those
who would detain earth in the center of the universe.
Instead, it is better to follow the wisdom of nature,
which just as it strongly avoids producing anything
superfluous or useless, so it often prefers to endow
a single thing with multiple effects.
This
whole matter is difficult, almost paradoxical, and certainly
contrary to many people’s way of thinking. In what
follows, however, God helping me, I shall make these
things clearer than sunlight, at least to those not
ignorant of the art of astronomy. And so, with the first
principle firmly established (for nobody can propose
one more fitting than that the magnitude of a planet’s
orbit is proportionate to its period of revolution),
the order of the spheres is as follows, beginning with
the highest:
First and highest of all is the sphere of the fixed
stars, containing itself and all things, and therefore
immovable, the very location of the universe, that to
which the motion and position of all the other heavenly
bodies is referred....
This
is followed by the first of the planets, Saturn, which
completes his circuit in thirty years. Then comes Jupiter,
moving in a revolution with a twelve-year period. Next,
the circuit of Mars is two years. Fourth comes the annual
revolution in which, as mentioned earlier, the earth
is carried along, with the moon as it were in an epicycle.
Venus, in fifth place, circles round in nine months.
And then in sixth place Mercury completes his course
in the space of eighty days.
And
behold, in the midst of all resides the sun. For who,
in this most beautiful temple, would set this lamp in
another or a better place, whence to illuminate all
things at once?
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