1 Giovanni Battista Riccioli and the New Almagestundpress/excerpts/P03169-ex.pdf · 1 Giovanni Battista Riccioli and the New Almagest The New Almagest was astronomy. What was not

1 Giovanni Battista Riccioli

and the New Almagest

The New Almagest was astronomy. What was not in the New Almagest did

not need to be known. England’s top astronomer—the first Astronomer

Royal, John Flamsteed—used the New Almagest as a textbook for public

lectures at Gresham College in 1665. Indeed, anyone carrying a copy of the

New Almagest to a lecture would have looked quite learned, for the book

was printed in two volumes, each the size of one of today’s large coffee-

table books. Within those volumes were over fifteen hundred pages, filled

with dense text and diagrams. Clearly, anyone who read the New Almagest,

which was published in 1651 by an Italian astronomer by the name of Gio-

vanni Battista Riccioli (1598– 1671), knew something about astronomy.

Information on every conceivable topic in seventeenth-century astron-

omy could be found in the pages of the New Almagest. There were chap-

ters devoted to the motions of celestial bodies, to discussions of geometry,

and to representations of the appearance of Jupiter, Venus, and other plan-

ets as seen through the best telescopes. There were reports on, and tables

of data from, physics experiments of different sorts, such as those in-

volving bodies falling through air and through water. There were lots of ta-

bles of astronomical data. There was a highly detailed, full-spread map of

the Moon, which featured an interesting new naming system for lunar fea-

tures. On the map one lunar crater was named “Copernicus.” Another was

named “Galileo.” A large smooth area was named the “Sea of Tranquility.”

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These names would stick—when the Apollo 11 lander the “Eagle” touched

down on the moon in 1969, it landed in the “Sea of Tranquility,” and Neil

Armstrong would radio, “Houston, Tranquility Base here. The Eagle has

landed.”

Inside each volume of the New Almagest was an impressive fron-

tispiece that represented the state of astronomical knowledge in the mid-

seventeenth century (fig. 1.1). The frontispiece showed Jupiter having four

moons, as Galileo had reported in his groundbreaking Starry Messenger of

1610. But the frontispiece also showed Jupiter having cloud bands1—a dis-

covery made since Galileo. It showed Venus having a crescent phase, as

Galileo had first observed with his telescope. It also showed Mercury with

a crescent phase—another discovery made since Galileo. Of course it fea-

tured a cratered moon, Mars and Saturn, and more. The New Almagest

frontispiece presented all the key discoveries that had been revealed by the

telescope since Galileo had turned one to the heavens in 1609 (fig. 1.2).

Yet the main feature of the frontispiece was a set of scales, being held by

Urania, the Greek muse of astronomy, while the many-eyed Argus, holding

a telescope, looked on (fig. 1.3). The modern reader who studies the fron-

tispiece will immediately recognize, on the left side of the scales, a represen-

tation of the world system of Nicolaus Copernicus (1473– 1543)—the

“heliocentric hypothesis.” There is the Sun, in the middle of everything,

with planets circling around it, and the Moon circling the third planet

from the Sun.

On the right side of the scales is not a representation of the “geocentric

hypothesis,” the ancient world system of Ptolemy (who wrote the origi-

nal Almagest) and Aristotle, in which Earth is in the center of everything,

and everything circles around Earth. Galileo’s famous Dialogue of 1632

concerned “the two chief world systems: Ptolemaic and Copernican.” But

in the New Almagest, the Ptolemaic system is not what is being weighed

against the Copernican system. In Riccioli’s frontispiece, the Ptolemaic

world system is sitting off to the side, on the ground, looking a little for-

lorn. Clearly the telescopic discoveries shown above the scales, especially

the phases of Venus and Mercury (which proved those bodies circle the

Sun), have removed that ancient system from Riccioli’s consideration.

Rather, on the right side of the scales is a representation of a world

system that is definitely geocentric. There is the Earth, right in the center,

2 SETTING ASIDE ALL AUTHORITY



Figure 1.1. Frontispiece of Giovanni Battista Riccioli’s 1651 New Almagest. Image

courtesy History of Science Collections, University of Oklahoma Libraries.



Figure 1.2. Details from the New

Almagest frontispiece, showing Jupiter

with moons and cloud bands (left), and showing Mercury and Venus each with a

crescent phase (right). Images courtesy History of Science Collections, University of

Oklahoma Libraries.

Figure 1.3.

Detail from the New

Almagest frontispiece,

showing the world

systems being

weighed in the

balance. Image

courtesy History of

Science Collections,

University of

Oklahoma Libraries.



with the Sun and Moon circling it. But this world system is not purely

geocentric. Planets circle the Sun. This world system may be geocentric,

but it has some heliocentric features. It is a “hybrid geocentric” (or “geo-

heliocentric”) hypothesis.

Moreover, the balance is obviously tipping in favor of this hybrid

geo centric world system. The New Almagest is clearly promoting the view

that, in the age of new telescopic discoveries, this hybrid geocentrism is

superior to Copernican heliocentrism. And yet the hand of God reaches

down from above the page, indicating “Numerus,” “Mensura,” “Pondus”

(“Number,” “Measure,” “Weight”), while verses from the Vulgate Bible2

grace the picture:

“dies diei eructat verbum et nox nocti indicat scientiam”—“Day to day

uttereth speech, and night to night sheweth knowledge” (Psalm 18:3)

“videbo caelos tuos; opera digitorum tuorum”—“I will behold thy

heavens, the works of thy fingers” (Psalm 8:4)

“non inclinabitur in saeculum saeculi”—“[Earth] shall not be moved

for ever and ever” (Psalm 103:5)

What is Riccioli saying, anyway, by representing the latest discoveries with

all this?

Riccioli, a Jesuit priest who was originally trained as a theologian, be-

fore he discovered and fell in love with astronomy,3 appears to be saying

that, in light of telescopic discoveries, in light of a serious scientific analy-

sis (numbering, measuring, weighing), Copernicus is wrong. The Earth

does not move. Indeed, beyond the frontispiece, a very large part of the

New Almagest consists of an analysis of the world system debate, and this

analysis concludes with a question and a main conclusion. The question is

this: according purely to reason, and setting aside all authority, which hy-

pothesis may be asserted as true—that which supposes the motion of the

Earth, or that which supposes the immobility of the Earth?4 And what was

the conclusion?

Reasoning and intrinsic arguments alone considered, and every au-

thority set aside; the hypothesis supposing the immobility or quiet of

Giovanni Battista Riccioli and the New Almagest 5



the Earth absolutely must be asserted as true; and the hypothesis that

bestows to the Earth motion (either solely diurnal, or diurnal and an-

nual) absolutely must be asserted as false and disagreeing with physi -

cal and indeed physico-mathematical demonstrations.5

In other words, in the age of the telescope, science shows the Copernican

hypothesis to be wrong. And after this main conclusion, Riccioli includes

copies of the condemnation of the Copernican system by church authori-

ties in Rome, of the judgment against Galileo, and of Galileo’s abjuration.6

In his analysis of the heliocentrism vs. geocentrism (of the hybrid

sort) world-system debate in the New Almagest, Riccioli reviewed 126 ar-

guments put forward by both sides. Edward Grant has described this as

“probably the lengthiest, most penetrating, and authoritative analysis

made by any author of the sixteenth and seventeenth centuries.”7 Forty-

nine of the arguments Riccioli reviewed favored heliocentrism; seventy-

seven favored geocentrism.8 But to Riccioli, this was not merely a count-

ing of arguments, for numbers of arguments were not what tipped the

balance of Urania’s scales.

The vast majority of arguments on both sides, he said, were uncon-

vincing. Some were unconvincing because they were so bad (Riccioli says

he is ashamed to bring up some, but does so because they have been used

by various people).9 Others were reasonable, but still unconvincing. For

example, consider pro-heliocentrism argument number 22:

The sun is the center of the Planetary System—as is demonstrated in

the case of Mercury and Venus [by telescopic observations of their

phases, illustrated in the frontispiece], and conjectured in the case of

the others—so it ought to be the center of the Universe.10

This seems like a very reasonable argument. Riccioli notes, however, that

the geocentrists have a valid answer to it. The answer is that the Sun is nei-

ther the center of the Moon’s orbit, nor the center of motion for the fall of

heavy bodies and the rise of fire, nor the center of the stars.11 As another

example, consider pro-geocentrism argument number 42, which says that

the weighty Earth must be at the center of the universe because there is no

explanation as to what would keep it in any other position. Here Riccioli

notes that the heliocentrists can answer that the entire Earth has a natural




circular motion about the center of the universe, in which its weight is not

a factor.12 Then there is pro-geocentrism argument number 53 (one of

only two among the 126 that involve religious questions), which says that

if Earth is not the center of the universe, then Hell is not at the lowest

place, and someone going to Hell could conceivably ascend in doing so.

How could someone ascend into Hell? Riccioli says that the answer to this

argument is that Hell is a place defined by comparison to this world on

which men13 live and to God’s Heaven; the relationship between Heaven,

Hell, and the world of men is not affected by whether Earth moves.14

Riccioli did, however, find a select few arguments to be convincing—

all of them anti-Copernican arguments for which the heliocentrists had

no good answer. One of these concerned the question of detecting Earth’s

rotation. According to Riccioli, a rotating Earth must produce certain

observable phenomena. These phenomena were, in fact, not observed.

Thus the Earth must not rotate. These are the physical and “physico-

mathemati cal” demonstrations Riccioli mentions in his main conclusion

about which “hypothesis” can be asserted as being true.

A second anti-Copernican argument—one that Riccioli thought was

stronger, even though it was technically answerable by the heliocentrists—

concerned the sizes of stars. According to Riccioli, telescopic observations

of the stars showed that, were the Copernican hypothesis correct, the stars

would have to be huge. Indeed, he said, one single star in the Copernican

world system could conceivably be larger than the entire universe in the hy-

brid geocentric world system. By contrast, in the hybrid geocentric system

the stars would be reasonably sized. When the sizes of stars are taken into

consideration, Copernicus’s heliocentric world system looks absurd.

Riccioli devotes at least two chapters in the New Almagest to the star

sizes issue, discusses the issue in a line of pro-geocentrism arguments

(numbers 67– 70),15 and uses it to counter a pro-heliocentrism argument

(number 9).16 And while he grants to the heliocentrists the possibility that

the above-mentioned demonstrations to detect Earth’s rotation might

not work because experiments could be insufficiently precise,17 he grants

no such escape to them on the problem of star sizes. Their only answer to

this argument he says, is an appeal to Divine Omnipotence.18 Technically,

since he cannot deny the power of God, he cannot fully refute the Coper-

nican answer on this matter. But, he says, “even if this falsehood cannot be

refuted, nevertheless it cannot satisfy more prudent men.”19

Giovanni Battista Riccioli and the New Almagest 7



What is remarkable about Riccioli’s analysis is that he was right. His

analysis made sense, granted the knowledge available in his time. Today, in

our time, you the reader have doubtlessly heard that Galileo used science

to prove that the Earth circles the Sun—indeed, the back cover of the stan-

dard modern translation of Galileo’s 1632 Dialogue explicitly states just

that.20 But I believe that by the time you finish the pages of this book, you

will agree with Riccioli’s New Almagest frontispiece. You will conclude that

an objective and rational analysis of the best data on hand in the mid-

seventeenth century would lead one to concur with Riccioli that the Co -

pernican hypothesis, while certainly an improvement over the ideas of

Ptolemy, did not compare favorably against hybrid geocentrism. You will

find that some very strange ideas sprouted under Copernicanism—ideas

about giant stars pointing to the nature of God, or indeed being the “war-

riors” of God. You will find that Riccioli’s ideas can be traced back into the

sixteenth century, to the great Danish astronomer Tycho Brahe, who pro-

moted hybrid geocentrism. And you will find that between Brahe and Ric-

cioli these ideas even played a role in the condemnation of the Copernican

hypothesis by church authorities in Rome. Riccioli causes us to rethink our

ideas of “heliocentrism vs. geocentrism” as being perhaps not so much

about “science (and heliocentrism) vs. religion (and geocentrism)” as per-

haps “science vs. science,” or “religion vs. religion.” Riccioli may even cause

us to invert our view of the issue, wondering if at times the debate was

actually a matter of “religion (and heliocentrism) vs. science (and geo -

centrism).” Giovanni Battista Riccioli invites a reexamination of what we

believe we know about the Copernican Revolution.




Documents

1 Giovanni Battista Riccioli and the New Almagestundpress/excerpts/P03169-ex.pdf · 1 Giovanni Battista Riccioli and the New Almagest The New Almagest was astronomy. What was not