He is best known for being the first person known to calculate the circumference of the Earth,
which he did by using the extensive survey results he could access in
his role at the Library; his calculation was remarkably accurate. He was also the first to calculate Earth's axial tilt, which also proved to have remarkable accuracy. He created the first global projection of the world, incorporating parallels and meridians based on the available geographic knowledge of his era.
Eratosthenes was the founder of scientific chronology; he endeavoured to revise the dates of the main events of the semi-mythological Trojan War, dating the Sack of Troy to 1183 BC. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.
He was a figure of influence in many fields. According to an entry in the Suda (a 10th-century encyclopedia), his critics scorned him, calling him Beta (the second letter of the Greek alphabet) because he always came in second in all his endeavours. Nonetheless, his devotees nicknamed him Pentathlos after the Olympians
who were well rounded competitors, for he had proven himself to be
knowledgeable in every area of learning. Eratosthenes yearned to
understand the complexities of the entire world.
Life
The son of Aglaos, Eratosthenes was born in 276 BC in Cyrene. Now part of modern-day Libya, Cyrene had been founded by Greeks centuries earlier and became the capital of Pentapolis (North Africa), a country of five cities: Cyrene, Arsinoe, Berenice, Ptolemias, and Apollonia. Alexander the Great conquered Cyrene in 332 BC, and following his death in 323 BC, its rule was given to one of his generals, Ptolemy I Soter, the founder of the Ptolemaic Kingdom. Under Ptolemaic rule the economy prospered, based largely on the export of horses and silphium, a plant used for rich seasoning and medicine.
Cyrene became a place of cultivation, where knowledge blossomed. Like
any young Greek at the time, Eratosthenes would have studied in the
local gymnasium, where he would have learned physical skills and social discourse as well as reading, writing, arithmetic, poetry, and music.
Eratosthenes went to Athens to further his studies. There he was taught Stoicism by its founder, Zeno of Citium, in philosophical lectures on living a virtuous life. He then studied under Aristo of Chios, who led a more cynical school of philosophy. He also studied under the head of the Platonic Academy, who was Arcesilaus of Pitane. His interest in Plato led him to write his very first work at a scholarly level, Platonikos, inquiring into the mathematical foundation of Plato's philosophies. Eratosthenes was a man of many perspectives and investigated the art of poetry under Callimachus. He wrote poems: one in hexameters called Hermes, illustrating the god's life history; and another in elegiacs, called Erigone, describing the suicide of the Athenian maiden Erigone (daughter of Icarius). He wrote Chronographies, a text that scientifically depicted dates of importance, beginning with the Trojan War. This work was highly esteemed for its accuracy. George Syncellus was later able to preserve from Chronographies a list of 38 kings of the Egyptian Thebes. Eratosthenes also wrote Olympic Victors, a chronology of the winners of the Olympic Games. It is not known when he wrote his works, but they highlighted his abilities.
These works and his great poetic abilities led the pharaoh Ptolemy III Euergetes to seek to place him as a librarian at the Library of Alexandria
in the year 245 BC. Eratosthenes, then thirty years old, accepted
Ptolemy's invitation and traveled to Alexandria, where he lived for the
rest of his life. Within about five years he became Chief Librarian, a
position that the poet Apollonius Rhodius had previously held. As head of the library Eratosthenes tutored the children of Ptolemy, including Ptolemy IV Philopator
who became the fourth Ptolemaic pharaoh. He expanded the library's
holdings: in Alexandria all books had to be surrendered for duplication.
It was said that these were copied so accurately that it was impossible
to tell if the library had returned the original or the copy.
He sought to maintain the reputation of the Library of Alexandria
against competition from the Library of Pergamum.
Eratosthenes created a whole section devoted to the examination of
Homer, and acquired original works of great tragic dramas of Aeschylus, Sophocles and Euripides.
Eratosthenes made several important contributions to mathematics and science, and was a friend of Archimedes. Around 255 BC, he invented the armillary sphere. In On the Circular Motions of the Celestial Bodies, Cleomedes credited him with having calculated the Earth's circumference around 240 BC, with a high precision.
Eratosthenes believed there was both good and bad in every nation and criticized Aristotle for arguing that humanity was divided into Greeks and barbarians, as well as for arguing that the Greeks should keep themselves racially pure.[12] As he aged, he contracted ophthalmia,
becoming blind around 195 BC. Losing the ability to read and to observe
nature plagued and depressed him, leading him to voluntarily starve
himself to death. He died in 194 BC at 82 in Alexandria.[9]
Measure of Earth's circumference according to Cleomedes' simplified version, based on the approximation that Syene is on the Tropic of Cancer and on the same meridian as Alexandria
The measurement of Earth's circumference is the most famous among the results obtained by Eratosthenes, who estimated that the meridian has a length of 252,000 stadia
(39,060-40,320 km), with an error on the real value between −2.4% and
+0.8% (assuming a value for the stadion between 155 and 160 metres). Eratosthenes described his arc measurement technique, in a book entitled On the measure of the Earth, which has not been preserved. However, a simplified version of the method has been preserved, as described by Cleomedes.
The simplified method works by considering two cities along the same meridian and measuring both the distance between them and the difference in angles of the shadows cast by the sun on a vertical rod (a gnomon) in each city at noon on the summer solstice. The two cities used were Alexandria and Syene (modern Aswan), and the distance between the cities was measured by professional bematists.
A geometric calculation reveals that the circumference of the Earth is
the distance between the two cities divided by the difference in shadow
angles expressed as a fraction of one turn.
Eratosthenes now continued from his knowledge about the Earth. Using
his discoveries and knowledge of its size and shape, he began to sketch
it. In the Library of Alexandria he had access to various travel books,
which contained various items of information and representations of the
world that needed to be pieced together in some organized format. In his three-volume work Geography (Greek: Geographika), he described and mapped his entire known world, even dividing the Earth into five climate zones: two freezing zones around the poles, two temperate zones, and a zone encompassing the equator and the tropics.
He had invented geography. He created terminology that is still used
today. He placed grids of overlapping lines over the surface of the
Earth. He used parallels and meridians to link together every place in
the world. It was now possible to estimate one's distance from remote
locations with this network over the surface of the Earth. In the Geography the names of over 400 cities and their locations were shown, which had never been achieved before. However, his Geography has been lost to history, although fragments of the work can be pieced together from other great historians like Pliny, Polybius, Strabo, and Marcianus.
The first book was something of an introduction and gave a
review of his predecessors, recognizing their contributions that he
compiled in the library. In this book Eratosthenes denounced Homer
as not providing any insight into what he now described as geography.
His disapproval of Homer's topography angered many who believed the
world depicted in the Odyssey to be legitimate.
He also commented on the ideas of the nature and origin of the Earth:
he thought of Earth as an immovable globe while its surface was
changing. He hypothesized that at one time the Mediterranean
had been a vast lake that covered the countries that surrounded it and
that it only became connected to the ocean to the west when a passage
opened up sometime in its history.
The second book contains his calculation of the circumference of the
Earth. This is where, according to Pliny, "The world was grasped." Here
Eratosthenes described his famous story of the well in Syene, wherein
at noon each summer solstice, the Sun's rays shone straight down into
the city-center well. This book would now be considered a text on mathematical geography.
His third book of the Geography contained political geography.
He cited countries and used parallel lines to divide the map into
sections, to give accurate descriptions of the realms. This was a
breakthrough and can be considered the beginning of geography. For this,
Eratosthenes was named the "Father of Modern Geography."
Achievements
Eratosthenes was described by the Suda Lexicon
as a Πένταθλος (Pentathlos) which can be translated as "All-Rounder",
for he was skilled in a variety of things: He was a true polymath. He
was nicknamed Beta because he was great at many things and tried to get
his hands on every bit of information but never achieved the highest
rank in anything; Strabo accounts Eratosthenes as a mathematician among geographers and a geographer among mathematicians.
Eusebius of Caesarea in his Preparatio Evangelica includes a brief chapter of three sentences on celestial distances (Book XV, Chapter 53). He states simply that Eratosthenes found the distance to the Sun to be "σταδίων μυριάδας τετρακοσίας καὶ ὀκτωκισμυρίας" (literally "of stadiamyriads
400 and 80,000") and the distance to the Moon to be 780,000 stadia. The
expression for the distance to the Sun has been translated either as
4,080,000 stadia (1903 translation by E. H. Gifford), or as 804,000,000
stadia (edition of Edouard des Places, dated 1974–1991). The meaning
depends on whether Eusebius meant 400 myriad plus 80,000 or "400 and
80,000" myriad. With a stade of 185 m (607 ft), 804,000,000 stadia is
149,000,000 km (93,000,000 mi), approximately the distance from the
Earth to the Sun.
Eratosthenes also calculated the Sun's diameter. According to
Macrobious, Eratosthenes made the diameter of the Sun to be about 27
times that of the Earth. The actual figure is approximately 109 times.
During his time at the Library of Alexandria, Eratosthenes devised a calendar using his predictions about the ecliptic of the Earth. He calculated that there are 365 days in a year and that every fourth year there would be 366 days.
He was also very proud of his solution for Doubling the Cube.
His motivation was that he wanted to produce catapults. Eratosthenes
constructed a mechanical line drawing device to calculate the cube,
called the mesolabio. He dedicated his solution to King Ptolemy,
presenting a model in bronze with it a letter and an epigram. Archimedes was Eratosthenes' friend and he, too, worked on the war instrument with mathematics. Archimedes dedicated his book The Method to Eratosthenes, knowing his love for learning and mathematics.
Number theory
Sieve of Eratosthenes: algorithm steps for primes below 121 (including optimization of starting from the prime's square).
In mathematics, the sieve of Eratosthenes (Greek: κόσκινον Ἐρατοσθένους), one of a number of prime number sieves,
is a simple, ancient algorithm for finding all prime numbers up to any
given limit. It does so by iteratively marking as composite, i.e.,
not prime, the multiples of each prime, starting with the multiples of
2. The multiples of a given prime are generated starting from that
prime, as a sequence of numbers with the same difference, equal to that
prime, between consecutive numbers. This is the sieve's key distinction
from using trial division to sequentially test each candidate number for
divisibility by each prime.
Works
Eratosthenes
was one of the most pre-eminent scholarly figures of his time, and
produced works covering a vast area of knowledge before and during his
time at the Library. He wrote on many topics—geography, mathematics,
philosophy, chronology, literary criticism, grammar, poetry, and even
old comedies. Unfortunately, there are no documents left of his work
after the destruction of the Library of Alexandria.
Titles
Platonikos
Hermes
Erigone
Chronographies
Olympic Victors
Περὶ τῆς ἀναμετρήσεως τῆς γῆς (On the Measurement of the Earth) (lost, summarized by Cleomedes)
Гεωγραϕικά (Geographika) (lost, criticized by Strabo)
Astrology
consists of a number of belief systems that hold that there is a
relationship between astronomical phenomena and events or descriptions
of personality in the human world. Astrology has been rejected by the
scientific community as having no explanatory power for describing the
universe. Scientific testing has found no evidence to support the premises or purported effects outlined in astrological traditions.
Where astrology has made falsifiable predictions, it has been falsified. The most famous test was headed by Shawn Carlson and included a committee of scientists and a committee of astrologers. It led to the conclusion that natal astrology
performed no better than chance. Astrologer and psychologist Michel
Gauquelin claimed to have found statistical support for "the Mars effect" in the birth dates of athletes, but it could not be replicated in further studies.
The organisers of later studies claimed that Gauquelin had tried to
influence their inclusion criteria for the study by suggesting specific
individuals be removed. It has also been suggested, by Geoffrey Dean,
that the reporting of birth times by parents (before the 1950s) may have
caused the apparent effect.
Astrology has not demonstrated its effectiveness in controlled studies and has no scientific validity, and is thus regarded as pseudoscience.
There is no proposed mechanism of action by which the positions and
motions of stars and planets could affect people and events on Earth in
the way astrologers say they do that does not contradict
well-understood, basic aspects of biology and physics.
Modern scientific inquiry into astrology is primarily focused on drawing a correlation between astrological traditions and the influence of seasonal birth in humans.
Introduction
The
majority of professional astrologers rely on performing astrology-based
personality tests and making relevant predictions about the
remunerator's future.
Those who continue to have faith in astrology have been characterised
as doing so "in spite of the fact that there is no verified scientific
basis for their beliefs, and indeed that there is strong evidence to the
contrary". AstrophysicistNeil deGrasse Tyson
commented on astrological belief, saying that "part of knowing how to
think is knowing how the laws of nature shape the world around us.
Without that knowledge, without that capacity to think, you can easily
become a victim of people who seek to take advantage of you".
The continued belief in astrology despite its lack of credibility is seen as a demonstration of low scientific literacy, although some continue to believe in it even though they are scientifically literate.
The foundations of the theoretical structure used in astrology
originate with the Babylonians, although widespread usage did not occur
till the start of the Hellenistic period after Alexander the Great swept through Greece. It was not known to the Babylonians that the constellations are not on a celestial sphere
and are very far apart. The appearance of them being close is illusory.
The exact demarcation of what a constellation is, is cultural, and
varied between civilisations.Ptolemy's work on astronomy was driven to some extent by the desire, like all astrologers of the time, to easily calculate the planetary movements. Early western astrology operated under the ancient Greek concepts of the Macrocosm and microcosm; and thus medical astrology
related what happened to the planets and other objects in the sky to
medical operations. This provided a further motivator for the study of
astronomy.
While still defending the practice of astrology, Ptolemy acknowledged
that the predictive power of astronomy for the motion of the planets and
other celestial bodies ranked above astrological predictions.
During the Islamic Golden Age, astronomy was funded so that the astronomical parameters, such as the eccentricity of the sun's orbit, required for the Ptolemaic model could be calculated to a sufficient accuracy and precision. Those in positions of power, like the Fatimid Caliphatevizier
in 1120, funded the construction of observatories so that astrological
predictions, fuelled by precise planetary information, could be made.
Since the observatories were built to help in making astrological
predictions, few of these observatories lasted long due to the
prohibition against astrology within Islam, and most were torn down
during or just after construction.
The clear rejection of astrology in works of astronomy started in 1679, with the yearly publication La Connoissance des temps. Unlike the west, in Iran, the rejection of heliocentrism
continued up towards the start of the 20th century, in part motivated
by a fear that this would undermine the widespread belief in astrology
and Islamic cosmology in Iran.
The first work, Falak al-sa'ada by Ictizad al-Saltana, aimed at
undermining this belief in astrology and "old astronomy" in Iran was
published in 1861. On astrology, it cited the inability of different
astrologers to make the same prediction about what occurs following a conjunction, and described the attributes astrologers gave to the planets as implausible.
Philosophy of science
Philosopher
Karl Popper proposed falsifiability as ideas that distinguish science
from non-science, using astrology as the example of an idea that has not
dealt with falsification during experiment.
Astrology provides the quintessential example of a pseudoscience since it has been tested repeatedly and failed all the tests.
Falsifiability
Science and non-science are often distinguished by the criterion of falsifiability. The criterion was first proposed by philosopher of scienceKarl Popper. To Popper, science does not rely on induction;
instead, scientific investigations are inherently attempts to falsify
existing theories through novel tests. If a single test fails, then the
theory is falsified.
Therefore, any test of a scientific theory must prohibit certain
results that falsify the theory, and expect other specific results
consistent with the theory. Using this criterion of falsifiability,
astrology is a pseudoscience.
Astrology was Popper's most frequent example of pseudoscience.
Popper regarded astrology as "pseudo-empirical" in that "it appeals to
observation and experiment", but "nevertheless does not come up to
scientific standards".
In contrast to scientific disciplines, astrology does not respond
to falsification through experiment. According to Professor of
neurology Terence Hines, this is a hallmark of pseudoscience.
"No puzzles to solve"
In contrast to Popper, the philosopher Thomas Kuhn
argued that it was not lack of falsifiability that makes astrology
unscientific, but rather that the process and concepts of astrology are
non-empirical.
To Kuhn, although astrologers had, historically, made predictions that
"categorically failed", this in itself does not make it unscientific,
nor do the attempts by astrologers to explain away the failure by
claiming it was due to the creation of a horoscope being very difficult (through subsuming, after the fact, a more general horoscope that leads to a different prediction).
Rather, in Kuhn's eyes, astrology is not science because it was always more akin to medieval medicine;
they followed a sequence of rules and guidelines for a seemingly
necessary field with known shortcomings, but they did no research
because the fields are not amenable to research, and so, "They had no puzzles to solve and therefore no science to practise."
While an astronomer could correct for failure, an astrologer
could not. An astrologer could only explain away failure but could not
revise the astrological hypothesis
in a meaningful way. As such, to Kuhn, even if the stars could
influence the path of humans through life astrology is not scientific.
Progress, practice and consistency
Philosopher Paul Thagard
believed that astrology can not be regarded as falsified in this sense
until it has been replaced with a successor. In the case of predicting
behaviour, psychology is the alternative.
To Thagard a further criterion of demarcation of science from
pseudoscience was that the state of the art must progress and that the
community of researchers should be attempting to compare the current
theory to alternatives, and not be "selective in considering
confirmations and disconfirmations".
Progress is defined here as explaining new phenomena and solving
existing problems, yet astrology has failed to progress having only
changed little in nearly 2000 years. To Thagard, astrologers are acting as though engaged in normal science
believing that the foundations of astrology were well established
despite the "many unsolved problems", and in the face of better
alternative theories (Psychology). For these reasons Thagard viewed
astrology as pseudoscience.
To Thagard, astrology should not be regarded as a pseudoscience
on the failure of Gauquelin to find any correlation between the various
astrological signs and someone's career, twins not showing the expected
correlations from having the same signs in twin studies, lack of
agreement on the significance of the planets discovered since Ptolemy's
time and large scale disasters wiping out individuals with vastly
different signs at the same time. Rather, his demarcation of science requires three distinct foci: "theory, community [and] historical context".
While verification and falsifiability focused on the theory,
Kuhn's work focused on the historical context, but the astrological
community should also be considered. Whether or not they:
are focused on comparing their approach to others.
have a consistent approach.
try to falsify their theory through experiment.
In this approach, true falsification rather than modifying a theory
to avoid the falsification only really occurs when an alternative theory
is proposed.
Irrationality
For
the philosopher Edward W. James, astrology is irrational not because of
the numerous problems with mechanisms and falsification due to
experiments, but because an analysis of the astrological literature
shows that it is infused with fallacious logic and poor reasoning.
What if throughout astrological
writings we meet little appreciation of coherence, blatant insensitivity
to evidence, no sense of a hierarchy of reasons, slight command over
the contextual force of critieria, stubborn unwillingness to pursue an
argument where it leads, stark naivete concerning the efficacy of
explanation and so on? In that case, I think, we are perfectly justified
in rejecting astrology as irrational. ... Astrology simply fails to
meet the multifarious demands of legitimate reasoning.
— Edward W. James
This poor reasoning includes appeals to ancient astrologers
such as Kepler despite any relevance of topic or specific reasoning,
and vague claims. The claim that evidence for astrology is that people
born at roughly "the same place have a life pattern that is very
similar" is vague, but also ignores that time is reference frame dependent
and gives no definition of "same place" despite the planet's moving in
the reference frame of the solar system. Other comments by astrologers
are based on severely erroneous interpretations of basic physics, such
as the general belief by medieval astrologers that the geocentric
solar system corresponded to an atom. Further, James noted that
response to criticism also relies on faulty logic, an example of which
was a response to twin studies with the statement that coincidences in
twins are due to astrology, but any differences are due to "heredity and
environment", while for other astrologers the issues are too difficult
and they just want to get back to their astrology.
Further, to astrologers, if something appears in their favour, they
latch upon it as proof, while making no attempt to explore its
implications, preferring to refer to the item in favour as definitive;
possibilities that do not make astrology look favourable are ignored.
Quinean dichotomy
From the Quinean
web of knowledge, there is a dichotomy where one must either reject
astrology or accept astrology but reject all established scientific
disciplines that are incompatible with astrology.
Tests of astrology
Astrologers
often avoid making verifiable predictions, and instead rely on vague
statements that let them try to avoid falsification.
Across several centuries of testing, the predictions of astrology have
never been more accurate than that expected by chance alone. One approach used in testing astrology quantitatively is through blind experiment.
When specific predictions from astrologers were tested in rigorous
experimental procedures in the Carlson test, the predictions were falsified. All controlled experiments have failed to show any effect.
Carlson's experiment
Shawn
Carlson's now renowned experiment was performed by 28 astrologers
matching over 100 natal charts to psychological profiles generated by
the California Psychological Inventory (CPI) test using double blind methods.
The experimental protocol used in Carlson's study was agreed to
by a group of physicists and astrologers prior to the experiment. Astrologers, nominated by the National Council for Geocosmic Research, acted as the astrological advisors, and helped to ensure, and agreed, that the test was fair. They also chose 26 of the 28 astrologers for the tests, the other two being interested astrologers who volunteered afterwards. The astrologers came from Europe and the United States. The astrologers helped to draw up the central proposition of natal astrology to be tested. Published in Nature
in 1985, the study found that predictions based on natal astrology were
no better than chance, and that the testing "clearly refutes the
astrological hypothesis".
Dean and Kelly
Scientist and former astrologer Geoffrey Dean and psychologist Ivan Kelly conducted a large-scale scientific test, involving more than one hundred cognitive, behavioural, physical and other variables, but found no support for astrology. A further test involved 45 confident
astrologers, with an average of 10 years' experience and 160 test
subjects (out of an original sample size of 1198 test subjects) who
strongly favoured certain characteristics in the Eysenck Personality Questionnaire to extremes.
The astrologers performed much worse than merely basing decisions off
the individuals' ages, and much worse than 45 control subjects who did
not use birth charts at all.
Other tests
A meta-analysis
was conducted, pooling 40 studies consisting of 700 astrologers and
over 1,000 birth charts. Ten of the tests, which had a total of 300
participating, involved the astrologers picking the correct chart
interpretation out of a number of others that were not the
astrologically correct chart interpretation (usually three to five
others). When the date and other obvious clues were removed, no
significant results were found to suggest there was any preferred chart.
In 10 studies, participants picked horoscopes that they felt were
accurate descriptions, with one being the "correct" answer. Again the
results were no better than chance.
In a study of 2011 sets of people born within 5 minutes of each
other ("time twins") to see if there was any discernible effect; no
effect was seen.
Quantitative sociologist David Voas
examined the census data for more than 20 million individuals in
England and Wales to see if star signs corresponded to marriage
arrangements. No effect was seen.
The initial Mars effect finding, showing the relative frequency of the diurnal position of Mars in the birth charts (N = 570) of "eminent athletes" (red solid line) compared to the expected results [after Michel Gauquelin 1955]
In 1955, astrologer and psychologist Michel Gauquelin stated that although he had failed to find evidence to support such indicators as the zodiacal signs and planetary aspects in astrology, he had found positive correlations between the diurnal positions of some of the planets
and success in professions (such as doctors, scientists, athletes,
actors, writers, painters, etc.), which astrology traditionally
associates with those planets. The best-known of Gauquelin's findings is based on the positions of Mars in the natal charts of successful athletes and became known as the "Mars effect". A study conducted by seven French scientists attempted to replicate the claim, but found no statistical evidence.
They attributed the effect to selective bias on Gauquelin's part,
accusing him of attempting to persuade them to add or delete names from
their study.
Geoffrey Dean has suggested that the effect may be caused by
self-reporting of birth dates by parents rather than any issue with the
study by Gauquelin. The suggestion is that a small subset of the parents
may have had changed birth times to be consistent with better
astrological charts for a related profession. The sample group was taken
from a time where belief in astrology was more common. Gauquelin had
failed to find the Mars effect in more recent populations,
where a nurse or doctor recorded the birth information. The number of
births under astrologically undesirable conditions was also lower,
indicating more evidence that parents choose dates and times to suit
their beliefs.
Theoretic obstacles
Beyond
the scientific tests astrology has failed, proposals for astrology face
a number of other obstacles due to the many theoretical flaws in
astrology
including lack of consistency, lack of ability to predict missing
planets, lack of connection of the zodiac to the constellations in
western astrology, and lack of any plausible mechanism. The
underpinnings of astrology tend to disagree with numerous basic facts
from scientific disciplines.
Lack of consistency
Testing
the validity of astrology can be difficult because there is no
consensus amongst astrologers as to what astrology is or what it can
predict. Dean and Kelly documented 25 studies, which had found that the degree of agreement amongst astrologers' predictions was measured as a low 0.1.
Most professional astrologers are paid to predict the future or
describe a person's personality and life, but most horoscopes only make
vague untestable statements that can apply to almost anyone.
Georges Charpak and Henri Broch dealt with claims from western astrology in the book Debunked! ESP, Telekinesis, and other Pseudoscience.
They pointed out that astrologers have only a small knowledge of
astronomy and that they often do not take into account basic features
such as the precession of the equinoxes. They commented on the example of Elizabeth Teissier
who claimed that "the sun ends up in the same place in the sky on the
same date each year" as the basis for claims that two people with the
same birthday but a number of years apart should be under the same
planetary influence. Charpak and Broch noted that "there is a difference
of about twenty-two thousand miles between Earth's location on any
specific date in two successive years" and that thus they should not be
under the same influence according to astrology. Over a 40 years period
there would be a difference greater than 780,000 miles.
Lack of physical basis
Edward
W. James, commented that attaching significance to the constellation on
the celestial sphere the sun is in at sunset was done on the basis of
human factors—namely, that astrologers didn't want to wake up early, and
the exact time of noon was hard to know. Further, the creation of the
zodiac and the disconnect from the constellations was because the sun is
not in each constellation for the same amount of time.
This disconnection from the constellations led to the problem with
precession separating the zodiac symbols from the constellations that
they once were related to. Philosopher of science, Massimo Pigliucci commenting on the movement, opined "Well then, which sign should I look up when I open my Sunday paper, I wonder?"
The tropical zodiac has no connection to the stars, and as long
as no claims are made that the constellations themselves are in the
associated sign, astrologers avoid the concept that precession seemingly moves the constellations because they don't reference them.
Charpak and Broch, noting this, referred to astrology based on the
tropical zodiac as being "...empty boxes that have nothing to do with
anything and are devoid of any consistency or correspondence with the
stars." Sole use of the tropical zodiac is inconsistent with references made, by the same astrologers, to the Age of Aquarius, which depends on when the vernal point enters the constellation of Aquarius.
Lack of predictive power
Shown
in the image is Pluto and its satellites. Astrology was claimed to work
before the discovery of Neptune, Uranus and Pluto and they have now
been included in the discourse on an ad hoc basis.
Some astrologers make claims that the position of all the planets
must be taken into account, but astrologers were unable to predict the
existence of Neptune based on mistakes in horoscopes. Instead Neptune was predicted using Newton's law of universal gravitation. The grafting on of Uranus, Neptune and Pluto into the astrology discourse was done on an ad hoc basis.
On the demotion of Pluto to the status of dwarf planet, Philip Zarka of the Paris Observatory in Meudon, France wondered how astrologers should respond:
Should astrologers remove it from
the list of luminars [Sun, Moon and the 8 planets other than earth] and
confess that it did not actually bring any improvement? If they decide
to keep it, what about the growing list of other recently discovered
similar bodies (Sedna, Quaoar. etc), some of which even have satellites
(Xena, 2003EL61)?
Lack of mechanism
Astrology has been criticised for failing to provide a physical mechanism that links the movements of celestial bodies to their purported effects on human behaviour. In a lecture in 2001, Stephen Hawking
stated "The reason most scientists don't believe in astrology is
because it is not consistent with our theories that have been tested by
experiment." In 1975, amid increasing popular interest in astrology, The Humanist magazine presented a rebuttal of astrology in a statement put together by Bart J. Bok, Lawrence E. Jerome, and Paul Kurtz.
The statement, entitled "Objections to Astrology", was signed by 186
astronomers, physicists and leading scientists of the day. They said
that there is no scientific foundation for the tenets of astrology and
warned the public against accepting astrological advice without
question. Their criticism focused on the fact that there was no
mechanism whereby astrological effects might occur:
We can see how infinitesimally
small are the gravitational and other effects produced by the distant
planets and the far more distant stars. It is simply a mistake to
imagine that the forces exerted by stars and planets at the moment of
birth can in any way shape our futures.
Astronomer Carl Sagan
declined to sign the statement. Sagan said he took this stance not
because he thought astrology had any validity, but because he thought
that the tone of the statement was authoritarian, and that dismissing
astrology because there was no mechanism (while "certainly a relevant
point") was not in itself convincing. In a letter published in a
follow-up edition of The Humanist, Sagan confirmed that he would
have been willing to sign such a statement had it described and refuted
the principal tenets of astrological belief. This, he argued, would have
been more persuasive and would have produced less controversy.
The use of poetic imagery based on the concepts of the macrocosm and microcosm, "as above so below" to decide meaning such as Edward W. James' example of "Mars above is red, so Mars below means blood and war", is a false cause fallacy.
Many astrologers claim that astrology is scientific. If one were to attempt to try to explain it scientifically, there are only four fundamental forces (conventionally), limiting the choice of possible natural mechanisms. Some astrologers have proposed conventional causal agents such as electromagnetism and gravity. The strength of these forces drops off with distance. Scientists reject these proposed mechanisms as implausible
since, for example, the magnetic field, when measured from earth, of a
large but distant planet such as Jupiter is far smaller than that
produced by ordinary household appliances. Astronomer Phil Plait
noted that in terms of magnitude, the sun is the only object with an
electromagnetic field of note, but astrology isn't based just off the
sun alone. While astrologers could try to suggest a fifth force, this is inconsistent with the trends in physics
with the unification of electromagnetism and the weak force into the
electroweak force. If the astrologer insisted on being inconsistent with
the current understanding and evidential basis of physics, that would
be an extraordinary claim. It would also be inconsistent with the other forces which drop off with distance. If distance is irrelevant, then, logically, all objects in space should be taken into account.
Carl Jung sought to invoke synchronicity,
the claim that two events have some sort of acausal connection, to
explain the lack of statistically significant results on astrology from a
single study he conducted. However, synchronicity itself is considered
neither testable nor falsifiable.
The study was subsequently heavily criticised for its non-random sample
and its use of statistics and also its lack of consistency with
astrology.
From the literature, astrology believers often tend to
selectively remember those predictions that turned out to be true and do
not remember those that turned out false. Another, separate, form of
confirmation bias also plays a role, where believers often fail to
distinguish between messages that demonstrate special ability and those
that do not.
Thus there are two distinct forms of confirmation bias that are under study with respect to astrological belief.
The Barnum effect
is the tendency for an individual to give a high accuracy rating to a
description of their personality that supposedly tailored specifically
for them, but is, in fact, vague and general enough to apply to a wide
range of people. If more information is requested for a prediction, the
more accepting people are of the results.
In 1949 Bertram Forer conducted a personality test on students in his classroom.
Each student was given a supposedly individual assessment but actually
all students received the same assessment. The personality descriptions
were taken from a book on astrology. When the students were asked to
comment on the accuracy of the test, more than 40% gave it the top mark
of 5 out of 5, and the average rating was 4.2. The results of this study have been replicated in numerous other studies.
The study of the Barnum/Forer effect has been focused mostly on
the level of acceptance of fake horoscopes and fake astrological
personality profiles.
Recipients of these personality assessments consistently fail to
distinguish between common and uncommon personality descriptors.
In a study by Paul Rogers and Janice Soule (2009), which was consistent
with previous research on the issue, it was found that those who
believed in astrology are generally more susceptible to giving more
credence to the Barnum profile than sceptics.
By a process known as self-attribution, it has been shown in
numerous studies that individuals with knowledge of astrology tend to
describe their personalities in terms of traits compatible with their
sun signs. The effect is heightened when the individuals were aware that
the personality description was being used to discuss astrology.
Individuals who were not familiar with astrology had no such tendency.
Sociology
In 1953, sociologist Theodor W. Adorno
conducted a study of the astrology column of a Los Angeles newspaper as
part of a project that examined mass culture in capitalist society.
Adorno believed that popular astrology, as a device, invariably led to
statements that encouraged conformity—and that astrologers who went
against conformity with statements that discouraged performance at work
etc. risked losing their jobs.
Adorno concluded that astrology was a large-scale manifestation of
systematic irrationalism, where flattery and vague generalisations
subtly led individuals to believe the author of the column addressed
them directly. Adorno drew a parallel with the phrase opium of the people, by Karl Marx, by commenting, "Occultism is the metaphysic of the dopes."
False balance is where a false, unaccepted or spurious viewpoint
is included alongside a well reasoned one in media reports and TV
appearances and as a result the false balance implies "there were two
equal sides to a story when clearly there were not". During Wonders of the Solar System, a TV programme by the BBC, the physicist Brian Cox
said: "Despite the fact that astrology is a load of rubbish, Jupiter
can in fact have a profound influence on our planet. And it's through a
force... gravity." This upset believers in astrology who complained that
there was no astrologer to provide an alternative viewpoint. Following
the complaints of astrology believers, Cox gave the following statement
to the BBC: "I apologise to the astrology community for not making
myself clear. I should have said that this new age drivel is undermining
the very fabric of our civilisation." In the programme Stargazing Live, Cox further commented by saying: "in the interests of balance on the BBC, yes astrology is nonsense." In an editorial in the medical journal BMJ, editor Trevor Jackson cited this incident showing where false balance could occur.
Studies and polling has shown that the belief in astrology is higher in western countries than might otherwise be expected. In 2012, in polls 42% of Americans said they thought astrology was at least partially scientific. This belief decreased with education and education is highly correlated with levels of scientific knowledge.
Some of the reported belief levels are due to a confusion of astrology with astronomy (the scientific study of celestial objects). The closeness of the two words varies depending on the language. A plain description of astrology as an "occult influence of stars,
planets etc. on human affairs" had no impact on the general public's
assessment of whether astrology is scientific or not in a 1992 eurobarometer
poll. This may partially be due to the implicit association amongst the
general public, of any wording ending in "-ology" with a legitimate
field of knowledge.
In Eurobarometers 224 and 225 performed in 2004, a split poll was used
to isolate confusion over wording. In half of the polls, the word
"astrology" was used, while in the other the word "horoscope" was used.
Belief that astrology was at least partially scientific was 76%, but
belief that horoscopes were at least partially scientific was 43%. In
particular, belief that astrology was very scientific was 26% while that
of horoscopes was 7%.
This appeared to indicate that the high level of apparent polling
support for astrology in the EU was indeed due to confusion over
terminology.
Astrology and astronomy were archaically treated together (Latin: astrologia), and were only gradually separated in Western 17th century philosophy (the "Age of Reason")
with the rejection of astrology. During the later part of the medieval
period, astronomy was treated as the foundation upon which astrology
could operate.
Since the 18th century they have come to be regarded as completely separate disciplines. Astronomy, the study of objects and phenomena originating beyond the Earth's atmosphere, is a science and is a widely studied academic discipline. Astrology, which uses the apparent positions of celestial objects as the basis for the prediction of future events, is a form of divination and a pseudoscience having no scientific validity.
Overview
Early science, particularly geometry and astronomy/astrology (astronomia), was connected to the divine for most medieval scholars. The compass in this 13th-century manuscript is a symbol of God's act of creation, as many believed that there was something intrinsically divine or perfect that could be found in circles.
In pre-modern times, most cultures did not make a clear distinction
between the two disciplines, putting them both together as one. In
ancient Babylonia, famed for its astrology, there were not separate roles for the astronomer as predictor of celestial phenomena, and the astrologer
as their interpreter; both functions were performed by the same person.
This overlap does not mean that astrology and astronomy were always
regarded as one and the same. In ancient Greece, pre-Socratic thinkers such as Anaximander, Xenophanes, Anaximenes, and Heraclides speculated about the nature and substance of the stars and planets. Astronomers such as Eudoxus (contemporary with Plato) observed planetary motions and cycles, and created a geocentric cosmological model that would be accepted by Aristotle. This model generally lasted until Ptolemy, who added epicycles to explain the retrograde motion of Mars. (Around 250 BC, Aristarchus of Samos postulated a proto-heliocentric theory, which would not be reconsidered for nearly two millennia (Copernicus), as Aristotle's geocentric model continued to be favored.) The Platonic school
promoted the study of astronomy as a part of philosophy because the
motions of the heavens demonstrate an orderly and harmonious cosmos. In
the third century BC, Babylonian astrology began to make its presence
felt in Greece. Astrology was criticized by Hellenistic philosophers
such as the Academic SkepticCarneades and Middle StoicPanaetius. However, the notions of the Great Year
(when all the planets complete a full cycle and return to their
relative positions) and eternal recurrence were Stoic doctrines that
made divination and fatalism possible.
In the Hellenistic world, the Greek words 'astrologia' and
'astronomia' were often used interchangeably, but they were conceptually
not the same. Plato taught about 'astronomia' and stipulated that
planetary phenomena should be described by a geometrical model. The
first solution was proposed by Eudoxus. Aristotle favored a physical
approach and adopted the word 'astrologia'. Eccentrics and epicycles
came to be thought of as useful fictions. For a more general public,
the distinguishing principle was not evident and either word was
acceptable. For the Babylonian horoscopic practice, the words specifically used were 'apotelesma' and 'katarche', but otherwise it was subsumed under the aristotelian term 'astrologia'.
In his compilatory work Etymologiae, Isidore of Seville
noted explicitly the difference between the terms astronomy and
astrology (Etymologiae, III, xxvii) and the same distinction appeared
later in the texts of Arabian writers.
Isidore identified the two strands entangled in the astrological
discipline and called them astrologia naturalis and astrologia
superstitiosa.
Astrology was widely accepted in medieval Europe as astrological texts from Hellenistic and Arabic astrologers were translated into Latin. In the late Middle Ages, its acceptance or rejection often depended on its reception in the royal courts of Europe. Not until the time of Francis Bacon
was astrology rejected as a part of scholastic metaphysics rather than
empirical observation. A more definitive split between astrology and
astronomy in the West took place gradually in the seventeenth and
eighteenth centuries, when astrology was increasingly thought of as an
occult science or superstition by the intellectual elite. Because of
their lengthy shared history, it sometimes happens that the two are
confused with one another even today. Many contemporary astrologers,
however, do not claim that astrology is a science, but think of it as a
form of divination like the I-Ching, an art, or a part of a spiritual belief structure (influenced by trends such as Neoplatonism, Neopaganism, Theosophy, and Hinduism).
Distinguishing characteristics
Astrologer–astronomer Richard of Wallingford is shown measuring an equatorium with a pair of compasses in this 14th-century work.
Astrologers practice their discipline geocentrically
and they consider the universe to be harmonious, changeless and static,
while astronomers have employed the scientific method to infer that the
universe is without a center and is dynamic, expanding outward per the Big Bang theory.
Astrologers believe that the position of the stars and planets
determine an individual's personality and future. Astronomers study the
actual stars and planets, but have found no evidence supporting
astrological theories. Psychologists study personality, and while there
are many theories of personality, no mainstream theories in that field
are based on astrology. (The Myers-Briggs personality typology, based on the works of Carl Jung,
has four major categories that correspond to the astrological elements
of fire, air, earth, and water. This theory of personality is used by
career counselors and life coaches but not by psychologists.)
Both astrologers and astronomers see Earth as being an integral
part of the universe, that Earth and the universe are interconnected as
one cosmos (not as being separate and distinct from each other).
However, astrologers philosophically and mystically portray the cosmos
as having a supernatural, metaphysical and divineessence that actively influences world events and the personal lives of people.
Astronomers, as members of the scientific community, cannot use in
their scientific articles explanations that are not derived from
empirically reproducible conditions, irrespective of their personal convictions.
Historical divergence
An engraving by Albrecht Dürer featuring Mashallah, from the title page of the De scientia motus orbis (Latin version with engraving, 1504). As in many medieval illustrations, the compass here is an icon of religion as well as science, in reference to God as the architect of creation.
For a long time the funding from astrology supported some astronomical research, which was in turn used to make more accurate ephemerides for use in astrology. In Medieval Europe the word Astronomia
was often used to encompass both disciplines as this included the study
of astronomy and astrology jointly and without a real distinction; this
was one of the original Seven Liberal Arts.
Kings and other rulers generally employed court astrologers to aid them
in the decision making in their kingdoms, thereby funding astronomical
research. University medical students were taught astrology as it was
generally used in medical practice.
Astronomy and astrology diverged over the course of the 17th through 19th centuries. Copernicus didn't practice astrology (nor empirical astronomy; his work was theoretical), but the most important astronomers before Isaac Newton were astrologers by profession – Tycho Brahe, Johannes Kepler, and Galileo Galilei.
Also relevant here was the development of better timekeeping instruments, initially for aid in navigation;
improved timekeeping made it possible to make more exact astrological
predictions—predictions which could be tested, and which consistently
proved to be false.
By the end of the 18th century, astronomy was one of the major sciences
of the Enlightenment model, using the recently codified scientific method, and was altogether distinct from astrology.
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