Search This Blog

Monday, April 16, 2018

Astrology and science

From Wikipedia, the free encyclopedia

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 of astrology has been conducted, and no evidence has been found to support the premises or purported effects outlined in astrological traditions.[1]

Where astrology has made falsifiable predictions, it has been falsified.[1]:424 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[this quote needs a citation] . 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,[1][2]:85 and as such, is regarded as pseudoscience.[3][4]:1350 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.[5]:249[6]

Introduction

The majority of professional astrologers rely on performing astrology-based personality tests and making relevant predictions about the remunerator's future.[2]:83 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".[7] Astrophysicist Neil 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".[8]
The continued belief in astrology despite its lack of credibility is seen as one demonstration of low scientific literacy.[9]

Historical relationship with astronomy

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.[10]:62 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.[11]:40 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.[11]:73 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.[12]:344
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 Caliphate vizier in 1120, funded the construction of observatories so that astrological predictions, fuelled by precise planetary information, could be made.[11]:55–56 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.[11]:57

The clear rejection of astrology in works of astronomy started in 1679, with the yearly publication La Connoissance des temps.[11]:220 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.[13]:10 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.[13]:17–18

Philosophy of science

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.[10]:62

Falsifiability

Science and non-science are being often distinguished by the criterion of falsifiability. The criterion was first proposed by philosopher of science Karl 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.[14][15]:10

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.[14]

Astrology was Popper's most frequent example of pseudoscience.[16]:7 Popper regarded astrology as "pseudo-empirical" in that "it appeals to observation and experiment", but "nevertheless does not come up to scientific standards".[17]:44

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.[18]:206

"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.[19]:401 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,[16]:8 and so, "They had no puzzles to solve and therefore no science to practise."[16]:8[19]:401

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.[16]:8

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.[20]:228 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".[20]:227–228

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.[20]:228[21]:549 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.[20]:228

To Thagard, astrology should not be regarded as a pseudoscience on the failure of Gauquelin's 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.[20]:226–227 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:[20]:226–227
  • 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.[20]:228

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.[22]:34
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[22]:34
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 a claim by one astrologer[who?] that the solar system looks like 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.[22]:32 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.[22]:33

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.[15]:24

Tests of astrology

Astrologers often avoid making verifiable predictions, and instead rely on vague statements that let them try to avoid falsification.[17]:48–49 Across several centuries of testing, the predictions of astrology have never been more accurate than that expected by chance alone.[2] 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.[1] All controlled experiments have failed to show any effect.[15]:24

Carlson's experiment

The Shawn Carlson's double-blind chart matching tests, in which 28 astrologers agreed to match over 100 natal charts to psychological profiles generated by the California Psychological Inventory (CPI) test, is one of the most renowned tests of astrology,[23][24] and was published in a highly prestigious journal, Nature.[10]:67 Double blinding helps to practically eliminate all bias from a study, including from participants as well as the person performing the study.[10]:67 The experimental protocol used in Carlson's study was agreed to by a group of physicists and astrologers prior to the experiment.[1] 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.[24]:117[25]:420 They also chose 26 of the 28 astrologers for the tests, the other 2 being interested astrologers who volunteered afterwards.[25]:420 The astrologers came from Europe and the United States.[24]:117 The astrologers helped to draw up the central proposition of natal astrology to be tested.[25]:419 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".[25]

Dean and Kelly

Scientist and former astrologer Geoffrey Dean and psychologist Ivan Kelly[26] conducted a large-scale scientific test, involving more than one hundred cognitive, behavioural, physical and other variables, but found no support for astrology.[27] A further test involved 45 confident[a] 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.[27]:191 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.[b][27]:191

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.[27]:190

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.[10]:66–67

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.[10]:67

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.[10]:67

Mars effect

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][28]

In 1955, astrologer[29] 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.[28] 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".[30]:213 A study conducted by seven French scientists attempted to replicate the claim, but found no statistical evidence.[30]:213–214 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.[31]

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.[24]:116

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[10]:62[15]:24 including lack of consistency, lack of ability to predict missing planets, lack of any connection of the zodiac to the constellations, and lack of any plausible mechanism. The underpinnings of astrology tend to disagree with numerous basic facts from scientific disciplines.[15]:24

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.[2]:83 Dean and Kelly documented 25 studies, which had found that the degree of agreement amongst astrologers' predictions was measured as a low 0.1.[c][10]:66 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.[2]:83

Georges Charpak and Henri Broch dealt with claims from western astrology in the book Debunked! ESP, Telekinesis, and other Pseudoscience.[32] 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, which would change the position of the sun with time. 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.[33]:6–7

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.[22]:25 This disconnection from the constellations led to the problem with precession separating the zodiac symbols from the constellations that they once were related to.[22]:26 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?"[10]:64

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.[33] 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."[33] 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.[1]

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.[2] The grafting on of Uranus, Neptune and Pluto into the astrology discourse was done on an ad hoc basis.[1]

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:[1]
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."[34] 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.[7] 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.[7]
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.[7]

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.[22]:26

Many astrologers claim that astrology is scientific.[35] 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.[10]:65 Some astrologers have proposed conventional causal agents such as electromagnetism and gravity.[35][36] The strength of these forces drops off with distance.[10]:65 Scientists reject these proposed mechanisms as implausible[35] 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.[36] 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.[10]:65[37] 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.[10]:65 It would also be inconsistent with the other forces which drop off with distance.[10]:65 If distance is irrelevant, then, logically, all objects in space should be taken into account.[10]:66

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.[38] The study was subsequently heavily criticised for its non-random sample and its use of statistics and also its lack of consistency with astrology.[d][39]

Psychology

It has also been shown that confirmation bias is a psychological factor that contributes to belief in astrology.[9]:344[40]:180–181[41]:42–48 Confirmation bias is a form of cognitive bias.[e][42]:553
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.[40]:180–181

Thus there are two distinct forms of confirmation bias that are under study with respect to astrological belief.[40]:180–181

The Barnum effect is the tendency for an individual to give a high accuracy rating to a description of their personality that supposedly is 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.[9]:344

In 1949 Bertram Forer conducted a personality test on students in his classroom.[9]:344 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.[43]:134, 135 The results of this study have been replicated in numerous other studies.[44]:382

The study of the Barnum/Forer effect has been focused mostly on the level of acceptance of fake horoscopes and fake astrological personality profiles.[44]:382 Recipients of these personality assessments consistently fail to distinguish common and uncommon personality descriptors.[44]:383 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 skeptics.[44]:393

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 astrological 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.[45]

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.[46]:326 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.[46]:327 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.[47] Adorno drew a parallel with the phrase opium of the people, by Karl Marx, by commenting, "Occultism is the metaphysic of the dopes."[46]:329

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".[48] 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." [48] In the programme Stargazing Live, Cox further commented by saying: "in the interests of balance on the BBC, yes astrology is nonsense." [49] In an editorial in the medical journal BMJ, editor Trevor Jackson cited this incident showing where false balance could occur.[48]

Studies and polling has shown that the belief in astrology is higher in western countries than might otherwise be expected.[9] In 2012, in polls 42% of Americans said they thought astrology was at least partially scientific.[50]:7/25 This belief decreased with education and education is highly correlated with levels of scientific knowledge.[9]:345

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.[9]:344, 346 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.[9]:346 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.[9]:349 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%.[9]:352 This appeared to indicate that the high level of apparent polling support for astrology in the EU was indeed due to confusion over terminology.[9]:362

Saturday, April 14, 2018

Red dwarf

From Wikipedia, the free encyclopedia

























A red dwarf is a small and relatively cool star on the main sequence, of M spectral type. Red dwarfs range in mass from a low of 0.075 to about 0.50 solar mass and have a surface temperature of less than 4,000 K. Sometimes K-type main-sequence stars, with masses between 0.50-0.8 solar mass, are also included.

Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one is visible to the naked eye.[1] Proxima Centauri, the nearest star to the Sun, is a red dwarf (Type M5, apparent magnitude 11.05), as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.[2]

Stellar models indicate that red dwarfs less than 0.35 M are fully convective.[3] Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding helium buildup at the core, thereby prolonging the period of fusion. Red dwarfs therefore develop very slowly, maintaining a constant luminosity and spectral type for trillions of years, until their fuel is depleted. Because of the comparatively short age of the universe, no red dwarfs exist at advanced stages of evolution.

Definition


Proxima Centauri, the closest star to the Sun at 4.2 ly, is a red dwarf

The term "red dwarf" when used to refer to a star does not have a strict definition. One of the earliest uses of the term was in 1915, used simply to contrast "red" dwarf stars from hotter "blue" dwarf stars.[4] It became established use, although the definition remained vague.[5] In terms of which spectral types qualify as red dwarfs, different researchers picked different limits, for example K8–M5[6] or "later than K5".[7] Dwarf M star, abbreviated dM, was also used, but sometimes it also included stars of spectral type K.[8]

In modern usage, the definition of a red dwarf still varies. When explicitly defined, it typically includes late K- and early to mid-M-class stars,[9] but in many cases it is restricted just to M-class stars.[10][11] In some cases all K stars are included as red dwarfs,[12] and occasionally even earlier stars.[13]

The coolest true main-sequence stars are thought to have spectral types around L2 or L3, but many objects cooler than about M6 or M7 are brown dwarfs, insufficiently massive to sustain hydrogen-1 fusion.[14]

Description and characteristics

Red dwarfs are very-low-mass stars.[15] As a result, they have relatively low pressures, a low fusion rate, and hence, a low temperature. The energy generated is the product of nuclear fusion of hydrogen into helium by way of the proton–proton (PP) chain mechanism. Hence, these stars emit little light, sometimes as little as ​110,000 that of the Sun. Even the largest red dwarfs (for example HD 179930, HIP 12961 and Lacaille 8760) have only about 10% of the Sun's luminosity.[16] In general, red dwarfs less than 0.35 M transport energy from the core to the surface by convection. Convection occurs because of opacity of the interior, which has a high density compared to the temperature. As a result, energy transfer by radiation is decreased, and instead convection is the main form of energy transport to the surface of the star. Above this mass, a red dwarf will have a region around its core where convection does not occur.[17]


The predicted main-sequence lifetime of a red dwarf plotted against its mass relative to the Sun.[18]

Because low-mass red dwarfs are fully convective, helium does not accumulate at the core, and compared to larger stars such as the Sun, they can burn a larger proportion of their hydrogen before leaving the main sequence. As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than 0.8 M have not had time to leave the main sequence. The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10-billion-year lifespan of our Sun by the third or fourth power of the ratio of the solar mass to their masses; thus, a 0.1 M red dwarf may continue burning for 10 trillion years.[15][19] As the proportion of hydrogen in a red dwarf is consumed, the rate of fusion declines and the core starts to contract. The gravitational energy released by this size reduction is converted into heat, which is carried throughout the star by convection.[20]
Typical characteristics[21]
Stellar
class
Mass
(M)
Radius
(R)
Luminosity
(L)
Teff
(K)
M0V 60% 62% 7.2% 3,800
M1V 49% 49% 3.5% 3,600
M2V 44% 44% 2.3% 3,400
M3V 36% 39% 1.5% 3,250
M4V 20% 26% 0.55% 3,100
M5V 14% 20% 0.22% 2,800
M6V 10% 15% 0.09% 2,600
M7V 9% 12% 0.05% 2,500
M8V 8% 11% 0.03% 2,400
M9V 7.5% 8% 0.015% 2,300

According to computer simulations, the minimum mass a red dwarf must have in order to eventually evolve into a red giant is 0.25 M; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs.[18]

The less massive the star, the longer this evolutionary process takes. It has been calculated that a 0.16 M red dwarf (approximately the mass of the nearby Barnard's Star) would stay on the main sequence for 2.5 trillion years, followed by five billion years as a blue dwarf, during which the star would have one third of the Sun's luminosity (L) and a surface temperature of 6,500–8,500 kelvins.[18]

The fact that red dwarfs and other low-mass stars still remain on the main sequence when more massive stars have moved off the main sequence allows the age of star clusters to be estimated by finding the mass at which the stars move off the main sequence. This provides a lower limit to the age of the Universe and also allows formation timescales to be placed upon the structures within the Milky Way, such as the Galactic halo and Galactic disk.

All observed red dwarfs contain "metals", which in astronomy are elements heavier than hydrogen and helium. The Big Bang model predicts that the first generation of stars should have only hydrogen, helium, and trace amounts of lithium, and hence would be of low metallicity. With their extreme lifespans, any red dwarfs that were a part of that first generation (population III stars) should still exist today. Low metallicity red dwarfs, however, are rare. There are several explanations for the missing population of metal-poor red dwarfs. The preferred explanation is that, without heavy elements, only large stars can form. Large stars rapidly burn out and explode as supernova, spewing heavy elements that then allow higher metallicity stars population II stars, including red dwarfs to form. Alternative explanations of the scarcity of metal-poor red dwarfs, such as their dimness and scarcity, are considered less likely because they appear to conflict with stellar-evolution models.[citation needed]

Spectral standard stars


Gliese 623 is a pair of red dwarfs, with GJ 623a on the left and the fainter GJ 623b to the right of center.

The spectral standards for M-type stars have changed slightly over the years, but settled down somewhat since the early 1990s. Part of this is due to the fact that even the nearest red dwarfs are fairly faint, and the study of mid- to late-M dwarfs has progressed only in the past few decades due to evolution of astronomical techniques, from photographic plates to charged-couple devices (CCDs) to infrared-sensitive arrays.

The revised Yerkes Atlas system (Johnson & Morgan 1953)[22] listed only 2 M-type spectral standard stars: HD 147379 (M0 V) and HD 95735/Lalande 21185 (M2 V). While HD 147379 was not considered a standard by expert classifiers in later compendia of standards, Lalande 21185 is still a primary standard for M2 V. Robert Garrison[23] does not list any "anchor" standards among the red dwarfs, but Lalande 21185 has survived as a M2 V standard through many compendia.[22][24][25] The review on MK classification by Morgan & Keenan (1973) did not contain red dwarf standards. In the mid-1970s, red dwarf standard stars were published by Keenan & McNeil (1976)[26] and Boeshaar (1976),[27] but unfortunately there was little agreement among the standards. As later cooler stars were identified through the 1980s, it was clear that an overhaul of the red dwarf standards was needed. Building primarily upon the Boeshaar standards, a group at Steward Observatory (Kirkpatrick, Henry, & McCarthy 1991)[25] filled in the spectral sequence from K5 V to M9 V. It is these M-type dwarf standard stars which have largely survived as the main standards to the modern day. There have been negligible changes in the red dwarf spectral sequence since 1991. Additional red dwarf standards were compiled by Henry et al. (2002),[28] and D. Kirkpatrick has recently reviewed the classification of red dwarfs and standard stars in Gray & Corbally's 2009 monograph.[29] The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).

Planets


Artist's conception of a red dwarf, the most common type of star in the Sun's stellar neighborhood, and in the universe. Although termed a red dwarf, the surface temperature of this star would give it an orange hue when viewed from close proximity.

Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare. Doppler surveys of a wide variety of stars indicate about 1 in 6 stars with twice the mass of the Sun are orbited by one or more Jupiter-sized planets, versus 1 in 16 for Sun-like stars and only 1 in 50 for red dwarfs. On the other hand, microlensing surveys indicate that long-orbital-period Neptune-mass planets are found around one in three red dwarfs. [30] Observations with HARPS further indicate 40% of red dwarfs have a "super-Earth" class planet orbiting in the habitable zone where liquid water can exist on the surface.[31] Computer simulations of the formation of planets around low mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans. [32]

At least four and possibly up to six exoplanets were discovered orbiting within the Gliese 581 planetary system between 2005 and 2010. One planet has about the mass of Neptune, or 16 Earth masses (M). It orbits just 6 million kilometers (0.04 AU) from its star, and is estimated to have a surface temperature of 150 °C, despite the dimness of its star. In 2006, an even smaller exoplanet (only 5.5 M) was found orbiting the red dwarf OGLE-2005-BLG-390L; it lies 390 million km (2.6 AU) from the star and its surface temperature is −220 °C (56 K).

In 2007, a new, potentially habitable exoplanet, Gliese 581c, was found, orbiting Gliese 581. The minimum mass estimated by its discoverers (a team led by Stephane Udry) is 5.36 M. The discoverers estimate its radius to be 1.5 times that of Earth (R). Since then Gliese 581d, which is also potentially habitable, was discovered.

Gliese 581c and d are within the habitable zone of the host star, and are two of the most likely candidates for habitability of any exoplanets discovered so far.[33] Gliese 581g, detected September 2010,[34] has a near-circular orbit in the middle of the star's habitable zone. However, the planet's existence is contested.[35]

On 23 February 2017 NASA announced the discovery of seven Earth-sized planets orbiting the red dwarf star TRAPPIST-1 approximately 39 light-years away in the constellation Aquarius. The planets were discovered through the transit method, meaning we have mass and radius information for all of them. TRAPPIST-1e, f and g appear to be within the habitable zone and may have liquid water on the surface.[36]

Habitability


An artist's impression of a planet with two exomoons orbiting in the habitable zone of a red dwarf.

Planetary habitability of red dwarf systems is subject to some debate. In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked. This would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other. Such conditions would appear to make it difficult for forms of life similar to those on Earth to evolve. And it appears there is a great problem with the atmosphere of such tidally locked planets: the perpetual night zone would be cold enough to freeze the main gases of their atmospheres, leaving the daylight zone nude and dry. On the other hand, recent theories propose that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet.[37]

Variability in stellar energy output may also have negative impacts on the development of life. Red dwarfs are often flare stars, which can emit gigantic flares, doubling their brightness in minutes. This variability may also make it difficult for life to develop and persist near a red dwarf. It may be possible for a planet orbiting close to a red dwarf to keep its atmosphere even if the star flares.[38] However, more-recent research suggests that these stars may be the source of constant high-energy flares and very large magnetic fields, diminishing the possibility of life as we know it. Whether this is a peculiarity of the star under examination or a feature of the entire class remains to be determined.[39]

Sunday, April 8, 2018

Great Oxygenation Event

From Wikipedia, the free encyclopedia
 
O2 build-up in the Earth's atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
 
Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere. The oceans were also largely anoxic with the possible exception of O2 gases in the shallow oceans.
 
Stage 2 (2.45–1.85 Ga): O2 produced, and rose to values of 0.02 and 0.04 atm, but absorbed in oceans and seabed rock.
 
Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces. There was no significant change in terms of oxygen level.
 
Stages 4 and 5 (0.85–present): O2 sinks filled and the gas accumulates.[1]

The Great Oxygenation Event, the beginning of which is commonly known in scientific media as the Great Oxidation Event (GOE, also called the Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust,[2] Oxygen Revolution, or Great Oxidation) was the biologically induced appearance of dioxygen (O2) in Earth's atmosphere.[3] Geological, isotopic, and chemical evidence suggest that this major environmental change happened around 2.45 billion years ago (2.45 Ga),[4] during the Siderian period, at the beginning of the Proterozoic eon. The causes of the event are not clear.[5] The current geochemical and biomarker evidence for the development of oxygenic photosynthesis before the Great Oxidation Event has been mostly inconclusive.[6]

Oceanic cyanobacteria, which evolved into coordinated (but not multicellular or even colonial) macroscopic forms more than 2.3 billion years ago (approximately 200 million years before the GOE),[7] are believed to have become the first microbes to produce oxygen by photosynthesis.[8] Before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter. The GOE started when these oxygen sinks became saturated, at which point oxygen produced by the cyanobacteria was free to escape into the atmosphere.

Cyanobacteria: Responsible for the buildup of oxygen in the Earth's atmosphere

The increased production of oxygen set Earth's original atmosphere off balance.[9] Free oxygen is toxic to obligate anaerobic organisms, and the rising concentrations may have destroyed most such organisms at the time. Cyanobacteria were therefore responsible for one of the most significant mass extinctions in Earth's history. Besides marine cyanobacteria, there is also evidence of cyanobacteria on land.[citation needed]

A spike in chromium contained in ancient rock deposits formed underwater shows the accumulation had been washed off from the continental shelves. Chromium is not easily dissolved and its release from rocks would have required the presence of a powerful acid. One such acid, sulfuric acid (H2SO4), might have been created through bacterial reactions with pyrite.[10] Mats of oxygen-producing cyanobacteria can produce a thin layer, one or two millimeters thick, of oxygenated water in an otherwise anoxic environment even under thick ice, and before oxygen started accumulating in the atmosphere, these organisms would already be adapted to oxygen.[11] Additionally, the free oxygen would have reacted with atmospheric methane, a greenhouse gas, greatly reducing its concentration and triggering the Huronian glaciation, possibly the longest episode of glaciation in Earth's history and called snowball Earth.[12]

Eventually, the evolution of aerobic organisms that consumed oxygen established an equilibrium in its availability. Free oxygen has been an important constituent of the atmosphere ever since.[12]

Timing

The most widely accepted chronology of the Great Oxygenation Event suggests that free oxygen was first produced by prokaryotic and then later eukaryotic organisms that carried out photosynthesis more efficiently, producing oxygen as a waste product. These organisms lived long before the GOE,[13] perhaps as early as 3,400 million years ago.[14][15]
Initially, the oxygen they produced would have quickly been removed from the atmosphere by the chemical weathering of reducing (oxidizable) minerals, most notably iron. This 'mass rusting' led to the deposition of iron(III) oxide in the form of banded-iron formations such as the sediments in Minnesota and Pilbara, Western Australia. The saturation of these mineral sinks, and the resulting persistence of oxygen in the atmosphere, led within 50 million years to the start of the GOE.[16] Oxygen could have accumulated very rapidly: at today's rates of photosynthesis (much greater than those in the Precambrian without land plants), modern atmospheric O2 levels could be produced in only 2,000 years.[17]

Another hypothesis is that oxygen producers did not evolve until a few million years before the major rise in atmospheric oxygen concentration.[18] This is based on a particular interpretation of a supposed oxygen indicator used in previous studies, the mass-independent fractionation of sulfur isotopes. This hypothesis would eliminate the need to explain a lag in time between the evolution of oxyphotosynthetic microbes and the rise in free oxygen.

In either case, oxygen did eventually accumulate in the atmosphere, with two major consequences.

Firstly, it oxidized atmospheric methane (a strong greenhouse gas) to carbon dioxide (a weaker one) and water. This decreased the greenhouse effect of the Earth's atmosphere, causing planetary cooling, and triggered the Huronian glaciation. Starting around 2.4 billion years ago, this lasted 300-400 million years, and may have been the longest ever snowball Earth episode.[18][19]

Secondly, the increased oxygen concentrations provided a new opportunity for biological diversification, as well as tremendous changes in the nature of chemical interactions between rocks, sand, clay, and other geological substrates and the Earth's air, oceans, and other surface waters. Despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen. This breakthrough in metabolic evolution greatly increased the free energy availabile to living organisms, with global environmental impacts. For example, mitochondria evolved after the GOE, giving organisms the energy to exploit new, more complex morphologies interacting in increasingly complex ecosystems.[20]

Timeline of glaciations, shown in blue.

Time lag theory

There may have been a gap of up to 900 million years between the start of photosynthetic oxygen production and the geologically rapid increase in atmospheric oxygen about 2.5–2.4 billion years ago. Several hypotheses propose to explain this time lag.

Tectonic trigger

2.1 billion year old rock showing banded iron formation

The oxygen increase had to await tectonically driven changes in the Earth, including the appearance of shelf seas, where reduced organic carbon could reach the sediments and be buried.[21] The newly produced oxygen was first consumed in various chemical reactions in the oceans, primarily with iron. Evidence is found in older rocks that contain massive banded iron formations apparently laid down as this iron and oxygen first combined; most present-day iron ore lies in these deposits. Evidence suggests oxygen levels spiked each time smaller land masses collided to form a super-continent. Tectonic pressure thrust up mountain chains, which eroded to release nutrients into the ocean to feed photosynthetic cyanobacteria.[22]

Nickel famine

Early chemosynthetic organisms likely produced methane, an important trap for molecular oxygen, since methane readily oxidizes to carbon dioxide (CO2) and water in the presence of UV radiation. Modern methanogens require nickel as an enzyme cofactor. As the Earth's crust cooled and the supply of volcanic nickel dwindled, oxygen-producing algae began to out-perform methane producers, and the oxygen percentage of the atmosphere steadily increased.[23] From 2.7 to 2.4 billion years ago, the rate of deposition of nickel declined steadily from a level 400 times today's.[24]

Bistability

Another hypothesis posits a model of the atmosphere that exhibits bistability: two steady states of oxygen concentration. The state of stable low oxygen conentration (0.02%) experiences a high rate of methane oxidation. If some event raises oxygen levels beyond a moderate threshold, the formation of an ozone layer shields UV rays and decreases methane oxidation, raising oxygen further to a stable state of 21% or more. The Great Oxygenation Event can then be understood as a transition from the lower to the upper steady states.[25]

Hydrogen gas

Another theory credits the appearance of cyanobacteria with suppressing hydrogen gas and increasing oxygen.

Some bacteria in the early oceans could separate water into hydrogen and oxygen. Under the Sun's rays, hydrogen molecules were incorporated into organic compounds, with oxygen as a by-product. If the hydrogen-heavy compounds were buried, it would have allowed oxygen to accumulate in the atmosphere.

However, in 2001 scientists realized that the hydrogen would instead escape into space through a process called methane photolysis, in which methane releases its hydrogen in a reaction with oxygen. This could explain why the early Earth stayed warm enough to sustain oxygen-producing lifeforms.[26]

Late evolution of oxy-photosynthesis theory

The oxygen indicator might have been misinterpreted. During the proposed lag era in the previous theory, there was a change in sediments from mass-independently fractionated (MIF) sulfur to mass-dependently fractionated (MDF) sulfur. This was assumed to show the appearance of oxygen in the atmosphere, since oxygen would have prevented the photolysis of sulfur dioxide, which causes MIF. However, the change from MIF to MDF of sulfur isotopes may instead have been caused by an increase in glacial weathering, or the homogenization of the marine sulfur pool as a result of an increased thermal gradient during the Huronian glaciation period (which in this interpretation was not caused by oxygenation).[18]

Role in mineral diversification

The Great Oxygenation Event triggered an explosive growth in the diversity of minerals, with many elements occurring in one or more oxidized forms near the Earth's surface.[27] It is estimated that the GOE was directly responsible for more than 2,500 of the total of about 4,500 minerals found on Earth today. Most of these new minerals were formed as hydrated and oxidized forms due to dynamic mantle and crust processes.[28]

Great Oxygenation
End of Huronian glaciation
Palæoproterozoic
Mesoproterozoic
Neoproterozoic
Palæozoic
Mesozoic
Cenozoic
−2500
−2300
−2100
−1900
−1700
−1500
−1300
−1100
−900
−700
−500
−300
−100
Million years ago. Age of Earth = 4,560

 

Origin of eukaryotes

It has been proposed that a local rise in oxygen levels due to cyanobacterial photosynthesis in ancient microenvironments was highly toxic to the surrounding biota, and that this selective pressure drove the evolutionary transformation of an archaeal lineage into the first eukaryotes.[29] Oxidative stress involving production of reactive oxygen species (ROS) might have acted in synergy with other environmental stresses (such as ultraviolet radiation and/or desiccation) to drive selection in an early archaeal lineage towards eukaryosis. This archaeal ancestor may already have had DNA repair mechanisms based on DNA pairing and recombination and possibly some kind of cell fusion mechanism.[30][31] The detrimental effects of internal ROS (produced by endosymbiont proto-mitochondria) on the archaeal genome could have promoted the evolution of meiotic sex from these humble beginnings.[30] Selective pressure for efficient DNA repair of oxidative DNA damages may have driven the evolution of eukaryotic sex involving such features as cell-cell fusions, cytoskeleton-mediated chromosome movements and emergence of the nuclear membrane.[29] Thus the evolution of eukaryotic sex and eukaryogenesis were likely inseparable processes that evolved in large part to facilitate DNA repair.[29][32] Constant pressure of endogenous ROS has been proposed to explain the ubiquitous maintenance of meiotic sex in eukaryotes.[30]

Operator (computer programming)

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Operator_(computer_programmin...