Archaeological Dating Methods (2)

Absolute Dating

Absolute dating assigns fixed dates to the age of an object, people or intangible concepts, such as human language development.It means absolute dating methods produce specific chronological dates for objects and occupations. Absolute dating largely relies on scientific developments of the 20th century, but it also can derive absolute dates from history and archaeology.These dating methods provides a computed numerical age in contrast with relative dating which provides only an order of events.In archeology, absolute dating is usually based on the physical or chemical properties of the materials of artifacts, buildings, or other items that have been modified by humans.This type of dating employs many dating techniques* like atomic clocks, carbon dating, annual cycle methods, and trapped electron method. 

*After 1950, the physical sciences contributed a number of absolute dating techniques that had a revolutionary effect on archaeology and geology. These techniques are based upon the measurement of radioactive processes (radiocarbon; potassium-argon, uranium-lead, thorium-lead, etc.; fission track; thermoluminescence; optically stimulated luminescence; and electron-spin resonance), chemical processes (amino-acid racemization and obsidian hydration), and the magnetic properties of igneous material, baked clay, and sedimentary deposits (paleomagnetism). Other techniques are occasionally useful, for example, historical or iconographic references to datable astronomical events such as solar eclipses (archaeoastronomy).

Prior to the discovery of radiometric dating which provided a means of absolute dating in the early 20th century, archaeologists and geologists were largely limited to the use of relative dating techniques to determine the age of geological events.Though relative dating can only determine the sequential order in which a series of events occurred, not when they occur, it remains a useful technique especially in materials lacking radioactive isotopes.The Law of Superposition was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.

The most popular method of radio dating is radiocarbon dating which is possible because of the presence of C-14, an unstable isotope of carbon. C-14 has a half life of 5730 years which means that only half of the original amount is left in the fossil after 5730 years while half of the remaining amount is left after another 5730 years. This gives away the true age of the fossil that contains C-14 that starts decaying after the death of the human being or animal. Dendrochronology is another of the popular method of finding the exact age through growth and patterns of thick and thin ring formation in fossil trees. It is clear then that absolute dating is based upon physical and chemical properties of artifacts that provide a clue regarding the true age. 

The absolute dating methods most widely used and accepted are based on the natural radioactivity of certain minerals found in rocks. Since the rate of radioactive decay of any particular isotope is known, the age of a specimen can be computed from the relative proportions of the remaining radioactive material and its decay products. By this method the age of the earth is estimated to be about 4.5 billion years old. Some of the radioactive elements used in dating and their decay products (their stable daughter isotopes) are uranium-238 to lead-206, uranium-235 to lead-207, thorium-232 to lead-208, samarium-147 to neodymium-143, rubidium-87 to strontium-87, and potassium-40 to argon-40. Each radioactive member of these series has a known, constant decay rate, measured by its half-life, that is unaffected by any physical or chemical changes. Each decay element has an effective age range, including uranium-238 (100 million to 4.5 billion years) and potassium-40 (100,000 to 4.5 billion years).

Radiometric dating - Principles and History 

In 1896, French physicist Henri Becquerel discovered radioactivity: the spontaneous emission of particles and energy from unstable nuclei of elements.The atoms of some chemical elements have different forms, called isotopes. These break down over time in a process scientists call radioactive decay. Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter. Each isotope is identified with what is called a ‘mass number’. When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.

Isotope:  A version of an atom that differs from other atoms of the same element only in the number of neutrons.  Different isotopes of an element have similar chemical properties (undergo similar chemical reactions) but have different physical properties (such as evaporation rates).

Stable Isotope:  An isotope that persists forever because it has a “stable” ratio of protons to neutrons.  For example, carbon-12 is a stable isotope.

Radioactive (or unstable) Isotope:  An isotope that decays into another element because it has an “unstable” ratio of protons to neutrons.  For example, carbon-14 is a radioactive isotope.

During radioactive decay, the radioactive parent isotope changes to a stable daughter isotope giving off heat in the process.  There are 3 types of radioactive emissions:

Alpha ray: Equivalent to two protons and two neutrons (essentially a helium nucleus).

Beta ray: A free electron is released when a neutron converts to a proton.

Gamma ray: Consists of a photon (a packet of energy).

Some radioactive parent isotopes decay directly to a daughter isotope.  However, some radioactive atoms decay to the daughter atom through a series of intermediate steps (called a decay series).  The U238 decay series is a good example.The half-life is the amount of time required for one half of the parent to decay to daughter.Initially, there are many radioactive parent atoms so there are more radioactive emissions.  As decay proceeds and there are fewer parent atoms and fewer emissions.  By the 1st half life, 50% of the parent atoms will have decayed to daughter.  By the 2nd half life, another 50% of the remaining parent will have decayed (leaving 25% parent and 75% daughter).

Absolute age dating is based upon the decay of radioactive (unstable) isotopes.Since the decay rate is constant over time, the parent:daughter ratio can be used to calculate the age of the mineral or rock.

Dating basically depends upon 3 measurements:

1) the amount of unstable parent isotope in the mineral

2) the amount of stable daughter isotope in the mineral

3) the decay constant (l) of the particular radioactive parent isotope.

Radiometric dating (also called radioactive dating) is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates (In radiometry, the rate of radioactive decay of a specific element provides an absolute date).The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating.

Radiocarbon dating measures radioactive isotopes in once-living organic material instead of rock, using the decay of carbon-14 to nitrogen-14 .Carbon-14 dating is probably one of the best-known dating methods, but the half-life of Carbon-14 is approximately 5730 years, plus or minus 40 years. Because of the fairly fast decay rate of carbon-14, it can only be used on material up to about 60,000 years old. Geologists use radiocarbon to date such materials as wood and pollen trapped in sediment, which indicates the date of the sediment itself. 

The atmospheric C 14 is incorporated into carbon dioxide molecules (CO2).  Organisms acquire C 14 from the air and water (along with 13C and 12C), and they acquire the environmental ratios of these isotopes.  However, when organisms die, they stop acquiring any carbon and the C 14starts to decay back to N 14 via beta decay.  The C 14 :N 14 ratio decreases over time, and this ratio can be used to calculate a material's age.All organic matter (bones, shells, wood, charcoal, cloth, and limestone) contains C-14and can be dated with this technique.

Carbon-14 has a relatively short half life of 5,730 years.  It is good for dating young rocks and artifacts.  Beyond 60,000 - 80,000 years, there is too little Carbon-14 left in the sample and this technique cannot be used.

Potassium-argon dating is another absolute dating method that is used to determine the age of igneous or sedimentary rocks. This, in turn, should provide some evidence for the dates of the fossils within the rocks. In this method, an absolute date is determined by measuring the amount of decay of potassium-40, a radioactive isotope of the element potassium that has transformed into the stable isotope argon-40.Potassium-40, for example, decays into Argon-40 with a half-life of 1.25 billion years, so that after 1.25 billion years half of the Potassium-40 in a rock will have become Argon-40. This means that if a rock sample contained equal amounts of Potassium-40 and Argon-40, it would be 1.25 billion years old.

Fission-track dating is a more recent application of the decay of radioisotopes, but this technique does not use the ratio of parent to daughter isotope to obtain an age.

Most U 238 undergoes alpha decay.  However, a very small proportion of U 238 nuclei undergo fission and the nucleus splits to form two smaller but very energetic nuclei that move away from each other.  When this happens in a mineral, the two departing nuclei leave behind a trail of destruction in the crystal lattice.  The trail is called a fission track.

The density of fission tracks in a mineral increase with age and can be used to calculate the mineral's age.

Fission track dating is ideal for samples from “recent” times back to 100,000,000 years.  Beyond 100,000,000 years, the density of the tracks becomes so great (saturated) that they cannot be counted reliably.

Fission tracks can “anneal” or heal with reheating, and so this method is affected by metamorphism.

Note : 

Measuring isotopes is particularly useful for dating igneous and some metamorphic rock, but not sedimentary rock. Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in. However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.

All radiometric dating methods measure isotopes in some way. Most directly measure the amount of isotopes in rocks, using a mass spectrometer. Others measure the subatomic particles that are emitted as an isotope decays. Some measure the decay of isotopes more indirectly. For example, fission track dating measures the microscopic marks left in crystals by subatomic particles from decaying isotopes. Another example is luminescence dating, which measures the energy from radioactive decay that is trapped inside nearby crystals.

More Info : 

click here ->  Modern Dating Methods

Archaeological Dating Methods (1)

Dating is a technique used in archeology to ascertain the age of artifacts, fossils and other items considered to be valuable by archaeologists.Archaeologists use different dating techniques to determine the age of a particular artifact, fossil,site, or part of a site. Two broad categories of dating or chronometric techniques that archaeologists use are called  relative and absolute dating . Relative dating determines the age of artifacts or site, as older or younger or the same age as others, but does not produce precise dates.Absolute dating methods produce specific chronological dates for objects and occupations.This method is not available to archaeology until well into the 20th century.

Relative dating

Relative dating is the science of determining the relative order of past events, without necessarily determining their absolute age.Methods for relative dating were developed when geology first emerged as a formal science.Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things,it is the science of rock strata, or layers.Stratigraphy is based on the law of superposition-like a layer cake, the lowest layers must have been formed first .Layering occurs in sedimentary rocks as they accumulate through time, so rock layers hold the key to deciphering the succession of historical events in Earth’s past.In other words, artifacts found in the upper layers of a site will have been deposited more recently than those found in the lower layers. Cross-dating of sites is still used today in which one compares geologic strata at one site with another location, and extrapolates relative ages in that manner.This method is used when sites are far too old for absolute dates to have much meaning.

However, geological strata are not always found to be in a neat chronological order. Wind and water erode strata and some areas are uplifted or even tilted. These processes result in geological unconformities , or breaks in the original stratigraphic sequence. In addition, people and other animals dig holes, resulting in a mixing of material from different strata.All of these processes confuse the stratigraphic record. In many cases, however, it is possible to reconstruct the original sequence of strata so that they can be used for relative dating.

For instance, if we find a fossil bone below the strata 3 rock level shown in the illustration above, we assume that the animal most likely lived at a time before that layer was formed. However, we must be careful to note whether or not the fossil comes from the mixed strata zone of the filled in hole.

When two objects are found in the same strata of a site, it is usually assumed that they date to the same time period. This is an application of the principle of association. However, the assumption of contemporaneity may not always be correct. This is due to the fact that one or both of the objects may have been moved or redeposited into a different location. In other words, they may no longer be in their primary context.

Biostratigraphy

Biostratigraphy is the use of fossils in stratigraphy. It relies on the study of in situ fossil distributions. Various fossil groups can be found in different sedimentary environments. The two main environments are land (terrestrial) and sea (marine).When the bones of our early ancestors are found in the same geological strata as those of other animals that are known to have lived only during a specific time period in the past, we assume that these ancestors must also have come from that time. This is referred to as dating by association with index fossils (also known as guide fossils, indicator fossils or zone fossils), or biostratigraphy .

Fluorine Analysis

When bones, teeth, or antlers are found at a site, fluorine analysis can be used to tell us whether or not the animals they were from actually lived at about the same time. This relative dating method is based on the fact that there are specific progressive chemical changes in skeletal remains that result from burial underground. As time passes, the organic components of bone (mostly fats and proteins) are lost primarily through bacterial action. Since these components contain nitrogen, there is a progressive loss of that element. At the same time, percolating ground water deposits trace amounts of fluorine and other elements, such as uranium, into the bone. As a result, the amount of fluorine and other trace elements progressively increase. If the bones of two animals are buried at the same time in the same site, they should have the same relative amount of nitrogen and fluorine. If they do not, they most likely come from different eras, despite the fact that they were found in association with each other.

Fluorine analysis can be used only as a relative dating method because the rate of decay and the amount of dissolved minerals in the ground water varies from site to site.Fluorine analysis is primarily used for verifying whether or not two fossils in the same strata at a site were in fact contemporaneous. If not, then at least one of them must be physically out of context.

A good example of the value of fluorine analysis was in bringing to light the Piltdown Man hoax. In 1912, Charles Dawson, an amateur paleontologist, found what was thought to be an early human skull and jaw in the Piltdown gravel deposits of England. Because it had an ape-like jaw and was found in association with the bones of extinct animals, this "Piltdown Man" was also believed to be a very ancient human. It was popularly referred to as "the missing link" in human evolution. In 1949, the Piltdown bones were finally tested for fluorine content by Kenneth Oakley and the fraud became apparent. After reexamining the strata at the Piltdown site, the evidence of a hoax was published in 1953. This was verified through the use of X-ray fluorescence examination. The skull and jaw clearly were not from the same time period. The jaw was likely to have come from a modern young adult orangutan. It had been cleverly carved to fit the skull and stained to look ancient. In addition, the associated bones from extinct animals had much older fluorine and nitrogen ratios than either the jaw or the human skull.

Geochronology

A relative dating method based on the association of early human sites with changing features of the land, such as the advance and retreat of glaciers or the rise and fall of sea levels. When these events are well dated, geochronology could be considered a reliable calibrated relative dating technique.

Artifact time marker

An artifact type that was made by a particular culture during a limited time period. When discovered clearly in association with ancient humans in an archaeological site, they are an indication of at least the relative time of the occupation. When the independent dating of the artifact types is reliable, this can be considered a calibrated relative dating method.

Seriation

When a stratigraphic sequence is lacking, another relative dating technique known as seriation may be applied. This technique dates a site based on the relative frequency of types of artifacts whose dates of use or manufacture are known. The basic assumption underlying seriation is that the popularity of culturally produced items (such as clay pipes or obelisk gravestone markers in America) varies through time, with a frequency pattern that has been called the "battleship curve." An item is introduced, it grows in popularity, then its use begins to wane as it is replaced by another form. Certain types of artifacts have been identified as particularly useful temporal markers, for example, gravestones, projectile points, lamps, pottery sherds.The frequency of artifact types in a stratum can be compared to known frequency changes previously recorded for an ancient culture. In this way, the stratum can be dated relative to other strata or sites. When a seriation sequence has been cross-calibrated with reliable chronometric dating methods, it can be considered a calibrated relative technique. Before being able to interpret materials found at a site, an archaeologist faces the task of sorting the artifacts into manageable units for analysis. This is frequently a difficult task. Sorting is usually based on form and function. What does it look like? What is it made of? Is it decorated in any way? Have you ever seen it before?

Patination

Patination is a technique involving the measuring of the patina on an artifact. The patina is the outermost surface of the artifact that differs in color, texture, luster or composition from the rest of the artifact. This difference is the result of chemical, physical or biological change in response to the surrounding soil and environmental condition. Although it is not an actual dating technique, patination is used when multiple artifacts of the same type are found in the same area and under the same conditions. The use of this technique is to determine the age of the artifacts, relative to the others, by comparing the thickness of the patina on them. There are many variables that have to be calculated, and this makes dating lithics from patina formations a relative dating technique.

Palaeontolgy - Dating by analysing Animal Remains 

This method is based on the assumption that changed climate will bring about the occurrence of different animals and plant species i.e., with change in climate,some species become extinct.This assumption helps in establishing relative dates.

Social Intelligence - Basics

Intelligence, as defined in standard dictionaries is individual's ability to learn and reason.

What is Social Intelligence (SI)?

Social Intelligence (SI) is the ability to get along well with others, and to get them to cooperate with you. Sometimes referred to simplistically as "people skills," SI includes an awareness of situations and the social dynamics that govern them, and a knowledge of interaction styles and strategies that can help a person achieve his or her objectives in dealing with others. It also involves a certain amount of self-insight and a consciousness of one's own perceptions and reaction patterns.As originally coined by E.L. Thorndike (1920), the term referred the person's ability to understand and manage other people, and to engage in adaptive social interactions.E.L. Thorndike divided intelligence into three parts, pertaining to the ability to understand and manage ideas (abstract intelligence), concrete objects (mechanical intelligence), and people (social intelligence). More recently, however, Cantor and Kihlstrom (1987) redefined social intelligence to refer to the individual's fund of knowledge about the social world.

Moss and Hunt (1927) defined social intelligence as the "ability to get along with others" . Vernon (1933), provided the most wide-ranging definition of social intelligence as the person's "ability to get along with people in general, social technique or ease in society, knowledge of social matters, susceptibility to stimuli from other members of a group, as well as insight into the temporary moods or underlying personality traits of strangers"

Persons with high social intelligence are usually good in recognizing subtle facial, verbal and behavioral clues in other people that can indicate their emotions and intentions. Social intelligence includes the following abilities:

a) the ability to observe and interpret very subtle facial expressions that signal particular emotions or intentions in other people;

b) the ability to detect and understand hidden meanings in verbal expressions of other people - such as when people say one thing, but actually mean the opposite;

c) the ability to interact with other people verbally and through gestures in such a way that these partners feel comfortable, relaxed and understood.

d) the ability to intentionally provoke other people through cynicism, mockery or insults;

d) the ability to tell and understand jokes;

f) the ability to motivate other people to actions by providing verbal encouragement;

g) the ability to incite rage, fanaticism, or (religious) ecstasy in other people;

h) the ability to coordinate one's actions with the behavior of other people;

Social intelligence should not be misunderstood as a particular political or social conviction, such as humanitarianism. All people with social intelligence may not have noble sentiment. Social intelligence is often used for political manipulation or brutal suppression of other people. Leaders such as Napoleon Bonaparte, Genghis Khan, Mao Zedong, Pol Pot, Adolf Hitler or Josef Stalin were able to initiate raw emotions and blind obedience among their followers at extreme levels. Religious leaders have been able to incite hundreds of millions of people with some of the deepest human emotions possible. Political and military power is not generated primarily by brutal force and suppression, but by winning over the "hearts and minds" of followers. We might not like it, but there can be no doubt that powerful political and military leaders must have high social intelligence to manipulate other people.When social intelligence is used for benign purposes it can lead to some of the most uplifting and noble human experiences.

Nicholas Humphrey points to a difference between intelligence and social intelligence. Some autistic children are extremely intelligent because they are very good at observing and memorising information, but they have low social intelligence. Similarly, chimpanzees are very adept at observation and memorisation, sometimes better than humans, but are, according to Humphrey, inept at handling interpersonal relationships. What they lack is a theory of other's minds.

More recently, popular science writer Daniel Goleman has drawn on social neuroscience research to propose that social intelligence is made up of social awareness (including empathy, attunement, empathic accuracy, and social cognition) and social facility (including synchrony, self-presentation, influence, and concern).Goleman’s  research indicates that our social relationships have a direct effect on our physical health.

Educational researcher Raymond H. Hartjen asserts that expanded opportunities for social interaction enhances intelligence.This suggests that children require continuous opportunities for interpersonal experiences in order to develop a keen 'inter-personal psychology'.Traditional classrooms do not permit the interaction of complex social behavior. Instead, students in traditional settings are treated as learners who must be infused with more and more complex forms of information. The structure of schools today allows very few of these skills, critical for survival in the world, to develop. Because we so limit the development of the skills of "natural psychologist" in traditional schools, graduates enter the job market handicapped to the point of being incapable of surviving on their own.

Relation with Emotional Intelligence : 

Social intelligence is closely related to cognition and emotional intelligence.

The emotional intelligence quadrant defines the four key competencies that enable a person to perform at their optimum in any given situation.

EI Quadrant

Social intelligence comes from our ability to be socially aware and to manage our relationships intelligently: the ability to pick up on emotions in other people and to work out what’s really going on with them; to appreciate another person’s perspective; to understand and appreciate the impact of your communication on others; to cultivate rapport and be attuned with a broad diversity of people; to manage interactions effectively; to engage with others for mutual benefit.

Social intelligence is separate from, but complimentary to emotional intelligence.Some deficits in SI arise from inadequate development of EI, conversely, some deficits in SI may lead to unsuccessful social experiences which may undermine a person's sense of self-worth which is part of EI.EI is about Self-Mastery, SI is about your ability to lead and inspire other people through your ability to influence, empathize and care.

Relation with Brain : 

Brain research in the last three decades has established that thinking and feeling originate from separate centers of the brain. The centers have been termed the “thinking mind” and the “emotional mind” respectively. The thinking mind is located in the cortex part of the brain while the emotional mind is in the area of the brain known as the limbic system. In particular, the amygdala in the limbic system is the structure that stores emotional experiences associated with various events. That structure is, therefore, the emotional center.

One of its functions, from what research has shown, is to communicate information of an emotional nature to the cortex — particularly to the prefrontal lobe of the cortex, instructing it to go into action or behavior mode. The prefrontal lobe considers the instructions from the amygdala in the context of the actual situation. Directly following that, it then decides whether to ignore the instructions or carry them through to action. If a person’s physiology is compromised — from drugs, alcohol, or moderate to high stress — the prefrontal lobe may fail to block the instructions from the amygdala, as it would in a more healthy state. In other words, we feel before we think. Emotions turn into action before the cognitive processes have a chance to interrupt the reaction.

More Info. 

International Politics

International politics is closely related to international relations, which is defined as the political relationship between foreign countries,study of the roles of sovereign states, inter-governmental organizations (IGO), international non-governmental organizations (INGO), non-governmental organizations (NGO), and multinational corporations (MNCs). IR explores how global, regional, and domestic factors influence relations between actors on the world stage.The study of international relations takes a wide range of theoretical approaches.Many theories of international relations are internally and externally contested, and few scholars believe only in one or another. In spite of this diversity, several major schools of thought are discernible, differentiated principally by the variables they emphasize — eg. military power, material interests, or ideological beliefs.

 International Relations - Theories : 

Realism

Realism is an international relations theory which states that world politics is driven by competitive self-interest.It emphasizes the role of the nation-state and makes a broad assumption that all nation-states are motivated by national interests, or, at best, national interests disguised as moral concerns.States are self-interested, power-seeking rational actors, who seek to maximize their security and chances of survival . Cooperation between states is a way to maximize each individual state's security (as opposed to more idealistic reasons). Similarly, any act of war must be based on self-interest, rather than on idealism. Many realists saw World War II as the vindication of their theory.

Realism is a tradition of international theory centered upon four propositions:

1.The international system is anarchic.

• There is no actor above states capable of regulating their interactions; states must arrive at relations with other states on their own, rather than it being dictated to them by some higher controlling entity.
• The international system exists in a state of constant antagonism .

2.States are the most important actors.

3.All states within the system are unitary, rational actors.

• States tend to pursue self-interest.
• Groups strive to attain as many resources as possible .

4.The primary concern of all states is survival.

• States build up military to survive, which may lead to a security dilemma.

In the domestic arena, the theory asserts that politicians do, or should, strive to maximize their power, whilst on the international stage, nation states are seen as the primary agents that maximize, or ought to maximize, their power. Most scholars and politicians during the Cold War viewed international relations through a realist lens. Neither the United States nor the Soviet Union trusted the other, and each sought allies to protect itself and increase its political and military influence abroad.

Realpolitik

Realpolitik is related to the philosophy of political realism, and both suggest working from the hypothesis that it is chiefly based on the pursuit, possession, and application of power. Realpolitik, however, is a prescriptive guideline limited to policy-making (like foreign policy), while realism is a descriptive paradigm, a wider theoretical and methodological framework, aimed at describing, explaining and, eventually, predicting events in the international relations domain.

Realpolitik -- "realistic", "practical", or "actual" politics -- is politics or diplomacy based primarily on power and on practical and material factors and considerations, rather than explicit ideological notions or moral or ethical premises. It is a system of politics based on a country's situation and its needs rather than on ideas about what is morally right and wrong.

In international politics it strives to be non-ideological, as in doing what is best for the national interest without getting hung up on unjustified diplomatic habits or popular sentiment.An example of Realpolitik would be the United States reaching out to China in the 1970s, despite protest that America should not associate with communists.

To its detractors, Realpolitik is sometimes seen as Machiavellian, based on "the ends justify the means," coercive, and amoral. To its proponents, Realpolitik is simply acknowledging reality and doing the best one can in international politics in light of obvious realities.

Liberalism

Liberalism is the theoretical perspective based on the assumption of the innate goodness of the individual and the value of political institutions in promoting social progress.According to liberalism individuals are basically good and capable of meaningful cooperation to promote positive change. Liberalism views states, nongovernmental organizations, and intergovernmental organizations as key actors in the international system. States have many interests and are not necessarily unitary and autonomous, although they remain sovereign.

Liberalism claims the following:

• The world is a harsh and dangerous place, but the consequences of using military power often outweigh the benefits. International cooperation is therefore in the interest of every state.
• Military power is not the only form of power. Economic and social power matter a great deal too.
• Exercising economic power has proven more effective than exercising military power.
• Different states often have different primary interests.
• International rules and organizations can help foster cooperation, trust, and prosperity. 

Example: Relations among the major Western powers fit a model of complex interdependence very well. The United States has significant disagreements with its European and Asian allies over trade and policy, but it is hard to imagine a circumstance in which the United States would use military power against any of these allies. Instead, the United States relies on economic pressure and incentives to achieve its policy aims.

More Info...

Liberalism resembles a family portrait of principles and institutions, recognizable by certain characteristics~such as individual freedom, political participation, private property, and equality of opportunity-that all liberal democratic societies,by definition, share to some degree. Political theorists identify liberalism with an essential principle: the importance of the freedom of the individual.Above all, this is a belief in the importance of moral freedom, of the right to be treated and a duty to treat others as ethical subjects and not as objects or means only.

The ideal version of liberalism is marked by a shared commitment to four essential institutions.First, citizens possess juridical equality and other fundamental civic rights such as freedom of religion and the press. Second, the effective sovereigns of the state are representative legislatures deriving their authority from the consent of the electorate and exercising their representative authority free from all restraint apart from the requirement that basic civic rights be preserved. Most pertinent, for the impact of liberalism on foreign affairs, the state is subject to neither the external authority of other states nor the internal authority of special prerogatives held, for example, by monarchs or military bureaucracies over foreign policy.Third, the economy rests on a recognition of the rights of private property, including the ownership of means of production. Property is justified by individual acquisition (e.g., by labor) or by social agreement or social utility. This excludes state socialism or state capitalism, but it need not exclude market socialism or various forms of the mixed economy.Fourth, economic decisions are predominantly shaped by the forces of supply and demand,domestically and internationally, and are free from strict control by bureaucracies.

Liberal internationalism consists, at its most fundamental level, in the attempt to promote the aforementioned principles and institutions across national borders and apply variations thereof to international relations.

Contemporary scholarship on liberalism and international relations looks back at three distinct traditions of liberalism, attributable to three groups of theorists: John Locke-the great founder of modern liberal individualism, who claimed that states have themselves rights derived from individual rights to life and liberty (political independence) and property (territorial integrity), thereby providing the liberal foundations of international law; Adam Smith, Baron de Montesquieu, and Joseph Schum peter-brilliant explicators of commercial liberalism and what they saw as its natural result, liberal pacifism; and finally, Immanuel Kant and Giuseppe Mazzini-liberal republicans who theorized an internationalism that institutes peace among fellow liberal republics.

Idealism

Idealism is a specific school of liberalism that stresses the need for states to pursue moral goals and to act ethically in the international arena. Idealists believe that behavior considered immoral on an interpersonal level is also immoral in foreign policy. Therefore, idealists argue that dishonesty, trickery, and violence should be shunned.

Neoliberal institutionalism (also called “neoliberalism” or “institutional liberalism”) emphasizes the importance of international institutions (Kant’s “federation of free states”) in maintaining peace. 

Cosmic Dust

Every ingredient in the human body is made from elements forged by stars. So are all of the building blocks of your food, your bike and your electronics. Similarly, every rock, plant, animal, scoop of seawater and breath of air owes its existence to distant suns.

All such stars are giant, long-lived furnaces. Their intense heat can cause atoms to collide, creating new elements. Late in life, most stars will explode, shooting the elements they forged out into the far-flung reaches of the universe.

New elements also may develop during stellar smash-ups. Astronomers have just witnessed evidence for the creation of gold and more during the distant collision between two dying stars.

Another team discovered the light from a long-gone “starburst” galaxy. Shortly after the universe formed, this galaxy churned out stars at an amazing speed. Special star factories like this one might help explain how enough elements built up to create the solar system.

Such discoveries are helping scientists better understand where everything in the universe got its start.

After the Big Bang

Elements are the basic building blocks of our universe. Earth hosts 92 natural elements with names like carbon, oxygen, sodium and gold. Their atoms are the amazingly tiny particles from which all known chemicals are made.

Each atom resembles a solar system. A tiny, but commanding structure sits at its center. This nucleus consists of a mix of bound particles known as protons and neutrons. The more particles in a nucleus, the heavier the element. Chemists have compiled charts that place the elements in order based on structural features, such as how many protons they have.

Topping their charts is hydrogen. Element one, it has a single proton. Helium, with two protons, comes next.

People and other living things are chock full of carbon, element 6. Earthly life also contains plenty of oxygen, element 8. Bones are rich in calcium, element 20. Number 26, iron, makes our blood run red. At the bottom of the periodic table of natural elements sits uranium, nature’s heavyweight, with 92 protons. Scientists have artificially created heavier elements in their laboratories. But these are extremely rare and short-lived.

The universe didn’t always boast so many elements. Blast back to the Big Bang, about 14 billion years ago. Physicists think that’s when matter, light and everything else exploded out of a fantastically dense, hot mass the size of a pea. This set in motion the expansion of the universe, an outward dispersion of mass that continues to this day.

The Big Bang was over in a flash. But it kick-started the whole universe.

After the Big Bang the only elements were hydrogen and helium. That was just about it. Assembling the next 90 took a lot more time. To build those heavier elements, nuclei of lighter atoms had to fuse together. This nuclear fusion requires serious heat and pressure. It takes stars.

Star power

For a few hundred million years after the Big Bang, the universe contained only giant gas clouds. These consisted of about 90 percent hydrogen atoms; helium made up the rest. Over time, gravity increasingly pulled the gas molecules toward each other. This increased their density, making the clouds hotter. Like cosmic lint, they began to gather into balls known as protogalaxies. Inside them, material continued to amass into ever-denser clumps. Some of these developed into stars. Stars are still being born this way, even in our Milky Way galaxy.

Converting lightweight elements into heavier ones is what stars do. The hotter the star, the heavier the elements it can make.

The center of our sun is some 15 million degrees Celsius (about 27 million degrees Fahrenheit). That may sound impressive. Yet as stars go, it’s pretty wimpy. Average-size stars like the sun don’t get hot enough to produce elements much heavier than nitrogen. In fact, they create mainly helium.

To forge heavier elements, the furnace must be immensely bigger and hotter than our sun.Stars at least eight times bigger can forge elements up to iron, element 26. To build elements heavier than that, a star must die.

In fact, making some of the heaviest metals, like platinum (element number 78) and gold (number 79), might require even more extreme celestial violence: collisions between stars!

In June 2013, the Hubble Space Telescope detected just such a collision of two ultra-dense bodies known as neutron stars. Astronomers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., measured the light emitted by this collision. That light provides “fingerprints” of the chemicals involved in those fireworks. And they show that gold formed. Lots of it: enough to equal several times the mass of Earth’s moon. Because a similar smash-up probably takes place in a galaxy once every 10,000 or 100,000 years, such crashes could account for all of the gold in the universe.

Death of a star

No star lives forever.Stars have a lifespan of about 10 billion years .

Gravity is always drawing the components of a star closer together. As long as a star still has fuel, pressure from nuclear fusion pushes outward and counter-balances the force of gravity. But once most of that fuel has burned up, so long star. Without fusion to counter it, “gravity forces the core to collapse,” .

The age at which a star dies depends on its size. Small to medium-size stars don’t explode.

While their core of iron or lighter elements collapses, the rest of the star expands gently, like a cloud. It swells into a huge growing, glowing ball. Along the way, such stars cool and darken. They become what astronomers call red giants. Many atoms in the outer halo surrounding such a star will just drift away into space.

Bigger stars come to a very different end. When they use up their fuel, their cores collapse. This leaves them extremely dense and hot. Instantly, that forges elements heavier than iron. The energy released by this atomic fusion triggers the star to expand yet again. At once, the star finds itself without enough fuel to sustain fusion. So the star collapses once again. Its massive density causes it to heat up again —after which it now fuses its atoms, creating heavier ones.

Pulse after pulse, star steadily builds up heavier and heavier elements. Amazingly, this all happens within a few seconds. Then, faster than you can say supernova, the star self-destructs in one ginormous explosion. The force of that supernova explosion is what forges elements heavier than iron.

Atoms go blasting out into space. They go a long way.

Some atoms drift gently from a red giant. Others rocket at warp speed from a supernova. Either way, when a star dies, many of its atoms spew into space. Eventually they become recycled by the processes that form new stars and even planets. All of this element-building “takes time” . Perhaps billions of years. But the universe is in no rush. It does suggest, however, that the longer a galaxy has been around, the more heavy elements it will contain.

Blast from the past

Consider the Milky Way. When our galaxy was young, 4.6 billion years ago, elements heavier than helium made up just 1.5 percent of the Milky Way. Today it’s up to 2 percent.

Last year, astronomers at the California Institute of Technology, or Caltech, discovered a very faint red dot in the night sky. They named this galaxy HFLS3. Hundreds of stars were forming inside it. Astronomers refer to such celestial bodies, with so many stars springing to life, as starburst galaxies. “HFLS3 was forming stars 2,000 times more rapidly than the Milky Way,” notes Caltech astronomer Jamie Bock.

To study distant stars, astronomers like Bock essentially become time travelers. They must look deep into the past. They can’t see what’s happening now because the light they study must first cross a vast expanse of the universe. And that can take months to years —sometimes thousands of millennia. So when describing star births and deaths, astronomers must use the past-tense.

A light-year is the distance light travels over a span of 365 days — 9.46 trillion kilometers (or some 6 trillion miles). HFLS3 was more than 13 billion light-years from Earth when it died. Its faint glow is just now reaching Earth. So what has happened in its vicinity during the past 12-billion-plus years won’t be known for eons.

But the just-arriving old news on HFLS3 did offer two surprises. First: It turns out to be the oldest starburst galaxy known. In fact, it is almost as old as the universe itself. “We found HFLS3 when the universe was a mere 880 million years old,” says Bock. At that point, the universe was a virtual baby.

Second, HFLS3 didn’t contain just hydrogen and helium, as astronomers might have expected for such an early galaxy. While studying its chemistry, Bock says his team discovered “it had heavy elements and dust that must have come from an earlier generation of stars.” He likens this to “finding a fully developed city early in human history where you were expecting to find villages.”

Lucky us

Astrophysicists think HFLS3 might help answer some important questions. The Milky Way galaxy is some 12 billion years old. But it doesn’t make stars fast enough to have created all of the 92 elements present on Earth. It’s always been a bit of a mystery how so many heavy elements built up so fast. Maybe starburst galaxies are not all that rare. If so, such high-speed star factories might have given the creation of heavy elements an early boost.

By about 5 billion years ago, stars in the Milky Way had generated all 92 elements now present on Earth. Indeed, gravity pulled them together, packing them into a hot cosmic stew that together would eventually coalesce to form our solar system. A few hundred million years later, Earth was born.

Within the next billion years, the first signs of life on Earth appeared. No one is exactly sure how life here got its start. But one thing is clear: Elements that formed Earth and all life upon it came from outer space. Every atom in your body was forged in the center of a star or from collisions between stars .

The Hindu Code Bill

The decade of 1940s was a vital decade in Indian history. The nation was bestowed with the unprecedented opportunity to transform itself as a modern nation. To build a modern nation, a variety of economic , political, social and cultural factors had to come to terms with each other. The vision of planned economic development and self reliance within a curious mixture of socialism and capitalism led to the evolution of political structures within the ambit a democratic set up.

As economic and political forces reconfigured themselves to contribute towards the emergence of the modern economy, the cultural milieu also experienced the need for alignment to the aspirations of an emerging nation.The protracted debate over the Hindu Code Bill with widespread participation across all regions and segments of the Indian society between 1941 and 1956 , known as the Hindu Code Bill debate , epitomised the necessity of the society to strike an alliance with the forces of modernization. Customary Hindu laws, frozen in religious beliefs of centuries , came to be challenged by the egalitarian, secular structure envisioned by the leaders of the modern Indian nation.The extensive Hindu Code Bill debate, in both public and legislative spheres, was of momentous importance to the entire project of carving a new, secular India. It was the debate that contributed to the family law reforms that influenced, to a great extent, the distribution of power and resources within the society, particularly at a granular level, within the family and enabled Indian society to align with the planned economic progress and modernisation.

While there may be a permanence of certain fundamental beliefs about the nature of life that is pervasive through Hinduism, Hindus as a group are highly non-homogenous. As Derrett says in his book on Hindu law, "We find the Hindus to be as diverse in race, psychology, habitat, employment and way of life as any collection of human beings that might be gathered from the ends of the earth." The Dharmaśāstra—the textual authority on matters of marriage, adoption, the joint family, minorities, succession, religious endowments, and caste privileges—has often been seen as the private law of the Hindus. However, whatever is known and interpreted about this Hindu law is a jumble of rules, often inconsistent and incompatible with one another, that are lacking in uniformity.

Hindu law's content and structure has ultimately survived as a result of its administration by British judges who gave a lot of attention to Hindu religious-legal texts, while simultaneously invoking English procedure, jurisprudence, and English law to fill any gaps. Opinions often differ as to the extent of the discrepancy between the current law and the public's needs, but most agree that a substantial inconsistency exists.The British colonial government administered India largely through a policy of noninterference, allowing civil matters to be dealt with through respective religious communities. Matters that fell under the jurisdiction of these communities were called "personal laws." The British began the intensive process of codifying Hindu personal law in the early 1940s in an attempt to notate and therefore organise the Indian political system.

In 1941, the colonial government had appointed a four-member Hindu Law Committee, known as the Rau Committee after its chairman B. N. Rau. The committee was to resolve doubts about the Deshmukh Act's(Hindu Women's Rights to Property Act 1937 -which had given the widow a son's share in property that was one of the most substantial steps towards the Hindu Code Bill.) construction,ensure that its introduction of new female heirs was not made at the expense of the decedent's own daughter, and consider bills introduced to abolish women's limited estate and to make polygamy a ground for separate residence and maintenance. Later in 1941 the Committee reported that the time had come for a Hindu Code. Social progress and modernization could only be achieved though fundamental reforms, which recognized gender equality. The code was to be shaped with the aid of orthodox, conservative and reformist Hindus and by a comprehensive blending of the best of the current schools of Hindu law and the ancient texts.

The 1941 Report was accompanied by two draft bills, each of which was laid before a select committee of both houses of the legislature. Much publicity was given to the project, and as a result of these committees' reports, the Hindu Law Committee itself was revived in 1944 and under its chairman, B. N. Rau, prepared a Draft Code dealing with Succession, Maintenance, Marriage and Divorce, Minority and Guardianship and Adoption. It was this Code which was widely circulated and discussed and given the name "Hindu Code Bill". After publication in twelve regional languages and a wide publicity campaign, the Rau Committee toured the country and examined witnesses.( The result 1947 report of the committee included and went far beyond the 1941 proposals, recommending the abolition of the joint-family property system, the introduction of the daughter's simultaneous succession with the son to the father's estate, the abolition of the barrier to intercaste marriages, the assimilation of civil and sacramental marriages, and the introduction of divorce for the higher castes.It was the intention of the Government that this first draft should become law on 1 January 1948, but the whole project was temporarily suspended when independence led to the priorities of the legislature to be consumed with the task of creating the new regime.)

In December 1946, the Constituent Assembly convened to devise a Constitution for the soon-to-be-independent India. There were extensive debates over the place of personal laws in the new Indian legal system. Some argued that India's various personal laws were too divisive and that a uniform civil code should be instituted in their place. And once the notion of a uniform civil code was put forward, it soon became accepted as an important part of the effort to construct an Indian national identity, over the separate identities of caste, religion and ethnicity.Some resistance to the code was on the grounds that its imposition would destroy the cultural identity of minorities, the protection of which is crucial to democracy. Certain feminists thus argue that the uniform civil code debate balances on the polarity of the state and community, rendering the gender-based axis upon which it turns, invisible.

A compromise was reached in the inclusion in the first draft of an article that compelled the state "to endeavour to secure for the citizens a uniform civil code throughout the territory of India." This clause—which equated to a goal, not a right—became Article 44 in the Constitution. It was widely criticised by proponents of a uniform code because it contained no mechanism and provided no timetable for enforcement. However, Prime Minister Jawaharlal Nehru and others insisted on its inclusion, arguing that though only symbolic it was an important step towards national unity.Though Nehru himself likely would have favored a uniform code, he knew that personal laws were linked with religious identity in India and therefore could not be easily abolished. Recognizing that what he wanted was not a political reality he settled for an unenforceable clause.

Following India's independence in 1947, the postcolonial government led by Prime Minister Jawaharlal Nehru completed the codification and reform of Hindu personal law, a process started by the British. According to the British policy of noninterference, reform of personal law should have arisen from a demand from the Hindu community. This was not the case, as there was significant opposition from various Hindu politicians, organisations and devotees who saw themselves unjustly singled out as the sole religious community whose laws were to be reformed. However, the Nehru administration saw such codification as necessary in order to unify the Hindu community, which ideally would be a first step towards unifying the nation.

The Ministry of Law revised the first draft in 1948 and made some small alterations to it, making it more suitable for discussion in the Constituent Assembly, where it was finally introduced. It was referred to a select committee under the chairmanship of law minister B. R. Ambedkar, and this committee made a number of important changes in the Bill. This edition had eight sections: part one delineated who would be considered a Hindu and did away with the caste system. Significantly, part one stipulated that the Hindu Code would apply to anyone who was not a Muslim, Parsi, Christian or Jew, and asserted that all Hindus would be governed under a uniform law. Part two of the bill concerned marriage; part three adoption; part four, guardianship; part five the policy on joint-family property, and was controversial as it included the nontraditional allocation of property to women. Part six concerned policies regarding women's property, and parts seven and eight established policies on succession and maintenance. By allowing for divorce, Ambedkar's version of the Hindu Code conflicted with traditional Hindu personal law, which did not sanction divorce (although it was practiced). It also "established one joint family system of property ownership for all Hindus", doing away with regional rules. Finally, it allotted portions of inheritance to daughters, while giving widows complete property rights where they had previously been restricted.

Conflicts also arose from the categorization of who would be considered Hindu. The Code established "Hindu" to be a negative category that would include all those who did not identify as a Muslim, Jew, Christian, or Parsi. Such a broad designation ignored the tremendous diversity of region, tradition and custom in Hinduism. Those who practised Sikhism, Jainism, and Buddhism were considered to be Hindus under the jurisdiction of the Code Bill. While these had originally included aspects of Hinduism, by this time they had evolved into unique religions with their own customs, traditions, and rituals. There was also significant controversy over what was established to be Hindu personal law. Sanctioned under Hinduism were a variety of practices and perspectives. Therefore, the administration had to arbitrate between these variations, legitimating some and disregarding or marginalising others.

The Hindu Code Bill's proponents included both men and women within and outside of Parliament belonging to various political parties. Significant support for the bills came from Congress' women's wing (All-India Women's Conference), and several other women's organizations. Advocates largely sought to convince the public that the bills did not stray far from classical Hindu personal law. Essentially, those in Parliament who opposed the bills were men, and largely came from Nehru's own Congress party. They believed that the code bills would institute reform that strayed too far from the classical Hindu social order, and were too radical. They argued that practices such as divorce were absolutely not condoned by Hinduism. "To a Hindu the marriage is sacramental and as such indissoluble."They also felt that should equal property rights be given to women, the Mitākṣarā concept of a joint family would crumble, as would the foundation of Hindu society. They also insisted that were daughters and wives given inheritance more conflicts would arise within families. Their main argument, however, was that the bills lacked public support. Therefore, they were a direct contradiction to the policy of noninterference and would mean the government was meddling in personal law. They implied that these were bills propagated by a small minority of Hindus onto the majority who did not want them.

The draft that Ambedkar submitted to the Constituent Assembly was opposed by several sections of lawmakers. The motion to begin discussion on the Hindu Code Bill was debated for over fifty hours, and discussion was postponed for over a year. Realizing that he would have to make significant concessions to get the bill passed, Nehru suggested that the proposed law be split into several sections. He told the Constituent Assembly they would only contend with the first 55 clauses concerning marriage and divorce, while the rest would be considered by the Parliament of India after the first general election. However, this compromise was largely ineffective in convincing conservatives to support the bill. When only 3 of the 55 clauses passed after an additional week of debating, Nehru had Ambedkar's committee distribute a new draft that complied with many of the critics' demands, including the reinstitution of the Mitākṣarā joint family system, an amendment to allow for brothers to buy out daughters' share of the inheritance, and a stipulation allowing divorce only after three years of marriage.However, after the bills were defeated again in the assembly, Ambedkar resigned. In a letter which he released to the press, he held that his decision was largely based on the treatment which had been accorded to the Hindu Code Bill as well as the administration's inability to get it passed.

In 1951–52, India held its first general elections. Nehru made the Hindu Code Bill one of his top campaign initiatives, declaring that should the Indian National Congress win, he would succeed in getting it passed through parliament. Congress won sweeping victories, with Nehru reinstated as prime minister, and he began a comprehensive effort to devise a Bill that could actually get passed. Nehru split the Code Bill into four separate bills, including the Hindu Marriage Act, the Hindu Succession Act, the Hindu Minority and Guardianship Act, and the Hindu Adoptions and Maintenance Act. These were met with significantly less opposition, and between the years of 1952 and 1956 each was effectively introduced in and passed by Parliament.

Nehru's primary purpose in instituting the Hindu code bills was to unify the Hindu community. Therefore, it made sense to define Hindu in the broadest possible sense. Through legal equity Nehru intended to "erase distinctions within the Hindu community and create Hindu social unity." "The integration of Hindus into a homogeneous society could best be done by enacting an all-embracing code which encompasses within its fold every sect, caste, and religious denomination." The debates over Article 44 in the Constitution revealed that many believed varied laws and legal divisions helped create, or at least were reflective of, social divisions.Nehru and his supporters insisted that the Hindu community, which comprised 80% of the Indian population, first needed to be united before any actions were taken to unify the rest of India. Therefore, the codification of Hindu personal law became a symbolic beginning on the road to establishing the Indian national identity.Nehru also felt that because he was Hindu, it was his prerogative to codify specifically Hindu law, as opposed to Muslim or Jewish law.

Those in Parliament who supported the bills also saw them as a vital move towards the modernization of Hindu society, as they would clearly delineate secular laws from religious law. Many also heralded the bills' opportunity to implement greater rights for women, which were established to be necessary for India's development.

Clouds

 

Clouds are visible accumulations of tiny water droplets or ice crystals in the Earth’s atmosphere.They are  the clumping of condensing water vapor.

Moist air near the Earth’s surface is raised from the ground to high in the atmosphere by the heat of the sun,orographic barrier(Orographic lift) or by a colder invading air mass, called a cold front, that pushes the warm, moist air upward. When the air is lifted, both the air pressure and temperature drops.As soon as the air temperature reaches the air’s dew point, the water vapor in the moist air condenses, and clouds form. Warm air can hold more water vapor than cold air, so lowering the temperature of an air mass is like squeezing a sponge. Clouds are the visible result of that squeeze of cooler, moist air.

Moist air becomes cloudy with only slight cooling.With further cooling, the water or ice particles that make up the cloud can grow into bigger particles that fall to Earth as precipitation.Clouds form when humid air cools enough for water vapor to condense into droplets or ice crystals. The altitude at which this happens depends on the humidity and the rate at which temperature drops with elevation.

Clouds differ greatly in size, shape, and color. They can appear thin and wispy, or bulky and lumpy.

Clouds usually appear white because the tiny water droplets inside them are tightly packed, reflecting most of the sunlight that hits them. White is how our eyes perceive all wavelengths of sunlight mixed together.

When it’s about to rain, clouds darken because the water vapor is clumping together into raindrops, leaving larger spaces between drops of water. Less light is reflected. The rain cloud appears black or gray.
 
Normally, water vapor can only condense onto condensation nuclei—tiny particles that serve as kernels around which drops can form.Condensation nuclei are often nothing but natural dust. But soot particles from automobile exhaust or other types of pollution can also serve the purpose.

Cloud  Types

Clouds are classified according to their height above and appearance (texture) from the ground.

The following cloud roots and translations summarize the components of this classification system:

 1) Cirro-: curl of hair, high.                                     
 2) Alto-: mid.                                                                       
 3) Strato-: layer.
 4) Cumulo-: heap.
 5) Nimbo-: rain, precipitation.

High-level clouds: 

High-level clouds occur above about 20,000 feet (6,000 meters)  and are given the prefix "cirro-". Due to cold tropospheric temperatures at these levels, the clouds primarily are  composed of ice crystals,  and often appear thin, streaky, and white (although a low sun angle, e.g., near sunset, can create an array  of color on the clouds).

The three main types of high clouds are cirrus, cirrostratus, and cirrocumulus.

Cirrus clouds are wispy, feathery, and composed entirely of ice crystals. They often are the first sign of an approaching warm front or upper-level jet streak.

Unlike cirrus, cirrostratus clouds form more of a widespread, veil-like layer (similar to what stratus clouds do in low levels).  When sunlight or moonlight passes through the hexagonal-shaped ice crystals of cirrostratus clouds, the light is dispersed or refracted (similar to light passing through a prism) in such a way that a familiar ring or halo may form. As a warm front approaches, cirrus clouds tend to thicken into cirrostratus, which may, in turn, thicken and lower into altostratus, stratus, and even nimbostratus.

Finally, cirrocumulus clouds are layered clouds permeated with small cumuliform lumpiness. They also may line up in streets or rows of clouds across the sky denoting localized areas of ascent (cloud axes) and descent (cloud-free channels).

 Mid-level clouds:

The bases of clouds in the middle level of the troposphere, given the prefix "alto-", appear between 6,500 and 20,000 feet (2,000 - 6,000 meters ). Depending on the altitude, time of year, and vertical temperature structure of the troposphere, these clouds may be composed of liquid water droplets, ice crystals, or a combination of the two, including supercooled droplets (i.e., liquid droplets whose temperatures are below freezing). 

The two main type of mid-level clouds are altostratus and altocumulus.

Altostratus clouds are "strato" type clouds that possess a flat and uniform type texture in the mid levels. They frequently indicate the approach of a warm front and may thicken and lower into stratus, then nimbostratus resulting in rain or snow. However, altostratus clouds themselves do not produce significant precipitation at the surface, although sprinkles or occasionally light showers may occur from a thick alto-stratus deck. 

Altocumulus clouds exhibit "cumulo" type characteristics in mid levels, i.e., heap-like clouds with convective elements.  Like cirrocumulus, altocumulus may align in rows or streets of clouds, with cloud axes indicating localized areas of ascending, moist air, and clear zones between rows suggesting locally descending, drier air. Altocumulus clouds with some vertical extent may denote the presence of elevated instability, especially in the morning, which could become boundary-layer based and be released into deep convection during the afternoon or evening. 

Low-level clouds:

Low-level clouds are not given a prefix, although their names are derived from "strato-" or "cumulo-", depending on their characteristics. Low clouds occur below 6500 feet (2000 mts), and normally consist of liquid water droplets or even supercooled droplets, except during cold winter storms when ice crystals (and snow) comprise much of the clouds.

The two main types of low clouds include stratus, which develop horizontally, and cumulus, which develop vertically.

Stratus clouds are uniform and flat, producing a gray layer of cloud cover which may be precipitation-free or may cause periods of light precipitation or drizzle.  Low stratus decks are common in winter in the Ohio Valley, especially behind a storm system when cold, dismal, gray weather can linger for several hours or even a day or two.

Stratocumulus clouds are hybrids of layered stratus and cellular cumulus, i.e., individual cloud elements, characteristic of cumulo type clouds, clumped together in a continuous distribution, characteristic of strato type clouds. Stratocumulus also can be thought of as a layer of cloud clumps with thick and thin areas. These clouds appear frequently in the atmosphere, either ahead of or behind a frontal system.

Nimbostratus clouds are generally thick, dense stratus or stratocumulus clouds producing steady rain or snow . 

In contrast to layered, horizontal stratus, cumulus clouds are more cellular (individual) in nature, have flat bottoms and rounded tops, and grow vertically. In fact, their name depends on the degree of vertical development. For instance, scattered cumulus clouds showing little vertical growth on an otherwise sunny day used to be termed "cumulus humilis" or "fair weather cumulus," although normally they simply are referred to just as cumulus or flat cumulus.

A cumulus cloud that exhibits significant vertical development (but is not yet a thunderstorm) is called cumulus congestus or towering cumulus. If enough atmospheric instability, moisture, and lift are present, then strong updrafts can develop in the cumulus cloud leading to a mature, deep cumulonimbus cloud, i.e., a thunderstorm producing heavy rain. In addition, cloud electrification occurs within cumulonimbus clouds due to many collisions between charged water droplet, graupel (ice-water mix), and ice crystal particles, resulting in lightning and thunder.  

 

click to enlarge

 Other Clouds :

Mammatus: Drooping underside (pouch-like appearance) of a cumulonimbus cloud in its latter stage of development. Mammatus most often are seen hanging from the anvil of a severe thunderstorm, but do not produce severe weather. They can accompany non-severe storms as well. 

Contrail: Narrow, elongated cloud formed as jet aircraft exhaust condenses in cold air at high altitudes, indicative of upper level humidity and wind drift.

Fog: Layer of stratus clouds on or near the ground. Different types include radiation fog (forms overnight and burns off in the morning) and advection fog.

Wall Cloud:  A localized lowering from the rain-free base of a strong thunderstorm. The lowering denotes a storm's updraft where rapidly rising air causes lower pressure just below the main updraft, which enhances condensation and cloud formation just under the primary cloud base. Wall clouds take on many shapes and sizes. Some exhibit strong upward motion and cyclonic rotation, leading to tornado formation, while others do not rotate and essentially are harmless.

Shelf Cloud: A low, horizontal, sometimes wedge-shaped cloud associated with the leading edge of a thunderstorm?s outflow or gust front and potentially strong winds. Although often appearing ominous, shelf clouds normally do not produce tornadoes. 

Hole-Punch Clouds: Also known as a fallstreak hole, this type of cloud is usually formed when the water temperature in the cloud is below freezing but the water has not frozen.  When sections of the water starts to freeze, the surrounding water vapor will also freeze and begin to descend. This leaves a rounded hole in the cloud.The theory on its creation is that a disruption of the cloud layer stability, which can be caused by a passing jet aircraft, creates a descending motion that can lead to the stimulation of evaporation, producing a hole.

Mackerel sky  is a popular term for a sky covered with extensive cirrocumulus or altocumulus clouds arranged in somewhat regular waves and showing blue sky in the gaps. The pattern resembles the scales on a mackerel fish, thus, the name.

Mackerel sky

Clouds above the troposphere

Clouds are found almost exclusively in the troposphere. The stratosphere is very dry, because vertical transfer is limited by the high stability and because any transfer would have to occur through the tropopause, which is so cold that the saturation vapour pressure is negligibly small. Yet on occasion thin veils of clouds are observed above the tropopause.

Nacreous clouds, also known as mother-of-pearl clouds, are stratospheric; they occur between 15 and 30 km. Large volcanic eruptions emit dust particles in the lower stratosphere. These may combine with ice to produce nacreous clouds. In fact, in the year following Mt Pinatubo eruption in 1991, many nacreous clouds where spotted by airline pilots flying in the twilight. Polar stratospheric clouds occur at about 20 km, where the air is at -80°C during the Antarctic winter. Their presence is a factor in the formation of the Antarctic ozone hole.

Nacreous Clouds

 Noctilucent clouds occur in the upper mesosphere, at about 80 km. Their name derives from the fact that they can be seen from the ground when the Sun is 7-10 degrees below the horizon and only reflects off these very high clouds . It arises from the water vapour released upon oxidation of methane. The recent observed increase of such clouds is related to increased atmospheric concentrations of methane, a greenhouse gas. Noctilucent clouds are most common in the summer in polar regions. At this time the mesospheric lapse rate is close to neutral, and this makes uplift easier. 

Noctilucent Clouds

Clouds and Weather

Certain types of clouds produce precipitation. Clouds also produce the bolt of electricity called lightning and the sound of thunder that accompanies it. Lightning is formed in a cloud when positively charged particles and negatively charged particles are separated, forming an electrical field. When the electrical field is strong enough, it discharges a superheated bolt of lightning to the Earth. Most of what we consider to be single lightning strikes are in fact three or four separate strokes of lightning.

The sound of thunder is actually the sonic shock wave that comes when the air, heated by the lightning bolt, expands very rapidly. Thunder sometimes sounds like it comes in waves because of the time it takes the sound to travel. Because the speed of light is faster than the speed of sound, lightning will always appear before its thunder is heard.

Meteorologists measure cloud cover, or the amount of the visible sky covered by clouds, in units called oktas. An okta estimates how many eighths of the sky (octo-) is covered in clouds. A clear sky is 0 oktas, while a totally overcast or gray sky is 8 oktas.

Scientists have experimented with a process called cloud seeding for many years. Cloud seeding aims to influence weather patterns. Seeds, or microscopic particles, are placed in clouds. These seeds are artificial cloud condensation nuclei (CCN), which are tiny particles of dust, salt, or pollution that collect in all clouds. Every raindrop and snowflake contains a CCN. Water or ice droplets accumulate around CCN. Scientists hope that cloud seeding will allow people to control precipitation.