The Smithsonian Institution, founded on August 10, 1846 "for the increase and diffusion of knowledge," is a group of museums and research centers administered by the Government of the United States. The institution is named after British scientist James Smithson. Organized as the "United States National Museum," that name ceased to exist as an administrative entity in 1967. Termed "the nation's attic" for its eclectic holdings of 154 million items, the Institution's nineteen museums, nine research centers, zoo include historical and architectural landmarks located in the District of Columbia. Additional facilities are located in Arizona, Massachusetts, New York City, Texas and Panama. More than 200 institutions and museums in 45 states, Puerto Rico, Panama are Smithsonian Affiliates; the Institution's thirty million annual visitors are admitted without charge. Its annual budget is around $1.2 billion with two-thirds coming from annual federal appropriations. Other funding comes from the Institution's endowment and corporate contributions, membership dues, earned retail and licensing revenue.
Institution publications include Air & Space magazines. The British scientist James Smithson left most of his wealth to his nephew Henry James Hungerford; when Hungerford died childless in 1835, the estate passed "to the United States of America, to found at Washington, under the name of the Smithsonian Institution, an Establishment for the increase & diffusion of knowledge among men", in accordance with Smithson's will. Congress accepted the legacy bequeathed to the nation, pledged the faith of the United States to the charitable trust on July 1, 1836; the American diplomat Richard Rush was dispatched to England by President Andrew Jackson to collect the bequest. Rush returned in August 1838 with 105 sacks containing 104,960 gold sovereigns. Once the money was in hand, eight years of Congressional haggling ensued over how to interpret Smithson's rather vague mandate "for the increase and diffusion of knowledge." The money was invested by the US Treasury in bonds issued by the state of Arkansas, which soon defaulted.
After heated debate, Massachusetts Representative John Quincy Adams persuaded Congress to restore the lost funds with interest and, despite designs on the money for other purposes, convinced his colleagues to preserve it for an institution of science and learning. On August 10, 1846, President James K. Polk signed the legislation that established the Smithsonian Institution as a trust instrumentality of the United States, to be administered by a Board of Regents and a Secretary of the Smithsonian. Though the Smithsonian's first Secretary, Joseph Henry, wanted the Institution to be a center for scientific research, it became the depository for various Washington and U. S. government collections. The United States Exploring Expedition by the U. S. Navy circumnavigated the globe between 1838 and 1842; the voyage amassed thousands of animal specimens, an herbarium of 50,000 plant specimens, diverse shells and minerals, tropical birds, jars of seawater, ethnographic artifacts from the South Pacific Ocean.
These specimens and artifacts became part of the Smithsonian collections, as did those collected by several military and civilian surveys of the American West, including the Mexican Boundary Survey and Pacific Railroad Surveys, which assembled many Native American artifacts and natural history specimens. In 1846, the regents developed a plan for weather observation; the Institution became a magnet for young scientists from 1857 to 1866, who formed a group called the Megatherium Club. The Smithsonian played a critical role as the U. S. partner institution in early bilateral scientific exchanges with the Academy of Sciences of Cuba. Construction began on the Smithsonian Institution Building in 1849. Designed by architect James Renwick Jr. its interiors were completed by general contractor Gilbert Cameron. The building opened in 1855; the Smithsonian's first expansion came with construction of the Arts and Industries Building in 1881. Congress had promised to build a new structure for the museum if the 1876 Philadelphia Centennial Exposition generated enough income.
It did, the building was designed by architects Adolf Cluss and Paul Schulze, based on original plans developed by Major General Montgomery C. Meigs of the United States Army Corps of Engineers, it opened in 1881. The National Zoological Park opened in 1889 to accommodate the Smithsonian's Department of Living Animals; the park was designed by landscape architect Frederick Law Olmsted. The National Museum of Natural History opened in June 1911 to accommodate the Smithsonian's United States National Museum, housed in the Castle and the Arts and Industries Building; this structure was designed by the D. C. architectural firm of Hornblower & Marshall. When Detroit philanthropist Charles Lang Freer donated his private collection to the Smithsonian and funds to build the museum to hold it, it was among the Smithsonian's first major donations from a private individual; the gallery opened in 1923. More than 40 years would pass before the next museum, the Museum of History and Technology, opened in 1964.
It was designed by the world-renowned firm of Mead & White. The Anacostia Community Museum, an "experimental store-front" museum created at the initiative of Smithsonian Secretary S. Dillon Ripley, opened in the Anacostia neighborhood of
A chemically pure and structurally perfect diamond is transparent with no hue, or color. However, in reality no gem-sized natural diamonds are perfect; the color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds can be more valuable. Of all colored diamonds, red diamonds are the rarest; the Aurora Pyramid of Hope displays a spectacular array of colored diamonds, including red diamonds. Diamonds occur in a variety of colors—steel gray, blue, orange, green, pink to purple and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, pure diamonds are transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption: Type I diamonds have nitrogen atoms as the main impurity at a concentration of 0.1%.
If the nitrogen atoms are in pairs they do not affect the diamond's color. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint. About 98% of gem diamonds are type Ia, most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region known as Cape Province in North Africa, whose deposits are Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites, they give the stone an intense yellow or brown tint. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb from 320 nm, they have a characteristic fluorescence and visible absorption spectrum. Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, transmit in the ultraviolet below 225 nm, unlike Type I diamonds, they have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare, but constitute a large percentage of Australian production.
Type IIb diamonds, which account for 0.1% of gem diamonds, are light blue due to scattered boron within the crystal matrix. However, a blue-grey color may occur in Type Ia diamonds and be unrelated to boron. Not restricted to type are green diamonds, whose color is caused by GR1 color centers in the crystal lattice produced by exposure to varying quantities of radiation. Pink and red are caused by plastic deformation of the crystal lattice from pressure. Black diamonds are caused by microscopic black or gray inclusions of other materials such as graphite or sulfides and/or microscopic fractures. Opaque or opalescent white diamonds are caused by microscopic inclusions. Purple diamonds are caused by a combination of high hydrogen content; the majority of diamonds that are mined are in a range of pale yellow or brown color, termed the normal color range. Diamonds that are of intense yellow or brown, or any other color are called fancy color diamonds. Diamonds that are of the highest purity are colorless, appear a bright white.
The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed. Diamonds have a color grading system; this system goes from D to Z. The more colorless a diamond is, the rarer and more valuable it is because it appears white and brighter to the eye. Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate; as the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, consistency; some early grading scales were. Numerous terms developed to describe diamonds of particular colors: golconda, jagers, blue white, fine white, gem blue, etc. Refers to a grading scale for diamonds in the normal color range used by internationally recognized laboratories; the scale ranges from D, colorless to Z, a pale yellow or brown color. Brown diamonds darker than K color are described using their letter grade, a descriptive phrase, for example M Faint Brown.
Diamonds with more depth of color than Z color fall into the fancy color diamond range. Diamond color is graded by comparing a sample stone to a master stone set of diamonds; each master stone is known to exhibit the least amount of body color that a diamond in that color grade may exhibit. A trained diamond grader compares a diamond of unknown grade against the series of master stones, assessing where in the range of color the diamond resides; this process occurs in a lighting box, fitted with daylight equivalent lamps. Accurate color grading can only be performed with diamond unset, as the comparison with master
Brazil the Federative Republic of Brazil, is the largest country in both South America and Latin America. At 8.5 million square kilometers and with over 208 million people, Brazil is the world's fifth-largest country by area and the fifth most populous. Its capital is Brasília, its most populated city is São Paulo; the federation is composed of the union of the 26 states, the Federal District, the 5,570 municipalities. It is the largest country to have Portuguese as an official language and the only one in the Americas. Bounded by the Atlantic Ocean on the east, Brazil has a coastline of 7,491 kilometers, it borders all other South American countries except Ecuador and Chile and covers 47.3% of the continent's land area. Its Amazon River basin includes a vast tropical forest, home to diverse wildlife, a variety of ecological systems, extensive natural resources spanning numerous protected habitats; this unique environmental heritage makes Brazil one of 17 megadiverse countries, is the subject of significant global interest and debate regarding deforestation and environmental protection.
Brazil was inhabited by numerous tribal nations prior to the landing in 1500 of explorer Pedro Álvares Cabral, who claimed the area for the Portuguese Empire. Brazil remained a Portuguese colony until 1808, when the capital of the empire was transferred from Lisbon to Rio de Janeiro. In 1815, the colony was elevated to the rank of kingdom upon the formation of the United Kingdom of Portugal and the Algarves. Independence was achieved in 1822 with the creation of the Empire of Brazil, a unitary state governed under a constitutional monarchy and a parliamentary system; the ratification of the first constitution in 1824 led to the formation of a bicameral legislature, now called the National Congress. The country became a presidential republic in 1889 following a military coup d'état. An authoritarian military junta came to power in 1964 and ruled until 1985, after which civilian governance resumed. Brazil's current constitution, formulated in 1988, defines it as a democratic federal republic. Due to its rich culture and history, the country ranks thirteenth in the world by number of UNESCO World Heritage Sites.
Brazil is considered an advanced emerging economy. It has the ninth largest GDP in the world by nominal, eight and PPP measures, it is one of the world's major breadbaskets, being the largest producer of coffee for the last 150 years. It is classified as an upper-middle income economy by the World Bank and a newly industrialized country, with the largest share of global wealth in Latin America. Brazil is a regional power and sometimes considered a great or a middle power in international affairs. On account of its international recognition and influence, the country is subsequently classified as an emerging power and a potential superpower by several analysts. Brazil is a founding member of the United Nations, the G20, BRICS, Union of South American Nations, Organization of American States, Organization of Ibero-American States and the Community of Portuguese Language Countries, it is that the word "Brazil" comes from the Portuguese word for brazilwood, a tree that once grew plentifully along the Brazilian coast.
In Portuguese, brazilwood is called pau-brasil, with the word brasil given the etymology "red like an ember", formed from brasa and the suffix -il. As brazilwood produces a deep red dye, it was valued by the European textile industry and was the earliest commercially exploited product from Brazil. Throughout the 16th century, massive amounts of brazilwood were harvested by indigenous peoples along the Brazilian coast, who sold the timber to European traders in return for assorted European consumer goods; the official Portuguese name of the land, in original Portuguese records, was the "Land of the Holy Cross", but European sailors and merchants called it the "Land of Brazil" because of the brazilwood trade. The popular appellation eclipsed and supplanted the official Portuguese name; some early sailors called it the "Land of Parrots". In the Guarani language, an official language of Paraguay, Brazil is called "Pindorama"; this was the name the indigenous population gave to the region, meaning "land of the palm trees".
Some of the earliest human remains found in the Americas, Luzia Woman, were found in the area of Pedro Leopoldo, Minas Gerais and provide evidence of human habitation going back at least 11,000 years. The earliest pottery found in the Western Hemisphere was excavated in the Amazon basin of Brazil and radiocarbon dated to 8,000 years ago; the pottery was found near Santarém and provides evidence that the tropical forest region supported a complex prehistoric culture. The Marajoara culture flourished on Marajó in the Amazon delta from 800 CE to 1400 CE, developing sophisticated pottery, social stratification, large populations, mound building, complex social formations such as chiefdoms. Around the time of the Portuguese arrival, the territory of current day Brazil had an estimated indigenous population of 7 million people semi-nomadic who subsisted on hunting, fishing and migrant agriculture; the indigenous population of Brazil comprised several large indigenous ethnic groups. The Tupí people were subdivided into the Tupiniquins and Tupinambás, there were many subdivisions of the other gro
Gemology or gemmology is the science dealing with natural and artificial gemstone materials. It is considered a branch of mineralogy; some jewelers are academically trained are qualified to identify and evaluate gems. Rudimentary education in gemology for jewelers and gemologists began in the nineteenth century, but the first qualifications were instigated after the National Association of Goldsmiths of Great Britain set up a Gemmological Committee for this purpose in 1908; this committee matured into the Gemmological Association of Great Britain, now an educational charity and accredited awarding body with its courses taught worldwide. The first US graduate of Gem-A's Diploma Course, in 1929, was Robert Shipley, who established both the Gemological Institute of America and the American Gem Society. There are now several professional schools and associations of gemologists and certification programs around the world; the first gemological laboratory serving the jewelry trade was established in London in 1925, prompted by the influx of the newly developed "cultured pearl" and advances in the synthesis of rubies and sapphires.
There are now numerous gem laboratories around the world requiring more advanced equipment and experience to identify the new challenges - such as treatments to gems, new synthetics, other new materials. It is difficult to obtain an expert judgement from a neutral laboratory. Analysis and estimation in the gemstone trade have to take place on site. Professional gemologists and gemstone buyers use mobile laboratories, which pool all necessary instruments in a travel case; such so-called travel labs have their own current supply, which makes them independent from infrastructure. They are suitable for gemological expeditions. Gemstones are categorized based on their crystal structure, specific gravity, refractive index, other optical properties, such as pleochroism; the physical property of "hardness" is defined by the non-linear Mohs scale of mineral hardness. Gemologists study these factors while appraising cut and polished gemstones. Gemological microscopic study of the internal structure is used to determine whether a gem is synthetic or natural by revealing natural fluid inclusions or melted exogenous crystals that are evidence of heat treatment to enhance color.
The spectroscopic analysis of cut gemstones allows a gemologist to understand the atomic structure and identify its origin, a major factor in valuing a gemstone. For example, a ruby from Burma will have definite internal and optical activity variance from a Thai ruby; when the gemstones are in a rough state, the gemologist studies the external structure. The stone is identified by its color, refractive index, optical character, specific gravity, examination of internal characteristics under magnification. Gemologists use a variety of tools and equipment which allow for the accurate tests to be performed in order to identify a gemstone by its specific characteristics and properties; these include: Corrected 10× loupe Microscope Refractometer Polarising filter Magnifying eyepiece Contact liquid for RI up to 1.81 Polariscope Optic figure sphere Dichroscope Spectroscope Penlight Tweezers Stone cloth Color filter Immersion cell Ultraviolet lamp Gem identification is a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity.
Any single test is indicative, only. For example, the specific gravity of ruby is 4.00, glass is 3.15–4.20, cubic zirconia is 5.6–5.9. So one can tell the difference between cubic zirconia and the other two. And, as with all occurring materials, no two gems are identical; the geological environment they are created in influences the overall process so that although the basics can be identified, the presence of chemical "impurities" and substitutions along with structural imperfections create "individuals". One test to determine the gem's identity is to measure the refraction of light in the gem; every material has a critical angle. This can be measured and thus used to determine the gem's identity; this is measured using a refractometer, although it is possible to measure it using a microscope. Specific gravity known as relative density, varies depending upon the chemical composition and crystal structure type. Heavy liquids with a known specific gravity are used to test loose gemstones. Specific gravity is measured by comparing the weight of the gem in air with the weight of the gem suspended in water.
This method uses a similar principle to how a prism works to separate white light into its component colors. A gemological spectroscope is employed to analyze the selective absorption of light in the gem material; when light passes from one medium to another, it bends. Blue light bends more than red light. How much the light bends will vary depending on the gem material. Coloring agents or chromophores show bands in the spectroscope and indicate which element is responsible for the gem's color. Inclusions can help gemologists to determine whether or not a gemstone is natural, synthetic or treated. Institutes and laboratories American Gem Society - AGS Asian Institute of Gemological Sciences - AIGS Canadian Gemmological Association - CGA Canadian Institute of Gemmology - CIG European Gemological Laboratory - EGL Gemmological Association of Australia - GAA Gemmological Association of Great Britain - Gem-A Gemological Institute of America - GIA Gübelin
Phosphorescence is a type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not re-emit the radiation it absorbs; the slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. As these transitions occur slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation. Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers and clock dials that glow after being charged with a bright light such as in any normal reading or room light; the glow fades out, sometimes within a few minutes or up to a few hours in a dark room. The study of phosphorescent materials led to the discovery of radioactivity in 1896. In simple terms, phosphorescence is a process in which energy absorbed by a substance is released slowly in the form of light; this is in some cases the mechanism used for "glow-in-the-dark" materials which are "charged" by exposure to light.
Unlike the swift reactions in fluorescence, such as those seen in a common fluorescent tube, phosphorescent materials "store" absorbed energy for a longer time, as the processes required to re-emit energy occur less often. Most photoluminescent events, in which a chemical substrate absorbs and re-emits a photon of light, are fast, in the order of 10 nanoseconds. Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon undergoes an unusual intersystem crossing into an energy state of higher spin multiplicity a triplet state; as a result, the excited electron can become trapped in the triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at slower time scales.
Most phosphorescent compounds are still fast emitters, with triplet lifetimes on the order of milliseconds. However, some compounds have triplet lifetimes up to minutes or hours, allowing these substances to store light energy in the form of slowly degrading excited electron states. If the phosphorescent quantum yield is high, these substances will release significant amounts of light over long time scales, creating so-called "glow-in-the-dark" materials. S 0 + h ν → S 1 → T 1 → S 0 + h ν ′ where S is a singlet and T a triplet whose subscripts denote states. Transitions can occur to higher energy levels, but the first excited state is denoted for simplicity; some examples of glow-in-the-dark materials do not glow by phosphorescence. For example, glow sticks glow due to a chemiluminescent process, mistaken for phosphorescence. In chemiluminescence, an excited state is created via a chemical reaction; the light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will transfer to a dye molecule known as a sensitizer or fluorophor, subsequently fluoresce back to the ground state.
Common pigments used in phosphorescent materials include strontium aluminate. Use of zinc sulfide for safety related products dates back to the 1930s. However, the development of strontium aluminate, with a luminance 10 times greater than zinc sulfide, has relegated most zinc sulfide based products to the novelty category. Strontium aluminate based pigments are now used in exit signs, pathway marking, other safety related signage. Phosphorescent pigments – zinc sulfide vs. strontium aluminate Phosphorescent Luminous gemstones Luminous paint Microsphere Persistent luminescence Phosphor Phosphoroscope Tritium
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form, but diamond never converts to it. Diamond has the highest hardness and thermal conductivity of any natural material, properties that are utilized in major industrial applications such as cutting and polishing tools, they are the reason that diamond anvil cells can subject materials to pressures found deep in the Earth. Because the arrangement of atoms in diamond is rigid, few types of impurity can contaminate it. Small numbers of defects or impurities color diamond blue, brown, purple, orange or red. Diamond has high optical dispersion. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometers in the Earth's mantle, although a few have come from as deep as 800 kilometers. Under high pressure and temperature, carbon-containing fluids dissolved minerals and replaced them with diamonds.
Much more they were carried to the surface in volcanic eruptions and deposited in igneous rocks known as kimberlites and lamproites. Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures or from hydrocarbon gas by chemical vapor deposition. Imitation diamonds can be made out of materials such as cubic zirconia and silicon carbide. Natural and imitation diamonds are most distinguished using optical techniques or thermal conductivity measurements. Diamond is a solid form of pure carbon with its atoms arranged in a crystal. Solid carbon comes in different forms known as allotropes depending on the type of chemical bond; the two most common allotropes of pure carbon are graphite. In graphite the bonds are sp2 orbital hybrids and the atoms form in planes with each bound to three nearest neighbors 120 degrees apart. In diamond they are sp3 and the atoms form tetrahedra with each bound to four nearest neighbors. Tetrahedra are rigid, the bonds are strong, of all known substances diamond has the greatest number of atoms per unit volume, why it is both the hardest and the least compressible.
It has a high density, ranging from 3150 to 3530 kilograms per cubic metre in natural diamonds and 3520 kg/m³ in pure diamond. In graphite, the bonds between nearest neighbors are stronger but the bonds between planes are weak, so the planes can slip past each other. Thus, graphite is much softer than diamond. However, the stronger bonds make graphite less flammable. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity, as well as wide bandgap and high optical dispersion. Diamond's ignition point is 720 -- 800 °C in 850 -- 1000 °C in air; the equilibrium pressure and temperature conditions for a transition between graphite and diamond is well established theoretically and experimentally. The pressure changes linearly between 1.7 GPa at 0 K and 12 GPa at 5000 K. However, the phases have a wide region about this line where they can coexist. At normal temperature and pressure, 20 °C and 1 standard atmosphere, the stable phase of carbon is graphite, but diamond is metastable and its rate of conversion to graphite is negligible.
However, at temperatures above about 4500 K, diamond converts to graphite. Rapid conversion of graphite to diamond requires pressures well above the equilibrium line: at 2000 K, a pressure of 35 GPa is needed. Above the triple point, the melting point of diamond increases with increasing pressure. At high pressures and germanium have a BC8 body-centered cubic crystal structure, a similar structure is predicted for carbon at high pressures. At 0 K, the transition is predicted to occur at 1100 GPa; the most common crystal structure of diamond is called diamond cubic. It is formed of unit cells stacked together. Although there are 18 atoms in the figure, each corner atom is shared by eight unit cells and each atom in the center of a face is shared by two, so there are a total of eight atoms per unit cell; each side of the unit cell is 3.57 angstroms in length. A diamond cubic lattice can be thought of as two interpenetrating face-centered cubic lattices with one displaced by 1/4 of the diagonal along a cubic cell, or as one lattice with two atoms associated with each lattice point.
Looked at from a <1 1 1> crystallographic direction, it is formed of layers stacked in a repeating ABCABC... pattern. Diamonds can form an ABAB... structure, known as hexagonal diamond or lonsdaleite, but this is far less common and is formed under different conditions from cubic carbon. Diamonds occur most as euhedral or rounded octahedra and twinned octahedra known as macles; as diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can be elongated. Diamonds are found coated in nyf, an opaque gum-like skin; some diamonds have opaque fibers. They are referred to as opaque if the fibers
Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which includes moths. Adult butterflies have large brightly coloured wings, conspicuous, fluttering flight; the group comprises the large superfamily Papilionoidea, which contains at least one former group, the skippers, the most recent analyses suggest it contains the moth-butterflies. Butterfly fossils date to the Paleocene, about 56 million years ago. Butterflies have the typical four-stage insect life cycle. Winged adults lay eggs on the food plant; the caterpillars grow, sometimes rapidly, when developed, pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, after its wings have expanded and dried, it flies off; some butterflies in the tropics, have several generations in a year, while others have a single generation, a few in cold locations may take several years to pass through their entire life cycle. Butterflies are polymorphic, many species make use of camouflage and aposematism to evade their predators.
Some, like the monarch and the painted lady, migrate over long distances. Many butterflies are attacked by parasites or parasitoids, including wasps, protozoans and other invertebrates, or are preyed upon by other organisms; some species are pests because in their larval stages they can damage domestic trees. Larvae of a few butterflies eat harmful insects, a few are predators of ants, while others live as mutualists in association with ants. Culturally, butterflies are a popular motif in the literary arts; the Oxford English Dictionary derives the word straightforwardly from Old English butorflēoge, butter-fly. A possible source of the name is the bright yellow male of the brimstone; the earliest Lepidoptera fossils are of a small moth, Archaeolepis mane, of Jurassic age, around 190 million years ago. Butterflies evolved from moths, so while the butterflies are monophyletic, the moths are not; the oldest butterflies are from the Palaeocene MoClay or Fur Formation of Denmark 55 million years old.
The oldest American butterfly is the Late Eocene Prodryas persephone from the Florissant Fossil Beds 34 million years old. Traditionally, the butterflies have been divided into the superfamily Papilionoidea excluding the smaller groups of the Hesperiidae and the more moth-like Hedylidae of America. Phylogenetic analysis suggests that the traditional Papilionoidea is paraphyletic with respect to the other two groups, so they should both be included within Papilionoidea, to form a single butterfly group, thereby synonymous with the clade Rhopalocera. Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name; these scales give butterfly wings their colour: they are pigmented with melanins that give them blacks and browns, as well as uric acid derivatives and flavones that give them yellows, but many of the blues, greens and iridescent colours are created by structural coloration produced by the micro-structures of the scales and hairs. As in all insects, the body is divided into three sections: the head and abdomen.
The thorax is composed of each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those of moths which may be threadlike or feathery; the long proboscis can be coiled. Nearly all butterflies are diurnal, have bright colours, hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are cryptically coloured, either hold their wings flat or fold them over their bodies; some day-flying moths, such as the hummingbird hawk-moth, are exceptions to these rules. Butterfly larvae, have a hard head with strong mandibles used for cutting their food, most leaves, they have cylindrical bodies, with ten segments to the abdomen with short prolegs on segments 3–6 and 10. Many are well camouflaged; the pupa or chrysalis, unlike that of moths, is not wrapped in a cocoon. Many butterflies are sexually dimorphic. Most butterflies have the ZW sex-determination system where females are the heterogametic sex and males homogametic. Butterflies are distributed worldwide except Antarctica.
Of these, 775 are Nearctic. The monarch butterfly is native to the Americas, but in the nineteenth century or before, spread across the world, is now found in Australia, New Zealand, other parts of Oceania, the Iberian Peninsula, it is not clear.