A radionuclide is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation. During those processes, the radionuclide is said to undergo radioactive decay; these emissions are considered ionizing radiation because they are powerful enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single element the decay rate, thus the half-life for that collection can be calculated from their measured decay constants; the range of the half-lives of radioactive atoms have no known limits and span a time range of over 55 orders of magnitude. Radionuclides occur or are artificially produced in nuclear reactors, particle accelerators or radionuclide generators.
There are about 730 radionuclides with half-lives longer than 60 minutes. Thirty-two of those are primordial radionuclides. At least another 60 radionuclides are detectable in nature, either as daughters of primordial radionuclides or as radionuclides produced through natural production on Earth by cosmic radiation. More than 2400 radionuclides have half-lives less than 60 minutes. Most of those are only produced artificially, have short half-lives. For comparison, there are about 253 stable nuclides. All chemical elements can exist as radionuclides; the lightest element, has a well-known radionuclide, tritium. Elements heavier than lead, the elements technetium and promethium, exist only as radionuclides. Unplanned exposure to radionuclides has a harmful effect on living organisms including humans, although low levels of exposure occur without harm; the degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure, the biochemical properties of the element.
However, radionuclides with suitable properties are used in nuclear medicine for both diagnosis and treatment. An imaging tracer made with radionuclides is called a radioactive tracer. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical. On Earth occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, cosmogenic radionuclides. Radionuclides are produced in stellar nucleosynthesis and supernova explosions along with stable nuclides. Most decay but can still be observed astronomically and can play a part in understanding astronomic processes. Primordial radionuclides, such as uranium and thorium, exist in the present time because their half-lives are so long that they have not yet decayed; some radionuclides have half-lives so long that decay has only been detected, for most practical purposes they can be considered stable, most notably bismuth-209: detection of this decay meant that bismuth was no longer considered stable.
It is possible decay may be observed in other nuclides adding to this list of primordial radionuclides. Secondary radionuclides are radiogenic isotopes derived from the decay of primordial radionuclides, they have shorter half-lives than primordial radionuclides. They arise in the decay chain of the primordial isotopes thorium-232, uranium-238 and uranium-235. Examples include the natural isotopes of radium. Cosmogenic isotopes, such as carbon-14, are present because they are continually being formed in the atmosphere due to cosmic rays. Many of these radionuclides exist only in trace amounts in nature, including all cosmogenic nuclides. Secondary radionuclides will occur in proportion to their half-lives, so short-lived ones will be rare, thus polonium can be found in uranium ores at about 0.1 mg per metric ton. Further radionunclides may occur in nature in undetectable amounts as a result of rare events such as spontaneous fission or uncommon cosmic ray interactions. Radionuclides are produced as an unavoidable result of nuclear thermonuclear explosions.
The process of nuclear fission creates a wide range of fission products, most of which are radionuclides. Further radionuclides can be created from irradiation of the nuclear fuel and of the surrounding structures, yielding activation products; this complex mixture of radionuclides with different chemistries and radioactivity makes handling nuclear waste and dealing with nuclear fallout problematic. Synthetic radionuclides are deliberately synthesised using nuclear reactors, particle accelerators or radionuclide generators: As well as being extracted from nuclear waste, radioisotopes can be produced deliberately with nuclear reactors, exploiting the high flux of neutrons present; these neutrons activate elements placed within the reactor. A typical product from a nuclear reactor is iridium-
Astrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the astronomical objects, rather than their positions or motions in space". Among the objects studied are the Sun, other stars, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, the properties examined include luminosity, density and chemical composition; because astrophysics is a broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including mechanics, statistical mechanics, quantum mechanics, relativity and particle physics, atomic and molecular physics. In practice, modern astronomical research involves a substantial amount of work in the realms of theoretical and observational physics; some areas of study for astrophysicists include their attempts to determine the properties of dark matter, dark energy, black holes.
Topics studied by theoretical astrophysicists include Solar System formation and evolution. Astronomy is an ancient science, long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its goal, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere. During the 17th century, natural philosophers such as Galileo and Newton began to maintain that the celestial and terrestrial regions were made of similar kinds of material and were subject to the same natural laws, their challenge was. For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects.
A new astronomy, soon to be called astrophysics, began to emerge when William Hyde Wollaston and Joseph von Fraunhofer independently discovered that, when decomposing the light from the Sun, a multitude of dark lines were observed in the spectrum. By 1860 the physicist, Gustav Kirchhoff, the chemist, Robert Bunsen, had demonstrated that the dark lines in the solar spectrum corresponded to bright lines in the spectra of known gases, specific lines corresponding to unique chemical elements. Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere. In this way it was proved that the chemical elements found in the Sun and stars were found on Earth. Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected bright, as well as dark, lines in solar spectra. Working with the chemist, Edward Frankland, to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements.
He thus claimed the line represented a new element, called helium, after the Greek Helios, the Sun personified. In 1885, Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme, accepted for worldwide use in 1922. In 1895, George Ellery Hale and James E. Keeler, along with a group of ten associate editors from Europe and the United States, established The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics, it was intended that the journal would fill the gap between journals in astronomy and physics, providing a venue for publication of articles on astronomical applications of the spectroscope.
Around 1920, following the discovery of the Hertsprung-Russell diagram still used as the basis for classifying stars and their evolution, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. At that time, the source of stellar energy was a complete mystery; this was a remarkable development since at that time fusion and thermonuclear energy, that stars are composed of hydrogen, had not yet been discovered. In 1
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
In situ is a Latin phrase that translates to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in many different contexts. For example, in fields such as physics, chemistry, or biology, in situ may describe the way a measurement is taken, that is, in the same place the phenomenon is occurring without isolating it from other systems or altering the original conditions of the test. In the aerospace industry, equipment on-board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may work but interference from nearby equipment may create unanticipated problems. Special test equipment is available for this in situ testing. In archaeology, in situ refers to an artifact that has not been moved from its original place of deposition. In other words, it is stationary, meaning "still." An artifact being in situ is critical to the interpretation of that artifact and of the culture which formed it.
Once an artifact's'find-site' has been recorded, the artifact can be moved for conservation, further interpretation and display. An artifact, not discovered in situ is considered out of context and as not providing an accurate picture of the associated culture. However, the out of context artifact can provide scientists with an example of types and locations of in situ artifacts yet to be discovered; when excavating a burial site or surface deposit "in situ" refers to cataloging, mapping, photographing human remains in the position they are discovered. The label in situ indicates. Thus, an archaeological in situ find may be an object, looted from another place, an item of "booty" of a past war, a traded item, or otherwise of foreign origin; the in situ find site may still not reveal its provenance, but with further detective work may help uncover links that otherwise would remain unknown. It is possible for archaeological layers to be reworked on purpose or by accident. For example, in a Tell mound, where layers are not uniform or horizontal, or in land cleared or tilled for farming.
The term in situ is used to describe ancient sculpture, carved in place such as the Sphinx or Petra. This distinguishes it from statues that were carved and moved like the Colossi of Memnon, moved in ancient times. In art, in situ refers to a work of art made for a host site, or that a work of art takes into account the site in which it is installed or exhibited. For a more detailed account see: Site-specific art; the term can refer to a work of art created at the site where it is to be displayed, rather than one created in the artist's studio and installed elsewhere. In architectural sculpture the term is employed to describe sculpture, carved on a building from scaffolds, after the building has been erected. Used to describe the site specific dance festival “Insitu”. Held in Queens, New York. A fraction of the globular star clusters in our galaxy, as well as those in other massive galaxies, might have formed in situ; the rest might have been accreted from now defunct dwarf galaxies. In astronomy, in situ refers to in situ planet formation, in which planets are hypothesized to have been formed in the orbit that they are observed to be in rather than migrating from a different orbit.
In biology and biomedical engineering, in situ means to examine the phenomenon in place where it occurs. In the case of observations or photographs of living animals, it means that the organism was observed in the wild as it was found and where it was found; this means. The organism had not been moved to another location such as an aquarium; this phrase in situ when used in laboratory science such as cell science can mean something intermediate between in vivo and in vitro. For example, examining a cell within a whole organ intact and under perfusion may be in situ investigation; this would not be in vivo as the donor is sacrificed by experimentation, but it would not be the same as working with the cell alone. In vitro was among the first attempts to qualitatively and quantitatively analyze natural occurrences in the lab; the limitation of in vitro experimentation was that they were not conducted in natural environments. To compensate for this problem, in vivo experimentation allowed testing to occur in the original organism or environment.
To bridge the dichotomy of benefits associated with both methodologies, in situ experimentation allowed the controlled aspects of in vitro to become coalesced with the natural environmental compositions of in vivo experimentation. In conservation of genetic resources, "in situ conservation" is the process of protecting an endangered plant or animal species in its natural habitat, as opposed to ex situ conservation. In chemistry, in situ means "in the reaction mixture." There are numerous situations in which chemical intermediates are synthesized in situ in various processes. This may be done because the species is unstable, cannot be isolated, or out of convenience. Examples of the former include the Corey-Chaykovsky adrenochrome. In biomedical engineering, protein nanogels made by the in situ polymerization method provide a versatile platform for storage and release of therapeutic
Boron is a chemical element with symbol B and atomic number 5. Produced by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar system and in the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common occurring compounds, the borate minerals; these are mined industrially as evaporites, such as kernite. The largest known boron deposits are in the largest producer of boron minerals. Elemental boron is a metalloid, found in small amounts in meteoroids but chemically uncombined boron is not otherwise found on Earth. Industrially pure boron is produced with difficulty because of refractory contamination by carbon or other elements. Several allotropes of boron exist: amorphous boron is a brown powder; the primary use of elemental boron is as boron filaments with applications similar to carbon fibers in some high-strength materials. Boron is used in chemical compounds. About half of all boron consumed globally is an additive in fiberglass for insulation and structural materials.
The next leading use is in polymers and ceramics in high-strength, lightweight structural and refractory materials. Borosilicate glass is desired for its greater strength and thermal shock resistance than ordinary soda lime glass. Boron as sodium perborate is used as a bleach. A small amount of boron is used as a dopant in semiconductors, reagent intermediates in the synthesis of organic fine chemicals. A few boron-containing organic pharmaceuticals are in study. Natural boron is composed of two stable isotopes, one of which has a number of uses as a neutron-capturing agent. In biology, borates have low toxicity in mammals, but are more toxic to arthropods and are used as insecticides. Boric acid is mildly antimicrobial, several natural boron-containing organic antibiotics are known. Boron is an essential plant nutrient and boron compounds such as borax and boric acid are used as fertilizers in agriculture, although it's only required in small amounts, with excess being toxic. Boron compounds play a strengthening role in the cell walls of all plants.
There is no consensus on whether boron is an essential nutrient for mammals, including humans, although there is some evidence it supports bone health. The word boron was coined from borax, the mineral from which it was isolated, by analogy with carbon, which boron resembles chemically. Borax, its mineral form known as tincal, glazes were used in China from AD 300, some crude borax reached the West, where the Perso-Arab alchemist Jābir ibn Hayyān mentioned it in AD 700. Marco Polo brought some glazes back to Italy in the 13th century. Agricola, around 1600, reports the use of borax as a flux in metallurgy. In 1777, boric acid was recognized in the hot springs near Florence and became known as sal sedativum, with medical uses; the rare mineral is called sassolite, found at Sasso, Italy. Sasso was the main source of European borax from 1827 to 1872. Boron compounds were rarely used until the late 1800s when Francis Marion Smith's Pacific Coast Borax Company first popularized and produced them in volume at low cost.
Boron was not recognized as an element until it was isolated by Sir Humphry Davy and by Joseph Louis Gay-Lussac and Louis Jacques Thénard. In 1808 Davy observed that electric current sent through a solution of borates produced a brown precipitate on one of the electrodes. In his subsequent experiments, he used potassium to reduce boric acid instead of electrolysis, he named the element boracium. Gay-Lussac and Thénard used iron to reduce boric acid at high temperatures. By oxidizing boron with air, they showed. Jöns Jakob Berzelius identified boron as an element in 1824. Pure boron was arguably first produced by the American chemist Ezekiel Weintraub in 1909; the earliest routes to elemental boron involved the reduction of boric oxide with metals such as magnesium or aluminium. However, the product is always contaminated with borides of those metals. Pure boron can be prepared by reducing volatile boron halides with hydrogen at high temperatures. Ultrapure boron for use in the semiconductor industry is produced by the decomposition of diborane at high temperatures and further purified by the zone melting or Czochralski processes.
The production of boron compounds does not involve the formation of elemental boron, but exploits the convenient availability of borates. Boron is similar to carbon in its capability to form stable covalently bonded molecular networks. Nominally disordered boron contains regular boron icosahedra which are, bonded randomly to each other without long-range order. Crystalline boron is a hard, black material with a melting point of above 2000 °C, it forms four major polymorphs: β-rhombohedral, γ and β-tetragonal. Most of the phases are based on B12 icosahedra, but the γ-phase can be described as a rocksalt-type arrangement of the icosahedra and B2 atomic pairs, it can be produced by compressing other boron phases to 12–20 GPa and heating to 1500–1800 °C. The T phase is produced at similar pressures, but higher temperatures of 1800–2200 °C; as to the α and β phases, they might both coexist at ambient conditions with the β phase being more stable
Neon is a chemical element with symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, inert monatomic gas under standard conditions, with about two-thirds the density of air, it was discovered in 1898 as one of the three residual rare inert elements remaining in dry air, after nitrogen, oxygen and carbon dioxide were removed. Neon was the second of these three rare gases to be discovered and was recognized as a new element from its bright red emission spectrum; the name neon is derived from the Greek νέον, neuter singular form of νέος, meaning new. Neon is chemically inert, no uncharged neon compounds are known; the compounds of neon known include ionic molecules, molecules held together by van der Waals forces and clathrates. During cosmic nucleogenesis of the elements, large amounts of neon are built up from the alpha-capture fusion process in stars. Although neon is a common element in the universe and solar system, it is rare on Earth, it composes about 18.2 ppm of air by a smaller fraction in Earth's crust.
The reason for neon's relative scarcity on Earth and the inner planets is that neon is volatile and forms no compounds to fix it to solids. As a result, it escaped from the planetesimals under the warmth of the newly ignited Sun in the early Solar System; the outer atmosphere of Jupiter is somewhat depleted of neon, although for a different reason. It is lighter than air, causing it to escape from Earth's atmosphere. Neon gives a distinct reddish-orange glow when used in low-voltage neon glow lamps, high-voltage discharge tubes and neon advertising signs; the red emission line from neon causes the well known red light of helium–neon lasers. Neon has few other commercial uses, it is commercially extracted by the fractional distillation of liquid air. Since air is the only source, it is more expensive than helium. Neon was discovered in 1898 by the British chemists Sir William Ramsay and Morris W. Travers in London. Neon was discovered when Ramsay chilled a sample of air until it became a liquid warmed the liquid and captured the gases as they boiled off.
The gases nitrogen and argon had been identified, but the remaining gases were isolated in their order of abundance, in a six-week period beginning at the end of May 1898. First to be identified was krypton; the next, after krypton had been removed, was a gas which gave a brilliant red light under spectroscopic discharge. This gas, identified in June, was named "neon", the Greek analogue of the Latin novum suggested by Ramsay's son; the characteristic brilliant red-orange color emitted by gaseous neon when excited electrically was noted immediately. Travers wrote: "the blaze of crimson light from the tube told its own story and was a sight to dwell upon and never forget."A second gas was reported along with neon, having the same density as argon but with a different spectrum – Ramsay and Travers named it metargon. However, subsequent spectroscopic analysis revealed it to be argon contaminated with carbon monoxide; the same team discovered xenon by the same process, in September 1898. Neon's scarcity precluded its prompt application for lighting along the lines of Moore tubes, which used nitrogen and which were commercialized in the early 1900s.
After 1902, Georges Claude's company Air Liquide produced industrial quantities of neon as a byproduct of his air-liquefaction business. In December 1910 Claude demonstrated modern neon lighting based on a sealed tube of neon. Claude tried to sell neon tubes for indoor domestic lighting, due to their intensity, but the market failed because homeowners objected to the color. In 1912, Claude's associate began selling neon discharge tubes as eye-catching advertising signs and was more successful. Neon tubes were introduced to the U. S. in 1923 with two large neon signs bought by a Los Angeles Packard car dealership. The glow and arresting red color made neon advertising different from the competition; the intense color and vibrancy of neon equated with American society at the time, suggesting a "century of progress" and transforming cities into sensational new environments filled with radiating advertisements and "electro-graphic architecture". Neon played a role in the basic understanding of the nature of atoms in 1913, when J. J. Thomson, as part of his exploration into the composition of canal rays, channeled streams of neon ions through a magnetic and an electric field and measured the deflection of the streams with a photographic plate.
Thomson observed two separate patches of light on the photographic plate, which suggested two different parabolas of deflection. Thomson concluded that some of the atoms in the neon gas were of higher mass than the rest. Though not understood at the time by Thomson, this was the first discovery of isotopes of stable atoms. Thomson's device was a crude version of the instrument. Neon is the second lightest inert gas. Neon has three stable isotopes: 21Ne and 22Ne. 21Ne and 22Ne are primordial and nucleogenic and their variations in natural abundance are well understood. In contrast, 20Ne is not known to be radiogenic; the causes of the variation of 20Ne in the Earth have thus been hotly debated. The princ
A scientist is someone who conducts scientific research to advance knowledge in an area of interest. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature called natural philosophy, a precursor of natural science, it was not until the 19th century that the term scientist came into regular use after it was coined by the theologian and historian of science William Whewell in 1833. The term'scientist' was first coined by him for Mary Somerville because the term "man of science", more custom at that time, was inappropriate here. In modern times, many scientists have advanced degrees in an area of science and pursue careers in various sectors of the economy such as academia, industry and nonprofit environments; the roles of "scientists", their predecessors before the emergence of modern scientific disciplines, have evolved over time. Scientists of different eras have had different places in society, the social norms, ethical values, epistemic virtues associated with scientists—and expected of them—have changed over time as well.
Accordingly, many different historical figures can be identified as early scientists, depending on which characteristics of modern science are taken to be essential. Some historians point to the Scientific Revolution that began in 16th century as the period when science in a recognizably modern form developed, it wasn't until the 19th century that sufficient socioeconomic changes occurred for scientists to emerge as a major profession. Knowledge about nature in classical antiquity was pursued by many kinds of scholars. Greek contributions to science—including works of geometry and mathematical astronomy, early accounts of biological processes and catalogs of plants and animals, theories of knowledge and learning—were produced by philosophers and physicians, as well as practitioners of various trades; these roles, their associations with scientific knowledge, spread with the Roman Empire and, with the spread of Christianity, became linked to religious institutions in most of European countries.
Astrology and astronomy became an important area of knowledge, the role of astronomer/astrologer developed with the support of political and religious patronage. By the time of the medieval university system, knowledge was divided into the trivium—philosophy, including natural philosophy—and the quadrivium—mathematics, including astronomy. Hence, the medieval analogs of scientists were either philosophers or mathematicians. Knowledge of plants and animals was broadly the province of physicians. Science in medieval Islam generated some new modes of developing natural knowledge, although still within the bounds of existing social roles such as philosopher and mathematician. Many proto-scientists from the Islamic Golden Age are considered polymaths, in part because of the lack of anything corresponding to modern scientific disciplines. Many of these early polymaths were religious priests and theologians: for example, Alhazen and al-Biruni were mutakallimiin. During the Italian Renaissance scientists like Leonardo Da Vinci, Galileo Galilei and Gerolamo Cardano have been considered as the most recognizable polymaths.
During the Renaissance, Italians made substantial contributions in science. Leonardo Da Vinci made significant discoveries in anatomy; the Father of modern Science,Galileo Galilei, made key improvements on the thermometer and telescope which allowed him to observe and describe the solar system. Descartes was not only a pioneer of analytic geometry but formulated a theory of mechanics and advanced ideas about the origins of animal movement and perception. Vision interested the physicists Young and Helmholtz, who studied optics and music. Newton extended Descartes' mathematics by inventing calculus, he investigated light and optics. Fourier founded a new branch of mathematics — infinite, periodic series — studied heat flow and infrared radiation, discovered the greenhouse effect. Girolamo Cardano, Blaise Pascal Pierre de Fermat, Von Neumann, Khinchin and Wiener, all mathematicians, made major contributions to science and probability theory, including the ideas behind computers, some of the foundations of statistical mechanics and quantum mechanics.
Many mathematically inclined scientists, including Galileo, were musicians. There are many compelling stories in medicine and biology, such as the development of ideas about the circulation of blood from Galen to Harvey. During the age of Enlightenment, Luigi Galvani, the pioneer of the bioelectromagnetics, discovered the animal electricity, he discovered that a charge applied to the spinal cord of a frog could generate muscular spasms throughout its body. Charges could make frog legs jump if the legs were no longer attached to a frog. While cutting a frog leg, Galvani's steel scalpel touched a brass hook, holding the leg in place; the leg twitched. Further experiments confirmed this effect, Galvani was convinced that he was seeing the effects of what he called animal electricity, the life force within the muscles of the frog. At the University of Pavia, Galvani's colleague Alessandro Volta was able to reproduce the results, but was sceptical o