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109-494: The GST is capable of observing the Sun in visible to near-infrared wavelengths and features a 1.7-meter primary mirror in an off-axis Gregorian configuration that provides a 1.6-meter clear, unobstructed aperture . Adaptive optics correct for atmospheric schlieren in the solar image known as astronomical seeing . The f/2.4 primary mirror is a 1.7-meter off-axis section of a 5.3-meter diameter, f/0.73 concave parabola . It

218-434: A body-centered cubic (bcc) crystal structure . As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite . At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. The physical properties of iron at very high pressures and temperatures have also been studied extensively, because of their relevance to theories about

327-563: A medium with matter , their wavelength is decreased. Wavelengths of electromagnetic radiation, whatever medium they are traveling through, are usually quoted in terms of the vacuum wavelength , although this is not always explicitly stated. Generally, electromagnetic radiation is classified by wavelength into radio wave , microwave , infrared , visible light , ultraviolet , X-rays and gamma rays . The behavior of EM radiation depends on its wavelength. When EM radiation interacts with single atoms and molecules , its behavior also depends on

436-430: A nuclear spin (− 1 ⁄ 2 ). The nuclide Fe theoretically can undergo double electron capture to Cr, but the process has never been observed and only a lower limit on the half-life of 4.4×10 years has been established. Fe is an extinct radionuclide of long half-life (2.6 million years). It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide Ni . Much of

545-425: A radio receiver . Earth's atmosphere is mainly transparent to radio waves, except for layers of charged particles in the ionosphere which can reflect certain frequencies. Radio waves are extremely widely used to transmit information across distances in radio communication systems such as radio broadcasting , television , two way radios , mobile phones , communication satellites , and wireless networking . In

654-422: A radio wave photon that has a wavelength of 21.12 cm. Also, frequencies of 30 Hz and below can be produced by and are important in the study of certain stellar nebulae and frequencies as high as 2.9 × 10  Hz have been detected from astrophysical sources. The types of electromagnetic radiation are broadly classified into the following classes (regions, bands or types): This classification goes in

763-499: A supernova for their formation, involving rapid neutron capture by starting Fe nuclei. In the far future of the universe, assuming that proton decay does not occur, cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into Fe nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron. Iron's abundance in rocky planets like Earth

872-446: A transmitter generates an alternating electric current which is applied to an antenna. The oscillating electrons in the antenna generate oscillating electric and magnetic fields that radiate away from the antenna as radio waves. In reception of radio waves, the oscillating electric and magnetic fields of a radio wave couple to the electrons in an antenna, pushing them back and forth, creating oscillating currents which are applied to

981-408: A digital CCD camera that samples the image of the Sun. The interference filter works as a band-pass filter that only transmits a selected color of the sunlight. Frequently used bands are 705.7 ± 0.5 nm ( Titanium(II) oxide (TiO) spectral line , dark-red) and 430.5 ± 0.25 nm ( G-band , blue-ish). The BFI camera captures 2048 × 2048 pixel images at a speed of 14 frames per second, covering an area on

1090-454: A distorted sodium chloride structure. The binary ferrous and ferric halides are well-known. The ferrous halides typically arise from treating iron metal with the corresponding hydrohalic acid to give the corresponding hydrated salts. Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common. Ferric iodide is an exception, being thermodynamically unstable due to

1199-439: A few meters of water. One notable use is diagnostic X-ray imaging in medicine (a process known as radiography ). X-rays are useful as probes in high-energy physics. In astronomy, the accretion disks around neutron stars and black holes emit X-rays, enabling studies of these phenomena. X-rays are also emitted by stellar corona and are strongly emitted by some types of nebulae . However, X-ray telescopes must be placed outside

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1308-553: A macroscopic piece of iron will have a nearly zero overall magnetic field. Application of an external magnetic field causes the domains that are magnetized in the same general direction to grow at the expense of adjacent ones that point in other directions, reinforcing the external field. This effect is exploited in devices that need to channel magnetic fields to fulfill design function, such as electrical transformers , magnetic recording heads, and electric motors . Impurities, lattice defects , or grain and particle boundaries can "pin"

1417-477: A mirror-like silvery-gray. Iron reacts readily with oxygen and water to produce brown-to-black hydrated iron oxides , commonly known as rust . Unlike the oxides of some other metals that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing more fresh surfaces for corrosion. Chemically, the most common oxidation states of iron are iron(II) and iron(III) . Iron shares many properties of other transition metals, including

1526-475: A mixture of O 2 /Ar. Iron(IV) is a common intermediate in many biochemical oxidation reactions. Numerous organoiron compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy . Many mixed valence compounds contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue ( Fe 4 (Fe[CN] 6 ) 3 ). The latter

1635-636: A radio communication system, a radio frequency current is modulated with an information-bearing signal in a transmitter by varying either the amplitude, frequency or phase, and applied to an antenna. The radio waves carry the information across space to a receiver, where they are received by an antenna and the information extracted by demodulation in the receiver. Radio waves are also used for navigation in systems like Global Positioning System (GPS) and navigational beacons , and locating distant objects in radiolocation and radar . They are also used for remote control , and for industrial heating. The use of

1744-471: A result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron. Iron is by far the most reactive element in its group; it is pyrophoric when finely divided and dissolves easily in dilute acids, giving Fe . However, it does not react with concentrated nitric acid and other oxidizing acids due to the formation of an impervious oxide layer, which can nevertheless react with hydrochloric acid . High-purity iron, called electrolytic iron ,

1853-415: A successful first light trebling the corrected field of view by strongly reducing anisoplanatism. By 2020, Clear became a facility instrument, largely replacing CAO and holding lock as well as CAO ever did. Clear is the only MCAO system operating at any solar observatory, and is the only MCAO system with more than two DMs, day or night. The BFI is a filtergraph made of an interference filter and

1962-455: A type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor shale and chert . The banded iron formations were laid down in the time between 3,700  million years ago and 1,800  million years ago . Materials containing finely ground iron(III) oxides or oxide-hydroxides, such as ochre , have been used as yellow, red, and brown pigments since pre-historical times. They contribute as well to

2071-435: A very large coordination and organometallic chemistry : indeed, it was the discovery of an iron compound, ferrocene , that revolutionalized the latter field in the 1950s. Iron is sometimes considered as a prototype for the entire block of transition metals, due to its abundance and the immense role it has played in the technological progress of humanity. Its 26 electrons are arranged in the configuration [Ar]3d 4s , of which

2180-437: A wave nature or a particle nature with René Descartes , Robert Hooke and Christiaan Huygens favouring a wave description and Newton favouring a particle description. Huygens in particular had a well developed theory from which he was able to derive the laws of reflection and refraction. Around 1801, Thomas Young measured the wavelength of a light beam with his two-slit experiment thus conclusively demonstrating that light

2289-412: Is able to ionize atoms, causing chemical reactions. Longer-wavelength radiation such as visible light is nonionizing; the photons do not have sufficient energy to ionize atoms. Throughout most of the electromagnetic spectrum, spectroscopy can be used to separate waves of different frequencies, so that the intensity of the radiation can be measured as a function of frequency or wavelength. Spectroscopy

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2398-646: Is also rarely found in basalts that have formed from magmas that have come into contact with carbon-rich sedimentary rocks, which have reduced the oxygen fugacity sufficiently for iron to crystallize. This is known as telluric iron and is described from a few localities, such as Disko Island in West Greenland, Yakutia in Russia and Bühl in Germany. Ferropericlase (Mg,Fe)O , a solid solution of periclase (MgO) and wüstite (FeO), makes up about 20% of

2507-632: Is an imaging spectrograph that, like the BFI, captures images of the Sun in narrow wavelength ranges. Instead of interference filters, however, VIS uses a Fabry–Pérot etalon to create a band-pass as narrow as 0.007 nm, tunable from 550 to 700 nm. VIS is frequently used to scan through the Fraunhofer lines at 656.3 nm ( H-alpha ), 630.2 nm ( Fe ), and 588.9 nm ( Na ). Per scan step multiple images frames are captured that also get processed for enhanced image detail. A dual Fabry–Pérot imaging interferometer for

2616-408: Is called fluorescence . UV fluorescence is used by forensics to detect any evidence like blood and urine, that is produced by a crime scene. Also UV fluorescence is used to detect counterfeit money and IDs, as they are laced with material that can glow under UV. At the middle range of UV, UV rays cannot ionize but can break chemical bonds, making molecules unusually reactive. Sunburn , for example,

2725-722: Is caused by the disruptive effects of middle range UV radiation on skin cells , which is the main cause of skin cancer . UV rays in the middle range can irreparably damage the complex DNA molecules in the cells producing thymine dimers making it a very potent mutagen . Due to skin cancer caused by UV, the sunscreen industry was invented to combat UV damage. Mid UV wavelengths are called UVB and UVB lights such as germicidal lamps are used to kill germs and also to sterilize water. The Sun emits UV radiation (about 10% of its total power), including extremely short wavelength UV that could potentially destroy most life on land (ocean water would provide some protection for life there). However, most of

2834-580: Is considered the transition from the Bronze Age to the Iron Age . In the modern world , iron alloys, such as steel , stainless steel , cast iron and special steels , are by far the most common industrial metals, due to their mechanical properties and low cost. The iron and steel industry is thus very important economically, and iron is the cheapest metal, with a price of a few dollars per kilogram or pound. Pristine and smooth pure iron surfaces are

2943-407: Is considered to be resistant to rust, due to its oxide layer. Iron forms various oxide and hydroxide compounds ; the most common are iron(II,III) oxide (Fe 3 O 4 ), and iron(III) oxide (Fe 2 O 3 ). Iron(II) oxide also exists, though it is unstable at room temperature. Despite their names, they are actually all non-stoichiometric compounds whose compositions may vary. These oxides are

3052-499: Is due to its abundant production during the runaway fusion and explosion of type Ia supernovae , which scatters the iron into space. Metallic or native iron is rarely found on the surface of the Earth because it tends to oxidize. However, both the Earth's inner and outer core , which together account for 35% of the mass of the whole Earth, are believed to consist largely of an iron alloy, possibly with nickel . Electric currents in

3161-474: Is experimentally well defined for pressures less than 50 GPa. For greater pressures, published data (as of 2007) still varies by tens of gigapascals and over a thousand kelvin. Below its Curie point of 770 °C (1,420 °F; 1,040 K), α-iron changes from paramagnetic to ferromagnetic : the spins of the two unpaired electrons in each atom generally align with the spins of its neighbors, creating an overall magnetic field . This happens because

3270-494: Is in Earth's crust only amounts to about 5% of the overall mass of the crust and is thus only the fourth most abundant element in that layer (after oxygen , silicon , and aluminium ). Most of the iron in the crust is combined with various other elements to form many iron minerals . An important class is the iron oxide minerals such as hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ), and siderite (FeCO 3 ), which are

3379-532: Is not harmless and does create oxygen radicals, mutations and skin damage. After UV come X-rays , which, like the upper ranges of UV are also ionizing. However, due to their higher energies, X-rays can also interact with matter by means of the Compton effect . Hard X-rays have shorter wavelengths than soft X-rays and as they can pass through many substances with little absorption, they can be used to 'see through' objects with 'thicknesses' less than that equivalent to

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3488-401: Is not like that of Mn with its weak, spin-forbidden d–d bands, because Fe has higher positive charge and is more polarizing, lowering the energy of its ligand-to-metal charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region. On

3597-407: Is possible, but nonetheless the sequence does effectively end at Ni because conditions in stellar interiors cause the competition between photodisintegration and the alpha process to favor photodisintegration around Ni. This Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in

3706-548: Is somewhat different). Pieces of magnetite with natural permanent magnetization ( lodestones ) provided the earliest compasses for navigation. Particles of magnetite were extensively used in magnetic recording media such as core memories , magnetic tapes , floppies , and disks , until they were replaced by cobalt -based materials. Iron has four stable isotopes : Fe (5.845% of natural iron), Fe (91.754%), Fe (2.119%) and Fe (0.282%). Twenty-four artificial isotopes have also been created. Of these stable isotopes, only Fe has

3815-442: Is such a strong oxidizing agent that it oxidizes ammonia to nitrogen (N 2 ) and water to oxygen: The pale-violet hex aquo complex [Fe(H 2 O) 6 ] is an acid such that above pH 0 it is fully hydrolyzed: As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous iron(III) oxide precipitates out of solution. Although Fe has a d configuration, its absorption spectrum

3924-502: Is supposed to have an orthorhombic or a double hcp structure. (Confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure has not changed. ) The inner core of the Earth is generally presumed to consist of an iron- nickel alloy with ε (or β) structure. The melting and boiling points of iron, along with its enthalpy of atomization , are lower than those of

4033-494: Is the part of the EM spectrum the human eye is the most sensitive to. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underlie human vision and plant photosynthesis. The light that excites the human visual system is a very small portion of the electromagnetic spectrum. A rainbow shows

4142-451: Is too long for ordinary dioxygen in air to absorb. This leaves less than 3% of sunlight at sea level in UV, with all of this remainder at the lower energies. The remainder is UV-A, along with some UV-B. The very lowest energy range of UV between 315 nm and visible light (called UV-A) is not blocked well by the atmosphere, but does not cause sunburn and does less biological damage. However, it

4251-451: Is used as the traditional "blue" in blueprints . Iron is the first of the transition metals that cannot reach its group oxidation state of +8, although its heavier congeners ruthenium and osmium can, with ruthenium having more difficulty than osmium. Ruthenium exhibits an aqueous cationic chemistry in its low oxidation states similar to that of iron, but osmium does not, favoring high oxidation states in which it forms anionic complexes. In

4360-437: Is used in chemical actinometry and along with its sodium salt undergoes photoreduction applied in old-style photographic processes. The dihydrate of iron(II) oxalate has a polymeric structure with co-planar oxalate ions bridging between iron centres with the water of crystallisation located forming the caps of each octahedron, as illustrated below. Iron(III) complexes are quite similar to those of chromium (III) with

4469-427: Is used to study the interactions of electromagnetic waves with matter. Humans have always been aware of visible light and radiant heat but for most of history it was not known that these phenomena were connected or were representatives of a more extensive principle. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, including reflection and refraction . Light

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4578-593: The CAO system has been routinely used since 2010 for the vast majority of observations and serves all post-focus instruments except CYRA. CAO is a classical adaptive optics system. It uses a Shack–Hartmann wavefront sensor that measures the average wavefront aberration over a field of view of 10 arcseconds and has a single DM with 357 actuators for wavefront correction. In 2016, the BBSO multi-conjugate AO ( MCAO ) called Clear with its three identical 357 actuator DMs enjoyed

4687-554: The Earth's crust , being mainly deposited by meteorites in its metallic state. Extracting usable metal from iron ores requires kilns or furnaces capable of reaching 1,500 °C (2,730 °F), about 500 °C (932 °F) higher than that required to smelt copper . Humans started to master that process in Eurasia during the 2nd millennium BC and the use of iron tools and weapons began to displace copper alloys – in some regions, only around 1200 BC. That event

4796-963: The radio spectrum is strictly regulated by governments, coordinated by the International Telecommunication Union (ITU) which allocates frequencies to different users for different uses. Microwaves are radio waves of short wavelength , from about 10 centimeters to one millimeter, in the SHF and EHF frequency bands. Microwave energy is produced with klystron and magnetron tubes, and with solid state devices such as Gunn and IMPATT diodes . Although they are emitted and absorbed by short antennas, they are also absorbed by polar molecules , coupling to vibrational and rotational modes, resulting in bulk heating. Unlike higher frequency waves such as infrared and visible light which are absorbed mainly at surfaces, microwaves can penetrate into materials and deposit their energy below

4905-432: The supernova remnant gas cloud, first to radioactive Co, and then to stable Fe. As such, iron is the most abundant element in the core of red giants , and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as Earth . It is also very common in the universe, relative to other stable metals of approximately the same atomic weight . Iron is the sixth most abundant element in

5014-491: The trans - chlorohydridobis(bis-1,2-(diphenylphosphino)ethane)iron(II) complex is used as a starting material for compounds with the Fe( dppe ) 2 moiety . The ferrioxalate ion with three oxalate ligands displays helical chirality with its two non-superposable geometries labelled Λ (lambda) for the left-handed screw axis and Δ (delta) for the right-handed screw axis, in line with IUPAC conventions. Potassium ferrioxalate

5123-466: The universe , and the most common refractory element. Although a further tiny energy gain could be extracted by synthesizing Ni , which has a marginally higher binding energy than Fe, conditions in stars are unsuitable for this process. Element production in supernovas greatly favor iron over nickel, and in any case, Fe still has a lower mass per nucleon than Ni due to its higher fraction of lighter protons. Hence, elements heavier than iron require

5232-537: The visible spectrum and the X-ray range. The UV wavelength spectrum ranges from 399 nm to 10 nm and is divided into 3 sections: UVA, UVB, and UVC. UV is the lowest energy range energetic enough to ionize atoms, separating electrons from them, and thus causing chemical reactions . UV, X-rays, and gamma rays are thus collectively called ionizing radiation ; exposure to them can damage living tissue. UV can also cause substances to glow with visible light; this

5341-456: The > 10 MeV region)—which is of higher energy than any nuclear gamma ray—is not called X-ray or gamma ray, but instead by the generic term of "high-energy photons". The region of the spectrum where a particular observed electromagnetic radiation falls is reference frame -dependent (due to the Doppler shift for light), so EM radiation that one observer would say is in one region of

5450-570: The 3d and 4s electrons are relatively close in energy, and thus a number of electrons can be ionized. Iron forms compounds mainly in the oxidation states +2 ( iron(II) , "ferrous") and +3 ( iron(III) , "ferric"). Iron also occurs in higher oxidation states , e.g., the purple potassium ferrate (K 2 FeO 4 ), which contains iron in its +6 oxidation state. The anion [FeO 4 ] with iron in its +7 oxidation state, along with an iron(V)-peroxo isomer, has been detected by infrared spectroscopy at 4 K after cocondensation of laser-ablated Fe atoms with

5559-650: The 7.6 eV (1.22 aJ) nuclear transition of thorium-229m ), and, despite being one million-fold less energetic than some muonic X-rays, the emitted photons are still called gamma rays due to their nuclear origin. The convention that EM radiation that is known to come from the nucleus is always called "gamma ray" radiation is the only convention that is universally respected, however. Many astronomical gamma ray sources (such as gamma ray bursts ) are known to be too energetic (in both intensity and wavelength) to be of nuclear origin. Quite often, in high-energy physics and in medical radiotherapy , very high energy EMR (in

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5668-424: The Earth's atmosphere to see astronomical X-rays, since the great depth of the atmosphere of Earth is opaque to X-rays (with areal density of 1000 g/cm ), equivalent to 10 meters thickness of water. This is an amount sufficient to block almost all astronomical X-rays (and also astronomical gamma rays—see below). After hard X-rays come gamma rays , which were discovered by Paul Ulrich Villard in 1900. These are

5777-603: The Earth's surface. Items made of cold-worked meteoritic iron have been found in various archaeological sites dating from a time when iron smelting had not yet been developed; and the Inuit in Greenland have been reported to use iron from the Cape York meteorite for tools and hunting weapons. About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Native iron

5886-530: The Sun of 50,000 km × 50,000 km (70 arcseconds) in the TiO line, and 40,000 km × 40,000 km (55 arcseconds) in the G-Band. Despite adaptive optics, each frame suffers from atmospheric aberrations hindering diffraction limited image detail. In order to obtain diffraction limited resolution, bursts of about 100 frames get digitally analyzed to be formed into a single sharpened image ( speckle-reconstruction ). The VIS

5995-429: The Sun's damaging UV wavelengths are absorbed by the atmosphere before they reach the surface. The higher energy (shortest wavelength) ranges of UV (called "vacuum UV") are absorbed by nitrogen and, at longer wavelengths, by simple diatomic oxygen in the air. Most of the UV in the mid-range of energy is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower energy part of which

6104-504: The amount of energy per quantum (photon) it carries. Spectroscopy can detect a much wider region of the EM spectrum than the visible wavelength range of 400  nm to 700 nm in a vacuum. A common laboratory spectroscope can detect wavelengths from 2 nm to 2500 nm. Detailed information about the physical properties of objects, gases, or even stars can be obtained from this type of device. Spectroscopes are widely used in astrophysics . For example, many hydrogen atoms emit

6213-450: The brown deposits present in a sizeable number of streams. Due to its electronic structure, iron has a very large coordination and organometallic chemistry. Many coordination compounds of iron are known. A typical six-coordinate anion is hexachloroferrate(III), [FeCl 6 ] , found in the mixed salt tetrakis(methylammonium) hexachloroferrate(III) chloride . Complexes with multiple bidentate ligands have geometric isomers . For example,

6322-844: The chemical mechanisms responsible for photosynthesis and the working of the visual system . The distinction between X-rays and gamma rays is partly based on sources: the photons generated from nuclear decay or other nuclear and subnuclear/particle process are always termed gamma rays, whereas X-rays are generated by electronic transitions involving highly energetic inner atomic electrons. In general, nuclear transitions are much more energetic than electronic transitions, so gamma rays are more energetic than X-rays, but exceptions exist. By analogy to electronic transitions, muonic atom transitions are also said to produce X-rays, even though their energy may exceed 6 megaelectronvolts (0.96 pJ), whereas there are many (77 known to be less than 10 keV (1.6 fJ)) low-energy nuclear transitions ( e.g. ,

6431-709: The color of various rocks and clays , including entire geological formations like the Painted Hills in Oregon and the Buntsandstein ("colored sandstone", British Bunter ). Through Eisensandstein (a jurassic 'iron sandstone', e.g. from Donzdorf in Germany) and Bath stone in the UK, iron compounds are responsible for the yellowish color of many historical buildings and sculptures. The proverbial red color of

6540-464: The cores of the Earth and other planets. Above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another hexagonal close-packed (hcp) structure, which is also known as ε-iron . The higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa and temperatures of at least 1500 K. It

6649-401: The domains in the new positions, so that the effect persists even after the external field is removed – thus turning the iron object into a (permanent) magnet . Similar behavior is exhibited by some iron compounds, such as the ferrites including the mineral magnetite , a crystalline form of the mixed iron(II,III) oxide Fe 3 O 4 (although the atomic-scale mechanism, ferrimagnetism ,

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6758-479: The earlier 3d elements from scandium to chromium , showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus; however, they are higher than the values for the previous element manganese because that element has a half-filled 3d sub-shell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium . The melting point of iron

6867-436: The effects of Compton scattering . Iron Iron is a chemical element ; it has the symbol Fe (from Latin ferrum  'iron') and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table . It is, by mass, the most common element on Earth , forming much of Earth's outer and inner core . It is the fourth most abundant element in

6976-436: The electromagnetic spectrum covers the range from roughly 300 GHz to 400 THz (1 mm – 750 nm). It can be divided into three parts: Above infrared in frequency comes visible light . The Sun emits its peak power in the visible region, although integrating the entire emission power spectrum through all wavelengths shows that the Sun emits slightly more infrared than visible light. By definition, visible light

7085-809: The electromagnetic spectrum was filled in with the discovery of gamma rays . In 1900, Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation that he at first thought consisted of particles similar to known alpha and beta particles , but with the power of being far more penetrating than either. However, in 1910, British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914, Ernest Rutherford (who had named them gamma rays in 1903 when he realized that they were fundamentally different from charged alpha and beta particles) and Edward Andrade measured their wavelengths, and found that gamma rays were similar to X-rays, but with shorter wavelengths. The wave-particle debate

7194-406: The exception of iron(III)'s preference for O -donor instead of N -donor ligands. The latter tend to be rather more unstable than iron(II) complexes and often dissociate in water. Many Fe–O complexes show intense colors and are used as tests for phenols or enols . For example, in the ferric chloride test , used to determine the presence of phenols, iron(III) chloride reacts with a phenol to form

7303-445: The eyes, this results in visual perception of the scene. The brain's visual system processes the multitude of reflected frequencies into different shades and hues, and through this insufficiently understood psychophysical phenomenon, most people perceive a bowl of fruit. At most wavelengths, however, the information carried by electromagnetic radiation is not directly detected by human senses. Natural sources produce EM radiation across

7412-407: The field. Analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light . This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave. Maxwell's equations predicted an infinite range of frequencies of electromagnetic waves , all traveling at the speed of light. This

7521-403: The following three physical properties: the frequency f , wavelength λ , or photon energy E . Frequencies observed in astronomy range from 2.4 × 10  Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency, so gamma rays have very short wavelengths that are fractions of

7630-462: The global stock of iron in use in society is 2,200 kg per capita. More-developed countries differ in this respect from less-developed countries (7,000–14,000 vs 2,000 kg per capita). Ocean science demonstrated the role of the iron in the ancient seas in both marine biota and climate. Iron shows the characteristic chemical properties of the transition metals , namely the ability to form variable oxidation states differing by steps of one and

7739-570: The increasing order of wavelength, which is characteristic of the type of radiation. There are no precisely defined boundaries between the bands of the electromagnetic spectrum; rather they fade into each other like the bands in a rainbow (which is the sub-spectrum of visible light). Radiation of each frequency and wavelength (or in each band) has a mix of properties of the two regions of the spectrum that bound it. For example, red light resembles infrared radiation in that it can excite and add energy to some chemical bonds and indeed must do so to power

7848-453: The liquid outer core are believed to be the origin of the Earth's magnetic field . The other terrestrial planets ( Mercury , Venus , and Mars ) as well as the Moon are believed to have a metallic core consisting mostly of iron. The M-type asteroids are also believed to be partly or mostly made of metallic iron alloy. The rare iron meteorites are the main form of natural metallic iron on

7957-446: The literature, this mineral phase of the lower mantle is also often called magnesiowüstite. Silicate perovskite may form up to 93% of the lower mantle, and the magnesium iron form, (Mg,Fe)SiO 3 , is considered to be the most abundant mineral in the Earth, making up 38% of its volume. While iron is the most abundant element on Earth, most of this iron is concentrated in the inner and outer cores. The fraction of iron that

8066-425: The low end of the band the atmosphere is mainly transparent, at the upper end of the band absorption of microwaves by atmospheric gases limits practical propagation distances to a few kilometers. Terahertz radiation or sub-millimeter radiation is a region of the spectrum from about 100 GHz to 30 terahertz (THz) between microwaves and far infrared which can be regarded as belonging to either band. Until recently,

8175-525: The low-frequency end of the spectrum, have the lowest photon energy and the longest wavelengths—thousands of kilometers , or more. They can be emitted and received by antennas , and pass through the atmosphere, foliage, and most building materials. Gamma rays, at the high-frequency end of the spectrum, have the highest photon energies and the shortest wavelengths—much smaller than an atomic nucleus . Gamma rays, X-rays, and extreme ultraviolet rays are called ionizing radiation because their high photon energy

8284-407: The major ores of iron . Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite . During weathering , iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as iron(III) oxide . Large deposits of iron are banded iron formations ,

8393-612: The meteorites Semarkona and Chervony Kut, a correlation between the concentration of Ni, the granddaughter of Fe, and the abundance of the stable iron isotopes provided evidence for the existence of Fe at the time of formation of the Solar System . Possibly the energy released by the decay of Fe, along with that released by Al , contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of Ni present in extraterrestrial material may bring further insight into

8502-708: The most energetic photons , having no defined lower limit to their wavelength. In astronomy they are valuable for studying high-energy objects or regions, however as with X-rays this can only be done with telescopes outside the Earth's atmosphere. Gamma rays are used experimentally by physicists for their penetrating ability and are produced by a number of radioisotopes . They are used for irradiation of foods and seeds for sterilization, and in medicine they are occasionally used in radiation cancer therapy . More commonly, gamma rays are used for diagnostic imaging in nuclear medicine , an example being PET scans . The wavelength of gamma rays can be measured with high accuracy through

8611-767: The near-infrared from 1.0 to 1.7 μm. A cryogenic Czerny-Turner spectrograph for the 1 to 5 μm regime. A scanning echelle long-slit spectrograph. Electromagnetic spectrum The electromagnetic spectrum is the full range of electromagnetic radiation , organized by frequency or wavelength . The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high frequency these are: radio waves , microwaves , infrared , visible light , ultraviolet , X-rays , and gamma rays . The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications. Radio waves, at

8720-559: The necessary levels, human iron metabolism requires a minimum of iron in the diet. Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. At least four allotropes of iron (differing atom arrangements in the solid) are known, conventionally denoted α , γ , δ , and ε . The first three forms are observed at ordinary pressures. As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has

8829-550: The optical (visible) part of the electromagnetic spectrum; infrared (if it could be seen) would be located just beyond the red side of the rainbow whilst ultraviolet would appear just beyond the opposite violet end. Electromagnetic radiation with a wavelength between 380 nm and 760 nm (400–790 terahertz) is detected by the human eye and perceived as visible light. Other wavelengths, especially near infrared (longer than 760 nm) and ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when

8938-436: The orbitals of those two electrons (d z and d x − y ) do not point toward neighboring atoms in the lattice, and therefore are not involved in metallic bonding. In the absence of an external source of magnetic field, the atoms get spontaneously partitioned into magnetic domains , about 10 micrometers across, such that the atoms in each domain have parallel spins, but some domains have other orientations. Thus

9047-539: The origin and early history of the Solar System . The most abundant iron isotope Fe is of particular interest to nuclear scientists because it represents the most common endpoint of nucleosynthesis . Since Ni (14 alpha particles ) is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (see silicon burning process ), it is the endpoint of fusion chains inside extremely massive stars . Although adding more alpha particles

9156-549: The other group 8 elements , ruthenium and osmium . Iron forms compounds in a wide range of oxidation states , −4 to +7. Iron also forms many coordination compounds ; some of them, such as ferrocene , ferrioxalate , and Prussian blue have substantial industrial, medical, or research applications. The body of an adult human contains about 4 grams (0.005% body weight) of iron, mostly in hemoglobin and myoglobin . These two proteins play essential roles in oxygen transport by blood and oxygen storage in muscles . To maintain

9265-444: The other hand, the pale green iron(II) hexaquo ion [Fe(H 2 O) 6 ] does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises quickly in air to form iron(III) oxide that accounts for

9374-581: The oxidizing power of Fe and the high reducing power of I : Ferric iodide, a black solid, is not stable in ordinary conditions, but can be prepared through the reaction of iron pentacarbonyl with iodine and carbon monoxide in the presence of hexane and light at the temperature of −20 °C, with oxygen and water excluded. Complexes of ferric iodide with some soft bases are known to be stable compounds. The standard reduction potentials in acidic aqueous solution for some common iron ions are given below: The red-purple tetrahedral ferrate (VI) anion

9483-497: The past work on isotopic composition of iron has focused on the nucleosynthesis of Fe through studies of meteorites and ore formation. In the last decade, advances in mass spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work is driven by the Earth and planetary science communities, although applications to biological and industrial systems are emerging. In phases of

9592-441: The primary focus before the secondary mirror limits the field of view to 120 arcseconds in order to reduce the solar heat load on subsequent optics. The GST is mounted on an equatorial mount made by DFM Engineering inside a ventilated dome resembling 5/8 of a sphere. The Goode Solar Telescope deploys adaptive optical systems to mitigate image blur caused by atmospheric turbulence . With its single deformable mirror (DM),

9701-414: The principal ores for the production of iron (see bloomery and blast furnace). They are also used in the production of ferrites , useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS 2 ), also known as fool's gold owing to its golden luster. It is not an iron(IV) compound, but is actually an iron(II) polysulfide containing Fe and S 2 ions in

9810-531: The properties of microwaves . These new types of waves paved the way for inventions such as the wireless telegraph and the radio . In 1895, Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage . He called this radiation " x-rays " and found that they were able to travel through parts of the human body but were reflected or stopped by denser matter such as bones. Before long, many uses were found for this radiography . The last portion of

9919-522: The range was rarely studied and few sources existed for microwave energy in the so-called terahertz gap , but applications such as imaging and communications are now appearing. Scientists are also looking to apply terahertz technology in the armed forces, where high-frequency waves might be directed at enemy troops to incapacitate their electronic equipment. Terahertz radiation is strongly absorbed by atmospheric gases, making this frequency range useless for long-distance communication. The infrared part of

10028-437: The second half of the 3d transition series, vertical similarities down the groups compete with the horizontal similarities of iron with its neighbors cobalt and nickel in the periodic table, which are also ferromagnetic at room temperature and share similar chemistry. As such, iron, cobalt, and nickel are sometimes grouped together as the iron triad . Unlike many other metals, iron does not form amalgams with mercury . As

10137-436: The size of atoms , whereas wavelengths on the opposite end of the spectrum can be indefinitely long. Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts ), while radio wave photons have very low energy (around a femtoelectronvolt ). These relations are illustrated by the following equations: where: Whenever electromagnetic waves travel in

10246-402: The spectrum could appear to an observer moving at a substantial fraction of the speed of light with respect to the first to be in another part of the spectrum. For example, consider the cosmic microwave background . It was produced when matter and radiation decoupled, by the de- excitation of hydrogen atoms to the ground state . These photons were from Lyman series transitions, putting them in

10355-399: The spectrum, and technology can also manipulate a broad range of wavelengths. Optical fiber transmits light that, although not necessarily in the visible part of the spectrum (it is usually infrared), can carry information. The modulation is similar to that used with radio waves. Next in frequency comes ultraviolet (UV). In frequency (and thus energy), UV rays sit between the violet end of

10464-498: The spectrum, as though these were different types of radiation. Thus, although these "different kinds" of electromagnetic radiation form a quantitatively continuous spectrum of frequencies and wavelengths, the spectrum remains divided for practical reasons arising from these qualitative interaction differences. Radio waves are emitted and received by antennas , which consist of conductors such as metal rod resonators . In artificial generation of radio waves, an electronic device called

10573-422: The spectrum, noticed what he called "chemical rays" (invisible light rays that induced certain chemical reactions). These behaved similarly to visible violet light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation. The study of electromagnetism began in 1820 when Hans Christian Ørsted discovered that electric currents produce magnetic fields ( Oersted's law ). Light

10682-564: The surface of Mars is derived from an iron oxide-rich regolith . Significant amounts of iron occur in the iron sulfide mineral pyrite (FeS 2 ), but it is difficult to extract iron from it and it is therefore not exploited. In fact, iron is so common that production generally focuses only on ores with very high quantities of it. According to the International Resource Panel 's Metal Stocks in Society report ,

10791-503: The surface. This effect is used to heat food in microwave ovens , and for industrial heating and medical diathermy . Microwaves are the main wavelengths used in radar , and are used for satellite communication , and wireless networking technologies such as Wi-Fi . The copper cables ( transmission lines ) which are used to carry lower-frequency radio waves to antennas have excessive power losses at microwave frequencies, and metal pipes called waveguides are used to carry them. Although at

10900-471: The ultraviolet (UV) part of the electromagnetic spectrum. Now this radiation has undergone enough cosmological red shift to put it into the microwave region of the spectrum for observers moving slowly (compared to the speed of light) with respect to the cosmos. Electromagnetic radiation interacts with matter in different ways across the spectrum. These types of interaction are so different that historically different names have been applied to different parts of

11009-421: The visibility to humans is not relevant. White light is a combination of lights of different wavelengths in the visible spectrum. Passing white light through a prism splits it up into the several colours of light observed in the visible spectrum between 400 nm and 780 nm. If radiation having a frequency in the visible region of the EM spectrum reflects off an object, say, a bowl of fruit, and then strikes

11118-455: The volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO 3 ; it also is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction γ- (Mg,Fe) 2 [SiO 4 ] ↔ (Mg,Fe)[SiO 3 ] + (Mg,Fe)O transforms γ-olivine into a mixture of silicate perovskite and ferropericlase and vice versa. In

11227-431: The waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light. Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media , in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin . In a later experiment, Hertz similarly produced and measured

11336-415: Was a wave. In 1800, William Herschel discovered infrared radiation. He was studying the temperature of different colours by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red. He theorized that this temperature change was due to "calorific rays", a type of light ray that could not be seen. The next year, Johann Ritter , working at the other end of

11445-653: Was cast from Zerodur by Schott and polished at the Richard F. Caris Mirror Laboratory Archived 2019-04-19 at the Wayback Machine of the University of Arizona . The figure error with respect to a parabola is 16 nm RMS . The secondary mirror , a concave ellipsoid , is mounted on a hexapod to compensate for thermal expansion and bending of the telescope structure keeping the mirror in its optimal position. A reflective, liquid-cooled circular field-stop in

11554-423: Was first linked to electromagnetism in 1845, when Michael Faraday noticed that the polarization of light traveling through a transparent material responded to a magnetic field (see Faraday effect ). During the 1860s, James Clerk Maxwell developed four partial differential equations ( Maxwell's equations ) for the electromagnetic field . Two of these equations predicted the possibility and behavior of waves in

11663-442: Was intensively studied from the beginning of the 17th century leading to the invention of important instruments like the telescope and microscope . Isaac Newton was the first to use the term spectrum for the range of colours that white light could be split into with a prism . Starting in 1666, Newton showed that these colours were intrinsic to light and could be recombined into white light. A debate arose over whether light had

11772-578: Was rekindled in 1901 when Max Planck discovered that light is absorbed only in discrete " quanta ", now called photons , implying that light has a particle nature. This idea was made explicit by Albert Einstein in 1905, but never accepted by Planck and many other contemporaries. The modern position of science is that electromagnetic radiation has both a wave and a particle nature, the wave-particle duality . The contradictions arising from this position are still being debated by scientists and philosophers. Electromagnetic waves are typically described by any of

11881-507: Was the first indication of the existence of the entire electromagnetic spectrum. Maxwell's predicted waves included waves at very low frequencies compared to infrared, which in theory might be created by oscillating charges in an ordinary electrical circuit of a certain type. Attempting to prove Maxwell's equations and detect such low frequency electromagnetic radiation, in 1886, the physicist Heinrich Hertz built an apparatus to generate and detect what are now called radio waves . Hertz found

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