1.
Hydrogen spectral series
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The emission spectrum of atomic hydrogen is divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two levels in the atom. The classification of the series by the Rydberg formula was important in the development of quantum mechanics, the spectral series are important in astronomical spectroscopy for detecting the presence of hydrogen and calculating red shifts. A hydrogen atom consists of an electron orbiting its nucleus, the electromagnetic force between the electron and the nuclear proton leads to a set of quantum states for the electron, each with its own energy. These states were visualized by the Bohr model of the atom as being distinct orbits around the nucleus. Each energy state, or orbit, is designated by an integer, Spectral emission occurs when an electron transitions, or jumps, from a higher energy state to a lower energy state. To distinguish the two states, the energy state is commonly designated as n′, and the higher energy state is designated as n. The energy of a photon corresponds to the energy difference between the two states. Because the energy of state is fixed, the energy difference between them is fixed, and the transition will always produce a photon with the same energy. The spectral lines are grouped into series according to n′, lines are named sequentially starting from the longest wavelength/lowest frequency of the series, using Greek letters within each series. For example, the 2 →1 line is called Lyman-alpha, there are emission lines from hydrogen that fall outside of these series, such as the 21 cm line. These emission lines correspond to much rarer atomic events such as hyperfine transitions, the fine structure also results in single spectral lines appearing as two or more closely grouped thinner lines, due to relativistic corrections. Meaningful values are returned only when n is greater than n′, note that this equation is valid for all hydrogen-like species, i. e. atoms having only a single electron, and the particular case of hydrogen spectral lines are given by Z=1. The series is named after its discoverer, Theodore Lyman, who discovered the lines from 1906–1914. All the wavelengths in the Lyman series are in the ultraviolet band, named after Johann Balmer, who discovered the Balmer formula, an empirical equation to predict the Balmer series, in 1885. Balmer lines are referred to as H-alpha, H-beta, H-gamma and so on. Four of the Balmer lines are in the visible part of the spectrum, with wavelengths longer than 400 nm. Parts of the Balmer series can be seen in the solar spectrum, H-alpha is an important line used in astronomy to detect the presence of hydrogen
2.
Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
3.
Atomic physics
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Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and this comprises ions, neutral atoms and, unless otherwise stated, it can be assumed that the term atom includes ions. The term atomic physics can be associated with power and nuclear weapons, due to the synonymous use of atomic. Physicists distinguish between atomic physics — which deals with the atom as a system consisting of a nucleus and electrons — and nuclear physics, which considers atomic nuclei alone. As with many fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of atomic, molecular. Physics research groups are usually so classified, Atomic physics primarily considers atoms in isolation. Atomic models will consist of a nucleus that may be surrounded by one or more bound electrons. It is not concerned with the formation of molecules, nor does it examine atoms in a state as condensed matter. It is concerned with such as ionization and excitation by photons or collisions with atomic particles. This means that the atoms can be treated as if each were in isolation. By this consideration atomic physics provides the underlying theory in physics and atmospheric physics. Electrons form notional shells around the nucleus and these are normally in a ground state but can be excited by the absorption of energy from light, magnetic fields, or interaction with a colliding particle. Electrons that populate a shell are said to be in a bound state, the energy necessary to remove an electron from its shell is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy, the atom is said to have undergone the process of ionization. If the electron absorbs a quantity of less than the binding energy. After a certain time, the electron in a state will jump to a lower state. In a neutral atom, the system will emit a photon of the difference in energy, if an inner electron has absorbed more than the binding energy, then a more outer electron may undergo a transition to fill the inner orbital. The Auger effect allows one to multiply ionize an atom with a single photon, there are rather strict selection rules as to the electronic configurations that can be reached by excitation by light — however there are no such rules for excitation by collision processes
4.
Spectral line
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Spectral lines are often used to identify atoms and molecules from their characteristic spectral lines. Spectral lines are the result of interaction between a system and a single photon. When a photon has about the amount of energy to allow a change in the energy state of the system. A spectral line may be observed either as a line or an absorption line. Which type of line is observed depends on the type of material, an absorption line is produced when photons from a hot, broad spectrum source pass through a cold material. The intensity of light, over a frequency range, is reduced due to absorption by the material. By contrast, a bright, emission line is produced when photons from a hot material are detected in the presence of a spectrum from a cold source. The intensity of light, over a frequency range, is increased due to emission by the material. Spectral lines are highly atom-specific, and can be used to identify the composition of any medium capable of letting light pass through it. Several elements were discovered by means, such as helium, thallium. Mechanisms other than atom-photon interaction can produce spectral lines, depending on the exact physical interaction, the frequency of the involved photons will vary widely, and lines can be observed across the electromagnetic spectrum, from radio waves to gamma rays. In other cases the lines are designated according to the level of ionization by adding a Roman numeral to the designation of the chemical element, so that Ca+ also has the designation Ca II. Neutral atoms are denoted with the roman number I, singly ionized atoms with II, more detailed designations usually include the line wavelength and may include a multiplet number or band designation. Many spectral lines of hydrogen also have designations within their respective series. A spectral line extends over a range of frequencies, not a single frequency, in addition, its center may be shifted from its nominal central wavelength. There are several reasons for this broadening and shift and these reasons may be divided into two general categories – broadening due to local conditions and broadening due to extended conditions. Broadening due to conditions is due to effects which hold in a small region around the emitting element. Broadening due to extended conditions may result from changes to the distribution of the radiation as it traverses its path to the observer
5.
Hydrogen atom
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A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the mass of the universe. In everyday life on Earth, isolated hydrogen atoms are extremely rare, instead, hydrogen tends to combine with other atoms in compounds, or with itself to form ordinary hydrogen gas, H2. Atomic hydrogen and hydrogen atom in ordinary English use have overlapping, yet distinct, for example, a water molecule contains two hydrogen atoms, but does not contain atomic hydrogen. Attempts to develop an understanding of the hydrogen atom have been important to the history of quantum mechanics. The most abundant isotope, hydrogen-1, protium, or light hydrogen, contains no neutrons and is just a proton, protium is stable and makes up 99. 9885% of naturally occurring hydrogen by absolute number. Deuterium contains one neutron and one proton, deuterium is stable and makes up 0. 0115% of naturally occurring hydrogen and is used in industrial processes like nuclear reactors and Nuclear Magnetic Resonance. Tritium contains two neutrons and one proton and is not stable, decaying with a half-life of 12.32 years, because of the short half life, Tritium does not exist in nature except in trace amounts. Higher isotopes of hydrogen are only created in artificial accelerators and reactors and have half lives around the order of 10−22 seconds, the formulas below are valid for all three isotopes of hydrogen, but slightly different values of the Rydberg constant must be used for each hydrogen isotope. Hydrogen is not found without its electron in ordinary chemistry, as ionized hydrogen is highly chemically reactive. When ionized hydrogen is written as H+ as in the solvation of classical acids such as hydrochloric acid, in that case, the acid transfers the proton to H2O to form H3O+. Ionized hydrogen without its electron, or free protons, are common in the interstellar medium, experiments by Ernest Rutherford in 1909 showed the structure of the atom to be a dense, positive nucleus with a light, negative charge orbiting around it. This immediately caused problems on how such a system could be stable, classical electromagnetism had shown that any accelerating charge radiates energy described through the Larmor formula. If this were true, all atoms would instantly collapse, however seem to be stable. Furthermore, the spiral inward would release a smear of electromagnetic frequencies as the orbit got smaller, instead, atoms were observed to only emit discrete frequencies of radiation. The resolution would lie in the development of quantum mechanics, in 1913, Niels Bohr obtained the energy levels and spectral frequencies of the hydrogen atom after making a number of simple assumptions in order to correct the failed classical model. The assumptions included, Electrons can only be in certain, discrete circular orbits or stationary states, thereby having a set of possible radii
6.
Johann Jakob Balmer
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Johann Jakob Balmer was a Swiss mathematician and mathematical physicist. Balmer was born in Lausen, Switzerland, the son of a Chief Justice also named Johann Jakob Balmer and his mother was Elizabeth Rolle Balmer, and he was the oldest son. During his schooling he excelled in mathematics, and so decided to focus on that field when he attended university. He studied at the University of Karlsruhe and the University of Berlin, Johann then spent his entire life in Basel, where he taught at a school for girls. He also lectured at the University of Basel, in 1868 he married Christine Pauline Rinck at the age of 43. The couple had a total of six children, in his 1885 notice, he referred to h as the fundamental number of hydrogen. Balmer then used this formula to predict the wavelength for m =7, two of his colleagues, Hermann Wilhelm Vogel and William Huggins, were able to confirm the existence of other lines of the series in the spectrum of hydrogen in white stars. Balmers formula was found to be a special case of the Rydberg formula. 1 λ =4 h = R H with R H being the Rydberg constant for hydrogen, n 1 =2 for Balmers formula, and n 2 > n 1. A full explanation of why these formulas worked, however, had to wait until the presentation of the Bohr model of the atom by Niels Bohr in 1913, Balmer lines and Balmer series are named after him. The crater Balmer on the Moon is named after him, minor planet 12755 Balmer is named after him. OConnor, John J. Robertson, Edmund F. Johann Jakob Balmer, MacTutor History of Mathematics archive, University of St Andrews
7.
Spectrum
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A spectrum is a condition that is not limited to a specific set of values but can vary, without steps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism, as scientific understanding of light advanced, it came to apply to the entire electromagnetic spectrum. Spectrum has since been applied by analogy to topics outside of optics, thus, one might talk about the spectrum of political opinion, or the spectrum of activity of a drug, or the autism spectrum. In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or definitions, such uses imply a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion. Nonscientific uses of the spectrum are sometimes misleading. For instance, a single left–right spectrum of opinion does not capture the full range of peoples political beliefs. Political scientists use a variety of biaxial and multiaxial systems to accurately characterize political opinion. In most modern usages of spectrum there is a theme between the extremes at either end. This was not always true in older usage, in Latin spectrum means image or apparition, including the meaning spectre. Spectral evidence is testimony about what was done by spectres of persons not present physically and it was used to convict a number of persons of witchcraft at Salem, Massachusetts in the late 17th century. The word spectrum was used to designate a ghostly optical afterimage by Goethe in his Theory of Colors and Schopenhauer in On Vision. The prefix spectro- is used to form words relating to spectra, for example, a spectrometer is a device used to record spectra and spectroscopy is the use of a spectrometer for chemical analysis. In the 17th century the word spectrum was introduced into optics by Isaac Newton, soon the term referred to a plot of light intensity or power as a function of frequency or wavelength, also known as a spectral density plot. The term spectrum was expanded to apply to other waves, such as sound waves that could also be measured as a function of frequency, frequency spectrum and power spectrum of a signal. The term now applies to any signal that can be measured or decomposed along a variable such as energy in electron spectroscopy or mass to charge ratio in mass spectrometry. Spectrum is also used to refer to a representation of the signal as a function of the dependent variable. Devices used to measure an electromagnetic spectrum are called spectrograph or spectrometer, the visible spectrum is the part of the electromagnetic spectrum that can be seen by the human eye. The wavelength of light ranges from 390 to 700 nm
8.
Light
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Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to light, which is visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m. This wavelength means a range of roughly 430–750 terahertz. The main source of light on Earth is the Sun, sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the used by living things. Historically, another important source of light for humans has been fire, with the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence, for example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. Visible light, as all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term sometimes refers to electromagnetic radiation of any wavelength. In this sense, gamma rays, X-rays, microwaves and radio waves are also light, like all types of light, visible light is emitted and absorbed in tiny packets called photons and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality, the study of light, known as optics, is an important research area in modern physics. Generally, EM radiation, or EMR, is classified by wavelength into radio, microwave, infrared, the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths, when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. There exist animals that are sensitive to various types of infrared, infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it, above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nanometers and the internal lens below 400. Furthermore, the rods and cones located in the retina of the eye cannot detect the very short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, various sources define visible light as narrowly as 420 to 680 to as broadly as 380 to 800 nm
9.
Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
10.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
11.
Metre
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The metre or meter, is the base unit of length in the International System of Units. The metre is defined as the length of the path travelled by light in a vacuum in 1/299792458 seconds, the metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a metre bar. In 1960, the metre was redefined in terms of a number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted, the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Measuring devices are spelled -meter in all variants of English, the suffix -meter has the same Greek origin as the unit of length. This range of uses is found in Latin, French, English. Thus calls for measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. In 1668, Wilkins proposed using Christopher Wrens suggestion of defining the metre using a pendulum with a length which produced a half-period of one second, christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches. This is the equivalent of what is now known to be 997 mm, no official action was taken regarding this suggestion. In the 18th century, there were two approaches to the definition of the unit of length. One favoured Wilkins approach, to define the metre in terms of the length of a pendulum which produced a half-period of one second. The other approach was to define the metre as one ten-millionth of the length of a quadrant along the Earths meridian, that is, the distance from the Equator to the North Pole. This means that the quadrant would have defined as exactly 10000000 metres at that time. To establish a universally accepted foundation for the definition of the metre, more measurements of this meridian were needed. This portion of the meridian, assumed to be the length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator
12.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
13.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
14.
Bohr model
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After the cubic model, the plum-pudding model, the Saturnian model, and the Rutherford model came the Rutherford–Bohr model or just Bohr model for short. The improvement to the Rutherford model is mostly a physical interpretation of it. The models key success lay in explaining the Rydberg formula for the emission lines of atomic hydrogen. While the Rydberg formula had been known experimentally, it did not gain a theoretical underpinning until the Bohr model was introduced. Not only did the Bohr model explain the reason for the structure of the Rydberg formula, the Bohr model is a relatively primitive model of the hydrogen atom, compared to the valence shell atom. A related model was proposed by Arthur Erich Haas in 1910. The quantum theory of the period between Plancks discovery of the quantum and the advent of a quantum mechanics is often referred to as the old quantum theory. In the early 20th century, experiments by Ernest Rutherford established that atoms consisted of a cloud of negatively charged electrons surrounding a small, dense. The laws of mechanics, predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would rapidly spiral inwards and this atom model is disastrous, because it predicts that all atoms are unstable. Also, as the electron spirals inward, the emission would rapidly increase in frequency as the orbit got smaller and faster and this would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharges have shown that atoms will emit light at certain discrete frequencies. To overcome this difficulty, Niels Bohr proposed, in 1913 and he suggested that electrons could only have certain classical motions, Electrons in atoms orbit the nucleus. The electrons can only orbit stably, without radiating, in certain orbits at a discrete set of distances from the nucleus. These orbits are associated with definite energies and are called energy shells or energy levels. In these orbits, the electrons acceleration does not result in radiation, the Bohr model of an atom was based upon Plancks quantum theory of radiation. The frequency of the radiation emitted at an orbit of period T is as it would be in classical mechanics, it is the reciprocal of the orbit period. The significance of the Bohr model is that the laws of classical mechanics apply to the motion of the electron about the nucleus only when restricted by a quantum rule, is called the principal quantum number, and ħ = h/2π
15.
H-alpha
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H-alpha is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm, it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha light is important to astronomers as it is emitted by many emission nebulae and can be used to observe features in the Suns atmosphere, according to the Bohr model of the atom, electrons exist in quantized energy levels surrounding the atoms nucleus. These energy levels are described by the quantum number n =1,2,3. Electrons may only exist in these states, and may only transit between these states, for the Lyman series the naming convention is, n =2 to n =1 is called Lyman-alpha, n =3 to n =1 is called Lyman-beta, etc. H-alpha has a wavelength of 656.281 nm, is visible in the red part of the electromagnetic spectrum, instead, after being ionized, the electron and proton recombine to form a new hydrogen atom. In the new atom, the electron may begin in any energy level, approximately half the time, this cascade will include the n =3 to n =2 transition and the atom will emit H-alpha light. Therefore, the H-alpha line occurs where hydrogen is being ionized, instead, molecules such as carbon dioxide, carbon monoxide, formaldehyde, ammonia, or acetonitrile are typically used to determine the mass of a cloud. A hydrogen-alpha filter is a filter designed to transmit a narrow bandwidth of light generally centred on the H-alpha wavelength. They are characterized by a width that measures the width of the wavelength band that is transmitted. These filters can be dichroic filters manufactured by multiple vacuum-deposited layers and these layers are selected to produce interference effects that filter out any wavelengths except at the requisite band. Taken in isolation, H-alpha dichroic filters are useful in astrophotography and they do not have narrow enough bandwidth for observing the suns atmosphere. This combination will pass only a range of wavelengths of light centred on the H-alpha emission line. The physics of the etalon and the dichroic interference filters are essentially the same, due to the high velocities sometimes associated with features visible in H-alpha light, solar H-alpha etalons can often be tuned to cope with the associated Doppler effect. Commercially available H-alpha filters for amateur solar observing usually state bandwidths in Angstrom units and are typically 0. 7Å, by using a second etalon, this can be reduced to 0. 5Å leading to improved contrast in details observed on the suns disc. An even more narrow band filter can be using a Lyot filter. Hydrogen spectral series Rydberg formula Spectrohelioscope Description of etalon filter by Colin Kaminski
16.
Electromagnetic spectrum
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The electromagnetic spectrum is the collective term for all known frequencies and their linked wavelengths of the known photons. The electromagnetic spectrum of an object has a different meaning, and is instead the characteristic distribution of radiation emitted or absorbed by that particular object. Visible light lies toward the end, with wavelengths from 400 to 700 nanometres. The limit for long wavelengths is the size of the universe itself, until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous. Nearly all types of radiation can be used for spectroscopy, to study. Other technological uses are described under electromagnetic radiation, for most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, the study of light continued, and during the 16th and 17th centuries conflicting theories regarded light as either a wave or a particle. The first discovery of electromagnetic radiation other than visible light came in 1800 and he was studying the temperature of different colors by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red and he theorized that this temperature change was due to calorific rays that were a type of light ray that could not be seen. The next year, Johann Ritter, working at the end of the spectrum. These behaved similarly to visible light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation, during the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and behavior of, 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, maxwells equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light. This was the first indication of the existence of the electromagnetic spectrum. Maxwells predicted waves included waves at very low compared to infrared. Hertz found the waves and was able to infer 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 the properties of microwaves
17.
Red
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Red is the color at the longer-wavelengths end of the spectrum of visible light next to orange, at the opposite end from violet. Red color has a predominant light wavelength of roughly 620–740 nanometers, light with a longer wavelength than red but shorter than terahertz radiation and microwave is called infrared. Red is one of the secondary colors, resulting from the combination of yellow. Traditionally, it was viewed as a primary colour, along with yellow and blue, in the RYB color space and traditional color wheel formerly used by painters. Reds can vary in shade from light pink to very dark maroon or burgundy. Red is the color of cyan. In nature, the red color of blood comes from hemoglobin, the red color of the Grand Canyon and other geological features is caused by hematite or red ochre, both forms of iron oxide. It also causes the red color of the planet Mars, the color of autumn leaves is caused by pigments called anthocyanins, which are produced towards the end of summer, when the green chlorophyll is no longer produced. One to two percent of the population has red hair, the color is produced by high levels of the reddish pigment pheomelanin. Since red is the color of blood, it has historically been associated with sacrifice, danger, modern surveys in the United States and Europe show red is also the color most commonly associated with heat, activity, passion, sexuality, anger, love and joy. In China, India and many other Asian countries it is the color of symbolizing happiness, since the 19th century, red has also been associated with socialism and communism. The word red is derived from the Old English rēad, the word can be further traced to the Proto-Germanic rauthaz and the Proto-Indo European root rewdʰ-. In Sanskrit, the word means red or blood. In the Akkadian language of Ancient Mesopotamia and in the modern Inuit language of Inuit, the words for colored in Latin and Spanish both also mean red. In Portuguese the word for red is vermelho, which comes from Latin vermiculus, in the Russian language, the word for red, Кра́сный, comes from the same old Slavic root as the words for beautiful—красивый and excellent—прекрасный. Thus Red Square in Moscow, named long before the Russian Revolution, in heraldry, the word gules is used for red. Red can vary in hue from orange-red to violet-red, and for each hue there is a variety of shades and tints. Red hematite powder was found scattered around the remains at a grave site in a Zhoukoudian cave complex near Beijing
18.
Blue
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Blue is the colour between violet and green on the optical spectrum of visible light. Human eyes perceive blue when observing light with a wavelength between 450 and 495 nanometres, which is between 4500 and 4950 ångströms. Blues with a frequency and thus a shorter wavelength gradually look more violet, while those with a lower frequency. Pure blue, in the middle, has a wavelength of 470 nanometers, in painting and traditional colour theory, blue is one of the three primary colours of pigments, along with red and yellow, which can be mixed to form a wide gamut of colours. Red and blue mixed together form violet, blue and yellow together form green, Blue is also a primary colour in the RGB colour model, used to create all the colours on the screen of a television or computer monitor. The clear sky and the sea appear blue because of an optical effect known as Rayleigh scattering. When sunlight passes through the atmosphere, the wavelengths are scattered more widely by the oxygen and nitrogen molecules. An optical effect called Tyndall scattering, similar to Rayleigh scattering, explains blue eyes, distant objects appear more blue because of another optical effect called atmospheric perspective. Blue has been used for art and decoration since ancient times and it is the most important color in Judaism. In the Middle Ages, cobalt blue was used to colour the stained glass windows of cathedrals, beginning in the 9th century, Chinese artists used cobalt to make fine blue and white porcelain. Blue dyes for clothing were made from woad in Europe and indigo in Asia, in 1828 a synthetic ultramarine pigment was developed, and synthetic blue dyes and pigments gradually replaced mineral pigments and vegetable dyes. Pierre-Auguste Renoir, Vincent van Gogh and other late 19th century painters used ultramarine and cobalt blue not just to depict nature, in the late 18th century and 19th century, blue became a popular colour for military uniforms and police uniforms. In the 20th century, because blue was associated with harmony, it was chosen as the colour of the flags of the United Nations. Surveys in the US and Europe show that blue is the colour most commonly associated with harmony, faithfulness, confidence, distance, infinity, the imagination, cold, and sometimes with sadness. In US and European public opinion polls it is the most popular colour, Blue is the colour of light between violet and green on the visible spectrum. Blues also vary in shade or tint, darker shades of blue contain black or grey, darker shades of blue include ultramarine, cobalt blue, navy blue, and Prussian blue, while lighter tints include sky blue, azure, and Egyptian blue. Today most blue pigments and dyes are made by a chemical process, the modern English word blue comes from Middle English bleu or blewe, from the Old French bleu, a word of Germanic origin, related to the Old High German word blao. In heraldry, the azure is used for blue
19.
Rydberg formula
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The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. It was formulated by the Swedish physicist Johannes Rydberg, and presented on 5 November 1888, in 1880, Rydberg worked on a formula describing the relation between the wavelengths in spectral lines of alkali metals. He noticed that lines came in series and he found that he could simplify his calculations by using the wavenumber as his unit of measurement and he plotted the wavenumbers of successive lines in each series against consecutive integers which represented the order of the lines in that particular series. Finding that the curves were similarly shaped, he sought a single function which could generate all of them. This did not work very well, Rydberg therefore rewrote Balmers formula in terms of wavenumbers, as n = n 0 −4 n 0 m 2. This suggested that the Balmer formula for hydrogen might be a case with m ′ =0 and C0 =4 n 0, where n 0 =1 h. The term Co was found to be a universal constant common to all elements and this constant is now known as the Rydberg constant, and m is known as the quantum defect. As stressed by Niels Bohr, expressing results in terms of wavenumber, the fundamental role of wavenumbers was also emphasized by the Rydberg-Ritz combination principle of 1908. The fundamental reason for this lies in quantum mechanics, lights wavenumber is proportional to frequency 1 λ = f c, and therefore also proportional to lights quantum energy E. Thus,1 λ = E h c. Rydbergs 1888 classical expression for the form of the series was not accompanied by a physical explanation. In Bohrs conception of the atom, the integer Rydberg n numbers represent electron orbitals at different integral distances from the atom. A frequency emitted in a transition from n1 to n2 therefore represents the energy emitted or absorbed when an electron makes a jump from orbital 1 to orbital 2. Later models found that the values for n1 and n2 corresponded to the quantum numbers of the two orbitals. The number of protons in the nucleus of this element, n 1 and n 2 are integers such that n 1 < n 2, corresponding to the principal quantum numbers of the orbitals occupied before. Examples would include He+, Li2+, Be3+ etc. where no other electrons exist in the atom and this is analogous to the Lyman-alpha line transition for hydrogen, and has the same frequency factor. Its frequency is thus the Lyman-alpha hydrogen frequency, increased by a factor of 2. This formula of f = c/λ = ⋅2 is historically known as Moseleys law, see the biography of Henry Moseley for the historical importance of this law, which was derived empirically at about the same time it was explained by the Bohr model of the atom. Rydberg–Ritz combination principle Balmer series Hydrogen line Sutton, Mike, getting the numbers right, The lonely struggle of the 19th century physicist/chemist Johannes Rydberg
20.
Visible spectrum
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The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called light or simply light. A typical human eye will respond to wavelengths from about 390 to 700 nm, in terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not, however, contain all the colors that the human eyes, unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths. Colors containing only one wavelength are called pure colors or spectral colors. Visible wavelengths pass through the window, the region of the electromagnetic spectrum that allows wavelengths to pass largely unattenuated through the Earths atmosphere. An example of this phenomenon is that clean air scatters blue light more than red wavelengths, the optical window is also referred to as the visible window because it overlaps the human visible response spectrum. The near infrared window lies just out of the vision, as well as the Medium Wavelength IR window. In the 13th century, Roger Bacon theorized that rainbows were produced by a process to the passage of light through glass or crystal. In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light and he was the first to use the word spectrum in this sense in print in 1671 in describing his experiments in optics. The result is red light is bent less sharply than violet as it passes through the prism. Newton divided the spectrum into seven named colors, red, orange, yellow, green, blue, indigo, the human eye is relatively insensitive to indigos frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right. However, the evidence indicates that what Newton meant by indigo, comparing Newtons observation of prismatic colors to a color image of the visible light spectrum shows that indigo corresponds to what is today called blue, whereas blue corresponds to cyan. In the 18th century, Goethe wrote about optical spectra in his Theory of Colours, Goethe used the word spectrum to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors. Goethe argued that the spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow, the spectrum appears only when these edges are close enough to overlap. Young was the first to measure the wavelengths of different colors of light, the connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century
21.
Emission nebula
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An emission nebula is a nebula formed of ionized gases that emit light of various colors. The most common source of ionization is high-energy photons emitted from a hot star. Usually, a star will ionize part of the same cloud from which it was born although only massive. In many emission nebulae, an cluster of young stars is doing the work. The nebulas color depends on its composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its low energy of ionization. If more energy is available, other elements will be ionized and green, by examining the spectra of nebulae, astronomers infer their chemical content. Most emission nebulae are about 90% hydrogen, with the helium, oxygen, nitrogen. Further in the southern hemisphere is the bright Carina Nebula NGC3372, emission nebulae often have dark areas in them which result from clouds of dust which block the light. Many nebulae are made up of both reflection and emission components such as the Trifid Nebula
22.
Orion Nebula
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The Orion Nebula is a diffuse nebula situated in the Milky Way, being south of Orions Belt in the constellation of Orion. It is one of the brightest nebulae, and is visible to the eye in the night sky. M42 is located at a distance of 1,344 ±20 light years and is the closest region of star formation to Earth. The M42 nebula is estimated to be 24 light years across and it has a mass of about 2000 times the mass of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula, the Orion Nebula is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely studied celestial features. The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas, astronomers have directly observed protoplanetary disks, brown dwarfs, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula. The nebula is visible with the eye even from areas affected by some light pollution. It is seen as the star in the sword of Orion. The star appears fuzzy to sharp-eyed observers, and the nebulosity is obvious through binoculars or a small telescope, the peak surface brightness of the central region is about 17 Mag/arcsec2 and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec2. The Orion Nebula contains a young open cluster, known as the Trapezium due to the asterism of its primary four stars. Two of these can be resolved into their component binary systems on nights with good seeing, giving a total of six stars, the stars of the Trapezium, along with many other stars, are still in their early years. The Trapezium is a component of the much larger Orion Nebula Cluster, observers have long noted a distinctive greenish tint to the nebula, in addition to regions of red and of blue-violet. The red hue is a result of the Hα recombination line radiation at a wavelength of 656.3 nm, the blue-violet coloration is the reflected radiation from the massive O-class stars at the core of the nebula. The green hue was a puzzle for astronomers in the part of the 20th century because none of the known spectral lines at that time could explain it. There was some speculation that the lines were caused by a new element, and this radiation was all but impossible to reproduce in the laboratory at the time, because it depended on the quiescent and nearly collision-free environment found in the high vacuum of deep space. This has led to speculation that a flare-up of the illuminating stars may have increased the brightness of the nebula. The first published observation of the nebula was by the Jesuit mathematician, charles Messier first noted the nebula on March 4,1769, and he also noted three of the stars in Trapezium. Messier published the first edition of his catalog of deep sky objects in 1774, as the Orion Nebula was the 42nd object in his list, it became identified as M42
23.
H II region
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An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. The short-lived blue stars created in these regions emit copious amounts of light that ionize the surrounding gas. H II regions—sometimes several hundred light-years across—are often associated with giant molecular clouds, the Orion Nebula, now known to be an H II region, was observed in 1610 by Nicolas-Claude Fabri de Peiresc by telescope, the first such object discovered. The term H II is pronounced H two by astronomers, such regions may be of any shape, because the distribution of the stars and gas inside them is irregular. They often appear clumpy and filamentary, sometimes showing bizarre shapes such as the Horsehead Nebula, H II regions may give birth to thousands of stars over a period of several million years. H II regions can be seen to considerable distances in the universe, spiral and irregular galaxies contain many H II regions, while elliptical galaxies are almost devoid of them. In spiral galaxies, including our Milky Way, H II regions are concentrated in the spiral arms, some galaxies contain huge H II regions, which may contain tens of thousands of stars. Examples include the 30 Doradus region in the Large Magellanic Cloud, a few of the brightest H II regions are visible to the naked eye. However, none seem to have been noticed before the advent of the telescope in the early 17th century, even Galileo did not notice the Orion Nebula when he first observed the star cluster within it. The French observer Nicolas-Claude Fabri de Peiresc is credited with the discovery of the Orion Nebula in 1610, since that early observation large numbers of H II regions have been discovered in the Milky Way and other galaxies. William Herschel observed the Orion Nebula in 1774, and described it later as an unformed fiery mist, confirmation of Herschels hypothesis of star formation had to wait another hundred years, when William Huggins together with his wife Mary Huggins turned his spectroscope on various nebulae. Some, such as the Andromeda Nebula, had quite similar to those of stars. Rather than a strong continuum with absorption lines superimposed, the Orion Nebula, in planetary nebulae, the brightest of these spectral lines was at a wavelength of 500.7 nanometres, which did not correspond with a line of any known chemical element. However, while helium was isolated on earth soon after its discovery in the spectrum of the sun, nebulium was not. In the early 20th century, Henry Norris Russell proposed that rather than being a new element, interstellar matter, considered dense in an astronomical context, is at high vacuum by laboratory standards. Electron transitions from these levels in doubly ionized oxygen give rise to the 500.7 nm line and these spectral lines, which can only be seen in very low density gases, are called forbidden lines. Spectroscopic observations thus showed that planetary nebulae consisted largely of extremely rarefied ionised oxygen gas, in H II regions, however, the dominant spectral line has a wavelength of 656.3 nm. This is the well-known H-alpha line emitted by atomic hydrogen, specifically, a photon of this wavelength is emitted when the electron of a hydrogen atom changes its excitation state from n=3 to n=2
24.
Fine structure
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In atomic physics, the fine structure describes the splitting of the spectral lines of atoms due to electron spin and relativistic corrections to the non-relativistic Schrödinger equation. The gross structure of spectra is the line spectra predicted by the quantum mechanics of non-relativistic electrons with no spin. For a hydrogenic atom, the gross structure energy levels depend on the principal quantum number n. However, an accurate model takes into account relativistic and spin effects. The fine structure energy corrections can be obtained by using perturbation theory, to do this one adds three corrective terms to the Hamiltonian, the leading order relativistic correction to the kinetic energy, the correction due to the spin-orbit coupling, and the Darwinian term. These corrections can also be obtained from the limit of the Dirac equation, since Diracs theory naturally incorporates relativity. Classically, the energy term of the Hamiltonian is T = p 22 m where p is the momentum. However, when considering a more accurate theory of nature via, R is the distance of the electron from the nucleus. The spin-orbit correction can be understood by shifting from the frame of reference into one where the electron is stationary. In this case the orbiting nucleus functions as a current loop. However, the electron itself has a magnetic moment due to its angular momentum. The two magnetic vectors, B → and μ → s couple together so there is a certain energy cost depending on their relative orientation. Remark, On the = and = energy level, which the fine structure said their level are the same, if we take the g-factor to be 2.0031904622, then, the calculated energy level will be different by using 2 as g-factor. Only using 2 as the g-factor, we can match the level in the 1st order approximation of the relativistic correction. When using the higher order approximation for the term, the 2.0031904622 g-factor may agree with each other. However, if we use the g-factor as 2.0031904622, the result does not agree with the formula, there is one last term in the non-relativistic expansion of the Dirac equation. This is because the function of an electron with l >0 vanishes at the origin. For example, it gives the 2s-orbit the same energy as the 2p-orbit by raising the 2s-state by 9. 057×10−5 eV, the Darwin term changes the effective potential at the nucleus
25.
Deuterium arc lamp
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A deuterium arc lamp is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the ultraviolet region is needed. Plasma arc or discharge lamps using hydrogen are notable for their output in the ultraviolet, with comparatively little output in the visible. This is similar to the situation in a hydrogen flame, arc lamps made with ordinary light-hydrogen provide a very similar UV spectrum to deuterium, and have been used in UV spectroscopes. However, lamps using deuterium have a life span and an emissivity at the far end of their UV range which is three to five times that of an ordinary hydrogen arc bulb, at the same temperature. Deuterium arc lamps, therefore, despite being several times more expensive, are considered a light source to light-hydrogen arc lamps. A deuterium lamp uses a tungsten filament and anode placed on opposite sides of a box structure designed to produce the best output spectrum. Unlike an incandescent bulb, the filament is not the source of light in deuterium lamps, instead an arc is created from the filament to the anode, a similar process to arc lamps. Because the filament must be very hot before it can operate, because the discharge process produces its own heat, the heater is turned down after discharge begins. Although firing voltages are 300 to 500 volts, once the arc is created voltages drop to around 100 to 200 volts, the arc created excites the molecular deuterium contained within the bulb to a higher energy state. The deuterium then emits light as it transitions back to its initial state and this continuous cycle is the origin of the continuous UV radiation. This process is not the same as the process of decay of excited states. Instead, a molecular emission process, where radiative decay of excited states in molecular deuterium and this causes a larger population of molecules and a greater emissivity of UV in the molecular part of the spectrum that is farthest into the ultraviolet. Because the lamp operates at high temperatures, normal glass housings cannot be used for a casing and they would also block UV radiation. Instead, a fused quartz, UV glass, or magnesium fluoride envelope is used depending on the function of the lamp. The typical lifetime of a lamp is approximately 2000 hours. The deuterium lamp emits radiation extending from 112 nm to 900 nm, the spectrum intensity does not actually decrease from 250 nm to 300 nm as shown in the spectrum plot above. The decrease in the plot is due to decreased efficiency at low wavelengths of the detector used to measure the lamp intensity. The deuterium lamps continuous spectrum is useful as both a reference in UV radiometric work and to generate a signal in various photometric devices, due to the high intensity of UV radiation emitted by the bulb, eye protection is suggested when using a deuterium bulb
26.
Spectroscopy
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Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers, daily observations of color can be related to spectroscopy. Neon lighting is an application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies, neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their characteristics in order to generate specific colors. A commonly encountered molecular spectrum is that of nitrogen dioxide, gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky, Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms, Spectroscopy is also used in astronomy and remote sensing on earth. The measured spectra are used to determine the composition and physical properties of astronomical objects. One of the concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums, mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency and this plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Plancks constant, spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states
27.
Johannes Rydberg
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The physical constant known as the Rydberg constant is named after him, as is the Rydberg unit. Excited atoms with very high values of the quantum number. Rydbergs anticipation that spectral studies could assist in an understanding of the atom. An important spectroscopic constant based on an atom of infinite mass is called the Rydberg in his honour. He was active at Lund University, Sweden, for all of his working life, the crater Rydberg on the Moon and asteroid 10506 Rydberg are named in his honour. There is a pub night held in Rydbergs honour every Wednesday at the Department of Physics at Lund University, Rydberg matter Rydberg state Rydberg atom Sutton, Mike. “Getting the numbers right – the lonely struggle of Rydberg. ”Martinson, Indrek, Curtis, L. J. Janne Rydberg – his life, oConnor, John J. Robertson, Edmund F. Johannes Rydberg, MacTutor History of Mathematics archive, University of St Andrews
28.
Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
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Universe
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The Universe is all of time and space and its contents. It includes planets, moons, minor planets, stars, galaxies, the contents of intergalactic space, the size of the entire Universe is unknown. The earliest scientific models of the Universe were developed by ancient Greek and Indian philosophers and were geocentric, over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of gravitation, Sir Isaac Newton built upon Copernicuss work as well as observations by Tycho Brahe. Further observational improvements led to the realization that our Solar System is located in the Milky Way galaxy and it is assumed that galaxies are distributed uniformly and the same in all directions, meaning that the Universe has neither an edge nor a center. Discoveries in the early 20th century have suggested that the Universe had a beginning, the majority of mass in the Universe appears to exist in an unknown form called dark matter. The Big Bang theory is the prevailing cosmological description of the development of the Universe, under this theory, space and time emerged together 13. 799±0.021 billion years ago with a fixed amount of energy and matter that has become less dense as the Universe has expanded. After the initial expansion, the Universe cooled, allowing the first subatomic particles to form, giant clouds later merged through gravity to form galaxies, stars, and everything else seen today. Some physicists have suggested various multiverse hypotheses, in which the Universe might be one among many universes that likewise exist, the Universe can be defined as everything that exists, everything that has existed, and everything that will exist. According to our current understanding, the Universe consists of spacetime, forms of energy, the Universe encompasses all of life, all of history, and some philosophers and scientists suggest that it even encompasses ideas such as mathematics and logic. The word universe derives from the Old French word univers, which in turn derives from the Latin word universum, the Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used. Another synonym was ὁ κόσμος ho kósmos, synonyms are also found in Latin authors and survive in modern languages, e. g. the German words Das All, Weltall, and Natur for Universe. The same synonyms are found in English, such as everything, the cosmos, the world, the prevailing model for the evolution of the Universe is the Big Bang theory. The Big Bang model states that the earliest state of the Universe was extremely hot and dense, the model is based on general relativity and on simplifying assumptions such as homogeneity and isotropy of space. The Big Bang model accounts for such as the correlation of distance and redshift of galaxies, the ratio of the number of hydrogen to helium atoms. The initial hot, dense state is called the Planck epoch, after the Planck epoch and inflation came the quark, hadron, and lepton epochs. Together, these epochs encompassed less than 10 seconds of time following the Big Bang, the observed abundance of the elements can be explained by combining the overall expansion of space with nuclear and atomic physics. As the Universe expands, the density of electromagnetic radiation decreases more quickly than does that of matter because the energy of a photon decreases with its wavelength
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Stellar classification
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In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with absorption lines, each line indicates an ion of a certain chemical element, with the line strength indicating the abundance of that ion. The relative abundance of the different ions varies with the temperature of the photosphere, the spectral class of a star is a short code summarizing the ionization state, giving an objective measure of the photospheres temperature and density. Most stars are classified under the Morgan–Keenan system using the letters O, B, A, F, G, K, and M. Each letter class is subdivided using a numeric digit with 0 being hottest and 9 being coolest. The sequence has been expanded with classes for other stars and star-like objects that do not fit in the system, such as class D for white dwarfs. In the MK system, a luminosity class is added to the class using Roman numerals. This is based on the width of absorption lines in the stars spectrum. The full spectral class for the Sun is then G2V, indicating a main-sequence star with a temperature around 5,800 K, the conventional color description takes into account only the peak of the stellar spectrum. This means that the assignment of colors of the spectrum can be misleading. There are no green, indigo, or violet stars, likewise, the brown dwarfs do not literally appear brown. The modern classification system is known as the Morgan–Keenan classification, each star is assigned a spectral class from the older Harvard spectral classification and a luminosity class using Roman numerals as explained below, forming the stars spectral type. The spectral classes O through M, as well as more specialized classes discussed later, are subdivided by Arabic numerals. For example, A0 denotes the hottest stars in the A class, fractional numbers are allowed, for example, the star Mu Normae is classified as O9.7. The Sun is classified as G2, the conventional color descriptions are traditional in astronomy, and represent colors relative to the mean color of an A-class star, which is considered to be white. The apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. However, most stars in the sky, except the brightest ones, red supergiants are cooler and redder than dwarfs of the same spectral type, and stars with particular spectral features such as carbon stars may be far redder than any black body. O-, B-, and A-type stars are called early type
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Radial velocity
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The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the velocity is the component of the objects velocity that points in the direction of the radius connecting the object. In astronomy, the point is taken to be the observer on Earth. In astronomy, radial velocity is measured to the first order of approximation by Doppler spectroscopy. The quantity obtained by this method may be called the barycentric radial-velocity measure or spectroscopic radial velocity, by contrast, astrometric radial velocity is determined by astrometric observations. A positive radial velocity indicates the distance between the objects is or was increasing, a radial velocity indicates the distance between the source and observer is or was decreasing. In many binary stars, the orbital motion usually causes radial velocity variations of several kilometers per second, as the spectra of these stars vary due to the Doppler effect, they are called spectroscopic binaries. Radial velocity can be used to estimate the ratio of the masses of the stars and it has been suggested that planets with high eccentricities calculated by this method may in fact be two-planet systems of circular or near-circular resonant orbit. When the star moves towards us, its spectrum is blueshifted, by regularly looking at the spectrum of a star—and so, measuring its velocity—it can be determined, if it moves periodically due to the influence of a companion. From the instrumental perspective, velocities are measured relative to the telescopes motion, in the case of spectroscopic measurements corrections of the order of ±20 cm/s with respect to aberration. Proper motion Peculiar velocity Relative velocity The Radial Velocity Equation in the Search for Exoplanets
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Doppler effect
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The Doppler effect is the change in frequency or wavelength of a wave for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, a common example of Doppler shift is the change of pitch heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the frequency, the received frequency is higher during the approach, identical at the instant of passing by. When the source of the waves is moving towards the observer, therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency, while they are travelling, the distance between successive wave fronts is reduced, so the waves bunch together. The distance between wave fronts is then increased, so the waves spread out. For waves that propagate in a medium, such as sound waves, the total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately, for waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered. Doppler first proposed this effect in 1842 in his treatise Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels, the hypothesis was tested for sound waves by Buys Ballot in 1845. He confirmed that the pitch was higher than the emitted frequency when the sound source approached him. Hippolyte Fizeau discovered independently the same phenomenon on electromagnetic waves in 1848, in Britain, John Scott Russell made an experimental study of the Doppler effect. The frequency is decreased if either is moving away from the other, the above formula assumes that the source is either directly approaching or receding from the observer. If the source approaches the observer at an angle, the frequency that is first heard is higher than the objects emitted frequency. When the observer is close to the path of the object. When the observer is far from the path of the object, to understand what happens, consider the following analogy. Someone throws one ball every second at a man, assume that balls travel with constant velocity. If the thrower is stationary, the man will receive one every second. However, if the thrower is moving towards the man, he will receive balls more frequently because the balls will be spaced out
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Binary star
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A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems and these systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of star systems. The term double star is used synonymously with binary star, however. Optical doubles are so called because the two stars close together in the sky as seen from the Earth, they are almost on the same line of sight. Nevertheless, their doubleness depends only on this effect, the stars themselves are distant from one another. A double star can be revealed as optical by means of differences in their measurements, proper motions. Most known double stars have not been studied closely to determine whether they are optical doubles or they are doubles physically bound through gravitation into a multiple star system. This also determines an empirical mass-luminosity relationship from which the masses of stars can be estimated. Binary stars are often detected optically, in case they are called visual binaries. Many visual binaries have long periods of several centuries or millennia. They may also be detected by indirect techniques, such as spectroscopy or astrometry, if components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, examples of binaries are Sirius, and Cygnus X-1. Binary stars are common as the nuclei of many planetary nebulae. This should be called a double star, and any two stars that are thus mutually connected, form the binary sidereal system which we are now to consider. By the modern definition, the binary star is generally restricted to pairs of stars which revolve around a common center of mass. Binary stars which can be resolved with a telescope or interferometric methods are known as visual binaries, for most of the known visual binary stars one whole revolution has not been observed yet, they are observed to have travelled along a curved path or a partial arc. The more general term double star is used for pairs of stars which are seen to be together in the sky
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Exoplanet
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An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first scientific detection of an exoplanet was in 1988, HARPS has discovered about a hundred exoplanets while the Kepler space telescope has found more than two thousand. Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives, on average, there is at least one planet per star, with a percentage having multiple planets. About 1 in 5 Sun-like stars have an Earth-sized planet in the habitable zone, the least massive planet known is Draugr, which is about twice the mass of the Moon. There are planets that are so near to their star that they take only a few hours to orbit, some are so far out that it is difficult to tell whether they are gravitationally bound to the star. Almost all of the planets detected so far are within the Milky Way, the nearest exoplanet is Proxima Centauri b, located 4.2 light-years from Earth and orbiting Proxima Centauri, the closest star to the Sun. The discovery of exoplanets has intensified interest in the search for extraterrestrial life, there is special interest in planets that orbit in a stars habitable zone, where it is possible for liquid water, a prerequisite for life on Earth, to exist on the surface. The study of planetary habitability also considers a range of other factors in determining the suitability of a planet for hosting life. The rogue planets in the Milky Way possibly number in the billions, the convention for designating exoplanets is an extension of the system used for designating multiple-star systems as adopted by the International Astronomical Union. For exoplanets orbiting a star, the designation is normally formed by taking the name or, more commonly, designation of its parent star. The first planet discovered in a system is given the designation b, if several planets in the same system are discovered at the same time, the closest one to the star gets the next letter, followed by the other planets in order of orbital size. A provisional IAU-sanctioned standard exists to accommodate the designation of circumbinary planets, a limited number of exoplanets have IAU-sanctioned proper names. Various detection claims made in the century were rejected by astronomers. The first scientific detection of an exoplanet began in 1988, However, the first confirmed detection came in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a star was made in 1995. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method, in the eighteenth century the same possibility was mentioned by Isaac Newton in the General Scholium that concludes his Principia. Claims of exoplanet detections have been made since the nineteenth century, some of the earliest involve the binary star 70 Ophiuchi. In 1855 William Stephen Jacob at the East India Companys Madras Observatory reported that orbital anomalies made it highly probable that there was a body in this system
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Neutron star
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A neutron star is the collapsed core of a large star. Neutron stars are the smallest and densest stars known to exist, though neutron stars typically have a radius on the order of 10 km, they can have masses of about twice that of the Sun. They result from the explosion of a massive star, combined with gravitational collapse. They are supported against further collapse by neutron degeneracy pressure, a described by the Pauli exclusion principle. If the remnant has too great a density, something which occurs in excess of a limit of the size of neutron stars at 2–3 solar masses. Neutron stars that can be observed are very hot and typically have a temperature around 6×105 K. They are so dense that a normal-sized matchbox containing neutron-star material would have a mass of approximately 3 billion tonnes and their magnetic fields are between 108 and 1015 times as strong as that of the Earth. The gravitational field at the stars surface is about 2×1011 times that of the Earth. As the stars core collapses, its rotation rate increases as a result of conservation of angular momentum, some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars. Indeed, the discovery of pulsars in 1967 was the first observational suggestion that stars exist. The radiation from pulsars is thought to be emitted from regions near their magnetic poles. The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c. There are thought to be around 100 million neutron stars in the Milky Way, however, most are old and cold, and neutron stars can only be easily detected in certain instances, such as if they are a pulsar or part of a binary system. Soft gamma repeaters are conjectured to be a type of neutron star with strong magnetic fields, known as magnetars, or alternatively. Additionally, such accretion can recycle old pulsars and potentially cause them to mass and spin-up to very fast rotation rates. The merger of binary stars may be the source of short-duration gamma-ray bursts and are likely strong sources of gravitational waves. Any main-sequence star with a mass of above 8 times the mass of the sun has the potential to produce a neutron star. As the star evolves away from the sequence, subsequent nuclear burning produces an iron-rich core
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Black hole
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A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon, although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like a black body. Moreover, quantum theory in curved spacetime predicts that event horizons emit Hawking radiation. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. Black holes were considered a mathematical curiosity, it was during the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality, black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings, by absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies, despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an accretion disk heated by friction. If there are other stars orbiting a black hole, their orbits can be used to determine the black holes mass, such observations can be used to exclude possible alternatives such as neutron stars.3 million solar masses. On 15 June 2016, a detection of a gravitational wave event from colliding black holes was announced. The idea of a body so massive that light could not escape was briefly proposed by astronomical pioneer John Michell in a letter published in 1783-4. Michell correctly noted that such supermassive but non-radiating bodies might be detectable through their effects on nearby visible bodies. In 1915, Albert Einstein developed his theory of general relativity, only a few months later, Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the solution for the point mass. This solution had a peculiar behaviour at what is now called the Schwarzschild radius, the nature of this surface was not quite understood at the time
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Accretion disk
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An accretion disk is a structure formed by diffused material in orbital motion around a massive central body. The central body is typically a star, gravity causes material in the disk to spiral inward towards the central body. Gravitational and frictional forces compress and raise the temperature of the material, the frequency range of that radiation depends on the central objects mass. Accretion disks of stars and protostars radiate in the infrared. The study of modes in accretion disks is referred to as diskoseismology. Accretion disks are a phenomenon in astrophysics, active galactic nuclei, protoplanetary disks. These disks very often give rise to astrophysical jets coming from the vicinity of the central object, jets are an efficient way for the star-disk system to shed angular momentum without losing too much mass. The most spectacular accretion disks found in nature are those of active galactic nuclei and of quasars, as matter enters the accretion disc, it follows a trajectory called a tendex line, which describes an inward spiral. The loss of angular momentum manifests as a reduction in velocity, at a slower velocity, as the particle falls to this lower orbit, a portion of its gravitational potential energy is converted to increased velocity and the particle gains speed. Thus, the particle has lost energy even though it is now travelling faster than before, however, the large luminosity of quasars is believed to be a result of gas being accreted by supermassive black holes. Elliptical accretion disks formed at tidal disruption of stars can be typical in galactic nuclei, Accretion process can convert about 10 percent to over 40 percent of the mass of an object into energy as compared to around 0.7 percent for nuclear fusion processes. A gas flow then develops from the star to the primary. Angular momentum conservation prevents a straight flow from one star to the other, Accretion disks surrounding T Tauri stars or Herbig stars are called protoplanetary disks because they are thought to be the progenitors of planetary systems. The accreted gas in this case comes from the molecular cloud out of which the star has formed rather than a companion star, in the 1940s, models were first derived from basic physical principles. In order to agree with observations, those models had to invoke a yet unknown mechanism for angular momentum redistribution, if matter is to fall inwards it must lose not only gravitational energy but also lose angular momentum. In other words, angular momentum should be transported outwards for matter to accrete and this prevents the existence of a hydrodynamic mechanism for angular momentum transport. On one hand, it was clear that viscous stresses would eventually cause the matter towards the center to heat up, on the other hand, viscosity itself was not enough to explain the transport of angular momentum to the exterior parts of the disk. Turbulence-enhanced viscosity was the thought to be responsible for such angular-momentum redistribution
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Moving group
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In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. The subject of stellar kinematics encompasses the measurement of velocities in the Milky Way. Stellar kinematics is related to but distinct from the subject of stellar dynamics, the component of stellar motion toward or away from the Sun, known as radial velocity, can be measured from the spectrum shift caused by the Doppler effect. The transverse, or proper motion must be found by taking a series of positional determinations against more distant objects, once the distance to a star is determined through astrometric means such as parallax, the space velocity can be computed. This is the actual motion relative to the Sun or the local standard of rest. The Suns motion with respect to the LSR is called the solar motion. The peculiar motion of the Sun with respect to the LSR is = km/s, with statistical uncertainty km/s, the stars in the Milky Way can be subdivided into two general populations, based on their metallicity, or proportion of elements with atomic numbers higher than helium. Among nearby stars, it has found that population I, higher metallicity stars have generally lower velocities than older. The latter have elliptical orbits that are inclined to the plane of the Milky Way, comparison of the kinematics of nearby stars has also led to the identification of stellar associations. These are most likely groups of stars share a common point of origin in giant molecular clouds. Within the Milky Way, there are three components of stellar kinematics, the disk, halo and bulge or bar. The halo may be subdivided into an inner and outer halo, with the inner halo having a net prograde motion with respect to the Milky Way. Depending on the definition, a high-velocity star is a star moving faster than 65 km/s to 100 km/s relative to the motion of the stars in the Suns neighbourhood. The velocity is sometimes defined as supersonic relative to the surrounding interstellar medium. The three types of high-velocity stars are, runaway stars, halo stars and hypervelocity stars, a runaway star is one that is moving through space with an abnormally high velocity relative to the surrounding interstellar medium. The proper motion of a star often points exactly away from a stellar association, of which the star was formerly a member. In the second scenario, an explosion in a multiple star system can result in the remaining components moving away at high speed. Although both mechanisms are possible, astronomers generally favour the supernova mechanism as more common in practice
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Star cluster
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Star clusters or star clouds are groups of stars. Star clusters visible to the eye include Pleiades, Hyades. Globular clusters, or GC, are roughly spherical groupings of from 10,000 to several million stars packed into regions of from 10 to 30 light years across. They commonly consist of very old Population II stars—just a few hundred years younger than the universe itself—which are mostly yellow and red. Such stars predominate within clusters because hotter and more stars have exploded as supernovae. Yet a few rare blue stars exist in globulars, thought to be formed by mergers in their dense inner regions. In our galaxy, globular clusters are distributed roughly spherically in the halo, around the galactic centre. Super star clusters, such as Westerlund 1 in the Milky Way, may be the precursors of globular clusters. Our galaxy has about 150 globular clusters, some of which may have captured from small galaxies disrupted by the Milky Way. Some galaxies are much richer in globulars, the giant elliptical galaxy M87 contains over a thousand. A few of the brightest globular clusters are visible to the eye, with the brightest, Omega Centauri, having been known since antiquity. The best known globular cluster in the northern hemisphere is M13, in 2005, astronomers discovered a completely new type of star cluster in the Andromeda Galaxy, which is, in several ways, very similar to globular clusters. Currently, there are not any intermediate clusters discovered in the Milky Way, the three discovered in Andromeda Galaxy are M31WFS C1 M31WFS C2, and M31WFS C3. These new-found star clusters contain hundreds of thousands of stars, a number of stars that can be found in globular clusters. The clusters also share characteristics with globular clusters, e. g. the stellar populations. What distinguishes them from the clusters is that they are much larger – several hundred light-years across –. The distances between the stars are, therefore, much greater within the newly discovered extended clusters, parametrically, these clusters lie somewhere between a globular cluster and a dwarf spheroidal galaxy. How these clusters are formed is not yet known, but their formation might well be related to that of globular clusters, why M31 has such clusters, while the Milky Way has not, is not yet known
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Galaxy cluster
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They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium, the ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as clusters, which are structures of stars within galaxies, or with globular clusters. Small aggregates of galaxies are referred to as groups of galaxies rather than clusters of galaxies, the groups and clusters can themselves cluster together to form superclusters. Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, a very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-CL J2106-5844, using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters. Galaxy clusters typically have the properties, They contain 100 to 1,000 galaxies, hot X-ray- emitting gas. Details are described in the Composition section, the distribution of the three components is approximately the same in the cluster. They have total masses of 1014 to 1015 solar masses and they typically have a diameter from 2 to 10 Mpc. The spread of velocities for the galaxies is about 800–1000 km/s. There are three components of a galaxy cluster. They are tabulated below, Stars, Star clusters, Galaxies, Galaxy clusters, Super clusters Abell catalogue Intracluster medium List of Abell clusters
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Redshift
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In physics, redshift happens when light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum. Some redshifts are an example of the Doppler effect, familiar in the change of apparent pitches of sirens, a redshift occurs whenever a light source moves away from an observer. Finally, gravitational redshift is an effect observed in electromagnetic radiation moving out of gravitational fields. However, redshift is a common term and sometimes blueshift is referred to as negative redshift. Knowledge of redshifts and blueshifts has been applied to develop several terrestrial technologies such as Doppler radar and radar guns, Redshifts are also seen in the spectroscopic observations of astronomical objects. Its value is represented by the letter z, a special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in contexts, such as black holes and Big Bang cosmology. Special relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws, the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842, the hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler correctly predicted that the phenomenon should apply to all waves, before this was verified, however, it was found that stellar colors were primarily due to a stars temperature, not motion. Only later was Doppler vindicated by verified redshift observations, the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is called the Doppler–Fizeau effect. In 1868, British astronomer William Huggins was the first to determine the velocity of a moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, in 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The word does not appear unhyphenated until about 1934 by Willem de Sitter, perhaps indicating that up to point its German equivalent. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies, Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years later, he wrote a review in the journal Popular Astronomy, Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable positive velocities
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Quasar
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A quasar is an active galactic nucleus of very high luminosity. A quasar consists of a black hole surrounded by an orbiting accretion disk of gas. As gas in the accretion disk falls toward the black hole, quasars emit energy across the electromagnetic spectrum and can be observed at radio, infrared, visible, ultraviolet, and X-ray wavelengths. The most powerful quasars have luminosities exceeding 1041 W, thousands of greater than the luminosity of a large galaxy such as the Milky Way. Quasars are found over a broad range of distances. The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, as of 2011, the most distant known quasar is at redshift z=7.085, light observed from this quasar was emitted when the Universe was only 770 million years old. Because quasars are distant objects, any light which reaches the Earth is redshifted due to the expansion of space. In early optical images, quasars appeared as point sources, indistinguishable from stars, with infrared telescopes and the Hubble Space Telescope, the host galaxies surrounding the quasars have been detected in some cases. These galaxies are normally too dim to be seen against the glare of the quasar, most quasars, with the exception of 3C273 whose average apparent magnitude is 12.9, cannot be seen with small telescopes. The luminosity of some quasars changes rapidly in the optical range, because these changes occur very rapidly they define an upper limit on the volume of a quasar, quasars are not much larger than the Solar System. This implies a high power density. The mechanism of brightness changes probably involves relativistic beaming of astrophysical jets pointed nearly directly toward Earth, the highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth. Since light cannot escape the black holes, the energy is actually generated outside the event horizon by gravitational stresses. Central masses of 105 to 109 solar masses have been measured in quasars by using reverberation mapping. The matter accreting onto the hole is unlikely to fall directly in. Quasars may also be ignited or re-ignited when normal galaxies merge, in fact, it has been suggested that a quasar could form as the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3–5 billion years. More than 200,000 quasars are known, most from the Sloan Digital Sky Survey, all observed quasar spectra have redshifts between 0.056 and 7.085. Applying Hubbles law to these redshifts, it can be shown that they are between 600 million and 28.85 billion light-years away
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Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
