1.
Heliophysics
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The term heliophysics means physics of the Sun, and appears to have been used only in that sense until quite recently. In the early times, heliophysics was concerned principally with the layers of the star. Usage was extended explicitly in 1981 to its meaning, denoting the physics of the entire Sun, from center to corona. As such it was a translation from the French héliophysique. It thus became a subdiscipline of heliology, heliophysics combines several other disciplines, including solar physics, and stellar physics in general, and also several branches of nuclear physics, plasma physics and space physics. The recent extension of heliophysics is closely tied to the study of weather and the phenomena that affect it. Heliophysics is now the name of one of four divisions within NASAs Science Mission Directorate, the title was used to simplify the name of the Sun--Solar-System Connections Division. NASAs restricted use of the term heliophysics has also adopted in naming the International Heliophysical Year in 2007-2008
2.
Solar phenomena
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Solar phenomena are the natural phenomena occurring within the magnetically heated outer atmospheres in the Sun. These phenomena take many forms, including wind, radio wave flux, energy bursts such as solar flares, coronal mass ejection or solar eruptions, coronal heating. The total sum of all solar fluctuations is referred to as solar variation, the collective effect of all solar variations within the Suns gravitational field is referred to as space weather. A major weather component is the wind, a stream of plasma released from the Suns upper atmosphere. It is responsible for the aurora, natural light displays in the sky in the Arctic and Antarctic, space weather disturbances can cause solar storms on Earth, disrupting communications, as well as geomagnetic storms in Earths magnetosphere and sudden ionospheric disturbances in the ionosphere. Variations in solar intensity also affect Earths climate and these variations can explain events such as ice ages and the Great Oxygenation Event, while the Suns future expansion into a red giant will likely end life on Earth. Solar activity and related events have been recorded since the 8th century BCE. Babylonians inscribed and possibly predicted solar eclipses, while the earliest extant report of sunspots dates back to the Chinese Book of Changes, c. The first extant description of the corona was in 968, while the earliest sunspot drawing was in 1128. The invention of the telescope allowed major advances in understanding, allowing the first detailed observations in the 1600s. Solar spectroscopy began in the 1800s, from which properties of the atmosphere could be determined. Photography assisted in the study of solar prominences, granulation and spectroscopy, early in the 20th century, interest in astrophysics surged in America. A number of new observatories were built with solar telescopes around the world, the 1931 invention of the coronagraph allowed the corona to be studied in full daylight. The Sun is a located at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma and magnetic fields and it has a diameter of about 1,392,684 kilometres, around 109 times that of Earth, and its mass accounts for some 99. 86% of the total mass of the Solar System. Chemically, about three quarters of the Suns mass consists of hydrogen, while the rest is mostly helium, the remaining 1. 69% consists of heavier elements, including oxygen, carbon, neon and iron. The Sun formed about 4.567 billion years ago from the collapse of a region within a large molecular cloud. Most of the matter gathered in the center, while the rest flattened into a disk that became the balance of the Solar System. The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core and it is actually white, but from the Earths surface it appears yellow because of atmospheric scattering of blue light
3.
Geomagnetic storm
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A geomagnetic storm is a temporary disturbance of the Earths magnetosphere caused by a solar wind shock wave and/or cloud of magnetic field that interacts with the Earths magnetic field. The increase in the wind pressure initially compresses the magnetosphere. The solar winds magnetic field interacts with the Earth’s magnetic field, both interactions cause an increase in plasma movement through the magnetosphere and an increase in electric current in the magnetosphere and ionosphere. During the main phase of a storm, electric current in the magnetosphere creates a magnetic force that pushes out the boundary between the magnetosphere and the solar wind. The frequency of geomagnetic storms increases and decreases with the sunspot cycle, CME driven storms are more common during the maximum of the solar cycle, while CIR driven storms are more common during the minimum of the solar cycle. Several space weather phenomena tend to be associated with or are caused by a geomagnetic storm, in 1989, a geomagnetic storm energized ground induced currents that disrupted electric power distribution throughout most of the province of Quebec and caused aurorae as far south as Texas. In 1931, Sydney Chapman and Vincenzo C. A. Ferraro wrote an article, A New Theory of Magnetic Storms and they argued that whenever the Sun emits a solar flare it also emits a plasma cloud, now known as a coronal mass ejection. This plasma will travel at a velocity such that it reaches Earth within 113 days, the cloud then compresses the Earths magnetic field and thus increases this field at the Earths surface. A geomagnetic storm is defined by changes in the Dst index, the Dst index estimates the globally averaged change of the horizontal component of the Earth’s magnetic field at the magnetic equator based on measurements from a few magnetometer stations. Dst is computed once per hour and reported in near-real-time, during quiet times, Dst is between +20 and −20 nano-Tesla. A geomagnetic storm has three phases, initial, main and recovery, the initial phase is characterized by Dst increasing by 20 to 50 nT in tens of minutes. The initial phase is referred to as a storm sudden commencement. However, not all geomagnetic storms have a phase and not all sudden increases in Dst or SYM-H are followed by a geomagnetic storm. The main phase of a storm is defined by Dst decreasing to less than −50 nT. The selection of −50 nT to define a storm is somewhat arbitrary, the minimum value during a storm will be between -50 and approximately -600 nT. The duration of the phase is typically 2–8 hours. The recovery phase is when Dst changes from its value to its quiet time value. The recovery phase may last as short as 8 hours or as long as 7 days, the size of a geomagnetic storm is classified as moderate, intense or super-storm
4.
Solar flare
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A solar flare is a sudden flash of brightness observed near the Suns surface. It involves a broad spectrum of emissions, an energy release of typically 1 ×1020 joules of energy for a well-observed event. A major event can emit up to 1 ×1025 joules, Flares are often, but not always, accompanied by a coronal mass ejection. The flare ejects clouds of electrons, ions, and atoms through the corona of the sun into space and these clouds typically reach Earth a day or two after the event. The term is used to refer to similar phenomena in other stars. Flares occur in regions around sunspots, where intense magnetic fields penetrate the photosphere to link the corona to the solar interior. Flares are powered by the release of magnetic energy stored in the corona. The same energy releases may produce coronal mass ejections, although the relation between CMEs and flares is still not well established, X-rays and UV radiation emitted by solar flares can affect Earths ionosphere and disrupt long-range radio communications. Direct radio emission at decimetric wavelengths may disturb the operation of radars, Solar flares were first observed on the Sun by Richard Christopher Carrington and independently by Richard Hodgson in 1859 as localized visible brightenings of small areas within a sunspot group. Stellar flares can be inferred by looking at the lightcurves produced from the telescope or satellite data of variety of other stars. The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly active to less than one week when the Sun is quiet. Large flares are less frequent than smaller ones, on July 23,2012, a massive, and potentially damaging, solar superstorm barely missed Earth, according to NASA. Flares occur when sped up charged particles, mainly electrons, interact with the plasma medium, scientific research suggests that the phenomenon of magnetic reconnection leads to this copious acceleration of charged particles. On the Sun, magnetic reconnection may happen on solar arcades – a series of closely occurring loops of magnetic lines of force and these lines of force quickly reconnect into a low arcade of loops leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy in this reconnection is the origin of the particle acceleration, the unconnected magnetic helical field and the material that it contains may violently expand outwards forming a coronal mass ejection. This also explains why solar flares erupt from what are known as the active regions on the Sun where magnetic fields are much stronger on average. Although there is an agreement on the source of a flares energy. It is not clear how the energy is transformed into the particle kinetic energy, nor is it known how some particles can accelerated to the GeV range
5.
Solar prominence
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A prominence is a large, bright, gaseous feature extending outward from the Suns surface, often in a loop shape. Prominences are anchored to the Suns surface in the photosphere, the prominence plasma is typically a hundred times more lit and denser than the coronal plasma. A prominence forms over timescales of about a day and may persist in the corona for several weeks or months, some prominences break apart and may then give rise to coronal mass ejections. Scientists are currently researching how and why prominences are formed, the red-glowing looped material is plasma, a hot gas composed of electrically charged hydrogen and helium. The prominence plasma flows along a tangled and twisted structure of magnetic fields generated by the sun’s internal dynamo, an erupting prominence occurs when such a structure becomes unstable and bursts outward, releasing the plasma. A typical prominence extends over thousands of kilometers, the largest on record was estimated at over 800,000 kilometres long – roughly the radius of the Sun. The first detailed description of a solar prominence was in 14th-century Laurentian Codex and they were described as flame-like tongues of live embers. When a prominence is viewed from a different perspective so that it is against the sun instead of against space and this formation is instead called a solar filament. It is possible for a projection to be both a filament and a prominence, some prominences are so powerful that they throw out matter from the Sun into space at speeds ranging from 600 km/s to more than 1000 km/s. Other prominences form huge loops or arching columns of glowing gases over sunspots that can reach heights of hundreds of thousands of kilometers, prominences may last for a few days or even for a few months. Coronal mass ejection Solar flare Corona Galsgaard, K. Longbottom, formation of solar prominences by flux convergence. The mass of a solar quiescent prominence
6.
Sunspot
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Sunspots are temporary phenomena on the photosphere of the Sun that appear as dark spots compared with surrounding regions. They are areas of reduced surface temperature caused by concentrations of field flux that inhibit convection. Sunspots usually appear in pairs of magnetic polarity. Their number varies according to the approximately 11-year solar cycle, individual sunspots may endure anywhere from a few days to a few months, but eventually decay. Sunspots expand and contract as they move across the surface of the Sun with sizes ranging from 16 kilometers to 160,000 kilometers in diameter, the larger variety are visible from Earth without the aid of a telescope. They may travel at speeds, or proper motions of a few hundred meters per second when they first emerge. Indicating intense magnetic activity, sunspots accompany secondary phenomena such as coronal loops, most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on other than the sun are commonly called starspots. Although they are at temperatures of roughly 3, 000–4,500 K, isolated from the surrounding photosphere a sunspot would be brighter than the Moon. If the stress on the tubes reaches a limit, they curl up. Convection is inhibited at the points, the energy flux from the Suns interior decreases. The Wilson effect implies that sunspots are depressions on the Suns surface, observations using the Zeeman effect show that prototypical sunspots come in pairs with opposite magnetic polarity. From cycle to cycle, the polarities of leading and trailing sunspots change from north/south to south/north, magnetic pressure should tend to remove field concentrations, causing the sunspots to disperse, but sunspot lifetimes are measured in days to weeks. Sunspot activity cycles about every eleven years, the point of highest sunspot activity during a cycle is known as solar maximum, and the point of lowest activity as solar minimum. This period is observed in most other solar activity and is linked to a variation in the solar magnetic field that changes polarity with this period. Early in the cycle, sunspots appear in the latitudes and then move towards the equator as the cycle approaches maximum. Spots from two adjacent cycles can co-exist for some time, spots from adjacent cycles can be distinguished by direction of their magnetic field. The Wolf number sunspot index counts the number of sunspots
7.
Nuclear electromagnetic pulse
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A nuclear electromagnetic pulse is a characteristic burst of electromagnetic radiation created by nuclear explosions. The resulting rapidly changing electric and magnetic fields may couple with electrical and electronic systems to produce damaging current, the specific characteristics of any particular nuclear EMP event vary according to a number of factors, the most important of which is the altitude of the detonation. The term electromagnetic pulse generally excludes optical and ionizing ranges, in military terminology, a nuclear warhead detonated hundreds of kilometers above the Earths surface is known as a high-altitude electromagnetic pulse device. The fact that a pulse is produced by a nuclear explosion was known in the earliest days of nuclear weapons testing. The magnitude of the EMP and the significance of its effects, during the first United States nuclear test on 16 July 1945, electronic equipment was shielded because Enrico Fermi expected the electromagnetic pulse. The official technical history for that first nuclear test states, All signal lines were completely shielded, in spite of this many records were lost because of spurious pickup at the time of the explosion that paralyzed the recording equipment. During British nuclear testing in 1952–1953 instrumentation failures were attributed to radioflash, the first openly reported observation of the unique aspects of high-altitude nuclear EMP occurred during the helium balloon lofted Yucca nuclear test of the Hardtack I series on 28 April 1958. In that test, the field measurements from the 1.7 kiloton weapon went off the scale of the test instruments and was estimated to be about 5 times the oscilloscope limits. The Yucca EMP was initially positive-going whereas low-altitude bursts were negative pulses, also, the polarization of the Yucca EMP signal was horizontal, whereas low-altitude nuclear EMP was vertically polarized. In spite of many differences, the unique EMP results were dismissed as a possible wave propagation anomaly. The larger scientific community aware of the significance of the EMP problem after a three-article series on nuclear EMP was published in 1981 by William J. Broad in Science. In July 1962, the US carried out the Starfish Prime test and this demonstrated that the effects of a high-altitude nuclear explosion were much larger than had been previously calculated. Starfish Prime was the first success in the series of United States high-altitude nuclear tests in 1962 known as Operation Fishbowl, subsequent tests gathered more data on the high-altitude EMP phenomenon. The EMP damage of the Starfish Prime test was quickly repaired because of the ruggedness of Hawaiis electrical and these calculations, combined with the accelerating reliance on EMP-sensitive microelectronics, heightened awareness that EMP could be a significant problem. In 1962, the Soviet Union also performed three EMP-producing nuclear tests in space over Kazakhstan, the last in the Soviet Project K nuclear tests. The geomagnetic storm–like E3 pulse from Test 184 induced a current surge in an underground power line that caused a fire in the power plant in the city of Karaganda. After the collapse of the Soviet Union, the level of damage was communicated informally to U. S. scientists. After the 1991 collapse of the Soviet Union, there was a period of a few years of cooperation between United States and Russian scientists on the HEMP phenomenon
8.
Plasma (physics)
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Plasma is one of the four fundamental states of matter, the others being solid, liquid, and gas. Yet unlike these three states of matter, plasma does not naturally exist on the Earth under normal surface conditions, the term was first introduced by chemist Irving Langmuir in the 1920s. However, true plasma production is from the separation of these ions and electrons that produces an electric field. Based on the environmental temperature and density either partially ionised or fully ionised forms of plasma may be produced. The positive charge in ions is achieved by stripping away electrons from atomic nuclei, the number of electrons removed is related to either the increase in temperature or the local density of other ionised matter. Plasma may be the most abundant form of matter in the universe, although this is currently tentative based on the existence. Plasma is mostly associated with the Sun and stars, extending to the rarefied intracluster medium, Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879. The nature of the Crookes tube cathode ray matter was identified by British physicist Sir J. J. The term plasma was coined by Irving Langmuir in 1928, perhaps because the glowing discharge molds itself to the shape of the Crookes tube and we shall use the name plasma to describe this region containing balanced charges of ions and electrons. Plasma is a neutral medium of unbound positive and negative particles. Although these particles are unbound, they are not ‘free’ in the sense of not experiencing forces, in turn this governs collective behavior with many degrees of variation. The average number of particles in the Debye sphere is given by the plasma parameter, bulk interactions, The Debye screening length is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, when this criterion is satisfied, the plasma is quasineutral. Plasma frequency, The electron plasma frequency is compared to the electron-neutral collision frequency. When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics, for plasma to exist, ionization is necessary. The term plasma density by itself refers to the electron density, that is. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma. The degree of ionization, α, is defined as α = n i n i + n n, where n i is the number density of ions and n n is the number density of neutral atoms
9.
Magnetic field
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A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
10.
Sun
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The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
11.
Corona
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A corona is an aura of plasma that surrounds the sun and other stars. The Suns corona extends millions of kilometres into space and is most easily seen during a solar eclipse. The word corona is a Latin word meaning crown, from the Ancient Greek κορώνη, the high temperature of the Suns corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a previously unknown element, coronium. Instead, these features have since been explained by highly ionized iron. Bengt Edlén, following the work of Grotrian, first identified the coronal spectral lines in 1940 as transitions from low-lying metastable levels of the configuration of highly ionised metals. These high stages of ionisation indicate a temperature in excess of 1,000,000 kelvins. Light from the corona comes from three sources, from the same volume of space. The suns corona is much hotter than the surface of the Sun. The corona is 10−12 times as dense as the photosphere, the corona is separated from the photosphere by the relatively shallow chromosphere. The exact mechanism by which the corona is heated is still the subject of some debate, the outer edges of the Suns corona are constantly being transported away due to open magnetic flux and hence generating the solar wind. The corona is not always evenly distributed across the surface of the sun, during periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions. However, during the Suns active periods, the corona is evenly distributed over the equatorial and polar regions, the solar cycle spans approximately 11 years, from solar minimum to the following minimum. Associated with sunspots are coronal loops, loops of magnetic flux, the magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the relatively dark sun spots. The astronomers usually distinguish several regions, as described below, active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops. They generally distribute in two zones of activity, which are parallel to the solar equator, the average temperature is between two and four million kelvins, while the density goes from 109 to 1010 particle per cm3. If flares are very violent, they can also perturb the photosphere, on the contrary, quiescent prominences are large, cool dense structures which are observed as dark, snake-like Hα ribbons on the solar disc. Their temperature is about 5000–8000 K, and so they are considered as chromospheric features. In 2013, images from the High Resolution Coronal Imager revealed never-before-seen magnetic braids of plasma within the layers of these active regions
12.
Solar wind
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The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and its particles can escape the Suns gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. At a distance of more than a few radii from the sun. The flow of the wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007, Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5 billion kilometer distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the shock into the heliosheath. Other related phenomena include the aurora, the tails of comets that always point away from the Sun. The existence of flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare, george FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days. In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the wind, without naming it. The idea never caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions. The first person to suggest that the material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed that activity was nearly uninterrupted. In 1916, Birkeland proposed that, From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, in other words, the solar wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun
13.
Coronagraph
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A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the stars bright glare – can be resolved. The coronagraph was introduced in 1931 by the French astronomer Bernard Lyot, since then, coronagraphs operating within Earths atmosphere suffer from scattered light in the sky itself, due primarily to Rayleigh scattering of sunlight in the upper atmosphere. At view angles close to the Sun, the sky is much brighter than the background corona even at high altitude sites on clear, dry days. Coronagraph instruments are examples of stray light rejection and precise photometry because the total brightness from the solar corona is less than one millionth the brightness of the Sun. The apparent surface brightness is even fainter because, in addition to delivering less total light, during a solar eclipse, the Moon acts as an occulting disk and any camera in the eclipse path may be operated as a coronagraph until the eclipse is over. More common is an arrangement where the sky is imaged onto a focal plane containing an opaque spot. Either way, the instrument design must take into account scattering, as an example, imaging instruments on the Hubble Space Telescope offer coronagraphic capability. A band-limited coronagraph uses a kind of mask called a band-limited mask. This mask is designed to light and also manage potangina effects caused by removal of the light. The band-limited coronagraph has served as the design for the canceled Terrestrial Planet Finder coronagraph. Band-limited masks will also be available on the James Webb Space Telescope, see also, A phase-mask coronagraph uses a transparent mask to shift the phase of the stellar light in order to create a self-destructive interference, rather than a simple opaque disc to block it. See also, An optical vortex coronagraph uses a phase-mask in which the phase-shift varies azimuthally around the center, several varieties of optical vortex coronagraphs exist, the scalar optical vortex coronagraph based on a phase ramp directly etched in a dielectric material, like fused silica. The vector vortex coronagraph employs a mask that rotates the angle of polarization of photons, a mask of this kind can be synthesized by various technologies, ranging from liquid crystal polymer, and micro-structured surfaces. Such a vector vortex coronagraph made out of liquid crystal polymers is currently in use at the 200-inch Hale telescope at the Palomar Observatory and it has recently been operated with adaptive optics to image extrasolar planets. This works with other than the sun because they are so far away their light is, for this purpose. The coronagraph using interference masks out the light along the axis of the telescope. Coronagraphs in outer space are more effective than the same instruments would be if located on the ground. This is because the absence of atmospheric scattering eliminates the largest source of glare present in a terrestrial coronagraph
14.
Solar maximum
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Solar maximum or solar max is a normal period of greatest solar activity in the 11 year solar cycle of the Sun. During solar maximum, large numbers of sunspots appear and the suns irradiance output grows by about 0. 07%, the increased energy output of solar maxima can impact Earths global climate and recent studies have shown some correlation with regional weather patterns. At solar maximum, the Suns magnetic field lines are the most distorted due to the field on the solar equator rotating at a slightly faster pace than at the solar poles. The solar cycle takes an average of about 11 years to go from one solar maximum to the next, large solar flares often occur during a maximum. For example, the storm of 1859 struck the Earth with such intensity that the northern lights were visible as far from the poles as Cuba. Predictions of a future maximums timing and strength are very difficult, there was a solar maximum in 2000. In 2006 NASA initially expected a solar maximum in 2010 or 2011, however, the solar maximum was not declared to have occurred until 2014, and even then was ranked among the weakest on record. IMAX documentary about solar maximum called Solarmax, NASA CME documentary X class Corona Mass Ejection 2012-07-14 documentary Grand solar maxima occur when several solar cycles exhibit greater than average activity for decades or centuries. Solar cycles still occur during these grand solar maximum periods but the intensity of those cycles are greater, Grand solar maxima have shown some correlation with global and regional climate changes. The idea of a Modern Maximum has now been thrown into question with the release of a paper at the International Astronomical Union General Assembly in August 2015, a list of historical Grand minima of solar activity includes also Grand minima ca. Solar wind Solar variation Solar minimum List of solar cycles – table of solar cycles Solar Maximum Mission
15.
Solar minimum
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Solar minimum is the period of least solar activity in the 11 year solar cycle of the sun. During this time, sunspot and solar flare activity diminishes, solar minima are not generally correlated with changes in climate but recent studies have shown a correlation with regional weather patterns. Solar minimum is contrasted with the maximum, where there may be hundreds of sunspots. Solar minima and maxima are the two extremes of the suns 11-year activity cycle, at a maximum, the sun is peppered with sunspots, solar flares erupt, and the sun hurls billion-ton clouds of electrified gas into space. Its a good time for sky watchers who enjoy auroras, power outages, satellite malfunction and communication disruptions, and GPS receiver malfunctions are just a few of the things that can happen during a solar maximum. At a solar minimum, there are fewer sunspots and solar flares subside, sometimes, days or weeks go by without a spot. It is a time to travel through space, but a less interesting time to watch polar skies. Their non-linear character makes predictions of solar activity very difficult, the solar minimum is characterized by a period of decreased solar activity with few, if any, sunspots. The accompanying decrease in solar radiation makes it the safest time for astronauts to carry out space missions, three NASA scientists were better able to predict solar cycles using a simple function with four parameters, which then led the ability to discover the duration of these solar cycles. In hindsight the prediction proved to be inaccurate and not representative of the observed sunspot numbers. During 2008-2009 NASA scientists noted that the Sun is undergoing a deep solar minimum, stating, prompted by these numbers, some observers suggested that the solar cycle had hit bottom in 2008. Sunspot counts for 2009 dropped even lower, as of September 14,2009 there were no sunspots on 206 of the years 257 days. It adds up to one conclusion, Were experiencing a very deep solar minimum. This is the quietest sun weve seen in almost a century, agrees sunspot expert David Hathaway of the National Space Science and its a natural part of the sunspot cycle, discovered by German astronomer Heinrich Schwabe in the mid-19th century. A clockwork pattern that has held true for more than 200 years, Grand solar minima occur when several solar cycles exhibit lesser than average activity for decades or centuries. Solar cycles still occur during these grand solar minimum periods but are at a lower intensity than usual, Grand solar minima have shown some correlation with global and regional climate changes. A list of historical Grand minima of solar activity includes also Grand minima ca
16.
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
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Proton
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A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as nucleons. One or more protons are present in the nucleus of every atom, the number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Since each element has a number of protons, each element has its own unique atomic number. The word proton is Greek for first, and this name was given to the nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a particle, and hence a building block of nitrogen. In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks, two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a protons mass, the remainder of a protons mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. At sufficiently low temperatures, free protons will bind to electrons, however, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, the result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom. Such free hydrogen atoms tend to react chemically with other types of atoms at sufficiently low energies. When free hydrogen atoms react with other, they form neutral hydrogen molecules. Protons are spin-½ fermions and are composed of three quarks, making them baryons. Protons have an exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton
18.
Magnetohydrodynamics
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Magnetohydrodynamics is the study of the magnetic properties of electrically conducting fluids. Examples of such magnetofluids include plasmas, liquid metals, salt water, the word magnetohydrodynamics is derived from magneto- meaning magnetic field, hydro- meaning water, and -dynamics meaning movement. The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970. The fundamental concept behind MHD is that magnetic fields can induce currents in a conductive fluid. The set of equations that describe MHD are a combination of the Navier-Stokes equations of fluid dynamics and these differential equations must be solved simultaneously, either analytically or numerically. The importance of the waves in this respect are pointed out. The ebbing salty water flowing past Londons Waterloo Bridge interacts with the Earths magnetic field to produce a difference between the two river-banks. Michael Faraday tried this experiment in 1832 but the current was too small to measure with the equipment at the time, however, by a similar process the voltage induced by the tide in the English Channel was measured in 1851. The simplest form of MHD, Ideal MHD, assumes that the fluid has so little resistivity that it can be treated as a perfect conductor and this is the limit of infinite magnetic Reynolds number. In ideal MHD, Lenzs law dictates that the fluid is in a sense tied to the field lines. To explain, in ideal MHD a small volume of fluid surrounding a field line will continue to lie along a magnetic field line. This is sometimes referred to as the field lines being frozen in the fluid. This difficulty in reconnecting magnetic field makes it possible to store energy by moving the fluid or the source of the magnetic field. The energy can become available if the conditions for ideal MHD break down. The ideal MHD equations consist of the continuity equation, the Cauchy momentum equation, Amperes Law neglecting displacement current, as with any fluid description to a kinetic system, a closure approximation must be applied to highest moment of the particle distribution equation. This is often accomplished with approximations to the flux through a condition of adiabaticity or isothermality. The main quantities which characterize the electrically conducting fluid are the plasma velocity field v, the current density J, the mass density ρ. The flowing electric charge in the plasma is the source of a magnetic field B, All quantities generally vary with time t
19.
Quebec
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Quebec is the second-most populous province of Canada and the only one to have a predominantly French-speaking population, with French as the sole provincial official language. Quebec is Canadas largest province by area and its second-largest administrative division and it also shares maritime borders with Nunavut, Prince Edward Island, and Nova Scotia. Quebec is Canadas second-most populous province, after Ontario, most inhabitants live in urban areas near the Saint Lawrence River between Montreal and Quebec City, the capital. Approximately half of Quebec residents live in the Greater Montreal Area, the Nord-du-Québec region, occupying the northern half of the province, is sparsely populated and inhabited primarily by Aboriginal peoples. Even in central Quebec at comparatively southerly latitudes winters are severe in inland areas, Quebec independence debates have played a large role in the politics of the province. Parti Québécois governments held referendums on sovereignty in 1980 and 1995, in 2006, the House of Commons of Canada passed a symbolic motion recognizing the Québécois as a nation within a united Canada. These many industries have all contributed to helping Quebec become an economically influential province within Canada, early variations in the spelling of the name included Québecq and Kébec. French explorer Samuel de Champlain chose the name Québec in 1608 for the colonial outpost he would use as the seat for the French colony of New France. The province is sometimes referred to as La belle province, the Province of Quebec was founded in the Royal Proclamation of 1763 after the Treaty of Paris formally transferred the French colony of Canada to Britain after the Seven Years War. The proclamation restricted the province to an area along the banks of the Saint Lawrence River, the Treaty of Versailles ceded territories south of the Great Lakes to the United States. After the Constitutional Act of 1791, the territory was divided between Lower Canada and Upper Canada, with each being granted an elected legislative assembly, in 1840, these become Canada East and Canada West after the British Parliament unified Upper and Lower Canada into the Province of Canada. This territory was redivided into the Provinces of Quebec and Ontario at Confederation in 1867, each became one of the first four provinces. In 1898, the Canadian Parliament passed the first Quebec Boundary Extension Act that expanded the provincial boundaries northward to include the lands of the aboriginal peoples. This was followed by the addition of the District of Ungava through the Quebec Boundaries Extension Act of 1912 that added the northernmost lands of the Inuit to create the modern Province of Quebec. In 1927, the border between Quebec and Newfoundland and Labrador was established by the British Judicial Committee of the Privy Council. Located in the part of Canada, and part of Central Canada. Its topography is very different from one region to another due to the composition of the ground, the climate. The Saint Lawrence Lowland and the Canadian Shield are the two main regions, and are radically different
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Ontario
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Ontario, one of the 13 provinces and territories of Canada, is located in east-central Canada. It is Canadas most populous province by a margin, accounting for nearly 40 percent of all Canadians. Ontario is fourth-largest in total area when the territories of the Northwest Territories and it is home to the nations capital city, Ottawa, and the nations most populous city, Toronto. There is only about 1 km of land made up of portages including Height of Land Portage on the Minnesota border. Ontario is sometimes divided into two regions, Northern Ontario and Southern Ontario. The great majority of Ontarios population and arable land is located in the south, in contrast, the larger, northern part of Ontario is sparsely populated with cold winters and is heavily forested. The province is named after Lake Ontario, a thought to be derived from Ontarí, io, a Huron word meaning great lake, or possibly skanadario. Ontario has about 250,000 freshwater lakes, the province consists of three main geographical regions, The thinly populated Canadian Shield in the northwestern and central portions, which comprises over half the land area of Ontario. Although this area mostly does not support agriculture, it is rich in minerals and in part covered by the Central and Midwestern Canadian Shield forests, studded with lakes, Northern Ontario is subdivided into two sub-regions, Northwestern Ontario and Northeastern Ontario. The virtually unpopulated Hudson Bay Lowlands in the north and northeast, mainly swampy. Southern Ontario which is further sub-divided into four regions, Central Ontario, Eastern Ontario, Golden Horseshoe, the highest point is Ishpatina Ridge at 693 metres above sea level located in Temagami, Northeastern Ontario. In the south, elevations of over 500 m are surpassed near Collingwood, above the Blue Mountains in the Dundalk Highlands, the Carolinian forest zone covers most of the southwestern region of the province. A well-known geographic feature is Niagara Falls, part of the Niagara Escarpment, the Saint Lawrence Seaway allows navigation to and from the Atlantic Ocean as far inland as Thunder Bay in Northwestern Ontario. Northern Ontario occupies roughly 87 percent of the area of the province. Point Pelee is a peninsula of Lake Erie in southwestern Ontario that is the southernmost extent of Canadas mainland, Pelee Island and Middle Island in Lake Erie extend slightly farther. All are south of 42°N – slightly farther south than the border of California. The climate of Ontario varies by season and location, the effects of these major air masses on temperature and precipitation depend mainly on latitude, proximity to major bodies of water and to a small extent, terrain relief. In general, most of Ontarios climate is classified as humid continental, Ontario has three main climatic regions
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Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
22.
Shock wave
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In physics, a shock wave, or shock, is a type of propagating disturbance. When a wave moves faster than the speed of sound in a fluid it is a shock wave. In supersonic flows, expansion is achieved through an expansion fan also known as a Prandtl-Meyer expansion fan, unlike solitons, the energy of a shock wave dissipates relatively quickly with distance. Also, the accompanying expansion wave approaches and eventually merges with the shock wave, when a shock wave passes through matter, energy is preserved but entropy increases. Shock waves can be, Normal, at 90° to the shock mediums flow direction, oblique, at an angle to the direction of flow. Bow, Occurs upstream of the front of a blunt object when the flow velocity exceeds Mach 1. Some other terms Shock Front, The boundary over which the physical conditions undergo a change because of a shock wave. Contact Front, in a wave caused by a driver gas. The Contact Front trails the Shock Front, when an object moves faster than the information about it can propagate into the surrounding fluid, fluid near the disturbance cannot react or get out of the way before the disturbance arrives. In a shock wave the properties of the fluid change almost instantaneously, measurements of the thickness of shock waves in air have resulted in values around 200 nm, which is on the same order of magnitude as the mean free gas molecule path. In reference to the continuum, this implies the shock wave can be treated as either a line or a plane if the field is two-dimensional or three-dimensional. Shock waves are formed when a pressure front moves at supersonic speeds, Shock waves are not conventional sound waves, a shock wave takes the form of a very sharp change in the gas properties. Shock waves in air are heard as a crack or snap noise. Over longer distances, a wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air. The sound wave is heard as the familiar thud or thump of a sonic boom, the shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. Some other methods are isentropic compressions, including Prandtl-Meyer compressions, the method of compression of a gas results in different temperatures and densities for a given pressure ratio which can be analytically calculated for a non-reacting gas. A shock wave compression results in a loss of pressure, meaning that it is a less efficient method of compressing gases for some purposes. The appearance of pressure-drag on supersonic aircraft is due to the effect of shock compression on the flow
23.
Magnetosphere
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A magnetosphere is the region of space surrounding an astronomical object in which charged particles are controlled by that objects magnetic field. The magnetic field near the surface of many astronomical objects resembles that of a dipole, the field lines farther away from the surface can be significantly distorted by the flow of electrically conducting plasma emitted from a nearby star. Study of Earths magnetosphere began in 1600, when William Gilbert discovered that the field on the surface of Earth resembled that on a terrella. In the 1940s, Walter M. Elsasser proposed the model of dynamo theory, through the use of magnetometers, scientists were able to study the variations in Earths magnetic field as functions of both time and latitude and longitude. Beginning in the late 1940s, rockets were used to study cosmic rays, in 1958, Explorer 1, the first of the Explorer series of space missions, was launched to study the intensity of cosmic rays above the atmosphere and measure the fluctuations in this activity. This mission observed the existence of the Van Allen radiation belt, also in 1958, Eugene Parker proposed the idea of the solar wind. The term magnetosphere was proposed by Thomas Gold in 1959, the Explorer 12 mission led to the observation by Cahill and Amazeen in 1963 of a sudden decrease in the strength of the magnetic field near the noon meridian, later named the magnetopause. In 1983, the International Cometary Explorer observed the magnetotail, or the distant magnetic field, the distance at which a planet can withstand the solar wind pressure is called the Chapman–Ferraro distance. Mercury, Earth, Jupiter, Ganymede, Saturn, Uranus, a magnetosphere is classified as induced when R C F ≪ R P, or when the solar wind is not opposed by the objects magnetic field. In this case, the solar wind interacts with the atmosphere or ionosphere of the planet, when R C F ≈ R P, the planet itself and its magnetic field both contribute. It is possible that Mars is of this type, the bow shock forms the outermost layer of the magnetosphere, the boundary between the magnetosphere and the ambient medium. For stars, this is usually the boundary between the wind and interstellar medium, for planets, the speed of the solar wind there decreases as it approaches the magnetopause. The magnetosheath is the region of the magnetosphere between the bow shock and the magnetopause and it is formed mainly from shocked solar wind, though it contains a small amount of plasma from the magnetosphere. It is an area exhibiting high particle flux, where the direction. This is caused by the collection of solar wind gas that has effectively undergone thermalization and it acts as a cushion that transmits the pressure from the flow of the solar wind and the barrier of the magnetic field from the object. The magnetopause is the area of the magnetosphere wherein the pressure from the magnetic field is balanced with the pressure from the solar wind. It is the convergence of the solar wind from the magnetosheath with the magnetic field of the object. Because both sides of this convergence contain magnetized plasma, the interactions between them are complex, the structure of the magnetopause depends upon the Mach number and beta of the plasma, as well as the magnetic field
24.
Power (physics)
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In physics, power is the rate of doing work. It is the amount of energy consumed per unit time, having no direction, it is a scalar quantity. In the SI system, the unit of power is the joule per second, known as the watt in honour of James Watt, another common and traditional measure is horsepower. Being the rate of work, the equation for power can be written, because this integral depends on the trajectory of the point of application of the force and torque, this calculation of work is said to be path dependent. As a physical concept, power requires both a change in the universe and a specified time in which the change occurs. This is distinct from the concept of work, which is measured in terms of a net change in the state of the physical universe. The output power of a motor is the product of the torque that the motor generates. The power involved in moving a vehicle is the product of the force of the wheels. The dimension of power is divided by time. The SI unit of power is the watt, which is equal to one joule per second, other units of power include ergs per second, horsepower, metric horsepower, and foot-pounds per minute. One horsepower is equivalent to 33,000 foot-pounds per minute, or the required to lift 550 pounds by one foot in one second. Other units include dBm, a logarithmic measure with 1 milliwatt as reference, food calories per hour, Btu per hour. This shows how power is an amount of energy consumed per unit time. If ΔW is the amount of work performed during a period of time of duration Δt and it is the average amount of work done or energy converted per unit of time. The average power is simply called power when the context makes it clear. The instantaneous power is then the value of the average power as the time interval Δt approaches zero. P = lim Δ t →0 P a v g = lim Δ t →0 Δ W Δ t = d W d t. In the case of constant power P, the amount of work performed during a period of duration T is given by, W = P t
25.
Atmosphere
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An atmosphere is a layer of gases surrounding a planet or other material body, that is held in place by the gravity of that body. An atmosphere is likely to be retained if the gravity it is subject to is high. The atmosphere of Earth is mostly composed of nitrogen, oxygen, argon with carbon dioxide, the atmosphere helps protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. Its current composition is the product of billions of years of modification of the paleoatmosphere by living organisms. The term stellar atmosphere describes the region of a star. Stars with sufficiently low temperatures may form compound molecules in their outer atmosphere, Atmospheric pressure is the force per unit area that is applied perpendicularly to a surface by the surrounding gas. It is determined by a gravitational force in combination with the total mass of a column of gas above a location. On Earth, units of air pressure are based on the recognized standard atmosphere. It is measured with a barometer, the pressure of an atmospheric gas decreases with altitude due to the diminishing mass of gas above. The height at which the pressure from an atmosphere declines by a factor of e is called the height and is denoted by H. For such an atmosphere, the pressure declines exponentially with increasing altitude. However, atmospheres are not uniform in temperature, so the determination of the atmospheric pressure at any particular altitude is more complex. Surface gravity, the force that holds down an atmosphere, differs significantly among the planets, for example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from objects with lower gravity. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite their relatively low gravities, rogue planets, theoretically, may also retain thick atmospheres. Since a collection of gas molecules may be moving at a range of velocities. Lighter molecules move faster than ones with the same thermal kinetic energy. It is thought that Venus and Mars may have lost much of their water when, after being photo dissociated into hydrogen and oxygen by solar ultraviolet, Earths magnetic field helps to prevent this, as, normally, the solar wind would greatly enhance the escape of hydrogen. However, over the past 3 billion years Earth may have lost gases through the polar regions due to auroral activity
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Aurora
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An aurora, sometimes referred to as a polar lights or northern lights, is a natural light display in the sky, predominantly seen in the high latitude regions. The resulting ionization and excitation of atmospheric constituents emits light of varying colour, the form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere, proton auroras are usually observed at lower latitudes. A region that currently displays an aurora is called the auroral oval, early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis, and later Hermann Fritz and S. Tromholt in more detail, day-to-day positions of the auroral ovals are posted on the internet. In northern latitudes, the effect is known as the Aurora Borealis or the Northern Lights, the former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind. The Aurora Australis is visible from southern latitudes in Antarctica, Chile, Argentina, New Zealand. A geomagnetic storm causes the auroral ovals to expand, and bring the aurora to lower latitudes and it was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The aurora can be seen best at this time, which is called magnetic midnight, Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be sub-visual. Auroras are occasionally seen in latitudes below the zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the sunspot cycle or during the three years after the peak. An aurora may appear overhead as a corona of rays, radiating from a distant and apparent central location, an electron spirals about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the “pitch angle” of the particle, the distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the travels to a region of greater field strength nearer to the atmosphere. Thus it is possible for particles to return, or mirror. Other particles that do not mirror enter the atmosphere and contribute to the display over a range of altitudes. Other types of auroras have been observed from space, e. g. poleward arcs stretching sunward across the cap, the related theta aurora. These are relatively infrequent and poorly understood, there are other interesting effects such as flickering aurora, black aurora and sub-visual red arcs
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Radio transmission
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
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Satellite
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In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are called artificial satellites to distinguish them from natural satellites such as Earths Moon. In 1957 the Soviet Union launched the worlds first artificial satellite, since then, about 6,600 satellites from more than 40 countries have been launched. According to a 2013 estimate,3,600 remained in orbit, of those, about 1,000 were operational, the rest have lived out their useful lives and become space debris. Approximately 500 operational satellites are in orbit,50 are in medium-Earth orbit. A few large satellites have been launched in parts and assembled in orbit. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, Satellites are used for many purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, well-known classes include low Earth orbit, polar orbit, and geostationary orbit. A launch vehicle is a rocket that throws a satellite into orbit, usually it lifts off from a launch pad on land. Some are launched at sea from a submarine or a mobile maritime platform, Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control, the first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale, The Brick Moon. The idea surfaced again in Jules Vernes The Begums Fortune, in 1903, Konstantin Tsiolkovsky published Exploring Space Using Jet Propulsion Devices, which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the speed required for a minimal orbit. In 1928, Herman Potočnik published his book, The Problem of Space Travel — The Rocket Motor. He described the use of orbiting spacecraft for observation of the ground, in a 1945 Wireless World article, the English science fiction writer Arthur C. Clarke described in detail the possible use of communications satellites for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet, the first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4,1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer. This in turn triggered the Space Race between the Soviet Union and the United States, Sputnik 1 helped to identify the density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere
29.
Electric power transmission
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Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network and this is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is known as the grid in North America. In the United Kingdom, the network is known as the National Grid, for example, there are four major interconnections in North America, and one large grid for most of continental Europe. Most transmission lines are high-voltage three-phase alternating current, although single phase AC is sometimes used in railway electrification systems, high-voltage direct-current technology is used for greater efficiency over very long distances. HVDC technology is used in submarine power cables, and in the interchange of power between grids that are not mutually synchronized. HVDC links are used to large power distribution networks where sudden new loads, or blackouts, in one part of a network can result in synchronization problems. Electricity is transmitted at high voltages to reduce the loss which occurs in long-distance transmission. Power is usually transmitted through overhead power lines, underground power transmission has a significantly higher installation cost and greater operational limitations, but reduced maintenance costs. Underground transmission is used in urban areas or environmentally sensitive locations. A lack of energy storage facilities in transmission systems leads to a key limitation. Electrical energy must be generated at the rate at which it is consumed. A sophisticated control system is required to ensure that the power generation very closely matches the demand, if the demand for power exceeds supply, the imbalance can cause generation plant and transmission equipment to automatically disconnect and/or shut down to prevent damage. In the worst case, this may lead to a series of shut downs. Examples include the US Northeast blackouts of 1965,1977,2003, Transmission companies determine the maximum reliable capacity of each line to ensure that spare capacity is available in the event of a failure in another part of the network. High-voltage overhead conductors are not covered by insulation, the conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for transmission, but aluminum is lighter, yields only marginally reduced performance. Overhead conductors are a commodity supplied by companies worldwide
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Power outage
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A power outage is a short-term or a long-term loss of the electric power to a particular area. There are many causes of failures in an electricity network. Power failures are particularly critical at sites where the environment and public safety are at risk, other critical systems, such as telecommunication, are also required to have emergency power. The battery room of a telephone exchange usually has arrays of lead–acid batteries for backup, Power is automatically restored once the fault is cleared. A brownout is a drop in voltage in a power supply. The term brownout comes from the experienced by lighting when the voltage sags. Brownouts can cause poor performance of equipment or even incorrect operation, a blackout is the total loss of power to an area and is the most severe form of power outage that can occur. Blackouts which result from or result in power stations tripping are particularly difficult to recover from quickly, outages may last from a few minutes to a few weeks depending on the nature of the blackout and the configuration of the electrical network. In power supply networks, the generation and the electrical load must be very close to equal every second to avoid overloading of network components. Protective relays and fuses are used to automatically detect overloads and to disconnect circuits at risk of damage, under certain conditions, a network component shutting down can cause current fluctuations in neighboring segments of the network leading to a cascading failure of a larger section of the network. This may range from a building, to a block, to an entire city, modern power systems are designed to be resistant to this sort of cascading failure, but it may be unavoidable. In a 2003 publication, Carreras and co-authors claimed that reducing the likelihood of small outages only increases the likelihood of larger ones, in that case, the short-term economic benefit of keeping the individual customer happy increases the likelihood of large-scale blackouts. Computer systems and other devices containing logic circuitry are susceptible to data loss or hardware damage that can be caused by the sudden loss of power. These can include data networking equipment, video projectors, alarm systems as well as computers, to protect against surges, which can damage hardware when power is restored, a special device called a surge protector that absorbs the excess voltage can be used. Restoring power after a wide-area outage can be difficult, as power stations need to be brought back on-line, normally, this is done with the help of power from the rest of the grid. In the total absence of power, a so-called black start needs to be performed to bootstrap the power grid into operation. It has been argued on the basis of data and computer modeling that power grids are self-organized critical systems. These systems exhibit unavoidable disturbances of all sizes, up to the size of the entire system and this phenomenon has been attributed to steadily increasing demand/load, the economics of running a power company, and the limits of modern engineering
31.
Ionosphere
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The ionosphere is a region of Earths upper atmosphere, from about 60 km to 1,000 km altitude, and includes the thermosphere and parts of the mesosphere and exosphere. It is ionized by radiation, plays an important part in atmospheric electricity. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth and it owes its existence primarily to ultraviolet radiation from the Sun. The lowest part of the Earths atmosphere, the troposphere extends from the surface to about 10 km, above 10 km is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer, at heights of above 80 km, in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma which is referred to as the ionosphere, in this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher than the one of ions and neutrals. The reverse process to ionization is recombination, in which an electron is captured by a positive ion. Recombination occurs spontaneously, and causes the emission of a photon carrying away the energy produced upon recombination, as gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between two processes determines the quantity of ionization present. Ionization depends primarily on the Sun and its activity, the amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is an effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation, the activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location, there are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as flares and the associated release of charged particles into the solar wind which reaches the Earth. At night the F layer is the layer of significant ionization present. During the day, the D and E layers become more heavily ionized, as does the F layer
32.
Cosmic ray
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Cosmic rays are high-energy radiation, mainly originating outside the Solar System. Upon impact with the Earths atmosphere, cosmic rays can produce showers of particles that sometimes reach the surface. Composed primarily of protons and atomic nuclei, they are of mysterious origin. Data from the Fermi space telescope have been interpreted as evidence that a significant fraction of cosmic rays originate from the supernovae explosions of stars. Active galactic nuclei probably also produce cosmic rays, the term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation. In current usage, the cosmic ray almost exclusively refers to massive particles. Massive particles – those that have rest mass – can gain additional, kinetic, mass-energy when they are moving, through this process, some particles acquire tremendously high mass-energies. These are significantly higher than the energy of even the highest-energy photons detected to date. The energy of the massless photon depends solely on frequency, not speed, at the higher end of the energy spectrum, relativistic kinetic energy is the main source of the mass-energy of cosmic rays. Hence, the highest-energy detected fermionic cosmic ray was around 3×106 times more energetic than the highest-energy detected cosmic photons, of primary cosmic rays, which originate outside of Earths atmosphere, about 99% are the nuclei of well-known atoms, and about 1% are solitary electrons. Of the nuclei, about 90% are simple protons, i. e. hydrogen nuclei, 9% are alpha particles, identical to helium nuclei, a very small fraction are stable particles of antimatter, such as positrons or antiprotons. The precise nature of this fraction is an area of active research. An active search from Earth orbit for anti-alpha particles has failed to detect them, one can show that such enormous energies might be achieved by means of the Centrifugal mechanism of acceleration in Active galactic nuclei. At 50 J, the highest-energy ultra-high-energy cosmic rays have energies comparable to the energy of a 90-kilometre-per-hour baseball. As a result of discoveries, there has been interest in investigating cosmic rays of even greater energies. Most cosmic rays, however, do not have such extreme energies, however, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911 Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth. In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5300 meters in a balloon flight
33.
Solar cycle 24
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Solar Cycle 24 is the 24th solar cycle since 1755, when extensive recording of solar sunspot activity began. It is the current solar cycle, and began on January 4,2008 and it is on track to be the smallest sunspot cycle in over a century. Prior to the minima between the end of Solar Cycle 23 and the beginning of Solar Cycle 24, there were two competing theories about how strong Solar Cycle 24 would be. The two camps could be distinguished by those postulating the Sun retained a long memory or whether it had a short memory, prior to 2006, the difference was very drastic with a minority set of researchers predicting the smallest solar cycle in 100 years. Another group of researchers, including one at NASA, were predicting that it looks like its going to be one of the most intense cycles since record-keeping began almost 400 years ago. By 2012, consensus was a cycle, as solar cycles are much more predictable 3 years after minima. In May 2009 the NOAA/Space Weather Prediction Centers Solar Cycle 24 Prediction Panel predicted the cycle to peak at 90 sunspots in May 2013, in May 2012 NASAs expert David Hathaway predicted that current solar cycle would peak by the Spring of 2013 with about 60 sunspots. NASA also directly funded and used Ken Schattens physics-based models, which utilized a solar Dynamo model to predict the low sunspot count in cycle 24. Careful comparison of Schattens predictions with those of Hathaway will demonstrate the superiority of Schattens predictions, they are accurate as soon as solar minima 5–6 years before solar max. In early 2013, after months of calm, it was obvious that the active 2011 was not a prelude to a widely predicted late 2012-early 2013 peak in solar flares, sunspots. This unexpected stage prompted some scientists to propose a double-peaked solar maximum, the first peak reached 99 in 2011 and the second peak came in early 2014 at 101. According to NASA, the intensity of storms during Solar Cycle 24 may be elevated in some areas where the Earths magnetic field is weaker than expected. This fact was discovered by the THEMIS spacecraft in 2008, a 20-fold increase in particle counts that penetrate the Earths magnetic field may be expected. Solar Cycle 24 has been the subject of various hypotheses and commentary pertaining to its effects on Earth. He asserts that governments should ensure the integrity of electrical infrastructures, the current solar cycle is currently the subject of research, as it is not generating sunspots in the manner which would be expected. Sunspots did not begin to appear immediately after the last minimum and although they started to reappear in late 2009, on April 19,2012, the National Astronomical Observatory of Japan predicted that the Suns magnetic field will assume a quadrupole configuration in Solar Cycle 24. Throughout 2012, NASA posted several news releases discrediting the 2012 phenomenon and the so-called Mayan prophecy, on January 4,2008, a reversed-polarity sunspot appeared, and this signaled the start of Solar Cycle 24. It was high latitude and magnetically reversed, NOAA named the spot AR10981, or sunspot 981 for short
34.
Solar and Heliospheric Observatory
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It began normal operations in May 1996. It is a joint project of cooperation between the European Space Agency and NASA. Originally planned as a mission, SOHO continues to operate after over 20 years in space. In June 2013, a mission lasting until December 2016 was approved. In addition to its mission, it is the main source of near-real-time solar data for space weather prediction. Rather it lies in the plane passes through L1 and is perpendicular to the line connecting the Sun. It stays in this plane, tracing out an elliptical lissajous orbit centered about L1 and it orbits L1 once every six months, while L1 itself orbits the Sun every 12 months as it is coupled with the motion of the Earth. This keeps SOHO at a position for communication with Earth at all times. In normal operation the spacecraft transmits a continuous 200 kbit/s data stream of photographs, SOHOs data about solar activity are used to predict coronal mass ejection arrival times at earth, so electrical grids and satellites can be protected from their damaging effects. CMEs directed toward the earth may produce geomagnetic storms, which in turn produce geomagnetically induced currents, in the most extreme cases creating black-outs, etc. In 2003 ESA reported the failure of the antenna Y-axis stepper motor, necessary for pointing the high-gain antenna, at the time, it was thought that the antenna anomaly might cause two- to three-week data-blackouts every three months. The SOHO Mission Interruption sequence of events began on June 24,1998, while the SOHO Team was conducting a series of spacecraft gyroscope calibrations and maneuvers. Operations proceeded until 23,16 UTC when SOHO lost lock on the Sun, the SOHO Team attempted to recover the observatory, but SOHO entered the emergency mode again on June 2502,35 UTC. Recovery efforts continued, but SOHO entered the emergency mode for the last time at 04,38 UTC, all contact with SOHO was lost, and the mission interruption had begun. SOHO was spinning, losing power, and no longer pointing at the Sun. Expert ESA personnel were dispatched from Europe to the United States to direct operations. Days passed without contact from SOHO, on July 23, the Arecibo Observatory and Goldstone Solar System Radar combined to locate SOHO with radar, and to determine its location and attitude. SOHO was close to its position, oriented with its side versus the usual front Optical Surface Reflector panel pointing toward the Sun
35.
Solar cycle
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The solar cycle or solar magnetic activity cycle is the nearly periodic 11-year change in the Suns activity and appearance. They have been observed for centuries, the changes on the sun cause effects in space, in the atmosphere, and on Earths surface. While it is the dominant variable in solar activity, aperiodic fluctuations also occur, Solar cycles have an average duration of about 11 years. Solar maximum and solar minimum refer respectively to periods of maximum and minimum sunspot counts, cycles span from one minimum to the next. The solar cycle was discovered in 1843 by Samuel Heinrich Schwabe, following Wolfs numbering scheme, the 1755–1766 cycle is traditionally numbered 1. Wolf created a standard sunspot number index, the Wolf index, the period between 1645 and 1715, a time of few sunspots, is known as the Maunder minimum, after Edward Walter Maunder, who extensively researched this peculiar event, first noted by Gustav Spörer. In the second half of the nineteenth century Richard Carrington and by Spörer independently noted the phenomena of sunspots appearing at different latitudes at different parts of the cycle, the cycles physical basis was elucidated by Hale and collaborators, who in 1908 showed that sunspots were strongly magnetized. In 1919 they showed that the polarity of sunspot pairs, Is constant throughout a cycle, Is opposite across the equator throughout a cycle. Hales observations revealed that the complete magnetic cycle spans two solar cycles, or 22 years, before returning to its original state, however, because nearly all manifestations are insensitive to polarity, the 11-year solar cycle remains the focus of research. In 1961 the father-and-son team of Harold and Horace Babcock established that the cycle is a spatiotemporal magnetic process unfolding over the Sun as a whole. Horaces Babcock model described the Suns oscillatory magnetic field, with a periodicity of 22 years. It covered the exchange of energy between poloidal and toroidal solar magnetic field ingredients. The level of activity beginning in the 1940s is exceptional – the last period of similar magnitude occurred around 9,000 years ago. The Sun was at a high level of magnetic activity for only ~10% of the past 11,400 years. Almost all earlier high-activity periods were shorter than the present episode, fossil records suggest that the Solar cycle has been stable for at least the last 290 million years. For example, the cycle length during the early Permian is estimated to be 10.62 years, since observations began, cycles have ranged from 9–14 years. The current solar cycle began on January 4,2008, with minimal activity until early 2010 and it is on track to have the lowest recorded sunspot activity since accurate records began in 1750. The cycle featured a double-peaked solar maximum, the first peak reached 99 in 2011 and the second in early 2014 at 101
36.
Sigmoid function
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A sigmoid function is a mathematical function having an S shaped curve. Often, sigmoid function refers to the case of the logistic function shown in the first figure. Other examples of similar shapes include the Gompertz curve and the ogee curve, sigmoid functions have finite limits at negative infinity and infinity, most often going either from 0 to 1 or from −1 to 1, depending on convention. A wide variety of functions have been used as the activation function of artificial neurons. A sigmoid function is a differentiable real function that is defined for all real input values and has a positive derivative at each point. In general, a function is real-valued and differentiable, having either a non-negative or non-positive first derivative which is bell shaped. There are also a pair of horizontal asymptotes as t → ± ∞, the differential equation d d t S = c 1 S, with the inclusion of a boundary condition providing a third degree of freedom, c 3, provides a class of functions of this type. The logistic function has this further, important property, that its derivative can be expressed by the function itself, many natural processes, such as those of complex system learning curves, exhibit a progression from small beginnings that accelerates and approaches a climax over time. When a detailed description is lacking, a function is often used. The integral of any smooth, positive, bump-shaped function will be sigmoidal, the most famous such example is the error function, which is related to the cumulative distribution function of a normal distribution. Properties of the sigmoid, including how it can shift along axes and how its domain may be transformed
37.
Moreton wave
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A Moreton wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar tsunami, they are generated by solar flares and they are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank who spotted them in 1959. He discovered them in photography of the chromosphere in the light of the Balmer alpha transition. There were few follow-up studies for decades, then the 1995 launch of the Solar and Heliospheric Observatory led to observation of coronal waves, which cause Moreton waves. Moreton waves were a topic again. The reality of Moreton waves has also confirmed by the two STEREO spacecraft. They observed a 100, 000-km-high wave of hot plasma and magnetism, moving at 250 km/s, Moreton measured the waves propagating at a speed of 500–1500 km/s. Yutaka Uchida interpreted Moreton waves as MHD fast mode shock waves propagating in the corona and he links them to type II radio bursts, which are radio-wave discharges created when coronal mass ejections accelerate shocks. Moreton waves can be observed primarily in the Hα band, Solar transition region Spicule Solar prominence Gravity wave Helioseismology Asteroseismology OSO8 More of Moretons papers can be found here. Have you ever heard the Sun, - many recordings of solar radio emissions including a solar flare shockfront
38.
Heliopause (astronomy)
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The heliosphere is the bubble-like region of space dominated by the Sun, which extends far beyond the orbit of Pluto. The solar wind flows outward from the Sun until encountering the termination shock, the overall shape of the heliosphere is controlled by the interstellar medium through which it is traveling, as well as the Sun, and is not perfectly spherical. The limited data available and unexplored nature of structures have resulted in many theories. On September 12,2013, NASA announced that Voyager 1 had exited the heliosphere on August 25,2012, originating at the extremely hot surface of the corona, solar wind particles reach escape velocity, streaming outwards at 300 to 800 km/s. As it begins to interact with the medium, its velocity slows before finally stopping altogether. The termination shock was traversed by Voyager 1 in 2004, and it may be a more gentle bow wave. Voyager data led to a new theory that the heliosheath has magnetic bubbles, the stagnation region within the heliosheath, starting around 113 au, was detected by Voyager 1 in 2010. There the solar wind velocity drops to zero, the field intensity doubles. Starting in May 2012 at 120 au, Voyager 1 detected an increase in cosmic rays. In the summer of 2013 NASA announced that Voyager 1 had reached interstellar space as of August 25,2012, cassini and IBEX data challenged the heliotail theory in 2009. In July 2013, IBEX results revealed a 4-lobed tail on the Solar Systems heliosphere, the solar wind consists of particles and fields. Because the Sun rotates once approximately every 25 days, the magnetic field transported by the wind gets wrapped into a spiral. Variations in the Suns magnetic field are carried outward by the solar wind, the heliospheric current sheet is a ripple in the heliosphere created by the rotating magnetic field of the Sun. Extending throughout the heliosphere, it is considered the largest structure in the Solar System and is said to resemble a ballerinas skirt, the outer structure of the heliosphere is determined by the interactions between the solar wind and the winds of interstellar space. The solar wind away from the Sun in all directions at speeds of several hundred km/s in the Earths vicinity. At some distance from the Sun, well beyond the orbit of Neptune and this takes place in several stages, The solar wind is traveling at supersonic speeds within the Solar System. At the termination shock, a shock wave, the solar wind falls below the speed of sound. However, observations in 2009 showed that model is incorrect
39.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
40.
Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
41.
Ulysses (spacecraft)
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Ulysses is a decommissioned robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990, made three fast latitude scans of the Sun in 1994/1995, 2000/2001, and 2007/2008, in addition, the probe studied several comets. Ulysses was a joint venture of NASA and the European Space Agency with participation from Canadas National Research Council, the last day for mission operations on Ulysses was June 30,2009. However the necessary amount of velocity change to achieve a high orbit of about 80° far exceeded the capabilities of any launch vehicle. The spacecraft was originally named Odysseus, because of its lengthy and it was renamed Ulysses, the Latin translation of Odysseus, at ESAs request in honour not only of Homers mythological hero but also with reference to Dantes description in Dantes Inferno. Ulysses was originally scheduled for launch in May 1986 aboard the Space Shuttle Challenger on STS-61-F, due to the loss of Challenger, the launch of Ulysses was delayed until October 6,1990 aboard Discovery. The spacecraft body was roughly a box, approximately 3.2 ×3.3 ×2.1 m in size, the box mounted the 1.65 m dish antenna and the GPHS-RTG radioisotope thermoelectric generator power source. The box was divided into noisy and quiet sections, the noisy section abutted the RTG, the quiet section housed the instrument electronics. Particularly loud components, such as the preamps for the dipole, were mounted outside the structure entirely. Ulysses was spin-stabilised about its z-axis which roughly coincides with the axis of the dish antenna, the RTG, whip antennas, and instrument boom were placed to stabilize this axis, with the spin rate nominally at 5 rpm. Inside the body was a fuel tank. Hydrazine monopropellant was used for course corrections inbound to Jupiter, the spacecraft was controlled by eight thrusters in two blocks. Thrusters were pulsed in the domain to perform rotation or translation. For fine attitude control, the S-band antenna feed was mounted slightly off-axis and this offset feed combined with the spacecraft spin introduced an oscillation to an S-band radio signal transmitted from Earth when received on board the spacecraft. The amplitude and phase of oscillation was proportional to the orientation of the spin axis relative to the Earth direction. This method of determining the orientation is called CONSCAN and was used by early radars for automated tracking of targets. The spacecraft used S-band for uplinked commands and downlinked telemetry, through dual redundant 5-watt transceivers, the spacecraft used X-band for science return, using dual 20 W TWTAs until the failure of the last remaining TWTA in January 2008. Both bands used the dish antenna with prime-focus feeds, unlike the Cassegrain feeds of most other spacecraft dishes, dual tape recorders, each of approximately 45-megabit capacity, stored science data between the nominal eight-hour communications sessions during the prime and extended mission phases
42.
Frame of reference
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In physics, a frame of reference consists of an abstract coordinate system and the set of physical reference points that uniquely fix the coordinate system and standardize measurements. In n dimensions, n+1 reference points are sufficient to define a reference frame. Using rectangular coordinates, a frame may be defined with a reference point at the origin. In Einsteinian relativity, reference frames are used to specify the relationship between an observer and the phenomenon or phenomena under observation. In this context, the phrase often becomes observational frame of reference, a relativistic reference frame includes the coordinate time, which does not correspond across different frames moving relatively to each other. The situation thus differs from Galilean relativity, where all possible coordinate times are essentially equivalent, the need to distinguish between the various meanings of frame of reference has led to a variety of terms. For example, sometimes the type of system is attached as a modifier. Sometimes the state of motion is emphasized, as in rotating frame of reference, sometimes the way it transforms to frames considered as related is emphasized as in Galilean frame of reference. Sometimes frames are distinguished by the scale of their observations, as in macroscopic and microscopic frames of reference, in this sense, an observational frame of reference allows study of the effect of motion upon an entire family of coordinate systems that could be attached to this frame. On the other hand, a system may be employed for many purposes where the state of motion is not the primary concern. For example, a system may be adopted to take advantage of the symmetry of a system. In a still broader perspective, the formulation of many problems in physics employs generalized coordinates, normal modes or eigenvectors and it seems useful to divorce the various aspects of a reference frame for the discussion below. A coordinate system is a concept, amounting to a choice of language used to describe observations. Consequently, an observer in a frame of reference can choose to employ any coordinate system to describe observations made from that frame of reference. A change in the choice of coordinate system does not change an observers state of motion. This viewpoint can be found elsewhere as well, which is not to dispute that some coordinate systems may be a better choice for some observations than are others. Choice of what to measure and with what observational apparatus is a separate from the observers state of motion. D. Norton, The discussion is taken beyond simple space-time coordinate systems by Brading, extension to coordinate systems using generalized coordinates underlies the Hamiltonian and Lagrangian formulations of quantum field theory, classical relativistic mechanics, and quantum gravity
. Bibcode:2012ApJS..199...10T. doi:10.1088/0067-0049/199/1/10.
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