1.
Stellar wind
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A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of stars by being less collimated. Different types of stars have different types of stellar winds, post-main-sequence stars nearing the ends of their lives often eject large quantities of mass in massive, slow winds. These include red giants and supergiants, and asymptotic giant branch stars and these winds are understood to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars. Massive stars of types O and B have stellar winds with lower mass loss rates, such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen. These high-energy stellar winds blow stellar wind bubbles, g-type stars like the Earths Sun have a wind driven by their hot, magnetized corona. The Suns wind is called the solar wind and these winds consist mostly of high-energy electrons and protons that are able to escape the stars gravity because of the high temperature of the corona. Stellar winds from main-sequence stars do not strongly influence the evolution of lower mass stars such as the Sun, solar wind Cosmic ray Cosmic wind
2.
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
3.
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
4.
Granule (solar physics)
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Granules on the photosphere of the Sun are caused by convection currents of plasma within the Suns convective zone. The grainy appearance of the photosphere is produced by the tops of these convective cells and is called granulation. The rising part of the granules is located in the center where the plasma is hotter, the outer edge of the granules is darker due to the cooler descending plasma. A typical granule has a diameter on the order of 1,500 kilometers, at any one time, the Suns surface is covered by about 4 million granules. Below the photosphere is a layer of supergranules up to 30,000 kilometers in diameter with lifespans of up to 24 hours
5.
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
6.
Photosphere
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The photosphere is a stars outer shell from which light is radiated. It extends into a stars surface until the plasma becomes opaque, in other words, a photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths. The surface of a star is defined to have a given by the effective temperature in the Stefan–Boltzmann law. Stars, excepting neutron stars, have no solid surface, therefore, the photosphere is typically used to describe the Suns or another stars visual surface. The Sun is composed primarily of the elements hydrogen and helium, they account for 74. 9% and 23. 8% of the mass of the Sun in the photosphere. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen, carbon, neon, and iron being the most abundant. The Suns photosphere has a temperature between 4,500 and 6,000 K and a density of about 2×10−4 kg/m3, each granule has a lifespan of only about eight minutes, resulting in a continually shifting boiling pattern. Grouping the typical granules are super granules up to 30,000 kilometers in diameter with lifespans of up to 24 hours and these details are too fine to see on other stars. The Suns visible atmosphere has other layers above the photosphere, the 2,000 kilometer-deep chromosphere lies just between the photosphere and the much hotter but more tenuous corona, other surface features on the photosphere are solar flares and sunspots. Animated explanation of the temperature of the Photosphere
7.
Chromosphere
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The chromosphere is the second of the three main layers in the Suns atmosphere and is roughly 3,000 to 5,000 kilometers deep. The chromospheres rosy red color is apparent during eclipses. The Chromosphere sits just above the photosphere and below the transition region. The layer of the chromosphere atop the photosphere is homogeneous, a forest of hairy appearing spicules rise from the homogeneous layer some of which extend 10,000 km into the corona above. The density of the chromosphere is only 10−4 times that of the photosphere, the layer beneath and this makes the chromosphere normally invisible and it can be seen only during a total eclipse, where its reddish color is revealed. The color hues are anywhere between pink and red, however, without special equipment, the chromosphere cannot normally be seen due to the overwhelming brightness of the photosphere beneath. The density of the chromosphere decreases with distance from the center of the Sun and this decreases logarithmically from 1017 particles per cubic centimeter, or approximately 2×10−4 kg/m3 to under 1. 6×10−11 kg/m3 at the outer boundary. Chromospheres have been observed also in other than the Sun. Whilst the photosphere has a line spectrum, the chromospheres spectrum is dominated by emission lines. In particular, one of its strongest lines is the Hα at a wavelength of 656.3 nm, a wavelength of 656.3 nm is in the red part of the spectrum, which causes the chromosphere to have its characteristic reddish colour. By analysing the spectrum of the chromosphere, it was found that the temperature of this layer of the atmosphere increases with increasing height in the chromosphere itself. The temperature at the top of photosphere is only about 4,400 K, while at the top of chromosphere, some 2,000 km higher and this is however the opposite of what we find in the photosphere, where the temperature drops with increasing height. It is not yet fully understood what causes the temperature of the chromosphere to paradoxically increase further from the Suns interior. However, it likely to be explained, partially or totally. Solar prominences rise up through the chromosphere from the photosphere, sometimes reaching altitudes of 150,000 km and these gigantic plumes of gas are the most spectacular of solar phenomena, aside from the less frequent solar flares. The most common feature is the presence of spicules, long fingers of luminous gas which appear like the blades of a huge field of fiery grass growing upwards from the photosphere below. Spicules rise to the top of the chromosphere and then back down again over the course of about 10 minutes. Similarly, there are horizontal wisps of gas called fibrils, which last about twice as long as spicules, images taken in typical chromospheric lines show the presence of bright cells, usually called as network, while the surrounding black regions are named internetwork
8.
Convection zone
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A convection zone, convective zone or convective region of a star is a layer which is unstable to convection. Energy is primarily or partially transported by convection in such a region, in a radiation zone, energy is transported by radiation and conduction. Stellar convection consists of movement of plasma within the star which usually forms a circular convection current with the heated plasma ascending. The Schwarzschild criterion expresses the conditions under which a region of a star is unstable to convection, a parcel of gas that rises slightly will find itself in an environment of lower pressure than the one it came from. As a result, the parcel will expand and cool and its buoyancy will then cause it to continue to rise. The region of the star in which this happens is the convection zone, in main sequence stars more than 1. The high temperature gradient in the region forms a convection zone that slowly mixes the hydrogen fuel with the helium product. The core convection zone of stars is overlaid by a radiation zone that is in thermal equilibrium. In the most massive stars, the zone may reach all the way from the core to the surface. In main sequence stars of less than about 10 solar masses, the relatively low temperature in this region simultaneously causes the opacity due to heavier elements to be high enough to produce a steep temperature gradient. This combination of circumstances produces an outer zone, the top of which is visible in the Sun as solar granulation. Low mass main sequences of stars, such as red dwarfs below 0.35 solar masses, as well as pre-main sequence stars on the Hayashi track, are convective throughout and do not contain a radiation zone. In main sequence stars similar to the Sun, which have a core and convective envelope. In red giant stars, and particularly during the giant branch phase. This causes dredge-up events, short-lived very deep convection zones that transport fusion products to the surface of the star, hansen, C. J. Kawaler, S. D. & Trimble, V. Animated explanation of the Convection zone, animated explanation of the temperature and density of the Convection zone
9.
Tachocline
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The tachocline is the transition region of the Sun between the radiative interior and the differentially rotating outer convective zone. It is in the third of the Sun. This causes the region to have a large shear as the rotation rate changes very rapidly. The convective exterior rotates as a fluid with differential rotation with the poles rotating slowly. The radiative interior exhibits solid-body rotation, possibly due to a fossil field, the rotation rate through the interior is roughly equal to the rotation rate at mid-latitudes, i. e. in-between the rate at the slow poles and the fast equator. Recent results from helioseismology indicate that the tachocline is located at a radius of at most 0.70 times the Solar radius and this would mean the area has a very large shear profile that is one way that large scale magnetic fields can be formed. The geometry and width of the plays a important role in models of the solar dynamo by winding up weaker poloidal field to create a much stronger toroidal field. The term tachocline was coined in a paper by Edward Spiegel, section 3.2 from Living Reviews in Solar Physics Charbonneau, P. Christensen-Dalsgaard, J. Henning, R. Larsen, R. M. Schou, J. Thompson, M. J. Tomczyk, S. 1999a, “Helioseismic Constraints on the Structure of the Solar Tachocline”, Astrophys. Basu, S. Antia, H. M. Narasimha, D.1994, “Helioseismic Measurement of the Extent of Overshoot Below the Solar Convection Zone”, Mon. 267, 209-224, Hughes, D. W. Rosner, R. Weiss, N. O.2007 The Solar Tachocline, 382pp
10.
Solar core
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The core of the Sun is considered to extend from the center to about 0.2 to 0.25 of solar radius. It is the hottest part of the Sun and of the Solar System and it has a density of 150 g/cm³ at the center, and a temperature of 15 million degrees Celsius. The core is made of hot, dense gas in the plasmic state, due to fusion, the composition of the solar plasma drops from 68-70% hydrogen by mass at the outer core, to 33% hydrogen at the core/Sun center. The core inside 0.20 of the radius, contains 34% of the Suns mass. Inside 0.24 solar radius, the core generates 99% of the power of the Sun. However, as depth into the Sun increases, fusion decreases the fraction of hydrogen, all but 2% of the remaining plasma mass is helium, at the center of the Sun. Approximately 3. 6×1038 protons, or roughly 299 million metric tons of hydrogen, are converted into helium nuclei every second releasing energy at a rate of 3. 86×1026 joules per second. The core produces almost all of the Suns heat via fusion, the energy conversion per unit time of fusion in the core varies with distance from the solar center. At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3, the Sun is much hotter than a compost heap due to the Suns enormous volume. At 19% of the radius, near the edge of the core, temperatures are about 10 million kelvin and fusion power density is 6.9 W/m3. The density here is about 40 g/cm3, or about 27% of that at the center, some 91% of the solar energy is produced within this radius. Within 24% of the radius, 99% of the Suns power is produced, beyond 30% of the solar radius, where temperature is 7 million K and density has fallen to 10 g/cm3 the rate of fusion is almost nil. There are two reactions in which 4 H nuclei may eventually result in one He nucleus, proton-proton chain reaction. The time that deuterium and helium-3 in the next reactions last and these later reactions proceed via the nuclear force and are thus much faster. The total energy released by reactions in turning 4 hydrogen atoms into 1 helium atom is 26.7 MeV. This involves carbon atoms which are not consumed in the overall process, the rate of nuclear fusion depends strongly on density. However the Sun gradually becomes hotter during its time on the main sequence and this increases the gravitational pressure on the core which is resisted by a gradual increase in the rate at which fusion occurs. This process speeds up time as the core gradually becomes heavier
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 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
13.
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
14.
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
15.
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
16.
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
17.
Alpha particle
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Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of decay. Alpha particles are named after the first letter in the Greek alphabet, the symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are sometimes written as He2+ or 4 2He2+ indicating a helium ion with a +2 charge. If the ion gains electrons from its environment, the particle can be written as a normal helium atom 4 2He. Some science authors may use doubly ionized helium nuclei and alpha particles as interchangeable terms, the nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors to be alpha particles. As with beta and gamma rays/particles, the used for the particle carries some mild connotations about its production process and energy. Thus, alpha particles may be used as a term when referring to stellar helium nuclei reactions. A higher energy version of alphas than produced in alpha decay is a product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators are less likely to be referred to as alpha particles, alpha particles, like helium nuclei, have a net spin of zero. Due to the mechanism of their production in standard alpha radioactive decay, alpha particles generally have an energy of about 5 MeV. They are a highly ionizing form of radiation, and have low penetration depth. They are able to be stopped by a few centimeters of air, however, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. To a lesser extent, this is true of very high-energy helium nuclei produced by particle accelerators. The best-known source of particles is alpha decay of heavier atoms. When an atom emits an alpha particle in alpha decay, the mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atomic number of the atom goes down by two, as a result of the loss of two protons – the atom becomes a new element. Examples of this sort of nuclear transmutation are when uranium becomes thorium, or radium becomes radon gas, alpha particles are commonly emitted by all of the larger radioactive nuclei such as uranium, thorium, actinium, and radium, as well as the transuranic elements
18.
Thermal energy
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In thermodynamics, thermal energy refers to the internal energy present in a system due to its temperature. Heat is energy transferred spontaneously from a hotter to a system or body. Heat is energy in transfer, not a property of the system, on the other hand, internal energy is a property of a system. The internal energy of a gas can in this sense be regarded as thermal energy. In this case, however, thermal energy and internal energy are identical, systems that are more complex than ideal gases can undergo phase transitions. Phase transitions can change the energy of the system without changing its temperature. Therefore, the thermal energy cannot be defined solely by the temperature, for these reasons, the concept of the thermal energy of a system is ill-defined and is not used in thermodynamics. In an 1847 lecture entitled On Matter, Living Force, and Heat, James Prescott Joule characterized various terms that are related to thermal energy. He identified the terms latent heat and sensible heat as forms of heat each effecting distinct physical phenomena, namely the potential and kinetic energy of particles, Heat transfer Ocean thermal energy conversion Thermal science Example of incorrect use of heat and thermal energy
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Electronvolt
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In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
20.
Density
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The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
21.
Temperature
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A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, geology, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale. Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, nevertheless, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials
22.
Speed
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In everyday use and in kinematics, the speed of an object is the magnitude of its velocity, it is thus a scalar quantity. Speed has the dimensions of distance divided by time, the SI unit of speed is the metre per second, but the most common unit of speed in everyday usage is the kilometre per hour or, in the US and the UK, miles per hour. For air and marine travel the knot is commonly used, the fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in a vacuum c =299792458 metres per second. Matter cannot quite reach the speed of light, as this would require an amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed, italian physicist Galileo Galilei is usually credited with being the first to measure speed by considering the distance covered and the time it takes. Galileo defined speed as the distance covered per unit of time, in equation form, this is v = d t, where v is speed, d is distance, and t is time. A cyclist who covers 30 metres in a time of 2 seconds, objects in motion often have variations in speed. If s is the length of the path travelled until time t, in the special case where the velocity is constant, this can be simplified to v = s / t. The average speed over a time interval is the total distance travelled divided by the time duration. Speed at some instant, or assumed constant during a short period of time, is called instantaneous speed. By looking at a speedometer, one can read the speed of a car at any instant. A car travelling at 50 km/h generally goes for less than one hour at a constant speed, if the vehicle continued at that speed for half an hour, it would cover half that distance. If it continued for one minute, it would cover about 833 m. Different from instantaneous speed, average speed is defined as the distance covered divided by the time interval. For example, if a distance of 80 kilometres is driven in 1 hour, likewise, if 320 kilometres are travelled in 4 hours, the average speed is also 80 kilometres per hour. When a distance in kilometres is divided by a time in hours, average speed does not describe the speed variations that may have taken place during shorter time intervals, and so average speed is often quite different from a value of instantaneous speed. If the average speed and the time of travel are known, using this equation for an average speed of 80 kilometres per hour on a 4-hour trip, the distance covered is found to be 320 kilometres. Linear speed is the distance travelled per unit of time, while speed is the linear speed of something moving along a circular path
23.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
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Supersonic speed
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Supersonic travel is a rate of travel of an object that exceeds the speed of sound. For objects traveling in dry air of a temperature of 20 °C at sea level, speeds greater than five times the speed of sound are often referred to as hypersonic. Flights during which some parts of the air surrounding an object, such as the ends of rotor blades. This occurs typically somewhere between Mach 0.8 and Mach 1.23, sounds are traveling vibrations in the form of pressure waves in an elastic medium. In gases, sound travels longitudinally at different speeds, mostly depending on the mass and temperature of the gas. Since air temperature and composition varies significantly with altitude, Mach numbers for aircraft may change despite a constant travel speed, in water at room temperature supersonic speed can be considered as any speed greater than 1,440 m/s. In solids, sound waves can be polarized longitudinally or transversely and have higher velocities. Supersonic fracture is crack motion faster than the speed of sound in a brittle material, at the beginning of the 20th century, the term supersonic was used as an adjective to describe sound whose frequency is above the range of normal human hearing. The modern term for this meaning is ultrasonic, the tip of a bullwhip is thought to be the first man-made object to break the sound barrier, resulting in the telltale crack. The wave motion traveling through the bullwhip is what makes it capable of achieving supersonic speeds, most modern fighter aircraft are supersonic aircraft, but there have been supersonic passenger aircraft, namely Concorde and the Tupolev Tu-144. Both these passenger aircraft and some modern fighters are also capable of supercruise, since Concordes final retirement flight on November 26,2003, there are no supersonic passenger aircraft left in service. Some large bombers, such as the Tupolev Tu-160 and Rockwell B-1 Lancer are also supersonic-capable, most modern firearm bullets are supersonic, with rifle projectiles often travelling at speeds approaching and in some cases well exceeding Mach 3. Most spacecraft, most notably the Space Shuttle are supersonic at least during portions of their reentry, during ascent, launch vehicles generally avoid going supersonic below 30 km to reduce air drag. Note that the speed of sound decreases somewhat with altitude, due to lower temperatures found there, at even higher altitudes the temperature starts increasing, with the corresponding increase in the speed of sound. When an inflated balloon is burst, the pieces of latex contracts at a supersonic speed. Supersonic aerodynamics is simpler than subsonic aerodynamics because the airsheets at different points along the plane often cant affect each other, Supersonic jets and rocket vehicles require several times greater thrust to push through the extra aerodynamic drag experienced within the transonic region. Designers use the Supersonic area rule and the Whitcomb area rule to minimize changes in size. However, in applications, a supersonic aircraft will have to operate stably in both subsonic and supersonic profiles, hence aerodynamic design is more complex
25.
Voyager 2
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Voyager 2 is a space probe launched by NASA on August 20,1977, to study the outer planets. Part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach Jupiter and Saturn but enabled further encounters with Uranus and it is the only spacecraft to have visited either of the ice giants. Voyager 2 is now in its mission to study the outer reaches of the Solar System and has been operating for 39 years,7 months and 17 days. It remains in contact through the Deep Space Network, at a distance of 114 AU from the Sun as of April 5th,2017, Voyager 2 is one of the most distant human-made objects, along with Voyager 1, New Horizons, Pioneer 10 and Pioneer 11. The probe was moving at a velocity of 15.4 km/s relative to the Sun as of December 2014 and is traveling through the heliosheath, upon reaching interstellar space, Voyager 2 is expected to provide the first direct measurements of the density and temperature of the interstellar plasma. The spacecraft would be designed with redundant systems to ensure survival through the entire tour, by 1972 the mission was scaled back and replaced with two Mariner-derived spacecraft, the Mariner Jupiter-Saturn probes. To keep apparent lifetime program costs low, the mission would include only flybys of Jupiter and Saturn, as the program progressed, the name was changed to Voyager. The primary mission of Voyager 1 was to explore Jupiter, Saturn, Voyager 2 was also to explore Jupiter and Saturn, but on a trajectory that would have option of continuing on to Uranus and Neptune, or being redirected to Titan as a backup for Voyager 1. Upon successful completion of Voyager 1s objectives, Voyager 2 would get an extension to send the probe on towards Uranus. Collectively these instruments are part of the Attitude and Articulation Control Subsystem along with redundant units of most instruments and 8 backup thrusters, the spacecraft also included 11 scientific instruments to study celestial objects as it traveled through space. Built with the intent for eventual interstellar travel, Voyager 2 included a large,3.7 m parabolic, when the spacecraft is unable to communicate with Earth, the Digital Tape Recorder can record about 64 kilobytes of data for transmission at another time. The spacecraft was built with 3 Multihundred-Watt radioisotope thermoelectric generators, each RTG includes 24 pressed plutonium oxide spheres and provides enough heat to generate approximately 157 watts of power at launch. Collectively, the RTGs supply the spacecraft with 470 watts at launch, for more details on the Voyager space probes identical instrument packages, see the separate article on the overall Voyager Program. The Voyager 2 probe was launched on August 20,1977, by NASA from Space Launch Complex 41 at Cape Canaveral, Florida, two weeks later, the twin Voyager 1 probe would be launched on September 5,1977. However, Voyager 1 would reach both Jupiter and Saturn sooner, as Voyager 2 had been launched into a longer, more circular trajectory, Voyager 2s closest approach to Jupiter occurred on July 9,1979. It came within 570,000 km of the cloud tops. It discovered a few rings around Jupiter, as well as volcanic activity on the moon Io, the Great Red Spot was revealed as a complex storm moving in a counterclockwise direction. An array of other storms and eddies were found throughout the banded clouds
26.
Voyager 1
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Voyager 1 is a space probe launched by NASA on September 5,1977. Part of the Voyager program to study the outer Solar System, Voyager 1 launched 16 days after its twin, having operated for 39 years,7 months and 1 day, the spacecraft still communicates with the Deep Space Network to receive routine commands and return data. At a distance of 138 AU from the Sun as of March 2017, the probes primary mission objectives included flybys of Jupiter, Saturn, and Saturns large moon, Titan. It studied the weather, magnetic fields, and rings of the two planets and was the first probe to provide detailed images of their moons. After completing its mission with the flyby of Saturn on November 20,1980, Voyager 1 began an extended mission to explore the regions. On August 25,2012, Voyager 1 crossed the heliopause to become the first spacecraft to enter interstellar space, in the 1960s, a Grand Tour to study the outer planets was proposed which prompted NASA to begin work on a mission in the early 1970s. Information gathered by the Pioneer 10 spacecraft helped Voyagers engineers design Voyager to cope effectively with the intense radiation environment around Jupiter. Initially, Voyager 1 was planned as Mariner 11 of the Mariner program, due to budget cuts, the mission was scaled back to be a flyby of Jupiter and Saturn and renamed the Mariner Jupiter-Saturn probes. As the program progressed, the name was changed to Voyager. Voyager 1 was constructed by the Jet Propulsion Laboratory and it has 16 hydrazine thrusters, three-axis stabilization gyroscopes, and referencing instruments to keep the probes radio antenna pointed toward Earth. Collectively, these instruments are part of the Attitude and Articulation Control Subsystem, the spacecraft also included 11 scientific instruments to study celestial objects such as planets as it travels through space. The radio communication system of Voyager 1 was designed to be used up to, the communication system includes a 3. 7-meter diameter parabolic dish high-gain antenna to send and receive radio waves via the three Deep Space Network stations on the Earth. The craft normally transmits data to Earth over Deep Space Network Channel 18, using a frequency of either 2.3 GHz or 8.4 GHz, while signals from Earth to Voyager are broadcast at 2.1 GHz. When Voyager 1 is unable to communicate directly with the Earth, signals from Voyager 1 take over 19 hours to reach Earth. Voyager 1 has three radioisotope thermoelectric generators mounted on a boom, each MHW-RTG contains 24 pressed plutonium-238 oxide spheres. The RTGs generated about 470 W of electric power at the time of launch, the power output of the RTGs declines over time, but the crafts RTGs will continue to support some of its operations until 2025. As of 2017-04-06, Voyager 1 has 73. 14% of the plutonium-238 that it had at launch, by 2050, it will have 56. 5% left. Since the 1990s, space probes usually have completely autonomous cameras, the computer command subsystem controls the cameras
27.
Heliosheath
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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
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Interstellar medium
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In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and it fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of radiation, is the interstellar radiation field. The interstellar medium is composed of phases, distinguished by whether matter is ionic, atomic, or molecular. The interstellar medium is composed primarily of hydrogen followed by helium with trace amounts of carbon, oxygen, the thermal pressures of these phases are in rough equilibrium with one another. Magnetic fields and turbulent motions also provide pressure in the ISM, in all phases, the interstellar medium is extremely tenuous by terrestrial standards. In cool, dense regions of the ISM, matter is primarily in molecular form, in hot, diffuse regions of the ISM, matter is primarily ionized, and the density may be as low as 10−4 ions per cm3. Compare this with a density of roughly 1019 molecules per cm3 for air at sea level. By mass, 99% of the ISM is gas in any form, and 1% is dust. Of the gas in the ISM, by number 91% of atoms are hydrogen and 9% are helium, with 0. 1% being atoms of elements heavier than hydrogen or helium, by mass this amounts to 70% hydrogen, 28% helium, and 1. 5% heavier elements. The hydrogen and helium are primarily a result of primordial nucleosynthesis, the ISM plays a crucial role in astrophysics precisely because of its intermediate role between stellar and galactic scales. Stars form within the densest regions of the ISM, molecular clouds, and replenish the ISM with matter and energy through planetary nebulae, stellar winds, and supernovae. This interplay between stars and the ISM helps determine the rate at which a galaxy depletes its gaseous content, voyager 1 reached the ISM on August 25,2012, making it the first artificial object from Earth to do so. Interstellar plasma and dust will be studied until the end in 2025. Table 1 shows a breakdown of the properties of the components of the ISM of the Milky Way, field, Goldsmith & Habing put forward the static two phase equilibrium model to explain the observed properties of the ISM. Their modeled ISM consisted of a dense phase, consisting of clouds of neutral and molecular hydrogen. McKee & Ostriker added a third phase that represented the very hot gas which had been shock heated by supernovae. These phases are the temperatures where heating and cooling can reach a stable equilibrium and their paper formed the basis for further study over the past three decades
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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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Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
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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
32.
Richard Christopher Carrington
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Carrington was born at Chelsea, the second son of Richard Carrington, the proprietor of a large brewery at Brentford, and his wife Esther Clarke Aplin. He entered upon his duties there in October 1849, but soon became dissatisfied with their narrow scope, the observatory was ill supplied with instruments, and the leisure left him for study served only to widen his aims. Bessels and Argelanders star-zones, above all, struck him as a model for imitation and he had not, however, been idle. His admission as a member of the Royal Astronomical Society,14 March 1851, in June 1852 he fixed upon a site for an observatory and dwelling-house at Redhill, Surrey. In July 1853 a transit-circle of 5½ feet focus, reduced in scale from the Greenwich model, and an equatoreal of 4½ inches aperture, both by Simms, were in their places, and work was begun. It included a comparison of Schwerds places for 680 stars with those obtained at Redhill. Ten corresponding maps, copper-engraved, accompanied the catalogue, meanwhile, Carrington had adopted, and was cultivating with his usual felicity of treatment, a ‘second subject’ at that juncture of peculiar interest and importance. He accordingly resolved to devote his energies to the sun. Solar physics as a whole, however, he excluded from his field of view. He limited his task to fixing the period of the suns rotation, to tracing the laws of distribution of maculæ. Adequately to compass these ends, new devices of observation, reduction, leaving photography to his successors as too undeveloped for immediate use, he chose a method founded on the idea of making the solar disc its own circular micrometer. An image of the sun was thrown upon a screen placed at such a distance from the eyepiece of the 4½-inch equatoreal as to give to the disc a diameter of 12 to 14 inches. In the focus of the telescope, which was firmly clamped, in this manner, during seven and a half years,5,290 observations were made of 954 separate groups, many of which were besides accurately depicted in drawings. The results appeared in a 4to volume, the publication of which was aided by a grant from the Royal Society and its title ran as follows, ‘Observations of the Spots on the Sun from November 9,1853, to March 24,1861, made at Redhill’. Never were data more opportunely furnished, perhaps more effectually than the pronouncements of spectrum analysis, they served to revolutionise ideas on solar physics. Efforts to ascertain the true rate of solar rotation had been baffled by what were called the ‘proper motions’ of the spots serving as indexes to it. Carrington showed that these were in reality due to a great ‘bodily drift’ of the photosphere, there was, then, no single period ascertainable through observations of the solar surface. By equatorial spots the circuit was found to be performed in two and a half days less than by spots at the extreme north and south limits of 45°
33.
Solar storm of 1859
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The Solar storm of 1859—known as the Carrington Event—was a powerful geomagnetic solar storm during solar cycle 10. A solar coronal mass ejection hit Earths magnetosphere and induced one of the largest geomagnetic storms on record, the associated white light flare in the solar photosphere was observed and recorded by English astronomers Richard C. Studies have shown that a storm of this magnitude occurring today would likely cause more widespread problems for a modern. The solar storm of 2012 was of magnitude, but it passed Earths orbit without striking the planet. From August 28 to September 2,1859, many sunspots appeared on the Sun, on August 29, southern auroras were observed as far north as Queensland, Australia. Just before noon on September 1, the English amateur astronomers Richard Carrington, the flare was associated with a major coronal mass ejection that travelled directly toward Earth, taking 17.6 hours to make the 150 million kilometre journey. Worldwide reports on the effects of the storm of 1859 were compiled and published by American mathematician Elias Loomis. On September 1–2,1859, one of the largest recorded geomagnetic storms occurred, people in the northeastern United States could read a newspaper by the auroras light. Estimates of the storm range from -800 nT to -1750 nT. Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks, some telegraph operators could continue to send and receive messages despite having disconnected their power supplies. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, the light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, between 12 and 1 oclock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance. S. Ice cores containing thin nitrate-rich layers have been analysed to reconstruct a history of past solar storms predating reliable observations and it is claimed that data from Greenland ice cores show evidence of individual solar-proton events, including the Carrington event. Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported, the March 1989 geomagnetic storm knocked out power across large sections of Quebec. On July 23,2012 a Carrington-class Solar Superstorm was observed, information about these observations was first shared publicly by NASA on April 28,2014. Description of a Singular Appearance seen in the Sun on September 1,1859, monthly Notices of the Royal Astronomical Society. Space storm alert,90 seconds from catastrophe, archived from the original on March 22,2009. CS1 maint, Unfit url The Largest Magnetic Storm on Record, the Sun Kings, The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began
34.
Coronal mass ejection
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A coronal mass ejection is an unusually large release of plasma and magnetic field from the solar corona. They often follow solar flares and are present during a solar prominence eruption. The plasma is released into the wind, and can be observed in coronagraph imagery. Coronal mass ejections are associated with other forms of solar activity. CMEs most often originate from active regions on the Suns surface, near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days. Coronal mass ejections release huge quantities of matter and electromagnetic radiation into space above the Suns surface, either near the corona, or farther into the planetary system, the ejected material is a plasma consisting primarily of electrons and protons. While solar flares are very fast, CMEs are relatively slow, Coronal mass ejections are associated with enormous changes and disturbances in the coronal magnetic field. They are usually observed with a white-light coronagraph, recent scientific research has shown that the phenomenon of magnetic reconnection is closely associated with CMEs and solar flares. In magnetohydrodynamic theory, the rearrangement of magnetic field lines when two oppositely directed magnetic fields are brought together is called magnetic reconnection. Reconnection releases energy stored in the original stressed magnetic fields and these magnetic field lines can become twisted in a helical structure, with a right-hand twist or a left hand twist. 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 during this process causes the solar flare, the helical magnetic field and the material that it contains may violently expand outwards forming a CME. This also explains why CMEs and solar flares erupt from what are known as the active regions on the Sun where magnetic fields are much stronger on average. When the magnetosphere reconnects on the nightside, it releases power on the order of terawatt scale, Solar energetic particles can cause particularly strong aurorae in large regions around Earths magnetic poles. These are also known as the Northern Lights in the hemisphere. Energetic protons released by a CME can cause an increase in the number of electrons in the ionosphere. The increase in free electrons can enhance radio wave absorption, especially within the D-region of the ionosphere, humans at high altitudes, as in airplanes or space stations, risk exposure to relatively intense cosmic rays. A typical coronal mass ejection may have any or all of three features, a cavity of low electron density, a dense core, and a bright leading edge
35.
George Francis FitzGerald
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Prof George Francis FitzGerald FRS FRSE was an Irish professor of natural and experimental philosophy at Trinity College in Dublin, Ireland, during the last quarter of the 19th century. He is known for his work in theory and for the Lorentz–FitzGerald contraction. The FitzGerald crater on the far side of the Moon is named for him, the FitzGerald Building at Trinity College, Dublin is named after him. 19, Lower Mount Street in Dublin on 3 August 1851 to the Reverend William FitzGerald, George returned to Dublin and entered Trinity as a student at the age of 16. He became a Fellow of Trinity in 1877 and spent the rest of his career at this college, in 1883, he was elected Fellow of the Royal Society. In 1899, was awarded a Royal Medal for his investigations in theoretical physics, in 1900, he was made an honorary fellow of the Royal Society of Edinburgh. FitzGerald suffered from digestive problems for much of his shortened life. He became very ill with stomach problems and he died at his home,7 Ely Place in Dublin, shortly after an operation on a perforated ulcer on 21 February 1901. He is buried in Mount Jerome cemetery, FitzGerald based this idea in part on the way electromagnetic forces were known to be affected by motion. In particular, FitzGerald used some equations that had been derived a short time before by his friend the electrical engineer Oliver Heaviside. The Dutch physicist Hendrik Lorentz hit on a similar idea in 1892 and developed it more fully into Lorentz transformations. The Lorentz–FitzGerald contraction hypothesis became a part of the Special Theory of Relativity. He demonstrated the kinematic nature of effect, by deriving it from the principle of relativity. FitzGerald married, on 21 December 1885, Harriette Mary, daughter of the Reverend John Hewitt Jellett and he had eight children by her, three sons and five daughters. FitzGerald was the nephew of George Johnstone Stoney, the Irish physicist who coined the term electron, after the particles were discovered by J. J. Thomson and Walter Kaufmann in 1896, FitzGerald was the one to propose calling them electrons. FitzGerald was also the nephew of Bindon Blood Stoney, an eminent Irish engineer and his cousin was Edith Anne Stoney, a pioneer female medical physicist. FitzGerald, in common with others at the end of the nineteenth century, FitzGerald took off his coat on these occasions, but retained his top hat, which was normal headgear for a Fellow at that time. The experiments were not crowned with success, and were eventually abandoned, the flying machine hung for many years in the Museum Building until an idle engineering student applied a match to the cord from which it was hanging
36.
Birkeland current
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A Birkeland current is a set of currents that flow along geomagnetic field lines connecting the Earth’s magnetosphere to the Earths high latitude ionosphere. In the Earth’s magnetosphere, the currents are driven by the wind and interplanetary magnetic field. The strength of the Birkeland currents changes with activity in the magnetosphere, small scale variations in the upward current sheets accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the Auroras Borealis and Australis. In the high latitude ionosphere, the Birkeland currents close through the region of the auroral electrojet, the Birkeland currents occur in two pairs of field-aligned current sheets. One pair extends from noon through the sector to the midnight sector. The other pair extends from noon through the sector to the midnight sector. The sheet on the high side of the auroral zone is referred to as the Region 1 current sheet. The currents were predicted in 1908 by Norwegian explorer and physicist Kristian Birkeland and this could only imply that currents were flowing in the atmosphere above. He theorized that somehow the Sun emitted a ray, and corpuscles from what is now known as a solar wind entered the Earth’s magnetic field and created currents. This view was scorned by other researchers, but in 1967 a satellite, launched into the auroral region, in honour of him and his theory these currents are named Birkeland currents. A good description of the discoveries by Birkeland is given in the book by Jago and these in turn lead to consequences such as acceleration of charged particles, both positive and negative, and element separation. Both of these classes of phenomena should have a general astrophysical interest far beyond that of understanding the environment of our own Earth. Auroral Birkeland currents carry about 100,000 amperes during quiet times, Birkeland had estimated currents at heights of several hundred kilometres, and strengths of up to a million amperes in 1908. The ionospheric currents that connect the field-aligned currents heat up the atmosphere due to the finite conductivity of the ionosphere. The heat is transferred from the plasma to the gas of the upper atmosphere. Birkeland currents can also be created in the laboratory with multi-terawatt pulsed power generators, the resulting cross-section pattern indicates a hollow beam of electrons in the form of a circle of vortices, a formation called the diocotron instability, that subsequently leads to filamentation. Such vortices can be seen in aurora as auroral curls, Birkeland currents are also one of a class of plasma phenomena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. This can also twist, producing a helical pinch that spirals like a twisted or braided rope, there is also a short-range circular component to the force between two Birkeland currents that is opposite to the longer-range parallel forces
37.
Terrella
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Terrellas had been used until the late 20th century to attempt to simulate the Earths magnetosphere, but have now been replaced by computer simulations. William Gilbert, the physician to Queen Elizabeth I, devoted much of his time, energy. It had been known for centuries that a freely suspended compass needle pointed north, earlier investigators found that direction deviated somewhat from true north, and Robert Norman showed the force on the needle was not horizontal but slanted into the Earth. William Gilberts explanation was that the Earth itself was a giant magnet, and he demonstrated this by creating a model of the magnetic Earth, a terrella. Gilbert later reported his findings in De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure, kristian Birkeland was a Norwegian physicist who, around 1895, tried to explain why the lights of the polar aurora appeared only in regions centered at the magnetic poles. Because of residual gas in the chamber, the glow also outlined the path of the particles, neither he nor his associate Carl Størmer could understand why the actual aurora avoided the area around the poles themselves. We now know this relates to the origin of the electrons, which is actually inside the Earths magnetosphere. Birkeland believed the electrons came from the Sun, since large auroral outbursts were associated with sunspot activity, one large terrella experiment was reconstructed in Tromsø, Norway. The German Baron Carl Reichenbach also experimented with a terrella and he used an electromagnet, placed within a large hollow iron sphere, and this was examined in the darkroom under varying degrees of electrification. The Baron referred to the globe as his terrella, or little earth. Brunberg and Dattner in Sweden, around 1950, used a terrella to simulate trajectories of particles in the Earths field, podgorny in the Soviet Union, around 1972, built terrellas at which a flow of plasma was directed, simulating the solar wind. Hafiz-Ur Rahman at the University of California, Riverside conducted more realistic experiments around 1990, NASA Educational Website on the Terrella
38.
Arthur Eddington
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Sir Arthur Stanley Eddington OM FRS was an English astronomer, physicist, and mathematician of the early 20th century who did his greatest work in astrophysics. He was also a philosopher of science and a populariser of science, the Eddington limit, the natural limit to the luminosity of stars, or the radiation generated by accretion onto a compact object, is named in his honour. He is famous for his work concerning the theory of relativity, Eddington wrote a number of articles that announced and explained Einsteins theory of general relativity to the English-speaking world. World War I severed many lines of communication and new developments in German science were not well known in England. Eddington was born 28 December 1882 in Kendal, Westmorland, England, the son of Quaker parents, Arthur Henry Eddington, headmaster of the Quaker School and his father taught at a Quaker training college in Lancashire before moving to Kendal to become headmaster of Stramongate School. He died in the epidemic which swept England in 1884. His mother was left to bring up her two children with little income. The family moved to Weston-super-Mare where at first Stanley was educated at home before spending three years at a preparatory school, the family lived at a house called Varzin,42 Walliscote Road, Weston-super-Mare. There is a plaque on the building explaining Sir Arthurs contribution to science. In 1893 Eddington entered Brynmelyn School and he proved to be a most capable scholar, particularly in mathematics and English literature. His performance earned him a scholarship to Owens College, Manchester in 1898 and he spent the first year in a general course, but turned to physics for the next three years. Eddington was greatly influenced by his physics and mathematics teachers, Arthur Schuster, at Manchester, Eddington lived at Dalton Hall, where he came under the lasting influence of the Quaker mathematician J. W. Graham. His progress was rapid, winning him several scholarships and he graduated with a B. Sc. in physics with First Class Honours in 1902, based on his performance at Owens College, he was awarded a scholarship to Trinity College at the University of Cambridge in 1902. His tutor at Cambridge was Robert Alfred Herman and in 1904 Eddington became the first ever student to be placed as Senior Wrangler. After receiving his M. A. in 1905, he began research on thermionic emission in the Cavendish Laboratory and this did not go well, and meanwhile he spent time teaching mathematics to first year engineering students. Through a recommendation by E. T, in January 1906, Eddington was nominated to the post of chief assistant to the Astronomer Royal at the Royal Greenwich Observatory. He left Cambridge for Greenwich the following month and he was put to work on a detailed analysis of the parallax of 433 Eros on photographic plates that had started in 1900. He developed a new statistical method based on the apparent drift of two stars, winning him the Smiths Prize in 1907
39.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
40.
Kristian Birkeland
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Kristian Olaf Bernhard Birkeland was a Norwegian scientist. He is best remembered as the person whose theories of electric currents elucidated the nature of the aurora borealis. In order to fund his research on the aurorae, he invented the electromagnetic cannon, Birkeland was nominated for the Nobel Prize seven times. Birkeland was born in Christiania to Reinart Birkeland and Ingeborg and wrote his first scientific paper at the age of 18, Birkeland married Ida Charlotte Hammer in May 1905. They had no children and, due to Birkelands preoccupation with his work, a post-mortem revealed that Birkeland had taken 10 g of veronal the night he died, instead of the 0.5 g recommended. The time of death was estimated at 7am on 15 June 1917, some authors have claimed that he committed suicide. On the nightstand lay a revolver, Birkeland organized several expeditions to Norways high-latitude regions where he established a network of observatories under the auroral regions to collect magnetic field data. The discovery of X-rays inspired Birkeland to develop vacuum chambers to study the influence of magnets on cathode rays and this is essentially the theory of the aurora today. Such field-aligned currents are known today as Birkeland currents in his honour, the book on the 1902–1903 expedition contains chapters on magnetic storms on the Earth and their relationship to the Sun, the origin of the Sun itself, Halleys comet, and the rings of Saturn. Birkelands theory of the continued to be dismissed by mainstream astrophysicists after his death in 1917. It was notably championed by the Swedish plasma scientist Hannes Alfvén, proof of Birkelands theory of the aurora only came in 1967 after a probe was sent into space. The crucial results were obtained from U. S. Navy satellite 1963-38C, launched in 1963, magnetic disturbances were observed on nearly every pass over the high-latitude regions of the Earth. These were originally interpreted as waves, but on later analysis it was realized that they were due to field-aligned or Birkeland currents. The scale of Birkelands research enterprises was such that funding became an overwhelming obstacle, recognizing that technological invention could bring wealth, he developed an electromagnetic cannon and, with some investors, formed a firearms company. The coil-gun worked, except the high muzzle velocities he predicted were not produced, the most he could get from his largest machine was 100 m/s, corresponding to a disappointing projectile range of only 1 km. So he renamed the device an aerial torpedo and arranged a demonstration with the aim of selling the company. At the demonstration, one of the coils shorted and produced a sensational inductive arc complete with noise, flame and this was the first failure of any of the launchers that Birkeland had built. It could easily have been repaired and another demonstration organized, however, fate intervened in the form of an engineer named Sam Eyde
41.
Frederick Lindemann, 1st Viscount Cherwell
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He advocated the area bombing of German cities during the Second World War and doubted the sophistication of Nazi Germanys radar technology and the existence of its V weapons programme. Lindemann was the second of three sons of Adolph Friedrich Lindemann, who had emigrated to the United Kingdom circa 1871, Frederick was born in Baden-Baden in Germany where his American mother Olga Noble, the widow of a wealthy banker, was taking the cure. After schooling in Scotland and Darmstadt, he attended the University of Berlin and he did research in physics at the Sorbonne that confirmed theories, first put forward by Albert Einstein, on specific heats at very low temperatures. For this and other work, Lindemann was elected a Fellow of the Royal Society in 1920. In 1911 he was invited to the Solvay Conference on Radiation, Lindemann was a teetotaler, non-smoker and a vegetarian, although Churchill would sometimes induce him to take a glass of brandy. He was an excellent pianist, and sufficiently able as a player to compete at Wimbledon. He was known to friends as the Prof in reference to his position at the University of Oxford, Lindemann believed that a small circle of the intelligent and the aristocratic should run the world, resulting in a peaceable and stable society, led by supermen and served by helots. Some sources say that he was Jewish, but Frederick Smiths biography and it was no longer necessary, he wrote, to wait for the haphazard process of natural selection to ensure that the slow and heavy mind gravitates to the lowest form of activity. At the outbreak of the First World War, Lindemann was playing tennis in Germany and had to leave in haste to avoid internment, in 1915, he joined the staff of the Royal Aircraft Factory at Farnborough. He developed a theory of aircraft spin recovery, and later learned to fly so that he could test his ideas himself. Prior to Lindemanns work, a aircraft was almost invariably unrecoverable. Also in 1919, he was one of the first people to suggest that in the solar wind particles of both polarities, protons as well as electrons, come from the Sun and he was probably not aware that Kristian Birkeland had made the same prediction three years earlier. At the same time he worked on the theory of specific heats, in the field of chemical kinetics, he proposed the Lindemann mechanism in 1921 for unimolecular chemical reactions, and showed that the first step is one of bimolecular activation. At the same time Churchills wife Clementine partnered with Lindemann for a charity tennis match and they became close friends and remained so for 35 years, with Lindemann visiting Chartwell more than 100 times from 1925 to 1939. Lindemann opposed the General Strike of 1926, and mobilised the reluctant staff of the Clarendon to produce copies of Churchills anti-strike newspaper, Lindemann was also alarmed and fearful of political developments in Germany. In the 1930s, Lindemann advised Winston Churchill when the latter was out of Government – the Wilderness Years – and he appointed to the Clarendon one of Churchills social set that included the Mitfords and the Cavendish family, the young Welshman Derek Jackson. This brilliant young physicist, the son of Sir Charles Jackson, transferred from the Nobel prize-winning labs at Cambridge, one frequently intoxicated visitor was a wayward Randolph Churchill, who would eventually find his destiny in the secret war of the Greek partisans. In 1932, Lindemann joined Winston to complete a trip throughout Europe and were dismayed at what they saw
42.
Anders Celsius
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Anders Celsius was a Swedish astronomer, physicist and mathematician. He was professor of astronomy at Uppsala University from 1730 to 1744 and he founded the Uppsala Astronomical Observatory in 1741, and in 1742 proposed the Celsius temperature scale which bears his name. Anders Celsius was born in Uppsala, Sweden on 27 November 1701 and his family originated from Ovanåker in the province of Hälsingland. Their family estate was at Doma, also known as Höjen or Högen, the name Celsius is a latinization of the estates name. As the son of a professor, Nils Celsius, and the grandson of the mathematician Magnus Celsius. He was a mathematician from an early age. Anders Celsius studied at Uppsala University, where his father was a teacher, in 1730, Celsius published the Nova Methodus distantiam solis a terra determinandi. He observed the variations of a needle and found that larger deflections correlated with stronger auroral activity. At Nuremberg in 1733, he published a collection of 316 observations of the aurora borealis made by himself, Celsius traveled frequently in the early 1730s, including to Germany, Italy and France, when he visited most of the major European observatories. In Paris he advocated the measurement of an arc of the meridian in Lapland, in 1736, he participated in the expedition organized for that purpose by the French Academy of Sciences, led by the French mathematician Pierre Louis Maupertuis to measure a degree of latitude. The aim of the expedition was to measure the length of a degree along a meridian, close to the pole, the expeditions confirmed Isaac Newtons belief that the shape of the earth is an ellipsoid flattened at the poles. In 1738, he published the De observationibus pro figura telluris determinanda and he was successful in the request, and Celsius founded the Uppsala Astronomical Observatory in 1741. The observatory was equipped with instruments purchased during his long voyage abroad, in astronomy, Celsius began a series of observations using colored glass plates to record the magnitude of certain stars. This was the first attempt to measure the intensity of starlight with an other than the human eye. He made observations of eclipses and various objects and published catalogues of carefully determined magnitudes for some 300 stars using his own photometric system. Celsius was the first to perform and publish careful experiments aiming at the definition of a temperature scale on scientific grounds. In his Swedish paper Observations of two persistent degrees on a thermometer he reports on experiments to check that the point is independent of latitude. He determined the dependence of the boiling of water with atmospheric pressure which was even by modern-day standards
43.
Sydney Chapman (mathematician)
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Sydney Chapman FRS was a British mathematician and geophysicist. His work on the theory of gases, solar-terrestrial physics. Chapman was born in Eccles, near Salford in England and began his studies at a technical institute, now the University of Salford. In 1904 at age 16, Chapman entered the University of Manchester and he competed for a scholarship to the university offered by his home county, and was the last student selected. Chapman later reflected, I sometimes wonder what would have happened if Id hit one place lower and he initially studied engineering in the department headed by Osborne Reynolds. Chapman was taught mathematics by Horace Lamb, the Beyer professor of mathematics, and J. E. Littlewood, although he graduated with an engineering degree, Chapman had become so enthusiastic for mathematics that he stayed for one further year to take a mathematics degree. Following Lambs suggestion, Chapman applied for a scholarship to Trinity College, Cambridge and he was at first awarded only a partial scholarship as a sizar, but from his second year onwards he received a full scholarship. He graduated as a wrangler in 1910 and he began his research in pure mathematics under G. H. Hardy, but later that year was asked by Sir Frank Dyson to be his chief assistant at the Royal Greenwich Observatory. From 1914 to 1919 he returned to Cambridge as a lecturer in mathematics and he held the Beyer Chair of Applied Mathematics at Manchester from 1919 to 1924, the same position as had been held by Lamb, and then moved to Imperial College London. During the Second World War he was Deputy Scientific Advisor to the Army Council, in 1946, Chapman was elected to the Sedleian Chair of Natural Philosophy at Oxford, and was appointed fellow of The Queens College, Oxford. As the Advisory Scientific Director of the University of Alaska Geophysical Institute from 1951 to 1970, much of the remainder of the year he spent at the High Altitude Observatory in Boulder, Colorado. The relationship of Chapman with some German geophysicists has been investigated by Wilfried Schröder, in 1970, Chapman died in Boulder, Colorado at the age of 82. Chapmans most noted mathematical accomplishments were in the field of stochastic processes, Chapman is credited with working out, in 1930, the photochemical mechanisms that give rise to the ozone layer. Chapman is also recognised as one of the pioneers of solar-terrestrial physics and this interest stemmed from his early work on the kinetic theory of gases. Chapman studied magnetic storms and aurorae, developing theories to explain their relation to the interaction of the Earths magnetic field with the solar wind and he disputed and ridiculed the work of Kristian Birkeland and Hannes Alfven, later adopting Birkelands theories as his own. Chapman and his first graduate student, V. C. A. Ferraro and they also predicted characteristics of the magnetosphere that were confirmed 30 years later by the Explorer 12 satellite. Chapman was President of the Special Committee for the International Geophysical Year, the idea of the IGY stemmed from a discussion in 1950 between Chapman and scientists including James Van Allen. The IGY was held in 1957–58, and resulted in progress in fields including Earth and space sciences
44.
Ludwig Biermann
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Ludwig Franz Benedict Biermann was a German astronomer, obtaining his Ph. D. from Göttingen University in 1932. He made important contributions to astrophysics and plasma physics, discovering the Biermann battery and he predicted the existence of the solar wind which in 1947 he dubbed solar corpuscular radiation. He was a scholar at the Institute for Advanced Study in the fall of 1961. He won the Bruce Medal in 1967 and the Gold Medal of the Royal Astronomical Society in 1974, asteroid 73640 Biermann is named in his honor. Bruce medal page Awarding of Bruce Medal Awarding of RAS gold medal MitAG6610 QJRAS27698
. Bibcode:2011ApJ...731..112A. doi:10.1088/0004-637X/731/2/112. ISSN 0004-637X.
