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Main sequence

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In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell. Stars on this band are known as main-sequence stars or „dwarf“ stars.
After a star has formed, it generates thermal energy in the dense core region through the nuclear fusion of hydrogen atoms into helium. During this stage of the star’s lifetime, it is located along the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and other factors. All main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. The strong dependence of the rate of energy generation in the core on the temperature and pressure helps to sustain this balance. Energy generated at the core makes its way to the surface and is radiated away at the photosphere. The energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.
The main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. Stars below about 1.5 times the mass of the Sun (or 1.5 solar masses (M☉)) primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton–proton chain. Above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the CNO cycle that produces helium from hydrogen atoms. Main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. Below this mass, stars have cores that are entirely radiative with convective zones near the surface. With decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases, whereas main-sequence stars below 0.4 M☉ undergo convection throughout their mass. When core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen.
In general, the more massive a star is, the shorter its lifespan on the main sequence. After the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the HR diagram. The behavior of a star now depends on its mass, with stars below 0.23 M☉ becoming white dwarfs directly, whereas stars with up to ten solar masses pass through a red giant stage. More massive stars can explode as a supernova, or collapse directly into a black hole.

In the early part of the 20th century, information about the types and distances of stars became more readily available. The spectra of stars were shown to have distinctive features, which allowed them to be categorized. Annie Jump Cannon and Edward C. Pickering at Harvard College Observatory developed a method of categorization that became known as the Harvard Classification Scheme, published in the Harvard Annals in 1901.
In Potsdam in 1906, the Danish astronomer Ejnar Hertzsprung noticed that the reddest stars—classified as K and M in the Harvard scheme—could be divided into two distinct groups. These stars are either much brighter than the Sun, or much fainter. To distinguish these groups, he called them „giant“ and „dwarf“ stars. The following year he began studying star clusters; large groupings of stars that are co-located at approximately the same distance. He published the first plots of color versus luminosity for these stars. These plots showed a prominent and continuous sequence of stars, which he named the Main Sequence.
At Princeton University, Henry Norris Russell was following a similar course of research. He was studying the relationship between the spectral classification of stars and their actual brightness as corrected for distance—their absolute magnitude. For this purpose he used a set of stars that had reliable parallaxes and many of which had been categorized at Harvard. When he plotted the spectral types of these stars against their absolute magnitude, he found that dwarf stars followed a distinct relationship. This allowed the real brightness of a dwarf star to be predicted with reasonable accuracy.
Of the red stars observed by Hertzsprung, the dwarf stars also followed the spectra-luminosity relationship discovered by Russell. However, the giant stars are much brighter than dwarfs and so, do not follow the same relationship. Russell proposed that the „giant stars must have low density or great surface-brightness, and the reverse is true of dwarf stars“. The same curve also showed that there were very few faint white stars.
In 1933, Bengt Strömgren introduced the term Hertzsprung–Russell diagram to denote a luminosity-spectral class diagram. This name reflected the parallel development of this technique by both Hertzsprung and Russell earlier in the century.
As evolutionary models of stars were developed during the 1930s, it was shown that, for stars of a uniform chemical composition, a relationship exists between a star’s mass and its luminosity and radius. That is, for a given mass and composition, there is a unique solution for determining the star’s radius and luminosity. This became known as the Vogt-Russell theorem; named after Heinrich Vogt and Henry Norris Russell. By this theorem, when a star’s chemical composition and its position on the main sequence is known, so too is the star’s mass and radius. (However, it was subsequently discovered that the theorem breaks down somewhat for stars of non-uniform composition.)
A refined scheme for stellar classification was published in 1943 by W. W. Morgan and P. C. Keenan. The MK classification assigned each star a spectral type—based on the Harvard classification—and a luminosity class. The Harvard classification had been developed by assigning a different letter to each star based on the strength of the hydrogen spectral line, before the relationship between spectra and temperature was known. When ordered by temperature and when duplicate classes were removed, the spectral types of stars followed, in order of decreasing temperature with colors ranging from blue to red, the sequence O, B, A, F, G, K and M. (A popular mnemonic for memorizing this sequence of stellar classes is „Oh Be A Fine Girl/Guy, Kiss Me“.) The luminosity class ranged from I to V, in order of decreasing luminosity. Stars of luminosity class V belonged to the main sequence.
When a protostar is formed from the collapse of a giant molecular cloud of gas and dust in the local interstellar medium, the initial composition is homogeneous throughout, consisting of about 70% hydrogen, 28% helium and trace amounts of other elements, by mass. The initial mass of the star depends on the local conditions within the cloud. (The mass distribution of newly formed stars is described empirically by the initial mass function.) During the initial collapse, this pre-main-sequence star generates energy through gravitational contraction. Upon reaching a suitable density, energy generation is begun at the core using an exothermic nuclear fusion process that converts hydrogen into helium.
When nuclear fusion of hydrogen becomes the dominant energy production process and the excess energy gained from gravitational contraction has been lost, the star lies along a curve on the Hertzsprung–Russell diagram (or HR diagram) called the standard main sequence. Astronomers will sometimes refer to this stage as „zero age main sequence“, or ZAMS. The ZAMS curve can be calculated using computer models of stellar properties at the point when stars begin hydrogen fusion. From this point, the brightness and surface temperature of stars typically increase with age.
A star remains near its initial position on the main sequence until a significant amount of hydrogen in the core has been consumed, then begins to evolve into a more luminous star. (On the HR diagram, the evolving star moves up and to the right of the main sequence.) Thus the main sequence represents the primary hydrogen-burning stage of a star’s lifetime.
The majority of stars on a typical HR diagram lie along the main-sequence curve. This line is pronounced because both the spectral type and the luminosity depend only on a star’s mass, at least to zeroth-order approximation, as long as it is fusing hydrogen at its core—and that is what almost all stars spend most of their „active“ lives doing.
The temperature of a star determines its spectral type via its effect on the physical properties of plasma in its photosphere. A star’s energy emission as a function of wavelength is influenced by both its temperature and composition. A key indicator of this energy distribution is given by the color index, B − V, which measures the star’s magnitude in blue (B) and green-yellow (V) light by means of filters.[note 1] This difference in magnitude provides a measure of a star’s temperature.
Main-sequence stars are called dwarf stars, but this terminology is partly historical and can be somewhat confusing. For the cooler stars, dwarfs such as red dwarfs, orange dwarfs, and yellow dwarfs are indeed much smaller and dimmer than other stars of those colors. However, for hotter blue and white stars, the size and brightness difference between so-called dwarf stars that are on the main sequence and the so-called giant stars that are not becomes smaller; for the hottest stars it is not directly observable. For those stars the terms dwarf and giant refer to differences in spectral lines which indicate if a star is on the main sequence or off it. Nevertheless, very hot main-sequence stars are still sometimes called dwarfs

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, even though they have roughly the same size and brightness as the „giant“ stars of that temperature.
The common use of dwarf to mean main sequence is confusing in another way, because there are dwarf stars which are not main-sequence stars. For example, a white dwarf is the dead core of a star that is left after the star has shed its outer layers, that is much smaller than a main-sequence star-—roughly the size of Earth. These represent the final evolutionary stage of many main-sequence stars.
By treating the star as an idealized energy radiator known as a black body, the luminosity L and radius R can be related to the effective temperature Teff by the Stefan–Boltzmann law:
L = 4πσR2Teff4
where σ is the Stefan–Boltzmann constant. As the position of a star on the HR diagram shows its approximate luminosity, this relation can be used to estimate its radius.
The mass, radius and luminosity of a star are closely interlinked, and their respective values can be approximated by three relations. First is the Stefan–Boltzmann law, which relates the luminosity L, the radius R and the surface temperature Teff. Second is the mass–luminosity relation, which relates the luminosity L and the mass M. Finally, the relationship between M and R is close to linear. The ratio of M to R increases by a factor of only three over 2.5 orders of magnitude of M. This relation is roughly proportional to the star’s inner temperature TI, and its extremely slow increase reflects the fact that the rate of energy generation in the core strongly depends on this temperature, whereas it has to fit the mass–luminosity relation. Thus, a too high or too low temperature will result in stellar instability.
A better approximation is to take ε = L/M, the energy generation rate per unit mass, as ε is proportional to TI15, where TI is the core temperature. This is suitable for stars at least as massive as the Sun, exhibiting the CNO cycle, and gives the better fit R ∝ M0.78.
The table below shows typical values for stars along the main sequence. The values of luminosity (L), radius (R) and mass (M) are relative to the Sun—a dwarf star with a spectral classification of G2 V. The actual values for a star may vary by as much as 20–30% from the values listed below.
All main-sequence stars have a core region where energy is generated by nuclear fusion. The temperature and density of this core are at the levels necessary to sustain the energy production that will support the remainder of the star. A reduction of energy production would cause the overlaying mass to compress the core, resulting in an increase in the fusion rate because of higher temperature and pressure. Likewise an increase in energy production would cause the star to expand, lowering the pressure at the core. Thus the star forms a self-regulating system in hydrostatic equilibrium that is stable over the course of its main sequence lifetime.
Main-sequence stars employ two types of hydrogen fusion processes, and the rate of energy generation from each type depends on the temperature in the core region. Astronomers divide the main sequence into upper and lower parts, based on which of the two is the dominant fusion process. In the lower main sequence, energy is primarily generated as the result of the proton-proton chain, which directly fuses hydrogen together in a series of stages to produce helium. Stars in the upper main sequence have sufficiently high core temperatures to efficiently use the CNO cycle. (See the chart.) This process uses atoms of carbon, nitrogen and oxygen as intermediaries in the process of fusing hydrogen into helium.
At a stellar core temperature of 18 Million Kelvin, the PP process and CNO cycle are equally efficient, and each type generates half of the star’s net luminosity. As this is the core temperature of a star with about 1.5 M☉, the upper main sequence consists of stars above this mass. Thus Cheap New Balance Shoes, roughly speaking, stars of spectral class F or cooler belong to the lower main sequence, while A-type stars or hotter are upper main-sequence stars. The transition in primary energy production from one form to the other spans a range difference of less than a single solar mass. In the Sun, a one solar-mass star, only 1.5% of the energy is generated by the CNO cycle. By contrast, stars with 1.8 M☉ or above generate almost their entire energy output through the CNO cycle.
The observed upper limit for a main-sequence star is 120–200 M☉. The theoretical explanation for this limit is that stars above this mass can not radiate energy fast enough to remain stable, so any additional mass will be ejected in a series of pulsations until the star reaches a stable limit. The lower limit for sustained proton–proton nuclear fusion is about 0.08 M☉ or 80 times the mass of Jupiter. Below this threshold are sub-stellar objects that can not sustain hydrogen fusion, known as brown dwarfs.
Because there is a temperature difference between the core and the surface, or photosphere, energy is transported outward. The two modes for transporting this energy are radiation and convection. A radiation zone, where energy is transported by radiation, is stable against convection and there is very little mixing of the plasma. By contrast, in a convection zone the energy is transported by bulk movement of plasma, with hotter material rising and cooler material descending. Convection is a more efficient mode for carrying energy than radiation, but it will only occur under conditions that create a steep temperature gradient.
In massive stars (above 10 M☉) the rate of energy generation by the CNO cycle is very sensitive to temperature, so the fusion is highly concentrated at the core. Consequently, there is a high temperature gradient in the core region, which results in a convection zone for more efficient energy transport. This mixing of material around the core removes the helium ash from the hydrogen-burning region, allowing more of the hydrogen in the star to be consumed during the main-sequence lifetime. The outer regions of a massive star transport energy by radiation, with little or no convection.
Intermediate-mass stars such as Sirius may transport energy primarily by radiation, with a small core convection region. Medium-sized, low-mass stars like the Sun have a core region that is stable against convection, with a convection zone near the surface that mixes the outer layers. This results in a steady buildup of a helium-rich core, surrounded by a hydrogen-rich outer region. By contrast, cool, very low-mass stars (below 0.4 M☉) are convective throughout. Thus the helium produced at the core is distributed across the star, producing a relatively uniform atmosphere and a proportionately longer main sequence lifespan.
As non-fusing helium ash accumulates in the core of a main-sequence star, the reduction in the abundance of hydrogen per unit mass results in a gradual lowering of the fusion rate within that mass. Since it is the outflow of fusion-supplied energy that supports the higher layers of the star, the core is compressed, producing higher temperatures and pressures. Both factors increase the rate of fusion thus moving the equilibrium towards a smaller, denser, hotter core producing more energy whose increased outflow pushes the higher layers further out. Thus there is a steady increase in the luminosity and radius of the star over time. For example, the luminosity of the early Sun was only about 70% of its current value. As a star ages this luminosity increase changes its position on the HR diagram. This effect results in a broadening of the main sequence band because stars are observed at random stages in their lifetime. That is, the main sequence band develops a thickness on the HR diagram; it is not simply a narrow line.
Other factors that broaden the main sequence band on the HR diagram include uncertainty in the distance to stars and the presence of unresolved binary stars that can alter the observed stellar parameters. However, even perfect observation would show a fuzzy main sequence because mass is not the only parameter that affects a star’s color and luminosity. Variations in chemical composition caused by the initial abundances, the star’s evolutionary status, interaction with a close companion, rapid rotation, or a magnetic field can all slightly change a main-sequence star’s HR diagram position, to name just a few factors. As an example, there are metal-poor stars (with a very low abundance of elements with higher atomic numbers than helium) that lie just below the main sequence and are known as subdwarfs. These stars are fusing hydrogen in their cores and so they mark the lower edge of main sequence fuzziness caused by variance in chemical composition.
A nearly vertical region of the HR diagram, known as the instability strip, is occupied by pulsating variable stars known as Cepheid variables. These stars vary in magnitude at regular intervals, giving them a pulsating appearance. The strip intersects the upper part of the main sequence in the region of class A and F stars, which are between one and two solar masses. Pulsating stars in this part of the instability strip that intersects the upper part of the main sequence are called Delta Scuti variables. Main-sequence stars in this region experience only small changes in magnitude and so this variation is difficult to detect. Other classes of unstable main-sequence stars, like Beta Cephei variables, are unrelated to this instability strip.
The total amount of energy that a star can generate through nuclear fusion of hydrogen is limited by the amount of hydrogen fuel that can be consumed at the core. For a star in equilibrium, the energy generated at the core must be at least equal to the energy radiated at the surface. Since the luminosity gives the amount of energy radiated per unit time, the total life span can be estimated, to first approximation, as the total energy produced divided by the star’s luminosity.
For a star with at least 0.5 M☉, when the hydrogen supply in its core is exhausted and it expands to become a red giant, it can start to fuse helium atoms to form carbon. The energy output of the helium fusion process per unit mass is only about a tenth the energy output of the hydrogen process, and the luminosity of the star increases. This results in a much shorter length of time in this stage compared to the main sequence lifetime. (For example, the Sun is predicted to spend 130 million years burning helium, compared to about 12 billion years burning hydrogen.) Thus, about 90% of the observed stars above 0.5 M☉ will be on the main sequence. On average, main-sequence stars are known to follow an empirical mass-luminosity relationship. The luminosity (L) of the star is roughly proportional to the total mass (M) as the following power law:
This relationship applies to main-sequence stars in the range 0.1–50 M☉.
The amount of fuel available for nuclear fusion is proportional to the mass of the star. Thus, the lifetime of a star on the main sequence can be estimated by comparing it to solar evolutionary models. The Sun has been a main-sequence star for about 4.5 billion years and it will become a red giant in 6.5 billion years, for a total main sequence lifetime of roughly 1010 years. Hence:
where M and L are the mass and luminosity of the star, respectively, is a solar mass, is the solar luminosity and is the star’s estimated main sequence lifetime.
Although more massive stars have more fuel to burn and might be expected to last longer, they also must radiate a proportionately greater amount with increased mass. Thus, the most massive stars may remain on the main sequence for only a few million years, while stars with less than a tenth of a solar mass may last for over a trillion years.
The exact mass-luminosity relationship depends on how efficiently energy can be transported from the core to the surface. A higher opacity has an insulating effect that retains more energy at the core, so the star does not need to produce as much energy to remain in hydrostatic equilibrium. By contrast, a lower opacity means energy escapes more rapidly and the star must burn more fuel to remain in equilibrium. Note, however, that a sufficiently high opacity can result in energy transport via convection, which changes the conditions needed to remain in equilibrium.
In high-mass main-sequence stars, the opacity is dominated by electron scattering, which is nearly constant with increasing temperature. Thus the luminosity only increases as the cube of the star’s mass. For stars below 10 M☉, the opacity becomes dependent on temperature, resulting in the luminosity varying approximately as the fourth power of the star’s mass. For very low-mass stars, molecules in the atmosphere also contribute to the opacity. Below about 0.5 M☉, the luminosity of the star varies as the mass to the power of 2.3, producing a flattening of the slope on a graph of mass versus luminosity. Even these refinements are only an approximation, however, and the mass-luminosity relation can vary depending on a star’s composition.
When a main-sequence star consumes the hydrogen at its core, the loss of energy generation causes its gravitational collapse to resume. Stars with less than 0.23 M☉ Sandro 2016, are predicted to directly become white dwarfs when energy generation by nuclear fusion of hydrogen at their core comes to a halt. In stars between this threshold and 10 M☉, the hydrogen surrounding the helium core reaches sufficient temperature and pressure to undergo fusion, forming a hydrogen-burning shell. In consequence of this change, the outer envelope of the star expands and decreases in temperature, turning it into a red giant. At this point the star is evolving off the main sequence and entering the giant branch. The path which the star now follows across the HR diagram, to the upper right of the main sequence, is called an evolutionary track.
The helium core of a red giant continues to collapse until it is entirely supported by electron degeneracy pressure—a quantum mechanical effect that restricts how closely matter can be compacted. For stars of more than about 0.5 M☉, the core eventually reaches a temperature where it becomes hot enough to burn helium into carbon via the triple alpha process. Stars with more than 5–7.5 M☉ can additionally fuse elements with higher atomic numbers. For stars with ten or more solar masses, this process can lead to an increasingly dense core that finally collapses, ejecting the star’s overlying layers in a Type II supernova explosion, Type Ib supernova or Type Ic supernova.
When a cluster of stars is formed at about the same time, the life span of these stars will depend on their individual masses. The most massive stars will leave the main sequence first, followed steadily in sequence by stars of ever lower masses. Thus the stars will evolve in order of their position on the main sequence, proceeding from the most massive at the left toward the right of the HR diagram. The current position where stars in this cluster are leaving the main sequence is known as the turn-off point. By knowing the main sequence lifespan of stars at this point, it becomes possible to estimate the age of the cluster.

Salizhan Sharipov

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Salizhan Shakirovich Sharipov (Russian: Салижан Шакирович Шарипов) (born 24 August 1964 in Uzgen, Osh oblast, Kirghiz SSR, now in Kyrgyzstan) is a Kyrgyzstani cosmonaut. Sharipov is a co-author and investigator for the Advanced Diagnostic Ultrasound in Microgravity project. He has been to space twice and has conducted two spacewalks. Sharipov retired on 18 July 2008.

Sharipov was the first cosmonaut of the Kyrgyz Republic. He is married to Nadezhda Mavlyanovna Sharipova. They have one daughter, Nigara Salizhanovna Sharipova, born in 1988 and one son, Zhakhongir Salizhanovich Sharipov, born in 1992. He is known to enjoy football and reading. His father, Mr. Shakirzhan Sharipov, resides in Uzgen. Sharipov is famous for his unibrow.
Sharipov graduated from the Soviet Air Force Pilot School in 1987. In 1994

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, he graduated from Moscow State University with a degree in cartography.
Pilot-Cosmonaut of the Russian Federation (1988), Hero of the Kyrgyz Republic (Kyrgyz Respublikasynyn Baatyry) (1998). He was decorated with Gold Star Medal of the Hero of the Kyrgyz Republic (Ak Shumkar Medal, 1998), Russian Federation Air Force Medals and NASA Space Flight Medal (1998).
On 20 April 2005, Kyrgyz Republic issued a postal stamp depicting Salizhan Sharipov.
After graduation from the Air Force Pilot School in 1987, Sharipov worked as a pilot-instructor and taught eight cadets. He has logged over 950 hours flying time. He has experience flying on MiG-21 and L-39 aircraft.
Selected by the Gagarin Cosmonaut Training Center (GCTC) Sharipov became a cosmonaut-candidate in 1990. In 1992, he completed general space training and became a test cosmonaut on 11 March 1992. As a member of the group he completed a full course of training for Mir spaceflights as a crew commander. From August 1997 to January 1998 he passed training as a member of the STS-89 crew at the Johnson Space Center.
Sharipov served as a mission specialist on the crew of STS-89 (22–31 January 1998), the eighth Shuttle-Mir docking mission during which the crew transferred more than 8,000 pounds of scientific equipment, logistical hardware and water from Space Shuttle Endeavour to Mir. In the fifth and last exchange of a U.S. astronaut, STS-89 delivered Andy Thomas to Mir and returned with David Wolf. Mission duration was 8 days, 19 hours and 47 seconds, traveling 3.6 million miles in 138 orbits of the Earth.
Sharipov was also Flight Engineer on Expedition 10 to the International Space Station (ISS). The Soyuz TMA-5 spacecraft carrying Shapripov, cosmonaut Yuri Shargin and NASA astronaut Leroy Chiao lifted off from the Baikonour cosmodrome on 14 October 2004 at 03:06 UTC. After two days of autonomous flight the Soyuz spacecraft docking with the ISS on 16 October at 4:16 UTC. Sharipov joined the Expedition 10 crew as a flight engineer. The main task of Expedition 10 was to support ISS in functional condition. During his stay, Sharipov conducted several science and human life sciences experiments for the Russian Space Program 2016 Maje Dresses. One experiment called SRS, which was a low-temperature synthesis in space hoped to develop new materials. Biotechnological experiments he performed used stem cells for possible development of a vaccination for HIV/AIDS treatment. He also participated in ecology studies of the Earth from space.
After spending 192 days in space, Shapirov returned to Earth on 24 April 2005 with Leroy Chiao and ESA astronaut Roberto Vittori aboard the Soyuz TMA-5 spacecraft. The Soyuz capsule landed at 22:08 UTC 90 km north of the town of Arkalyk.
Sharipov has conducted two career spacewalks totalling 10 hours and 34 minutes.
Sharipov conducted his first career spacewalk on 26 January 2005. He and NASA astronaut Leroy Chiao ventured outside the ISS at 7:43 GMT from the Pirs airlock. The spacewalk was conducted in Russian Orlan spacesuits with red stripes. The two spacewalkers worked swiftly to complete their spacewalk goals that included the installation of a new work platform and test robot outside the Zvezda module. Sharipov and Chiao also relocated a Japanese space environment exposure experiment called MPAC SEEDS and plugged in an antenna for the robot test bed. They also studied ISS vents used by the station’s Elektron oxygen generator and other life support systems. During the spacewalk, the space station’s stabilizing gyroscopes repeatedly became overloaded with a mysterious torque, and they had to be relieved periodically by firing rocket thrusters located on the Russian half of the ISS. On at least one occasion these thrusters were appeared to have been activated when the Sharipov and Chiao were working dangerously close to them. The spacewalk lasted 5 hours and 28 minutes.
Sharipov conducted his second career spacewalk on 28 March 2005. The spacewalk, in Russian Orlan suits using the airlock of the Pirs Docking Compartment began at 1:25 a Sandro 2016.m. EST. After opening the hatch and assembling equipment, Sharipov and astronaut Leroy Chiao moved to the small-diameter forward end of the Zvezda module. There the two spacewalkers installed the final three antennas on the Zvezda Service Module of a six-antenna set for the resupply spacecraft ATV. Installation of the antennas and their associated cabling took about two hours. Sharipov and Chiao also installed a Global Positioning System (GPS) antenna for the ATV. During this spacewalk, Sharipov and Chiao deployed a small Russian experiment called Nanosatellite. Sharipov deployed it from the ladder at Pirs, giving it a push in the direction opposite the direction the ISS was traveling. The tiny satellite was about a foot long, weighs 11 pounds and contained a transmitter. The two spacewalkers activated the satellite before leaving the Pirs airlock and stowed it on the outside of the docking compartment. The object of the experiment was to develop small satellite control techniques, monitor satellite operations and develop new attitude system sensors. The spacewalk lasted 4 hours and 30 minutes.
 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

The Boys of the Lough

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The Boys of the Lough is a Scottish-Irish Celtic music band active since the 1970s.

Their first album, called Boys of the Lough (1972) consisted of Aly Bain (fiddle), Cathal Mc’Connell (flute), Dick Gaughan (vocals and guitar) and Robin Morton (bodhran and vocals).
Since the 1960s the Forrest Hill Bar in Edinburgh had been a centre for folk singers and instrumentalists. In the pub, always nicknamed „Sandy Bell’s“ and now formally called that, fiddler Aly Bain played along with guitarist Mike Whellans and singer Dick Gaughan in sessions. Aly Bain was from the Shetland Islands, and steeped in the Shetland style of playing. Meanwhile in Ireland, Cathal Mc’Connell was an All-Ireland champion in both flute and whistle. He was from a family of flute players in County Fermanagh in Ireland. Cathal’s musical collaborators were Tommy Gunn and Robin Morton. The two halves met at Falkirk folk festival in Scotland, and formed Boys of the Lough.
Gaughan left to pursue a solo career and Dave Richardson (born David Richardson, 20.8.1948, in Corbridge, Northumberland) (mandolin) joined.
This line-up (without Gaughan) was constant for the next six albums. Dave Richardson was also a writer of new material. They played ensemble instrumentals and the occasional song, equally divided between traditional sources from Ireland and Scotland.
The Boys of the Lough 1978/79 tour was billed as their final tour. However they returned a year later with Regrouped (1980). Robin Morton had left to found a Scottish folk music label called Temple Records (featuring such groups as the Battlefield Band). The „Regrouped“ line-up had two new members, and eventually fiddler John Coakley was added, who remained with the group for the next 12 years. Their 1980s sound also included Christy O’Leary from County Kerry (uilleann pipes), who had previously toured with De Dannan. During a car accident in [Scotland] in 1984, Tich Richardson (guitar, bass) died. In 1992 Boys of the Lough played at Carnegie Hall.
In 1993, the band took out The Day Dawn (1994). John Coakley left the band.
Several years later, the band took out Lonesome Blues and Dancing Shoes (2002). The group invited guests to appear for a single album. Chris Newman (guitar) and Kathryn Tickell (Northumbrian pipes) sat in with the group on tours and albums. After 32 years, Aly Bain left to play with other musicians Sandro 2016, most notably Phil Cunningham (accordion), and was replaced in 2002 by fellow Shetland fiddler Kevin Henderson[dead link] of Fiddlers‘ Bid.
In 2006, Boys of the Lough participated in TG4’s „Geantraí“. An album of the same name was issued in 2007, with contributions from Boys of the Lough, Gerry O’Connor, Joe Burke, Noel Hill, Mairtín O’Connor and others.
In 2009 Paidraig O’Keefe’s/Con Cassidy’s from In The Tradition was included in Topic Records 70 year anniversary boxed set Three Score and Ten as track fourteen on the third CD.

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