Mythology.

The Babylonian constellation IKU (field) had four stars of which three were later part of the Greek constellation "Hippos" (Pegasus). Pegasus, in Greek mythology, was a winged horse with magical powers. One myth regarding his powers says that his hooves dug out a spring, Hippocrene, which blessed those who drank its water with the ability to write poetry. Pegasus was the one who delivered Medusa's head to Polydectes, after which he travelled to Mount Olympus in order to be the bearer of thunder and lightning for Zeus. Eventually, he became the horse to Bellerophon, who was asked to kill the Chimera and succeeded with the help of Athena and Pegasus. Despite this success, after the death of his children, Bellerophon asked Pegasus to take him to Mount Olympus. Though Pegasus agreed, he plummeted back to Earth after Zeus either threw a thunderbolt at him or made Pegasus buck him off.. Pegasus was also recognised in some myths as the son of the gorgon Medusa and the god Poseidon. In ancient Persia, Pegasus was depicted by al-Sufi as a complete horse facing east, unlike most other uranographers, who had depicted Pegasus as half of a horse, rising out of the ocean. In al-Sufi's depiction, Pegasus's head is made up of the stars of Lacerta the lizard. Its right foreleg is represented by β Peg and its left foreleg is represented by η Peg, μ Peg, and λ Peg; its hind legs are marked by 9 Peg. The back is represented by π Peg and μ Cyg, and the belly is represented by ι Peg and κ Peg.  In Chinese astronomy, the modern constellation of Pegasus lies in The Black Tortoise of the north (北方玄武), where the stars were classified in several separate asterisms of stars. Epsilon and Theta Pegasi are joined with Alpha Aquarii to form "Wei" 危 "rooftop", with Theta forming the roof apex.  In Hindu astronomy, the Great Square of Pegasus contained the 26th and 27th lunar mansions. More specifically, it represented a bedstead that was a resting place for the Moon.  For the Warrau and Arawak peoples in Guyana the stars in the Great Square, corresponding to parts of Pegasus and of Andromeda, represented a barbecue, taken up to the sky by the seven hunters of the myth of Siritjo.

Characteristics.

Covering 1121 square degrees, Pegasus is the seventh-largest of the 88 constellations. Pegasus is bordered by Andromeda to the north and east, Lacerta to the north, Cygnus to the northwest, Vulpecula, Delphinus and Equuleus to the west, Aquarius to the south and Pisces to the south and east. The three-letter abbreviation for the constellation, as adopted by the IAU in 1922, is "Peg". The official constellation boundaries, as set by Eugène Delporte in 1930, are defined as a polygon of 35 segments. In the equatorial coordinate system the right ascension coordinates of these borders lie between and, while the declination coordinates are between 2.33° and 36.61°. Its position in the Northern Celestial Hemisphere means that the whole constellation is visible to observers north of 53°S.  Pegasus is dominated by a roughly square asterism, although one of the stars, Delta Pegasi or Sirrah, is now officially considered to be Alpha Andromedae, part of Andromeda, and is more usually called "Alpheratz". Traditionally, the body of the horse consists of a quadrilateral formed by the stars α Peg, β Peg, γ Peg, and α And. The front legs of the winged horse are formed by two crooked lines of stars, one leading from η Peg to κ Peg and the other from μ Peg to 1 Pegasi. Another crooked line of stars from α Peg via θ Peg to ε Peg forms the neck and head; ε is the snout.

Features.

Stars.

Bayer catalogued what he counted as 23 stars in the constellation, giving them the Bayer designations Alpha to Psi. He saw Pi Pegasi as one star, and was uncertain of its brightness, wavering between magnitude 4 and 5. Flamsteed labelled this star 29 Pegasi, but Bode concluded that the stars 27 and 29 Pegasi should be Pi and Pi Pegasi and that Bayer had seen them as a single star. Flamsteed added lower case letters e through to y, omitting A to D as they had been used on Bayer's chart to designate neighbouring constellations and the equator. He numbered 89 stars (now with Flamsteed designations), though 6 and 11 turned out to be stars in Aquarius. Within the constellation's borders there are 177 stars of apparent magnitude 6.5 or greater.  Epsilon Pegasi, also known as Enif, marks the horse's muzzle. The brightest star in Pegasus, is an orange supergiant of spectral type K21b that is around 12 times as massive as the Sun and is around 690 light-years distant from Earth. It is an irregular variable, its apparent magnitude varying between 2.37 and 2.45. Lying near Enif is AG Pegasi, an unusual star that brightened to magnitude 6.0 around 1885 before dimming to magnitude 9. It is composed of a red giant and white dwarf, estimated to be around 2.5 and 0.6 times the mass of the Sun respectively. With its outburst taking over 150 years, it has been described as the slowest nova ever recorded.  Three stars with Bayer designations that lie within the Great Square are variable stars. Phi and Psi Pegasi are pulsating red giants, while Tau Pegasi (the proper name is Salm), is a Delta Scuti variable—a class of short period (six hours at most) pulsating stars that have been used as standard candles and as subjects to study astroseismology. Rotating rapidly with a projected rotational velocity of 150 km s, Kerb is almost 30 times as luminous as the Sun and has a pulsation period of 56.5 minutes. With an outer atmosphere at an effective temperature of 7,762 K,it a white star with a spectral type of A5IV.  Zeta, Xi, Rho and Sigma Pegasi mark the horse's neck. The brightest of these with a magnitude of 3.4 is Zeta, also traditionally known as Homam. Lying seven degrees southwest of Markab, it is a blue-white main sequence star of spectral type B8V located around 209 light-years distant. It is a slowly pulsating B star that varies slightly in luminosity with a period of 22.952 ± 0.804 hours, completing 1.04566 cycles per day. Xi lies 2 degrees northeast, and is a yellow-white main sequence star of spectral type F6V that is 86% larger and 17% more massive that the Sun, and radiate 4.5 times the solar luminosity. It has a red dwarf companion that is 192.3 au distant. If (as is likely) the smaller star is in orbit around the larger star, then it would take around 2000 years to complete a revolution. Theta Pegasi marks the horse's eye. Also known as Biham, it is a 3.43-magnitude white main sequence star of spectral type A2V, around 1.8 times as massive, 24 times as luminous, and 2.3 times as wide as the Sun.  Alpha (Markab), Beta (Scheat), and Gamma (Algenib), together with Alpha Andromedae (Alpheratz or Sirrah) form the large asterism known as the "Square of Pegasus". The brightest of these, Alpheratz was also known as both Delta Pegasi and Alpha Andromedae before being placed in Andromeda in 1922 with the setting of constellation boundaries. The second brightest star is Scheat, a red giant of spectral type M2.5II-IIIe located around 196 light-years away from Earth. It has expanded until it is some 95 times as large, and has a total luminosity 1,500 times that of the Sun. Beta Pegasi is a semi-regular variable that varies from magnitude 2.31 to 2.74 over a period of 43.3 days. Markab and Algenib are blue-white stars of spectral types B9III and B2IV located 133 and 391 light-years distant respectively. Appearing to have moved off the main sequence as their core hydrogen supply is being or has been exhausted, they are enlarging and cooling to eventually become red giant stars. Markab has an apparent magnitude of 2.48, while Algenib is a Beta Cephei variable that varies between magnitudes 2.82 and 2.86 every 3 hours 38 minutes, and also exhibits some slow pulsations every 1.47 days.  Eta and Omicron Pegasi mark the left knee and Pi Pegasi the left hoof, while Iota and Kappa Pegasi mark the right knee and hoof. Also known as Matar, Eta Pegasi is the fifth-brightest star in the constellation. Shining with an apparent magnitude of 2.94, it is a multiple star system composed of a yellow giant of spectral type G2 and a yellow-white main sequence star of spectral type A5V that are 3.2 and 2.0 times as massive as our Sun. The two revolve around each other every 2.24 years. Farther afield is a binary system of two G-type main sequence stars, that would take 170,000 years to orbit the main pair if they are in fact related. Omicron Pegasi has a magnitude of 4.79. Located 300 ± 20 light-years distant from Earth, it is a white subgiant that has begun to cool, expand and brighten as it exhausts its core hydrogen fuel and moves off the main sequence. Pi and Pi Pegasi appear as an optical double to the unaided eye as they are separated by 10 arcminutes, and are not a true binary system. Located 289 ± 8 light-years distant, Pi is an ageing yellow giant of spectral type G6III, 1.92 times as massive and around 200 times as luminous as the Sun. Pi is a yellow-white subgiant that is 2.5 times as massive as the Sun and has expanded to 8 times the Sun's radius and brightened to 92 times the Sun's luminosity. It is surrounded by a circumstellar disk spinning at 145 km a second, and is 263 ± 4 light-years distant from Earth.  IK Pegasi is a close binary comprising an A-type main-sequence star and white dwarf in very close orbit; the latter a candidate for a future type Ia supernova as its main star runs out of core hydrogen fuel and expands into a giant and transfers material to the smaller star.  Twelve star systems have been found to have exoplanets. 51 Pegasi was the first Sun-like star discovered to have an exoplanet companion; 51 Pegasi b (unofficially named Bellerophon) is a hot Jupiter close to its sun, completing an orbit every four days. Spectroscopic analysis of HD 209458 b, an extrasolar planet in this constellation, has provided the first evidence of atmospheric water vapor beyond the solar system, while extrasolar planets orbiting the star HR 8799 also in Pegasus are the first to be directly imaged. V391 Pegasi is a hot subdwarf star that has been found to have a planetary companion.

Deep-sky objects.

M15 (NGC 7078) is a globular cluster of magnitude 6.4, 34,000 light-years from Earth. It is a Shapley class IV cluster, which means that it is fairly rich and concentrated towards its center. M15 was discovered in 1746 by Jean-Dominique Maraldi.  NGC 7331 is a spiral galaxy located in Pegasus, 38 million light-years distant with a redshift of 0.0027. It was discovered by musician-astronomer William Herschel in 1784 and was later one of the first nebulous objects to be described as "spiral" by William Parsons. Another of Pegasus's galaxies is NGC 7742, a Type 2 Seyfert galaxy. Located at a distance of 77 million light-years with a redshift of 0.00555, it is an active galaxy with a supermassive black hole at its core. Its characteristic emission lines are produced by gas moving at high speeds around the central black hole.  Pegasus is also noted for its more unusual galaxies and exotic objects. Einstein's Cross is a quasar that has been lensed by a foreground galaxy. The elliptical galaxy is 400 million light-years away with a redshift of 0.0394, but the quasar is 8 billion light-years away. The lensed quasar resembles a cross because the gravitational force of the foreground galaxy on its light creates four images of the quasar. Stephan's Quintet is another unique object located in Pegasus. It is a cluster of five galaxies at a distance of 300 million light-years and a redshift of 0.0215. First discovered by Édouard Stephan, a Frenchman, in 1877, the Quintet is unique for its interacting galaxies. Two of the galaxies in the middle of the group have clearly begun to collide, sparking massive bursts of star formation and drawing off long "tails" of stars. Astronomers have predicted that all five galaxies may eventually merge into one large elliptical galaxy.

Namesakes.

USS "Pegasus" (AK-48) and USS "Pegasus" (PHM-1) are United States navy ships named after the constellation "Pegasus".  The Beyblade top Storm Pegasus 105RF and its evolutions Galaxy Pegasus W105R2F and Cosmic Pegasus F:D are based on Pegasus constellation.  Pegasus Seiya from the anime of Saint Seiya was named after the constellation Pegasus.

Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and is one of the 88 constellations recognised today.

Pegas je souhvězdí na severní obloze, které je pojmenováno podle legendárního Pegasa, okřídleného koně, syna boha moří Poseidóna a Medúsy. Jde o jedno z 88 moderních souhvězdí a jedno ze 48 starověkých souhvězdí uváděných Ptolemaiem.


History.

The existence of particles flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. Carrington. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare. This is a sudden, localised increase in brightness on the solar disc, which is now known to often occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a coronal mass ejection. On the following day, a geomagnetic storm was observed, and Carrington suspected that there might be a connection, which is now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with the Earth's magnetosphere. George FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days.  In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the solar wind, without naming it, in a footnote to an article on Comet Morehouse. The idea never fully caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the ejected material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions.  The first person to suggest that the ejected material consisted of both ions and electrons was Kristian Birkeland. His geomagnetic surveys showed that auroral activity was nearly uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". In 1916, Birkeland proposed that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds". In other words, the solar wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun.  Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space (as seen during total eclipses). Later spectroscopic work confirmed this extraordinary temperature. In the mid-1950s Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, Ludwig Biermann became interested in the fact that no matter whether a comet is headed towards or away from the Sun, its tail always points away from the Sun. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. Wilfried Schröder claimed that Paul Ahnert was the first to relate solar wind to comet tail direction based on observations of the comet Whipple-Fedke (1942g).  Eugene Parker realised heat flowing from the Sun in Chapman's model and the comet tail blowing away from the Sun in Biermann's hypothesis had to be the result of the same phenomenon, which he termed the "solar wind". In 1957, Parker showed, even though the Sun's corona is strongly attracted by solar gravity, it is such a good heat conductor that it is still very hot at large distances. Since gravity weakens as distance from the Sun increases, the outer coronal atmosphere escapes supersonically into interstellar space. Furthermore, Parker was the first person to notice that the weakening effect of the gravity has the same effect on hydrodynamic flow as a de Laval nozzle: it incites a transition from subsonic to supersonic flow.  Opposition to Parker's hypothesis on the solar wind was strong. The paper he submitted to "The Astrophysical Journal" in 1958 was rejected by two reviewers. It was saved by the editor Subrahmanyan Chandrasekhar.  In January 1959, the Soviet spacecraft "Luna 1" first directly observed the solar wind and measured its strength, using hemispherical ion traps. The discovery, made by Konstantin Gringauz, was verified by "Luna 2", "Luna 3" and by the more distant measurements of "Venera 1". Three years later a similar measurement was performed by Neugebauer and collaborators using the "Mariner 2" spacecraft.  In the late 1990s, the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about 4 solar radii from the photosphere (surface); but the transition (or "sonic point") now appears to be much lower, perhaps only 1 solar radius above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun. The acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. The gravitational and electromagnetic explanation for this acceleration is, however, detailed in an earlier paper by 1970 Nobel laureate for Physics, Hannes Alfvén.  The first numerical simulation of the solar wind in the solar corona including closed and open field lines was performed by Pneuman and Kopp in 1971. The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration.  In 1990, the "Ulysses" probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's ecliptic plane.  In 2006, the STEREO mission was launched to study coronal mass ejections and the solar corona using stereoscopy from two widely separated imaging systems. Each STEREO spacecraft carried two heliospheric imagers: highly sensitive wide-field cameras capable of imaging the solar wind itself, via Thomson scattering of sunlight off of free electrons. Movies from STEREO revealed the solar wind near the ecliptic, as a large-scale turbulent flow.  The "Voyager 1" probe reached the end of the solar wind bubble in 2012. The detection of solar wind dropped off precipitously at that time, and "Voyager 2" underwent a similar observation in 2018.  In 2018, NASA launched the "Parker Solar Probe", named in honor of Eugene Parker, on a mission to study the structure and dynamics of the solar corona, in an attempt to understand the mechanisms that cause particles to be heated and accelerated as solar wind. During its seven-year mission, the probe will make twenty-four orbits of the Sun, passing further into the corona with each orbit's perihelion, ultimately passing within 0.04 astronomical units of the Sun's surface. It is the first NASA spacecraft named for a living person, and Parker, at age 91, was on hand to observe the launch.

Acceleration.

While early models of the solar wind relied primarily on thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required and likely relates to magnetic fields in the solar atmosphere.  The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million kelvin. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about, which is well below the solar escape velocity of. However, a few of the particles achieve energies sufficient to reach the terminal velocity of, which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions away from the Sun.  The total number of particles carried away from the Sun by the solar wind is about per second. Thus, the total mass loss each year is about solar masses, or about 1.3–1.9 million tonnes per second. This is equivalent to losing a mass equal to the Earth every 150 million years. However, only about 0.01% of the Sun's total mass has been lost through the solar wind. Other stars have much stronger stellar winds that result in significantly higher mass loss rates.

Properties and structure.

Fast and slow solar wind.

The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of, a temperature of ~10 K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of, a temperature of and it nearly matches the composition of the Sun's photosphere. The slow solar wind is twice as dense and more variable in nature than the fast solar wind.  The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt", where coronal streamers are produced by magnetic flux open to the heliosphere draping over closed magnetic loops. The exact coronal structures involved in slow solar wind formation and the method by which the material is released is still under debate. Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred at latitudes up to 30–35° during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the solar cycle approached maximum. At solar maximum, the poles were also emitting a slow solar wind.  The fast solar wind originates from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field. Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 kilometers above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.

Pressure.

The wind exerts a pressure at typically in the range of (), although it can readily vary outside that range.  The ram pressure is a function of wind speed and density. The formula is  where m is the proton mass, pressure P is in nPa (nanopascals), n is the density in particles/cm and V is the speed in km/s of the solar wind.

Coronal mass ejection.

Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called coronal mass ejections, or CMEs. CMEs are caused by release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. CMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME.  When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora.  CMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs.

Solar System effects.

Over the Sun's lifetime, the interaction of its surface layers with the escaping solar wind has significantly decreased its surface rotation rate. The wind is considered responsible for comets' tails, along with the Sun's radiation. The solar wind contributes to fluctuations in celestial radio waves observed on the Earth, through an effect called interplanetary scintillation.

Magnetospheres.

Where the solar wind intersects with a planet that has a well-developed magnetic field (such as Earth, Jupiter or Saturn), the particles are deflected by the Lorentz force. This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface. The magnetosphere is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long wake on the opposite side. The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines.  The solar wind is responsible for the overall shape of Earth's magnetosphere. Fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind. These phenomena are collectively called space weather.  From the European Space Agency's Cluster mission, a new study has taken place that proposes that it is easier for the solar wind to infiltrate the magnetosphere than previously believed. A group of scientists directly observed the existence of certain waves in the solar wind that were not expected. A recent study shows that these waves enable incoming charged particles of solar wind to breach the magnetopause. This suggests that the magnetic bubble forms more as a filter than a continuous barrier. This latest discovery occurred through the distinctive arrangement of the four identical Cluster spacecraft, which fly in a controlled configuration through near-Earth space. As they sweep from the magnetosphere into interplanetary space and back again, the fleet provides exceptional three-dimensional insights on the phenomena that connect the sun to Earth.  The research characterised variances in formation of the interplanetary magnetic field (IMF) largely influenced by Kelvin–Helmholtz instability (which occur at the interface of two fluids) as a result of differences in thickness and numerous other characteristics of the boundary layer. Experts believe that this was the first occasion that the appearance of Kelvin–Helmholtz waves at the magnetopause had been displayed at high latitude dawnward orientation of the IMF. These waves are being seen in unforeseen places under solar wind conditions that were formerly believed to be undesired for their generation. These discoveries show how Earth's magnetosphere can be penetrated by solar particles under specific IMF circumstances. The findings are also relevant to studies of magnetospheric progressions around other planetary bodies. This study suggests that Kelvin–Helmholtz waves can be a somewhat common, and possibly constant, instrument for the entrance of solar wind into terrestrial magnetospheres under various IMF orientations.

Atmospheres.

The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind.  Venus, the nearest and most similar planet to Earth, has 100 times denser atmosphere, with little or no geo-magnetic field. Space probes discovered a comet-like tail that extends to Earth's orbit.  Earth itself is largely protected from the solar wind by its magnetic field, which deflects most of the charged particles; however some of the charged particles are trapped in the Van Allen radiation belt. A smaller number of particles from the solar wind manage to travel, as though on an electromagnetic energy transmission line, to the Earth's upper atmosphere and ionosphere in the auroral zones. The only time the solar wind is observable on the Earth is when it is strong enough to produce phenomena such as the aurora and geomagnetic storms. Bright auroras strongly heat the ionosphere, causing its plasma to expand into the magnetosphere, increasing the size of the plasma geosphere and injecting atmospheric matter into the solar wind. Geomagnetic storms result when the pressure of plasmas contained inside the magnetosphere is sufficiently large to inflate and thereby distort the geomagnetic field.  Although Mars is larger than Mercury and four times farther from the Sun, it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a layer 1/100th as dense as the Earth's. It is believed the mechanism for this atmospheric stripping is gas caught in bubbles of magnetic field, which are ripped off by solar winds. In 2015 the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission measured the rate of atmospheric stripping caused by the magnetic field carried by the solar wind as it flows past Mars, which generates an electric field, much as a turbine on Earth can be used to generate electricity. This electric field accelerates electrically charged gas atoms, called ions, in Mars' upper atmosphere and shoots them into space. The MAVEN mission measured the rate of atmospheric stripping at about 100 grams (≈1/4 lb) per second.

Moons and planetary surfaces.

Mercury, the nearest planet to the Sun, bears the full brunt of the solar wind, and since its atmosphere is vestigial and transient, its surface is bathed in radiation.  Mercury has an intrinsic magnetic field, so under normal solar wind conditions, the solar wind cannot penetrate its magnetosphere and particles only reach the surface in the cusp regions. During coronal mass ejections, however, the magnetopause may get pressed into the surface of the planet, and under these conditions, the solar wind may interact freely with the planetary surface.  The Earth's Moon has no atmosphere or intrinsic magnetic field, and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to sample the solar wind, and lunar soil returned for study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. These elements may prove useful resources for lunar colonies.

Outer limits.

The solar wind "blows a bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause and is often considered to be the outer border of the Solar System. The distance to the heliopause is not precisely known and probably depends on the current velocity of the solar wind and the local density of the interstellar medium, but it is far outside Pluto's orbit. Scientists hope to gain perspective on the heliopause from data acquired through the Interstellar Boundary Explorer (IBEX) mission, launched in October 2008.  The end of the heliosphere is noted as one of the ways defining the extent of the Solar System, along with the Kuiper Belt, and finally the radius at which of the Sun's gravitational influcence is matched by other stars. The maximum extend of that Gravity has been estimated at between 50,000 AU to 2 light-years, compared to the edge of the heliopause (the outer edge of the heliosphere) which has been detected to end about 120 AU by the "Voyager 1" spacecraft.

Further reading.

Fox, Karen C. (2012) "NASA Study Using Cluster Reveals New Insights Into Solar Wind" NASA.  S.Cuperman and N. Metzler, Role of fluctuations in the interplanetary magnetic field on the heat conduction in the Solar Wind.J.Geophys. Res. 78 (16), 3167–3168, 1973. S. Cuperman and N. Metzler. Astrophys. J., 182 (3), 961–975, 1973.  S. Cuperman and N. Metzler, Solution of 3-fluid model equations with anomalous transport coefficients for thequiet Solar Wind. Astrophys.J., 196 (1) 205–219, 1975  S. Cuperman, N. Metzler and M. Spygelglass, Confirmation of known numerical solutions for the quiet Solar Wind equations. Astrophys. J., 198 (3), 755–759, 1975.  S.Cuperman and N. Metzler, Relative magnitude of streaming velocities of alpha particles and protons at 1AU. Astrophys. and Space Sci. 45 (2) 411–417,1976.  N. Metzler. A multi-fluid model for stellar winds. Proceedings of the L.D.de Feiter Memorial Symposium on the Study of Traveling Interplanetary Phenomena. AFGL-TR-77-0309, Air Force Systems Command, USAF, 1978.  N. Metzler and M. Dryer, A self-consistent solution of the three-fluid model of the Solar Wind. Astrophys. J., 222 (2), 689–695, 1978.  S. Cuperman and N. Metzler, Comments on Acceleration of Solar Wind He++3 effects of Resonant and nonresonant interactions with transverse waves. J. Geophys. Res. 84 (NA5), 2139–2140 (1979) N. Metzler, S. Cuperman, M. Dryer and P. Rosenau, A time-dependent two-fluid model with thermal conduction for Solar Wind. Astrophys. J., 231 (3) 960–976, 1979.

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between. The composition of the solar wind plasma also includes a mixture of materials found in the solar plasma: trace amounts of heavy ions and atomic nuclei C, N, O, Ne, Mg, Si, S, and Fe. There are also rarer traces of some other nuclei and isotopes such as P, Ti, Cr, Ni, Fe 54 and 56, and Ni 58,60,62. Embedded within the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field.

Sluneční vítr je proud částic, který vychází ze Slunce. Má obvykle rychlost asi 450 km/s (1,5 ‰ rychlosti světla). Pochází-li z jiných hvězd než z našeho Slunce, je nazýván hvězdný vítr.


Territory.

It is generally believed that the tribal union included the regions of Moravia, Nitravia (Nitra), Silesia, Bohemia and Lusatia. According to Julius Bartl, the centre of the polity lay "somewhere in the area of southern Moravia, Lower Austria, and western Slovakia (Nitravia)".  According to J. B. Bury, "the assumption that his kingdom embraced Carantania, the country of the Alpine Slavs, rests only upon the Anonymus de conversione Bagariorum et Carantanorum".  Archaeological findings indicate that the empire was situated in present-day Moravia, Lower Austria and Slovakia. According to Slovak historian Richard Marsina, it is unlikely that the center of Samo's tribal union was in the whole territory of present-day Slovakia. The settlements of the later Moravian and Nitrian principalities (see Great Moravia) are often identical with those from the time of Samo's Empire.  According to the findings of some German archaeologists, the core of Samo's state was located north of the Danube, and in the upper Main region. In some historical sources of the early IX century, this region is described as ""regio Sclavorum"" or ""terra Slavorum"". Large amounts of early medieval Slavic ceramics are also found here. Many Slavic toponyms have also been found in this area, such as "Winideheim" ("The Hill of the Wends"), and "Knetzburg" (“Prince's Mountain”).

Prelude.

According to Fredegar, Samo, a Frankish merchant, went to the Slavs in 623–624. The dating has been questioned on the basis that the Wends would have most likely rebelled after the defeat of the Avars at the First Siege of Constantinople in 626. The Avars first arrived in the Pannonian Basin and subdued the local Slavs in the 560s. Samo may have been one of the merchants who supplied arms to the Slavs for their regular revolts. Whether he became king during a revolt of 623–24 or during the one which inevitably followed the Avar defeat in 626, he definitely took advantage of the latter to solidify his position. A string of victories over the Avars proved his ability to his subjects and secured his election as " (king). Samo went on to secure his throne by marriage into the major Wendish families, wedding at least twelve women and fathering twenty-two sons and fifteen daughters.  In 630–631, Valuk, the "duke of the Wends" (") was mentioned. These Wends referred to the Slavs of the Windic March, which according to some historians was the later March of Carinthia (Carantania) in present Slovenia and Austria. According to Jan Steinhubel, Valuk allowed Longobards to pass through his territory and attack Samo from south-west. Longobards were allies of Franks (Dagobert I.) against Samo. If Valuk allowed Longobards to go through his territory, his principality could have not been part of Samo's empire.

History.

The most famous event of Samo's career was his victory over the Frankish royal army under Dagobert I in 631 or 632. Provoked to action by a "violent quarrel in the Pannonian kingdom of the Avars or Huns", Dagobert led three armies against the Wends, the largest being his own Austrasian army. The Franks were routed near Wogastisburg; the majority of the besieging armies were slaughtered, while the rest of the troops fled, leaving weapons and other equipment lying on the ground. In the aftermath of the Wendish victory, Samo invaded Frankish Thuringia several times and undertook looting raids there. Dervan, the "duke of the Sorbs" (""), initially subordinate to the Franks, joined the Slavic tribal union after Samo defeated Dagobert I. The Sorbs lived to the east of the Saxon Saale. Dervan participated in the subsequent wars against the Franks, successfully fighting against Frankish Thuringia (631–634), until he was finally defeated by Radulf of Thuringia in 636.  In 641, the rebellious Radulf sought an alliance with Samo against his sovereign, Sigebert III. Samo also maintained long-distance trade relationships. On his death, however, his title was not inherited by his sons. Ultimately, Samo can be credited with forging a Wendish identity by speaking on behalf of the community which recognised his authority.

Aftermath.

The history of the tribal union after Samo's death in 658 or 659 is largely unclear, though it is generally assumed that it ended. Archaeological findings show that the Avars returned to their previous territories (at least to southernmost modern Slovakia) and entered into a symbiosis with the Slavs, whereas territories to the north of the Avar Khaganate were purely Slav territories. The first specific thing that is known about the fate of these Slavs and Avars is the existence of Moravian and Nitravian principalities in the late 8th century, which attacked the Avars, and the defeat of the Avars by the Franks under Charlemagne in 799 or 802–03, after which the Avars soon ceased to exist.  Great Moravia is viewed of as a continuation or successor state to Samo's Empire. The polity has been called the first Slavic state.

Samo's Empire (Also known as "Samo's Kingdom" or "Samo's State") is the historiographical name for the West Slavic tribal union established by King ("Rex") Samo, which existed between 631 and 658 in Central Europe. The centre of the union was most likely in Moravia and Nitravia (Nitra), additionally the union included Czech tribes, Sorbian tribes (under Dervan) and other West Slavic tribes along the river Danube (present Lower Austria). The polity has been called the first Slavic state.

Sámova říše byl kmenový svaz Slovanů existující ve střední Evropě v letech 624 – 659 (podle Fredegarovy kroniky). Pojil se s osobou franského kupce Sáma, který si získal velkou prestiž jako velitel během bojů Slovanů s Avary, ovládajícími dlouhá léta střední a jihovýchodní Evropu.


Etymology.

The Mariana Trench is named after the nearby Mariana Islands, which are named Las Marianas in honor of Spanish Queen Mariana of Austria, widow of Philip IV of Spain). The islands are part of the island arc that is formed on an over-riding plate, called the Mariana Plate (also named for the islands), on the western side of the trench.

Geology.

The Mariana Trench is part of the Izu-Bonin-Mariana subduction system that forms the boundary between two tectonic plates. In this system, the western edge of one plate, the Pacific Plate, is subducted (i.e., thrust) beneath the smaller Mariana Plate that lies to the west. Crustal material at the western edge of the Pacific Plate is some of the oldest oceanic crust on earth (up to 170 million years old), and is, therefore, cooler and denser; hence its great height difference relative to the higher-riding (and younger) Mariana Plate. The deepest area at the plate boundary is the Mariana Trench proper.  The movement of the Pacific and Mariana plates is also indirectly responsible for the formation of the Mariana Islands. These volcanic islands are caused by flux melting of the upper mantle due to the release of water that is trapped in minerals of the subducted portion of the Pacific Plate.

Research history.

The trench was first sounded during the "Challenger" expedition in 1875, using a weighted rope, which recorded a depth of. In 1877, a map was published called "Tiefenkarte des Grossen Ozeans" ("Depth map of the Great Ocean") by Petermann, which showed a "Challenger Tief" ("Challenger deep") at the location of that sounding. In 1899, USS Nero, a converted collier, recorded a depth of.  In 1951, "Challenger II" surveyed the trench using echo sounding, a much more precise and vastly easier way to measure depth than the sounding equipment and drag lines used in the original expedition. During this survey, the deepest part of the trench was recorded when the "Challenger II" measured a depth of at, known as the Challenger Deep.  In 1957, the Soviet vessel reported a depth of at a location dubbed the "Mariana Hollow".  In 1962, the surface ship M.V. "Spencer F. Baird" recorded a maximum depth of using precision depth gauges.  In 1984, the Japanese survey vessel "Takuyō" (拓洋) collected data from the Mariana Trench using a narrow, multi-beam echo sounder; it reported a maximum depth of, also reported as ±. Remotely Operated Vehicle "KAIKO" reached the deepest area of the Mariana Trench and made the deepest diving record of on 24 March 1995.  During surveys carried out between 1997 and 2001, a spot was found along the Mariana Trench that had depth similar to that of the Challenger Deep, possibly even deeper. It was discovered while scientists from the Hawaii Institute of Geophysics and Planetology were completing a survey around Guam; they used a sonar mapping system towed behind the research ship to conduct the survey. This new spot was named the HMRG (Hawaii Mapping Research Group) Deep, after the group of scientists who discovered it.  On 1 June 2009, mapping aboard the "RV Kilo Moana" (mothership of the Nereus vehicle), indicated a spot with a depth of. The sonar mapping of the Challenger Deep was possible by its Simrad EM120 sonar multibeam bathymetry system for deep water. The sonar system uses phase and amplitude bottom detection, with an accuracy of better than 0.2% of water depth across the entire swath (implying that the depth figure is accurate to ± ).<ref name="Daily Reports for R/V KILO MOANA"></ref><ref name="Scientic Equipment aboard the R/V KILO MOANA"></ref>  In 2011, it was announced at the American Geophysical Union Fall Meeting that a US Navy hydrographic ship equipped with a multibeam echosounder conducted a survey which mapped the entire trench to resolution. The mapping revealed the existence of four rocky outcrops thought to be former seamounts.  The Mariana Trench is a site chosen by researchers at Washington University and the Woods Hole Oceanographic Institution in 2012 for a seismic survey to investigate the subsurface water cycle. Using both ocean-bottom seismometers and hydrophones the scientists are able to map structures as deep as beneath the surface.

Descents.

Four manned descents and three unmanned descents have been achieved. The first was the manned descent by Swiss-designed, Italian-built, United States Navy-owned bathyscaphe "Trieste" which reached the bottom at 1:06 pm on 23 January 1960, with Don Walsh and Jacques Piccard on board. Iron shot was used for ballast, with gasoline for buoyancy. The onboard systems indicated a depth of 11,521 m (37,799 ft), but this was later revised to 10,916 m (35,814 ft). The depth was estimated from a conversion of pressure measured and calculations based on the water density from sea surface to seabed.  This was followed by the unmanned ROVs "Kaikō" in 1996 and "Nereus" in 2009. The first three expeditions directly measured very similar depths of. The fourth was made by Canadian film director James Cameron in 2012. On 26 March, he reached the bottom of the Mariana Trench in the submersible vessel "Deepsea Challenger," diving to a depth of 10,908 m (35,787 ft).  In July 2015, members of the National Oceanic and Atmospheric Administration, Oregon State University, and the Coast Guard submerged a hydrophone into the deepest part of the Mariana Trench, the Challenger Deep, never having deployed one past a mile. The titanium-shelled hydrophone was designed to withstand the immense pressure 7 miles under. Although researchers were unable to retrieve the hydrophone until November, the data capacity was full within the first 23 days. After months of analyzing the sounds, the experts were surprised to pick up natural sounds like earthquakes, a typhoon and baleen whales along with man-made sounds such as boats. Due to the mission's success, the researchers announced plans to deploy a second hydrophone in 2017 for an extended period of time.  Victor Vescovo achieved a new record descent to 10,927 metres (35,853 ft.), using the "DSV Limiting Factor", a Triton 36000/2 model manufactured by Florida-based Triton Submarines. He dived again in May 2019 and became the first person to dive the Challenger Deep twice.  In May 2020, a joint project between the Russian shipbuilders, scientific teams of the Russian Academy of Sciences with the support of Russian Foundation for Advanced Research Projects and the Pacific Fleet submerged an autonomous underwater vehicle "Vityaz" to the bottom of the Mariana Trench at a depth of 10,028 metres. "Vityaz" is the first underwater vehicle (AUV) to operate autonomously at the extreme depths of the Mariana Trench. The duration of the mission, excluding diving and surfacing, was more than 3 hours"."

Planned descents.

, at least one other team was planning a piloted submarine to reach the bottom of the Mariana Trench. DOER Marine, a marine technology company based near San Francisco and set up in 1992, plans for a crew of two or three to take 90 minutes to reach the seabed.

Life.

The expedition conducted in 1960 claimed to have observed, with great surprise because of the high pressure, large creatures living at the bottom, such as a flatfish about long, and shrimp. According to Piccard, "The bottom appeared light and clear, a waste of firm diatomaceous ooze". Many marine biologists are now skeptical of the supposed sighting of the flatfish, and it is suggested that the creature may instead have been a sea cucumber. During the second expedition, the unmanned vehicle Kaikō collected mud samples from the seabed. Tiny organisms were found to be living in those samples.  In July 2011, a research expedition deployed untethered landers, called dropcams, equipped with digital video cameras and lights to explore this region of the deep sea.  Amongst many other living organisms, some gigantic single-celled amoebas with a size of more than, belonging to the class of monothalamea were observed. Monothalamea are noteworthy for their size, their extreme abundance on the seafloor and their role as hosts for a variety of organisms.  In December 2014, a new species of snailfish was discovered at a depth of, breaking the previous record for the deepest living fish seen on video.  During the 2014 expedition, several new species were filmed including huge crustaceans known as supergiants. Deep-sea gigantism is the process where species grow larger than their shallow water relatives.  In May 2017, an unidentified type of snailfish was filmed at a depth of.

Pollution.

In 2016, a research expedition looked at the chemical makeup of crustacean scavengers collected from the range of 7,841–10,250 metres within the trench. Within these organisms, the researchers found extremely elevated concentrations of PCBs, a chemical toxin banned for its environmental harm in the 1970s, concentrated at all depths within the sediment of the trench. Further research has found that amphipods also ingest microplastics, with 100% of amphipods having at least one piece of synthetic material in their stomachs.  In 2019, Victor Vescovo reported finding a plastic bag and candy wrappers at the bottom of the trench. That year, "Scientific American" also reported that carbon-14 from nuclear bomb testing has been found in the bodies of aquatic animals found in the trench.

Possible nuclear waste disposal site.

Like other oceanic trenches, the Mariana Trench has been proposed as a site for nuclear waste disposal in 1972, in the hope that tectonic plate subduction occurring at the site might eventually push the nuclear waste deep into the Earth's mantle, the second layer of the Earth. However, ocean dumping of nuclear waste is prohibited by international law. Furthermore, plate subduction zones are associated with very large megathrust earthquakes, the effects of which are unpredictable for the safety of long-term disposal of nuclear wastes within the hadopelagic ecosystem.

The Mariana Trench or Marianas Trench is located in the western Pacific Ocean about east of the Mariana Islands; it is the deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maximum known depth is (± ) (6.825 miles) at the southern end of a small slot-shaped valley in its floor known as the Challenger Deep. However, some unrepeated measurements place the deepest portion at. By comparison: if Mount Everest were placed into the trench at this point, its peak would still be over under water.

Marianský příkop (v češtině obvykle psán Mariánský příkop) je asi 2550 km dlouhé a průměrně 69 km široké podmořské údolí tektonického původu, které se nachází východně od souostroví Mariany (Mariánské ostrovy), poblíž ostrova Guam. Jeho součástí je i vůči hladině moře nejhlubší místo zemského povrchu, hloubka podle posledního měření činí 10 994 m (dříve uváděno 10 911 m až 11 034 m) pod hladinou severního Tichého oceánu. Jedná se o nejhlubší známý podmořský příkop. Nejblíže ke středu Země je ale Polární hlubokomořská planina v Severním ledovém oceánu.


Structure.

The book is structured in four chapters:  Act 1: Prologue and Problem: Death and Emptiness (1:1–22)  Act 2: Ruth Meets Boaz, Naomi's Relative, on the Harvest Field (2:1–23)  Act 3: Naomi Sends Ruth to Boaz on the Threshing Floor (3:1–18)  Act 4: Resolution and Epilogue: Life and Fullness (4:1–22)  Genealogical appendix (4:18–22)

Summary.

During the time of the judges, an Israelite family from Bethlehem – Elimelech, his wife Naomi, and their sons Mahlon and Chilion – emigrated to the nearby country of Moab. Elimelech died, and the sons married two Moabite women: Mahlon married Ruth and Chilion married Orpah.  After about ten years, the two sons of Naomi also died in Moab (1:4). Naomi decided to return to Bethlehem. She told her daughters-in-law to return to their own mothers and remarry. Orpah reluctantly left; however, Ruth said, "Do not urge me to leave you, to turn back and not follow you. For wherever you go, I will go; wherever you lodge, I will lodge; your people shall be my people, and your God my God. Where you die, I will die, and there I will be buried. Thus and more may the Lord do to me if anything but death parts me from you." (Ruth 1:16–17 NJPS).  The two women returned to Bethlehem at the beginning of the barley harvest, and in order to support her mother-in-law and herself, Ruth went to the fields to glean. As it happened, the field she went to belonged to a man named Boaz, who was kind to her because he had heard of her loyalty to her mother-in-law. Ruth told Naomi of Boaz's kindness, and she gleaned in his field through the remainder of barley and wheat harvest.  Boaz was a close relative of Naomi's husband's family. He was therefore obliged by the Levirate law to marry Mahlon's widow, Ruth, in order to carry on his family's inheritance. Naomi sent Ruth to the threshing floor at night and told her to go where he slept, and "uncover his feet and lie down. He will tell you what you are to do." (3:4). Ruth did so. Boaz asked her who she was, and she replied: "I am your handmaid Ruth. Spread your robe over your handmaid, for you are a redeeming kinsman" (3:9 NJPS). Boaz blessed her and agreed to do all that is required, and he noted that, "all the elders of my town know what a fine woman you are" (3:11 NJPS). He then acknowledged that he was a close relative, but that there was one who was closer, and she remained in submission at his feet until she returned into the city in the morning.  Early that day, Boaz went to the city gate to meet with the other male relative before the town elders. The relative is not named: Boaz addresses him as "ploni almoni", literally "so and so". The unnamed relative is unwilling to jeopardize the inheritance of his own estate by marrying Ruth, and so relinquished his right of redemption, thus allowing Boaz to marry Ruth. They transferred the property and redeemed it, ratified by the nearer kinsman taking off his shoe and handing it over to Boaz. Ruth 4:7 notes for later generations that:  Boaz and Ruth were then married and have a son. The women of the city celebrate Naomi's joy, for Naomi found a redeemer for her family name, and Naomi takes the child and places it in her bosom.  The child is named Obed, who we discover is "the father of Jesse, the father of David" (Ruth 4:13–17), that is, the grandfather of King David.  The book concludes with an appendix which traces the Davidic genealogy all the way back from Perez, "whom Tamar bore to Judah", through to Obed, down to David.

Composition.

The book does not name its author. It is traditionally ascribed to the prophet Samuel, but Ruth's identity as a non-Israelite and the stress on the need for an inclusive attitude towards foreigners suggests an origin in the fifth century BC, when intermarriage had become controversial (as seen in Ezra 9:1 and Nehemiah 13:1). A substantial number of scholars therefore date it to the Persian period (6th–4th centuries BC). The genealogy that concludes the book is believed to be a post-exilic Priestly addition, as it adds nothing to the plot; nevertheless, it is carefully crafted and integrates the book into the history of Israel running from Genesis to Kings.

Themes and background.

Levirate marriage and the "redeemers".

The Book of Ruth illustrates the difficulty of trying to use laws given in books such as Deuteronomy as evidence of actual practice. Naomi plans to provide security for herself and Ruth by arranging a Levirate marriage with Boaz. She instructs Ruth to uncover Boaz's feet after he has gone to sleep and lie down. When Boaz wakes up, surprised to see a woman at his feet, Ruth explains she wants him to redeem (and thus marry) her. Many modern commentators see sexual allusions in this part of the story, with 'feet' as a euphemism for genitals.  Since there was no heir to inherit Elimelech's land, custom required a close relative (usually the dead man's brother) to marry the widow of the deceased in order to continue his family line (Deuteronomy 25:5–10). This relative was called the go'el, the "kinsman-redeemer". As Boaz is not Elimelech's brother, nor is Ruth his widow, scholars refer to the arrangement here as "Levirate-like". A complication arises in the story: another man is a closer relative to Elimelech than Boaz and has first claim on Ruth. It is resolved through the custom that required land to stay in the family: a family could mortgage land to ward off poverty, but the law required a kinsman to purchase it back into the family (Leviticus 25:25ff). Boaz meets the near kinsman at the city gate (the place where contracts are settled); the kinsman first says he will purchase Elimelech's (now Naomi's) land, but, upon hearing he must also take Ruth as his wife, withdraws his offer. Boaz thus becomes Ruth and Naomi's "kinsman-redeemer."

Mixed marriage.

The book can be read as a political parable relating to issues around the time of Ezra and Nehemiah (the 4th century BCE). The realistic nature of the story is established from the start through the names of the participants: the husband and father is Elimelech, meaning "My God is King", and his wife is Naomi, "Pleasing", but after the deaths of her sons Mahlon, "Sickness", and Chilion, "Wasting", she asks to be called Mara, "Bitter". The reference to Moab raises questions, since in the rest of the biblical literature it is associated with hostility to Israel, sexual perversity, and idolatry, and excluded an Ammonite or a Moabite from "the congregation of the ; even to their tenth generation". Despite this, Ruth the Moabite married a Judahite and even after his death still regarded herself a member of his family; she then married another Judahite and bore him a son who became an ancestor of David. Contrary to the message of Ezra–Nehemiah, where marriages between Jewish men and non-Jewish women were broken up, Ruth teaches that foreigners who convert to Judaism can become good Jews, foreign wives can become exemplary followers of Jewish law, and there is no reason to exclude them or their offspring from the community.

Contemporary interpretations.

Scholars have increasingly explored Ruth in ways which allow it to address contemporary issues. Feminists, for example, have recast the story as one of the dignity of labour and female self-sufficiency, and a model for lesbian relations, while others have seen in it a celebration of the relationship between strong and resourceful women. Others have criticised it for its underlying, and potentially exploitative, acceptance of a system of patriarchy in which a woman's worth can only be measured through marriage and child-bearing. Others again have seen it as a book that champions outcast and oppressed peoples.

The Book of Ruth (abbreviated Rth) (, "Megilath Ruth", "the Scroll of Ruth", one of the Five Megillot) is included in the third division, or the Writings (Ketuvim), of the Hebrew Bible; in most Christian canons it is treated as a history book and placed between Judges and 1 Samuel.

Kniha Rút,, Megilat Rut, „Svitek Rút“, je jednou ze starozákonních knih. Židovská tradice přisuzuje autorství Samuelovi. Kniha podle židovského kánonu patří mezi Spisy, podle křesťanského mezi dějepisné knihy. Židé ji rovněž zahrnují mezi "chameš megilot", tzv. pět svátečních svitků.


Geography.

Despite the existence of a large city of 5 million people, the Community of Madrid still retains some remarkably unspoiled and diverse habitats and landscapes. Madrid is home to mountain peaks rising above 2,000 m, holm oak dehesas and low-lying plains. The slopes of the Guadarrama mountain range are cloaked in dense forests of Scots pine and Pyrenean oak. The Lozoya Valley supports a large black (monk) vulture colony, and one of the last bastions of the Spanish imperial eagle in the world is found in the Park Regional del Suroeste in dehesa hills between the Gredos and Guadarrama ranges. The recent possible detection of the existence of Iberian lynx in the area between the Cofio and Alberche rivers is testament to the biodiversity of the area. Taking advantage of the orography, there are several reservoirs and dams in the region, with the Santillana reservoir being the largest.  When looking at a map of the Province of Madrid, it can be seen that it is almost an equilateral triangle, in whose center would be the city. First, by the western side, the region borders the "Sistema Central" (the Guadarrama mountain range), the southern border features a protrusion following the Tagus River in order to include the royal site of Aranjuez in the region; the eastern edge of the triangle comes from the rupture of the fluvial river basins. The region is located in the basin of the Tagus River. The Tagus passes through the southern border of the region in its path west toward the Atlantic Ocean, draining the waters of the Jarama River (collecting in turn the waters of the Lozoya, the Guadalix, the Manzanares, the Henares and the Tajuña), the Alberche and the Guadarrama in the region.  The region also includes the exclave of Dehesa de la Cepeda (part of the municipality of Santa María de la Alameda), a mostly open-area geographically located between the provinces of Ávila and Segovia in the autonomous community of Castile and León.  Province of Madrid occupies a surface area of approximately (1.6% of all Spanish territory). More specifically, the exact position of Madrid is 3° 40 ́ of longitude west of Greenwich, England, and 40° 23 ́ north of the equator.  Most of province lies between 600 and 1,000 m above sea level. However, there the altitude ranges from the 2,428 metres of Peñalara and the 430 metres of the Alberche river when it leaves Villa del Prado into the province of Toledo. Other considerable heights, as well as being famous, are the Bola del Mundo ("Ball of the World") in Navacerrada, at a height of 2,258 m, the Siete Picos ("Seven Peaks") in Cercedilla, at 2,138 m, and the Peña Cebollera (2,129 m) at the northernmost end of the province, a tripoint between the Madrid region and the provinces of Segovia and Guadalajara.  Among the protected species of birds nesting in the

Climate.

The Madrid region features a climate marked by dry summers, while average temperature varies with altitude, marking different climate subtypes. Most of the region (including the capital) has a climate intermediate between a hot-summer mediterranean climate (Köppen "Csa") and a cold semi-arid climate (Köppen "BSk"), with a dry summer and a moderate to low amount of rain primarily distributed throughout the rest of the year (in

History.

Prehistory.

The territory of the Community of Madrid has been populated since the Lower Paleolithic, mainly in the valleys between the

Romans and visigoths.

During the Roman Empire, the region was part of the Citerior Tarraconese province, except for the south-west portion of it, which belonged to Lusitania. It was crossed by two important Roman roads, the "via xxiv-xxix" (joining Astorga to laminium and "via xxv" (which joined Emerita Augusta and Caesaraugusta), and contained

Al-Andalus.

The centre of the peninsula (the Middle Mark of Al-Andalus or "aṯ-Ṯaḡr al-Awsaṭ") became a strategic military post in the 11th century. The Muslim rulers created a defensive system of fortresses and towers all across the region with which they tried to stop the advance of the Christian kingdoms of the north.  The fortress of "Mayrit"

Christian repopulation.

The recently conquered lands by the Christian kingdoms were desegregated into several constituencies, as a consequence of a long process of repopulation that took place over the course of four centuries. The feudal and ecclesiastical lords came into constant conflict with the different councils that had been granted the authority to repopulate. In the 13th century, Madrid was the only city of the region that preserved its own juridical personality, at first with the Old "Fuero" (Charter) and later with the Royal "Fuero", granted by Alfonso X of Castile in 1262 and ratified by Alfonso XI in 1339. On the

Madrid made the capital.

Castilian monarchs showed a predilection for the center of the peninsula, with abundant forests and game. "El Pardo" was a region visited frequently by kings since the time of Henry III, in the 14th century. The Catholic Monarchs started the construction of the Royal Palace of Aranjuez. In the 16th century, San Lorenzo de El Escorial was built and became another royal site of the province.  The town of Madrid, which was one of the eighteen cities with the right to vote in the Cortes of Castile, was seat of the Courts themselves on several occasions and was the residence of several monarchs, amongst them the emperor Charles I who reformed and expanded the "Alcázar" or Castle of the city. Alcalá de Henares grew in importance as cultural center since the foundation by the Cardinal

Province.

The current territory of the region was roughly defined with the 1833 reorganization of Spain into provinces promoted by Javier de Burgos, in which the province of Madrid was classified in the region of New Castile (lacking the later any sort of administrative institution at the regional level nonetheless). The government institution at the provincial level was the deputation ("diputación"). In addition to the former body, another provincial political authority was the civil governor discretionarily designated by the central government. A modest change to the 1833 provincial boundaries that concerned Madrid took place in 1850, when the small municipality of Valdeavero (19 km), until then part of the province of Guadalajara, joined the province of Madrid.  One of the limits so far for the growth of the capital, water supply, experienced a substantial change in 1858 following the arrival to the city of Madrid of water from the Lozoya River with the inauguration of the bringing

Autonomous community.

The creation of the contemporary Community of Madrid was preceded by an intense political debate. Autonomous communities were to be created by one or more provinces with a distinct regional identity. Since the 1833 provincial organization, Madrid was part of the historical region of New Castile along with the provinces of Guadalajara, Toledo, Cuenca and Ciudad Real. Thus, it was first planned that the province of Madrid would be part of the future community of Castile–La Mancha (which was roughly similar to New Castile, with the addition of Albacete) but with some special considerations as the home of the national capital. The other provinces that were to become part of the autonomous community of Castile–La Mancha expressed fears of inequality if Madrid were associated with them. These provinces opposed such a special status, and

Government and politics.

Regional institutions of government.

Like the rest of autonomous communities, the Community of Madrid is organized politically within a parliamentary system; that is, the head of government—known as the "president"—is dependent on the direct support from the regional legislature,

Delegation of the Central Government.

Since the creation of autonomous communities, the Government of Spain appoints a special representative to each region, the Government Delegate, part of the Peripheral

Administrative divisions.

The Community of Madrid, following the long-standing form of local government in Spain, is divided administratively into 179 municipalities (featuring 801 towns and entities). Its municipalities comprise 2.2% of the Spanish territory (8110). It is ranked 23rd amongst Spanish provinces in number of municipalities, which is slightly above average. The average is 165 municipalities by province. The "ayuntamiento", presided by its "alcalde" (Mayor) is the formal institution charged with the government and administration of most municipalities. The municipal councillors forming the deliberative assembly of the

Economy.

Madrid is the autonomous community with the highest income per capita in Spain at €31,004 in 2014 - significantly above the national average and ahead of the Basque Country (€29,683), Navarra (€28,124) and Catalonia (€26,996). In that year, the GDP growth was 1.0%. Madrid has a GDP of €230.8 billion as of 2018; this is first in Spain, ahead of Catalonia, where regional GDP amounted to €228.7 billion and the largest Spanish region, Andalusia (€160.6 billion).  In 2005, the Community of Madrid was the main receptor of foreign investment in the country, at 34.3% of the total. The community ranks 34th amongst all European regions (evaluated in 2002), and 50th amongst the most competitive cities-regions worldwide, ahead of Barcelona and Valencia, the other two largest metropolitan areas of Spain. The strengths of the economy of the community are its low unemployment rate, its high investment in research, its high development, and the added-value services therein performed. Its weaknesses include the low penetration of broadband and new technologies of information and an unequal male to female occupation.  The service, construction, and industry sectors are prominent in Madrid's commercial productive structure. According

Demographics.

The Community of Madrid is the third most populous region in Spain, after Andalusia and Catalonia, and the most populous province, with 6,369,167 inhabitants. Population density is 779.36 hab/km, much higher than the national average of 91.3 hab/km. Population density varies with the community itself; the municipality of Madrid has a density of 5,160.57 hab/km, whereas the Sierra Norte has a population density of less than 9.9 hab/km. The vast majority of the population lives in the capital and its metropolitan area, which is the most populated in Spain.  Madrid also has the greatest population density in Spain. Its inhabitants are mainly concentrated in the capital (which is the Spanish

Education.

State Education in Spain is free and compulsory from six to sixteen years of age. The current education system is called LOGSE (Ley de Ordenación General del Sistema Educativo).

Levels.

Children from three to five years old in Spain have the option of attending the pre-school stage, which is non-compulsory and free for all students. It is regarded as an integral part of the education system with infantil classes in almost every primary school. There are some separate Colegios Infantiles or nursery schools.  Spanish students aged six to sixteen

Universities.

Madrid is home to a large number of public and private universities. The Complutense University of Madrid is one of the most prestigious, and the largest, university in Spain and one of the oldest universities in the world. It has 10,000 staff members and a student population of 117,000. Nearly all academic staff are Spanish. It is located on two campuses, in the university quarter Ciudad Universitaria at Moncloa in Madrid, and in Somosaguas. The Complutense University of Madrid was founded in Alcalá de Henares, old Complutum, by Cardinal Cisneros in 1499. Nevertherless,

Transportation.

Air.

Madrid is served by Barajas International Airport. Barajas is the main hub of Iberia Airlines and consequently serves as the main gateway to the Iberian peninsula from Europe, the Americas, and the rest of the world. Current passenger volumes range upwards of

Commuter rail.

Cercanías Madrid is the commuter rail service that serves Madrid, the capital of Spain, and its metropolitan area. It is operated by Cercanías Renfe, the commuter rail division of RENFE, the former monopoly of rail services in Spain. The system is infamous for being the target of 11 March

High-speed rail.

The crown jewel of Spain's next decade of infrastructure construction is the Spanish high-speed rail network, Alta Velocidad Española AVE. Currently, an ambitious plan includes the construction of a network, centered on Madrid. The overall goal is to have all important provincial cities be no more than four hours away from Madrid and no more than six

Metro.

Serving the city's population of some six million, the Madrid Metro is one of the most extensive and fastest-growing metro networks in the world. With the addition of a loop serving suburbs to Madrid's south-west "Metrosur", it is now the second largest

Culture.

Symbols.

The flag, coat of arms and hymn of the Community of Madrid were set through the regional Law 2/1983 published in the official regional gazette on 24 December 1983: The flag is described as follows: ""the flag of the Community of Madrid is crimson red, with seven silver five-pointed stars, arranged 4 and 3 on the centre of the canvas"". According to the law, the flag should wave both at the outdoors (occupying a preferential place next to the flag

Cuisine.

Although the region does not produce enough food to be self-sufficient, the varied territory of the region outside the urbanised centre provides enough food commodities to create its own cuisine: cheese of Campo Real, vine with Vinos de Madrid DO, strawberries and aspargus from Aranjuez, muskmelons from Villaconejos, artichokes from Ciempozuelos, "judiones" from Montejo de la Sierra, garlic from Chinchón, chickpeas from Navalcarnero, lentils from Colmenar de Oreja, cauliflower from Griñón or

Religion.

The majority of the religious population is Catholic. The most important religious minorities are evangelicals, Jews and Muslims.  Among the evangelical denominations the following denominations stand out: Spanish Evangelical Church (IEE), several Presbiterian or Reformed Churches, the Spanish Reformed Episcopal Church (IERE), Baptist and Free churches (Unión Evangélica Bautista Española, Federación de las Iglesias Evangélicas Independientes de España), the Asambleas de Hermanos), Pentecostal Churches (Asambleas de Dios, Iglesia de la Biblia Abierta, Iglesia Filadelfia, Iglesia Cuadrangular), Charismatic churches (Iglesias de Buenas Noticias, Asamblea Cristiana, Asamblea para la Evangelización Mundial para Cristo), minor churches such as The Salvation Army, Mennonite Churches and Hermanos en Cristo), non-grouped evangelical churches, and adventist churches. Pentecostal churches have lately experienced a notable growth due to the arrival of immigrants from

Feasts.

The regional day is the 2 May, commemorating the Dos de Mayo Uprising of the citizens of Madrid against the French occupation in 1808 that triggered the wave of insurrections marking the beginning of the Peninsular War. It is a

Sports.

According to a 2010 study by the National Sports Council (CSD), madrilenians led the country in terms of grassroots sports practice.  Roughly a 52% of the regional population between 15 and 75 years old practised one sports modality, while a 10 % of the population between 15 and 75 years old practised two or more sports. The most practised sports modalities were: fitness gymnastics (43.6%), football (22.1%), swimming (20.7%), cycling (19.6%), jogging/running (16.2%), padel (9.9%), athletics (8.3%), basketball (6.9%), other football modalities (6.6%), hiking (6.1 %), martial

The Community of Madrid (; ) is one of the seventeen autonomous communities of Spain. It is located in the centre of the Iberian Peninsula, and of the Central Plateau ("Meseta Central"). Its capital is the city of Madrid, which is also the capital of the country. The Community of Madrid is bounded to the south and east by Castilla–La Mancha and to the north and west by Castile and León. It was formally created in 1983, based on the limits of the province of Madrid, which was until then conventionally included in the historical region of New Castile.

Madrid (oficiálně Madridské společenství, ) je provincie a současně jedno ze 17 autonomních společenství Španělska. Rozkládá se zhruba v geografickém středu Španělska a historicky tvoří severní pohraniční část Nové Kastilie. Hlavním městem regionu je velkoměsto Madrid, které je současně hlavním městem Španělského království. V něm žije více než polovina obyvatel regionu.


History.

The nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek (1632–1723). He observed a "lumen", the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei.  The nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under the microscope when he observed an opaque area, which he called the "areola" or "nucleus", in the cells of the flower's outer layer.  He did not suggest a potential function. In 1838, Matthias Schleiden proposed that the nucleus plays a role in generating cells, thus he introduced the name "cytoblast" (cell builder). He believed that he had observed new cells assembling around "cytoblasts". Franz Meyen was a strong opponent of this view, having already described cells multiplying by

Structures.

The nucleus is the largest organelle in animal cells. In mammalian cells, the average diameter of the nucleus is approximately 6 micrometres (μm), which occupies about 10% of the total cell volume. The contents of the nucleus are held in the nucleoplasm similar to the cytoplasm in the rest of the cell. The fluid component of this is termed the nucleosol, similar to the cytosol in the cytoplasm.  In most types of granulocyte, a white blood cell, the nucleus is lobated and can be bi-lobed, tri-lobed or multi-lobed.

Nuclear envelope and pores.

The nuclear envelope, otherwise known as nuclear membrane, consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nanometres (nm). The nuclear envelope completely encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm. The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes. The space between the membranes is called the perinuclear space and is continuous with the RER lumen.  Nuclear pores, which provide aqueous channels through the envelope, are composed of multiple proteins, collectively referred to as nucleoporins. The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast) to several hundred proteins (in vertebrates). The pores are 100 nm in total diameter; however, the gap through which molecules freely diffuse is only about 9 nm wide, due

Nuclear lamina.

In animal cells, two networks of intermediate filaments provide the nucleus with mechanical support: The nuclear lamina forms an organized meshwork on the internal face of the envelope, while less organized support is provided on the cytosolic face of the envelope. Both systems provide structural support for the nuclear envelope and anchoring sites for chromosomes and nuclear pores.  The nuclear lamina is composed mostly of lamin proteins. Like all proteins, lamins are synthesized in the cytoplasm and later transported to the nucleus interior, where they are assembled before being incorporated into the existing network of nuclear lamina. Lamins found on the cytosolic face of the membrane, such as emerin and nesprin, bind to the cytoskeleton to provide structural support. Lamins are also found inside the nucleoplasm where they form another regular structure, known as the nucleoplasmic veil, that

Chromosomes.

The cell nucleus contains the majority of the cell's genetic material in the form of multiple linear DNA molecules organized into structures called chromosomes. Each human cell contains roughly two meters of DNA. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well-defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.  There are two types of chromatin. Euchromatin is the less compact DNA form, and contains genes that are frequently expressed by the cell. The other type,

Nucleolus.

The nucleolus is the largest of the discrete densely stained, membraneless structures known as nuclear bodies found in the nucleus. It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA). These regions are called nucleolar organizer regions (NOR). The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes. The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association. This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.  In the first step of ribosome assembly, a protein called RNA polymerase I

Other nuclear bodies.

Besides the nucleolus, the nucleus contains a number of other nuclear bodies. These include Cajal bodies, gemini of Cajal bodies, polymorphic interphase karyosomal association (PIKA), promyelocytic leukaemia (PML) bodies, paraspeckles, and splicing speckles. Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not a uniform mixture, but rather contains organized functional subdomains.  Other subnuclear structures appear as part of abnormal disease processes. For example, the presence of small intranuclear rods has been reported in some cases of nemaline myopathy. This condition typically results from mutations in actin, and the rods themselves consist of mutant actin as well as other cytoskeletal proteins.

Cajal bodies and gems.

A nucleus typically contains between 1 and 10 compact structures called Cajal bodies or coiled bodies (CB), whose diameter measures between 0.2 μm and 2.0 μm depending on the cell type and species. When seen under an electron microscope, they resemble balls of tangled thread and are dense foci of distribution for the protein coilin. CBs are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.  Similar to Cajal bodies are

PIKA and PTF domains.

PIKA domains, or polymorphic interphase karyosomal associations, were first described in microscopy studies in 1991. Their function remains unclear, though they were not thought to

PML bodies.

Promyelocytic leukemia bodies (PML bodies) are spherical bodies found scattered throughout the nucleoplasm, measuring around 0.1–1.0 μm. They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains. PML

Splicing speckles.

Speckles are subnuclear structures that are enriched in pre-messenger RNA splicing factors and are located in the interchromatin regions of the nucleoplasm of mammalian cells. At the fluorescence-microscope level they appear as irregular, punctate structures, which vary in size and shape, and when examined by electron microscopy they are seen as clusters of interchromatin granules. Speckles are dynamic structures, and both their protein and RNA-protein components can cycle continuously between speckles and other nuclear locations, including active transcription sites. Studies on the

Paraspeckles.

Discovered by Fox et al. in 2002, paraspeckles are irregularly shaped compartments in the interchromatin space of the nucleus. First documented in HeLa cells, where there are generally 10–30 per nucleus, paraspeckles are now known to also exist in all human primary cells, transformed cell lines, and tissue sections. Their name is derived from their distribution in the nucleus; the "para" is short for parallel and the "speckles" refers to the splicing speckles to

Perichromatin fibrils.

Perichromatin fibrils are visible only under electron microscope. They are located

Clastosomes.

Clastosomes are small nuclear bodies (0.2–0.5 μm) described as having a thick ring-shape due to the peripheral capsule around these bodies. This name is derived from the Greek "klastos", broken and "soma", body. Clastosomes are not typically present in normal cells, making them hard to detect. They form

Fougaro System.

The fougaro system (Greek; Fougaro, chimney) is a sub-organelle system in the nucleus that may be a mechanism to recycle or remove molecules from the cell to the external medium. The molecules or peptides are ubiquitinated before being released from the nucleus of the cells. The ubiquitinated molecules are released independently or associated with endosomal proteins such as Beclin

Function.

The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes. The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.  The nucleus is an organelle found in eukaryotic cells. Inside its fully enclosed nuclear membrane, it contains the majority of the cell's genetic material. This material is organized as DNA molecules, along with a variety of proteins, to form chromosomes.

Cell compartmentalization.

The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary. This is important for controlling processes on either side of the nuclear membrane. In most cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes in the pathway. This regulatory mechanism occurs in the case of glycolysis, a cellular pathway for breaking down glucose to produce energy. Hexokinase is an enzyme responsible for the first the step of glycolysis, forming glucose-6-phosphate from glucose. At high concentrations of fructose-6-phosphate, a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus, where it forms a transcriptional repressor complex with nuclear

Gene expression.

Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to

Processing of pre-mRNA.

Newly synthesized mRNA molecules are known as primary transcripts or pre-mRNA. They must undergo post-transcriptional modification in the nucleus before being exported to the cytoplasm; mRNA that appears in the cytoplasm without these modifications is degraded rather than used for protein translation. The three main modifications are 5' capping, 3' polyadenylation, and RNA splicing. While in the nucleus, pre-mRNA is associated with a variety of proteins in complexes known as heterogeneous ribonucleoprotein particles (hnRNPs). Addition of the 5' cap occurs co-transcriptionally and is the

Dynamics and regulation.

Nuclear transport.

The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes. Although small molecules can enter the nucleus without regulation, macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit. "Cargo" proteins that must be translocated from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals, which are bound by importins, while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins. The ability of importins and exportins to transport their cargo is regulated by GTPases, enzymes that hydrolyze the molecule guanosine triphosphate (GTP) to release energy. The key GTPase in nuclear transport is Ran, which can

Assembly and disassembly.

During its lifetime, a nucleus may be broken down or destroyed, either in the process of cell division or as a consequence of apoptosis (the process of programmed cell death). During these events, the structural components of the nucleus — the envelope and lamina — can be systematically degraded. In most cells, the disassembly of the nuclear envelope marks the end of the prophase of mitosis. However, this disassembly of the nucleus is not a universal feature of mitosis and does not occur in all cells. Some unicellular eukaryotes (e.g., yeasts) undergo so-called closed mitosis, in which the

Disease-related dynamics.

Initially, it has been suspected that immunoglobulins in general and autoantibodies in particular do not

Nuclei per cell.

Most eukaryotic cell types usually have a single nucleus, but some have no nuclei, while others have several. This can result from normal development, as in the maturation of mammalian red blood cells, or from faulty cell division.

Anucleated cells.

An anucleated cell contains no nucleus and is, therefore, incapable of dividing to produce daughter cells. The best-known anucleated cell is the mammalian red blood cell, or erythrocyte, which also lacks other organelles such as mitochondria, and serves primarily as a transport vessel to ferry oxygen from the lungs to the body's tissues. Erythrocytes mature through erythropoiesis

Multinucleated cells.

Multinucleated cells contain multiple nuclei. Most acantharean species of protozoa and some fungi in mycorrhizae have naturally multinucleated cells. Other examples include the intestinal parasites in the genus "Giardia", which have two nuclei per cell. In humans, skeletal muscle cells, called myocytes and syncytium, become multinucleated during development; the resulting arrangement of nuclei near the periphery of the cells allows maximal intracellular space for

Evolution.

As the major defining characteristic of the eukaryotic cell, the nucleus' evolutionary origin has been the subject of much speculation. Four major hypotheses have been proposed to explain the existence of the nucleus, although none have yet earned widespread support.  The first model known as the "syntrophic model" proposes that a symbiotic relationship between the archaea and bacteria created the nucleus-containing eukaryotic cell. (Organisms of the Archaea and Bacteria domain have no cell nucleus.) It is hypothesized that the symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus. This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria. The archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins, including histones. Observations that myxobacteria are motile, can form multicellular complexes, and possess kinases and G proteins similar to eukarya, support a bacterial origin for the eukaryotic cell.  A second model proposes that proto-eukaryotic cells evolved from bacteria without an endosymbiotic stage. This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures. A similar proposal states that a eukaryote-like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell.  The most controversial model, known as "viral eukaryogenesis", posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus. The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes). One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator". Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes. It has been suggested that the unresolved question of the evolution of sex could be related to the viral eukaryogenesis hypothesis.  A more recent proposal, the "exomembrane hypothesis", suggests that the nucleus instead originated from a single ancestral cell that evolved a second exterior cell membrane; the interior membrane enclosing the original cell then became the nuclear membrane and evolved increasingly elaborate pore structures for passage of internally synthesized cellular components such as ribosomal subunits.

In cell biology, the nucleus (pl. nuclei; from Latin or, meaning "kernel" or "seed") is a membrane-bound organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.

Jádro (z lat. "nucleus" – jádro nebo oříšek, příp. řec. "karyon" – jádro) je organela eukaryotických buněk, v níž je uložena většina genetického materiálu (DNA) buňky. Jedná se o váček obalený dvěma buněčnými membránami, který má v průměru 5–10 mikrometrů. Uvnitř se nachází chromatin, tedy DNA a různé přidružené bílkoviny, ale i další struktury (např. jadérko), kde probíhají různé enzymatické procesy související s DNA a RNA.