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A Pietroburgo noi ci incontreremo ancora
come se lì avessimo sepolto il sole,
e la beata parola senza senso
pronunceremo per la prima volta.
Nel nero velluto della notte sovietica,
nel velluto del vuoto universale,
cantano sempre i cari occhi di beate mogli,
fioriscono ancora fiori immortali.
[...]
Osip Mandel'Å¡tam, Viaggio in Armenia, Adelphi ed.
Aegypius monachus.
Buitre negro.
La rapaz más grande de Europa. Llega a alcanzar 1 m de altura, 10 kg de peso y 250 cm de envergadura.
Especie monógama, suele permanecer fiel a la pareja durante toda su vida, criando siempre en el mismo nido.
Especie sin dimorfismo sexual.
Residente en Mallorca.
Hit 'L' to view on large.
Battersea Power Station is a decommissioned coal-fired power station located on the south bank of the River Thames, in Battersea, an inner-city district of South West London. It comprises two individual power stations, built in two stages in the form of a single building. Battersea A Power Station was built in the 1930s, with Battersea B Power Station to its east in the 1950s. The two stations were built to an identical design, providing the well known four-chimney layout.
The station ceased generating electricity in 1983, but over the past 50 years it has become one of the best known landmarks in London and is Grade II* listed. The station's celebrity owes much to numerous cultural appearances, which include a shot in The Beatles' 1965 movie Help!, appearing in the video for the 1982 hit single "Another Thing Comin´" by heavy metal band Judas Priest and being used in the cover art of Pink Floyd's 1977 album Animals, as well as a cameo appearance in Take That's music video "The Flood."
In addition, a photograph of the plant's control room was used as cover art on Hawkwind's 1977 album Quark, Strangeness and Charm.
The station is the largest brick building in Europe and is notable for its original, lavish Art Deco interior fittings and decor. However, the building's condition has been described as "very bad" by English Heritage and is included in its Buildings at Risk Register. In 2004, while the redevelopment project was stalled, and the building remained derelict, the site was listed on the 2004 World Monuments Watch by the World Monuments Fund. The combination of an existing debt burden of some £750 million, the need to make a £200 million contribution to a proposed extension to the London Underground, requirements to fund conservation of the derelict power station shell and the presence of a waste transfer station and cement plant on the river frontage make a commercial development of the site a significant challenge. In December 2011, the latest plans to develop the site collapsed with the debt called in by the creditors. In February 2012, the site was placed on sale on the open property market
through commercial estate agent Knight Frank. It has received interest from a variety of overseas consortia, most seeking to demolish or part-demolish the structure.
Built in the early 1930s, this iconic structure, with its four distinctive chimneys, was created to meet the energy demands of the new age. Sir Giles Gilbert Scott – the man who also designed what is now Tate Modern and brought the red telephone box to London – was hired by the London Power Company to create this first of a new generation of ‘superstations’, with the building beginning to produce power for the capital in 1933.
With dimensions of 160 m x 170 m, the roof of the boiler house 50 m tall, and its four 103 m tall, tapering chimneys, it is a truly massive structure. The building in fact comprised two stations – Battersea ‘A’ and Battersea ‘B’, which were conjoined when the identical B section was completed in the 1950s, and it was the world’s most thermally efficient building when it opened.
But Battersea Power Station was – and is – so much more besides. Gilbert Scott lifted it from the prosaic into the sublime by incorporating lavish touches such as the building’s majestic bronze doors and impressive wrought-iron staircase leading to the art deco control room. Here, amongst the controls which are still in situ today, those in charge of London’s electricity supply could enjoy the marble-lined walls and polished parquet flooring. Down in the turbine hall below, meanwhile, the station’s giant walls of polished marble would later prompt observers to liken the building to a Greek temple devoted to energy.
Over the course of its life, Battersea Power Station has been instilled in the public consciousness, not least when Pink Floyd famously adopted it for its Animals album cover and launch in 1977. As a result of its popularity, a great deal of energy has been expended in protecting this landmark.
Following the decommissioning of the ‘A’ station in 1975, the whole structure was listed at Grade II in 1980 before, in 1983, the B station was also closed. Since that time, and following the listing being upgraded to a Grade II* status in 2007, Battersea Power Station has become almost as famous for plans heralding its future as for its past. Until now, that is.
The transformation of Battersea Power Station – this familiar and much-loved silhouette on the London skyline – is set to arrive, along with the regeneration and revitalisation of this forgotten corner of central London. History is about to be made once more.
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A volt of turkey vultures nest in a tree prior to the sun coming out.
A group of vultures is called a wake, committee, venue, kettle, or volt. The term kettle refers to vultures in flight, while committee, volt, and venue refer to vultures resting in trees. Wake is reserved for a group of vultures that are feeding.
I primi probabili riferimenti alle macchie solari sono quelli degli astronomi cinesi del primo millennio d.C., che probabilmente potevano vedere i gruppi di macchie più grandi quando lo splendore del sole era diminuito dalla polvere sollevata dai vari deserti dell'Asia centrale.
Furono osservate telescopicamente per la prima volta nel 1610 dagli astronomi frisoni Johannes e David Fabricius, che pubblicarono una loro descrizione nel giugno del 1611. In questa data Galileo stava già mostrando le macchie solari agli astronomi a Roma e Christoph Scheiner aveva probabilmente osservato le macchie per due o tre mesi. La polemica tra Galileo e Scheiner per la prima osservazione, quando nessuno dei due sapeva del lavoro dei Fabricius, fu quindi tanto acida quanto inutile.
Le macchie solari ebbero una qualche importanza nel dibattito sulla natura del sistema solare. Mostravano che il Sole ruotava su se stesso, e il fatto che apparivano e scomparivano dimostrava che il Sole subiva dei cambiamenti, in contraddizione con gli insegnamenti di Aristotele.
Le ricerche sulle macchie solari segnarono il passo per la maggior parte del XVII e l'inizio del XVIII secolo, perché a causa del Minimo di Maunder quasi nessuna macchia solare fu visibile per molti anni. Ma dopo la ripresa dell'attività solare, Heinrich Schwabe poté riportare nel 1843 un cambiamento periodico nel numero delle macchie solari, che sarebbe poi stato chiamato il ciclo undecennale dell'attività solare.
Un flare estremamente potente fu emesso verso la Terra il 1º settembre 1859. Interruppe i servizi telegrafici e causò aurore boreali visibili molto a sud, fino alle Hawaii e a Roma, e in modo simile nell'emisfero sud. Il flare più luminoso osservato dai satelliti è avvenuto il 4 novembre 2003 alle 19:29 UTC, ed ha saturato gli strumenti per 11 minuti. La regione 486, responsabile del flare, ha prodotto un flusso di raggi X stimato a X28. Le osservazioni hanno mostrato che l'attività è continuata sulla faccia lontana del Sole, quando la sua rotazione ha nascosto la regione attiva alla nostra vista.
È stata registrata l'assenza di macchie solari per 266 giorni su 366 nel 2008, e per 78 giorni nei primi 90 del 2009.
Fisica [modifica]
Primo piano di una macchia solare all'ultravioletto. Immagine del satellite TRACE.
Anche se i dettagli della formazione delle macchie solari sono ancora oggetto di ricerca, è abbastanza chiaro che esse sono la controparte visibile di tubi di flusso magnetico nella zona convettiva del Sole che vengono "arrotolati" dalla rotazione differenziale della stella. Se lo stress su questi tubi supera un certo limite, rimbalzano come elastici e "forano" la superficie solare. Nei punti in cui essi attraversano la superficie la convezione non può operare, il flusso di energia che arriva dall'interno del Sole si riduce, e la temperatura di conseguenza scende. L'effetto Wilson suggerisce che le macchie solari siano anche delle depressioni rispetto al resto della superficie.
Questo modello è supportato da osservazioni che usano l'effetto Zeeman, che mostra come le macchie solari appena nate spuntino a coppie, di opposta polarità magnetica. Da ciclo a ciclo, la polarità delle macchie anteriori e posteriori (rispetto alla rotazione del Sole) cambia da nord/sud a sud/nord e viceversa. In genere le macchie solari appaiono a gruppi più o meno grandi.
Una macchia solare può essere divisa in due parti:
ombra, più scura e fredda
penombra, intermedia tra l'ombra e la superficie solare
La velocità delle onde sonore nei pressi di una macchia solare.
Le linee di campo magnetico dovrebbero respingersi l'un l'altra, facendo quindi disperdere rapidamente le macchie solari, ma la vita di una macchia è in media di appena due settimane, un periodo troppo breve. Osservazioni recenti condotte dalla sonda SOHO, utilizzando le onde sonore che viaggiano nella fotosfera solare per formare un'immagine dell'interno del Sole, hanno mostrato che sotto ogni macchia solare vi sono potenti correnti di materiale dirette verso l'interno del Sole, che formano dei vortici che concentrano le linee di campo magnetico. Di conseguenza le macchie sono delle tempeste auto-sostenentesi, simili in alcuni aspetti agli uragani terrestri.
L'attività delle macchie segue un ciclo di circa 11 anni (il ciclo undecennale dell'attività solare). Ogni ciclo di undici anni comprende un massimo ed un minimo, che sono identificati contando il numero di macchie solari che appaiono in quell'anno. All'inizio del ciclo, le macchie tendono ad apparire a latitudini elevate, per poi muoversi verso l'equatore quando il ciclo si avvicina al massimo (questo comportamento è chiamato legge di Spörer).
Oggi si conoscono molti periodi diversi nella variazione del numero di macchie, di cui quello di 11 anni è semplicemente il più evidente. Lo stesso periodo è osservato nella maggior parte delle altre espressioni di attività solare, ed è profondamente legato alle variazioni del campo magnetico solare. Non si sa se esistano periodi molto lunghi (di secoli o più), perché l'intervallo registrato dagli astronomi è troppo corto, ma se ne sospetta fortemente l'esistenza.
Conseguenze sull'ambiente [modifica]
Alcuni ritengono che le macchie solari siano la causa alla base del riscaldamento globale e l'uomo e i suoi consumi abbiano contribuito in minor parte al fenomeno rispetto ad esse.[1]. O, meglio, le macchie solari sono indice dell'attività solare, che determina la radiazione solare trasmessa al nostro pianeta. Piccole variazioni di questa radiazione, secondo gli ultimi studi, avrebbero una visibile influenza sul clima terrestre.[2] Le macchie solari, sappiamo oggi, sono intensi campi magnetici che appaiono durante periodi d’elevata attività solare, ma per secoli e da molto prima che se ne conoscesse la natura gli astronomi ne hanno registrato il numero, e dai dati raccolti si può notare tra il 1645 e il 1715 una drastica riduzione nel numero delle macchie solari (minimo di Maunder, dal nome dell’astronomo inglese che osservò la circostanza).
Quanto il numero di macchie solari sia un attendibile indicatore del clima lo scoprirono il ricercatore danese Friis-Christensen e i suoi collaboratori, che nel 1991 dimostrarono la stretta correlazione tra attività solare e temperatura globale in tutto il periodo compreso fra il 1860 e il 1990. Per escludere che quella correlazione fosse una semplice coincidenza, andarono indietro nel tempo per altri 400 anni e, di nuovo, accertarono la stretta correlazione tra attività solare e temperatura globale.
Il sole influenza il clima non solo, direttamente, col suo calore ma anche, indirettamente, attraverso la formazione delle nuvole, che hanno un potente effetto raffreddante.
La potenza di questo effetto è diventata chiara solo recentemente, dopo che si sono confrontate, nel corso degli anni, le temperature globali con il flusso di raggi cosmici, scoprendo, ancora una volta, una stretta correlazione tra temperatura globale e flusso cosmico, con la prima che aumenta ogni volta che il secondo diminuisce, e viceversa: il clima è controllato anche dalle nuvole, queste sono controllate dal flusso di raggi cosmici a sua volta controllato dall’intensità del campo magnetico dal sole, cioè dalla attività della nostra stella.
Va detto però che tali teorie sono ancora al vaglio della Comunità Scientifica, e al momento sono oggetto di dibattito e contestazione accademica.
Osservazione [modifica]
Le macchie solari si possono osservare piuttosto facilmente, basta un piccolo telescopio usato col metodo della proiezione dall'oculare. In alcune circostanze, specialmente all'alba e al tramonto, le macchie solari possono essere viste anche ad occhio nudo. Tuttavia, è bene non guardare mai il Sole senza l'ausilio di un filtro in quanto può causare danni permanenti alla retina.
Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature. They usually appear as pairs, with each sunspot having the opposite magnetic pole than the other.[1]
Although they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5,780 K (5,510 °C) leaves them clearly visible as dark spots, as the luminous intensity of a heated black body (closely approximated by the photosphere) is a function of temperature to the fourth power. If the sunspot were isolated from the surrounding photosphere it would be brighter than the Moon.[2] Sunspots expand and contract as they move across the surface of the Sun and can be as small as 16 kilometers (9.9 mi)[3] and as large as 160,000 kilometers (99,000 mi)[4] in diameter, making the larger ones visible from Earth without the aid of a telescope.[5] They may also travel at relative speeds ("proper motions") of a few hundred meters per second when they first emerge onto the solar photosphere.
Manifesting intense magnetic activity, sunspots host secondary phenomena such as coronal loops (prominences) and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured.[6]
]Prehistoric evidence
Studies of stratigraphic data have suggested that the solar cycles have been active for hundreds of millions of years, if not longer; measuring varves in precambrian sedimentary rock has revealed repeating peaks in layer thickness, with a pattern repeating approximately every eleven years. It is possible that the early atmosphere on Earth was more sensitive to changes in solar radiation than today, so that greater glacial melting (and thicker sediment deposits) could have occurred during years with greater sunspot activity.[7][8] This would presume annual layering; however, alternate explanations (diurnal) have also been proposed.[9]
Analysis of tree rings has revealed a detailed picture of past solar cycles: Dendrochronologically dated radiocarbon concentrations have allowed for a reconstruction of sunspot activity dating back 11,400 years, far beyond the four centuries of available, reliable records from direct solar observation.[10]
[edit]Early observations
A drawing of a sunspot in the Chronicles of John of Worcester
The earliest surviving record of sunspot observation dates from 364 BC, based on comments by Chinese astronomer Gan De in a star catalogue.[11] By 28 BC, Chinese astronomers were regularly recording sunspot observations in official imperial records.[12]
The first clear mention of a sunspot in Western literature, around 300 BC, was by the ancient Greek scholar Theophrastus, student of Plato and Aristotle and successor to the latter.[13] A more recent sunspot observation was made on 17 March 807 AD by the Benedictine monk Adelmus, who observed a large sunspot that was visible for eight days; however, Adelmus incorrectly concluded he was observing a transit of Mercury.[14] A large sunspot was also seen at the time of Charlemagne's death in 813 AD.[15] Sunspot activity in 1129 was described by John of Worcester, and Averroes provided a description of sunspots later in the 12th century;[16] however, these observations were also misinterpreted as planetary transits, until Galileo gave the correct explanation in 1612.[17]
[edit]17th and 18th centuries
Sunspots in 1794 Samuel Dunn Map
Sunspots were first observed telescopically in late 1610 by the English astronomer Thomas Harriot and Frisian astronomers Johannes and David Fabricius, who published a description in June 1611. At the latter time, Galileo had been showing sunspots to astronomers in Rome, and Christoph Scheiner had probably been observing the spots for two or three months using an improved helioscope of his own design. The ensuing priority dispute between Galileo and Scheiner, neither of whom knew of the Fabricius' work, was thus as pointless as it was bitter.
Sunspots had some importance in the debate over the nature of the Solar System. They showed that the Sun rotated, and their comings and goings showed that the Sun changed, contrary to Aristotle (who taught that all celestial bodies were perfect, unchanging spheres).
Rudolf Wolf studied the historical record in an attempt to establish a database on past cyclic variations. His database extended only to 1700, although the technology and techniques for careful solar observations were first available in 1610. Gustav Spörer later suggested a 70-year period before 1716 in which sunspots were rarely observed as the reason for Wolf's inability to extend the cycles into the 17th century.
Sunspots were rarely recorded during the second part of 17th century. Later analysis revealed the problem not to be a lack of observational data but included references to negative observations. Building upon Spörer's earlier work, Edward Maunder suggested that the Sun had changed from a period in which sunspots all but disappeared from the solar surface to a renewal of sunspot cycles starting in about 1700. Adding to this understanding of the absence of solar cycles were observations of aurorae, which were absent at the same time. Even the lack of a solar corona during solar eclipses was noted prior to 1715. The period of low sunspot activity from 1645 to 1717 is known as the "Maunder Minimum".
[edit]19th century
The cyclic variation of the number of sunspots was first observed by Heinrich Schwabe between 1826 and 1843 and led Wolf to make systematic observations starting in 1848. The Wolf number is a measure of individual spots and spot groupings, which correlates to a number of solar observables. Also in 1848, Joseph Henry projected an image of the Sun onto a screen and determined that sunspots were cooler than the surrounding surface.[18]
After the resumption of sunspot activity, Heinrich Schwabe in 1844 in Astronomische Nachrichten (Astronomical News) reported a periodic change in the number of sunspots.
The Sun emitted an extremely powerful flare on its visible hemisphere on 1 September 1859, leading to what is known as the Carrington Event. It interrupted electrical telegraph service and caused visible aurorae as far south as Havana, Hawaii, and Rome with similar activity in the southern hemisphere.
[edit]20th century
The American solar astronomer George Ellery Hale, as an undergraduate at MIT, invented the spectroheliograph, with which he made the discovery of solar vortices. In 1908, Hale used a modified spectroheliograph to show that the spectra of hydrogen exhibited the Zeeman effect whenever the area of view passed over a sunspot on the solar disc. This was the first indication that sunspots were basically magnetic phenomena, which appeared in pairs that corresponded with two magnetic poles of opposite polarity.[19] Subsequent work by Hale demonstrated a strong tendency for east-west alignment of magnetic polarities in sunspots, with mirror symmetry across the solar equator; and that the magnetic polarity for sunspots in each hemisphere switched orientation, from one sunspot cycle to the next.[20] This systematic property of sunspot magnetic fields is now commonly referred to as the "Hale-Nicholson law",[21] or in many cases simply "Hale's law".
[edit]21st century
The most powerful flare observed by satellite instrumentation began on 4 November 2003 at 19:29 UTC, and saturated instruments for 11 minutes. Region 486 has been estimated to have produced an X-ray flux of X28. Holographic and visual observations indicate significant activity continued on the far side of the Sun.
Measurements made in the latter part of the 2000s (decade) and based also on observation of infrared spectral lines, have suggested that sunspot activity may again be disappearing, possibly leading to a new minimum.[22] From 2007-2009, sunspot levels were far below average. In 2008, the Sun was spot-free 73 percent of the time, extreme even for a solar minimum. Only 1913 was more pronounced, with 85 percent of that year clear. The Sun continued to languish through mid-December 2009, when the largest group of sunspots to emerge for several years appeared. Even then, sunspot levels remained well below normal.[23]
Nasa's 2006 prediction. At 2010/2011, the sunspot count was expected to be at its maximum, but in reality in 2010 it was still at its minimum.
In 2006, NASA made a prediction for the next sunspot maximum, being between 150 and 200 around the year 2011 (30-50% stronger than cycle 23), followed by a weak maximum at around 2022.[24][25] The prediction did not come true. Instead, the sunspot cycle in 2010 was still at its minimum, where it should have been near its maximum, which shows the Sun's current unusual low activity.[26]
Due to a missing jet stream, fading spots, and slower activity near the poles, independent scientists of the National Solar Observatory (NSO) and the Air Force Research Laboratory (AFRL) now (2011) predict that the next 11-year solar sunspot cycle, Cycle 25, will be greatly reduced or may not happen at all.[27]
Cycle 24 is now well underway (as of March 2012); measurements indicate that the minimum occurred around December 2008 and that the next maximum will reach a sunspot number of 90 around May 2013.[28] Nothing has yet been stated for cycle 25.
[edit]Physics
Main article: Solar cycle
A sunspot viewed close-up in ultraviolet light, taken by the TRACE spacecraft
Although the details of sunspot generation are still a matter of research, it appears that sunspots are the visible counterparts of magnetic flux tubes in the Sun's convective zone that get "wound up" by differential rotation. If the stress on the tubes reaches a certain limit, they curl up like a rubber band and puncture the Sun's surface. Convection is inhibited at the puncture points; the energy flux from the Sun's interior decreases; and with it surface temperature.
The Wilson effect tells us that sunspots are actually depressions on the Sun's surface. Observations using the Zeeman effect show that prototypical sunspots come in pairs with opposite magnetic polarity. From cycle to cycle, the polarities of leading and trailing (with respect to the solar rotation) sunspots change from north/south to south/north and back. Sunspots usually appear in groups.
The sunspot itself can be divided into two parts:
The central umbra, which is the darkest part, where the magnetic field is approximately vertical (normal to the Sun's surface).
The surrounding penumbra, which is lighter, where the magnetic field is more inclined.
Magnetic pressure should tend to remove field concentrations, causing the sunspots to disperse, but sunspot lifetimes are measured in days or even weeks. In 2001, observations from the Solar and Heliospheric Observatory (SOHO) using sound waves traveling below the Sun's photosphere (local helioseismology) were used to develop a three-dimensional image of the internal structure below sunspots; these observations show that there is a powerful downdraft underneath each sunspot, forming a rotating vortex that concentrates the magnetic field.[29] Sunspots can thus be thought of as self-perpetuating storms, analogous in some ways to terrestrial hurricanes.
Butterfly diagram showing paired Spörer's law behavior
Sunspot activity cycles about every eleven years. The point of highest sunspot activity during this cycle is known as Solar Maximum, and the point of lowest activity is Solar Minimum. Early in the cycle, sunspots appear in the higher latitudes and then move towards the equator as the cycle approaches maximum: this is called Spörer's law.
Wolf number sunspot index displays various periods, the most prominent of which is at about 11 years in the mean. This period is also observed in most other expressions of solar activity and is deeply linked to a variation in the solar magnetic field that changes polarity with this period, too.
The modern understanding of sunspots starts with George Ellery Hale, who first linked magnetic fields and sunspots in 1908.[19] Hale suggested that the sunspot cycle period is 22 years, covering two polar reversals of the solar magnetic dipole field. Horace W. Babcock later proposed a qualitative model for the dynamics of the solar outer layers. The Babcock Model explains that magnetic fields cause the behavior described by Spörer's law, as well as other effects, which are twisted by the Sun's rotation.
[edit]Variation
Main article: Solar variation
400 year sunspot history
11,000 year sunspot reconstruction
Sunspot populations quickly rise and more slowly fall on an irregular cycle of 11 years, although significant variations in the number of sunspots attending the 11-year period are known over longer spans of time. For example, from 1900 to the 1960s, the solar maxima trend of sunspot count has been upward; from the 1960s to the present, it has diminished somewhat.[30] Over the last decades the Sun has had a markedly high average level of sunspot activity; it was last similarly active over 8,000 years ago.[10]
The number of sunspots correlates with the intensity of solar radiation over the period since 1979, when satellite measurements of absolute radiative flux became available. Since sunspots are darker than the surrounding photosphere it might be expected that more sunspots would lead to less solar radiation and a decreased solar constant. However, the surrounding margins of sunspots are brighter than the average, and so are hotter; overall, more sunspots increase the Sun's solar constant or brightness. The variation caused by the sunspot cycle to solar output is relatively small, on the order of 0.1% of the solar constant (a peak-to-trough range of 1.3 W·m−2 compared to 1366 W·m−2 for the average solar constant).[31][32] Sunspots were rarely observed during the Maunder Minimum in the second part of the 17th century (approximately from 1645 to 1715).
[edit]Observation
The Swedish 1-m Solar Telescope at Roque de los Muchachos Observatory
Sunspots are observed with land-based and Earth-orbiting solar telescopes. These telescopes use filtration and projection techniques for direct observation, in addition to various types of filtered cameras. Specialized tools such as spectroscopes and spectrohelioscopes are used to examine sunspots and sunspot areas. Artificial eclipses allow viewing of the circumference of the Sun as sunspots rotate through the horizon.
Since looking directly at the Sun with the naked eye permanently damages vision, amateur observation of sunspots is generally conducted indirectly using projected images, or directly through protective filters. Small sections of very dark filter glass, such as a #14 welder's glass are effective. A telescope eyepiece can project the image, without filtration, onto a white screen where it can be viewed indirectly, and even traced, to follow sunspot evolution. Special purpose hydrogen-alpha narrow bandpass filters as well as aluminum coated glass attenuation filters (which have the appearance of mirrors due to their extremely high optical density) on the front of a telescope provide safe observation through the eyepiece.
[edit]Application
Detail of a sunspot in 2005. The granulation of the Sun's surface can be seen clearly
Due to its link to other kinds of solar activity, sunspot occurrence can be used to help predict space weather, the state of the ionosphere, and hence the conditions of short-wave radio propagation or satellite communications. Solar activity (and the sunspot cycle) are frequently discussed in the context of global warming; Jack Eddy noted the apparent correlation between the Maunder Minimum of sunspot occurrence and the Little Ice Age in European climate.[citation needed] Sunspots themselves, in terms of the magnitude of their radiant-energy deficit, have only a weak effect on the terrestrial climate[33] in a direct sense. On longer time scales, such as the solar cycle, other magnetic phenomena (faculae and the chromospheric network) do correlate with sunspot occurrence. It is these other features that make the solar constant increase slightly at sunspot maxima, when naively one might expect that sunspots would make it decrease.[34]
British economist William Stanley Jevons suggested in the 1870s that there is a relationship between sunspots and business cycle crises. Jevons reasoned that sunspots affect Earth's weather, which, in turn, influences crops and, therefore, the economy.[35]
[edit]Spots on other stars
In 1947, G. E. Kron proposed that starspots were the reason for periodic changes in brightness on red dwarfs.[6] Since the mid-1990s, starspot observations have been made using increasingly powerful techniques yielding more and more detail: photometry showed starspot growth and decay and showed cyclic behavior similar to the Sun's; spectroscopy examined the structure of starspot regions by analyzing variations in spectral line splitting due to the Zeeman Effect; Doppler imaging showed differential rotation of spots for several stars and distributions different from the Sun's; spectral line analysis measured the temperature range of spots and the stellar surfaces. For example, in 1999, Strassmeier reported the largest cool starspot ever seen rotating the giant K0 star XX Triangulum (HD 12545) with a temperature of 3,500 K (3,230 °C), together with a warm spot of 4,800 K (4,530 °C).[6][36]
[edit]
Por volta de 1749, nas proximidades do Córrego Cortado, surgiu um pequeno povoado, formado por bandeirantes e tropeiros que buscavam estabelecer sesmarias na Capitania de Goiás, este foi o primeiro pouso do homem branco nas futuras terras da cidade de Taguatinga,[livro 1] antes ocupada por indÃgenas do tronco linguÃstico macro-jê, como os acroás, os xacriabás, os xavantes, os caiapós, os javaés, etc. No entanto, alguns desses aventureiros se fixaram animados pela possibilidade de ouro e diamantes, próximo ao Cortado. Às margens do mesmo córrego foi instalada a sede da fazenda Taguatinga, de propriedade de Gabriel da Cruz Miranda.[livro 1] Em 1781, a fazenda Taguatinga foi vendida a Antônio Couto de Abreu, filho do Bandeirante Urbano Couto e Menezes.[livro 1]
A consolidação da cidade se deu bem mais tarde, quase 2 séculos após esse perÃodo, gerada principalmente pelo grande contingente populacional atraÃdo pela construção de BrasÃlia
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Another experiment. The LEDs seem to be quite suitable to mimic a street light, inside the house there's a 9 Volt lighting. The contrast is quite nice, I think. The lantern is a smaller variation, maybe it should be a little taller. 100% Lego, even the light ;-)
guardo anche in basso....:-))
Buona domenica a tutti gli amici , quelli che ho conosciuto davvero, quelli che un po' ho imparato a conoscere anche solo qui, e quelli che conosco meno ma sono sempre presenti....
Oggi sarà unpiacevole pomeriggio...:-)))
Nella zona delle 5 Torri si insediò il Comando del gruppo di artiglieria da montagna. Qui furono dislocate le batterie di cannoni puntati contro le postazioni austriache del Lagazuoi e del Forte Tre Sassi.
Camminando sui sentieri della Grande Guerra, mi sembra di vedere impressi nella roccia i volti delle persone che qui han vissuto, han sofferto e sono morte.