Siding Spring Observatory
Siding Spring Observatory near Coonabarabran, New South Wales, part of the Research School of Astronomy & Astrophysics at the Australian National University, incorporates the Anglo-Australian Telescope along with a collection of other telescopes owned by the Australian National University, the University of New South Wales, other institutions. The observatory is situated 1,165 metres above sea level in the Warrumbungle National Park on Mount Woorat known as Siding Spring Mountain. Siding Spring Observatory is owned by the Australian National University and is part of the Mount Stromlo and Siding Spring Observatories research school. More than A$100 million worth of research equipment is located at the observatory. There are over 60 telescopes on site; the original Mount Stromlo Observatory was set up by the Commonwealth Government in 1924. After duty supplying optical components to the military in World War II, the emphasis on astronomical research changed in the late 1940s from solar to stellar research.
Between 1953 and 1974, the 74-inch reflecting telescope at Mount Stromlo was the largest optical telescope in Australia. In the 1950s, the artificial lights of Canberra, ACT, had brightened the sky at Mount Stromlo to such an extent that many faint astronomical objects had been overwhelmed by light pollution; the search for a new site was initiated by Bart Bok. After a site survey was undertaken the number of possible locations was narrowed down to two – Siding Spring and Mount Bingar near Griffith in New South Wales. Siding Spring was first suggested for astronomy by Harley Wood, the New South Wales Government Astronomer at the time. Arthur Hogg did much of the preliminary site testing; the Siding Spring site was selected by the ANU in 1962 from many other possible locations because of the dark and cloud-free skies. By the mid-1960s the ANU had set up three telescopes, together with supporting facilities, such as sealed roads, staff accommodation and water. In 1984, the Prime Minister, Bob Hawke, opened the ANU's largest telescope, the low-cost and innovative 2.3-metre aperture telescope, housed in a simple, co-rotating cuboid dome.
Since the 1950s, quite independently of developments at Siding Spring, the Australian and British governments had been negotiating about the construction of a large telescope. When these negotiations came to fruition in 1969, the infrastructure of Siding Spring Observatory was in place, it was the obvious site at which to locate the 3.9-metre aperture Anglo-Australian Telescope. During the construction of the AAT in the early 1970s, the British Science Research Council built the UK Schmidt Telescope, 1 kilometre to the northeast of the AAT dome; the wider field of view of the Schmidt optical design complements the narrower field of the AAT, in that larger areas of sky may be surveyed more quickly. Interesting objects so discovered are studied in greater detail on the larger instrument. In 1987, the Schmidt Telescope was amalgamated with the AAT. Siding Spring Observatory houses many telescopes from institutions across the world including, America, the UK, Hungary and Russia. In 1990, the earth-satellite tracking facility of the Royal Greenwich Observatory was closed down after 10 years of operation.
In 2012 the first publicly accessible Internet based observatory, working in partnership with the RSAA, was commissioned by iTelescope. Net with over 25 telescopes housed in a large roll-off roof observatory near the base of the UK Schmidt Telescope. Las Cumbres Observatory Global Telescope Network operate a 2-metre Ritchey Chretien telescope used for research, citizen science, education purposes by users across the globe, they operate inside the clam style dome 2 x 0.40 cm telescopes, a further 2 × 1 metre telescopes housed in individual domes outside the building. There are over one thousand registered users of the Faulkes Telescopes, who vary from schools and community groups to professional astronomers. A global network of robotic optical telescopes will not only provide continuous sky coverage and the ability to treat the network as a single instrument, but provide the resources for performing cutting edge science in collaboration with other organisations. ROTSE, Robotic Optical Transient Search Experiment is operated by the University of New South Wales, the 0.45 m, 3rd-generation robotic telescope has detected the transient optical emission from several GRB events.
The wide field of view and the fast response permit measurements inaccessible to more conventional instruments. HAT-South is a project to search for transiting extrasolar planets in the Southern Hemisphere, it uses a network of wide-field telescopes to monitor hundreds of thousands of bright stars, searching for the characteristic dip in light that occurs when a planet passes in front of its host star. Hat – South is made up of 3 sites in the Southern hemisphere with two "TH4" units, making that 8 x 0.2-metre telescopes each at every sites. These TH4 units consist of four 0.18 m Takahashi astrographs fitted with Apogee 4k x 4k CCDs. Each TH4 unit monitors 64 square degrees of sky at a time, so each site is capable of monitoring 128 square degrees of sky. Automated Patrol Telescope is operated by the University of NSW is a wide-field CCD imaging telescope; the 0.5 m telescope has a 5-degree field of view and can be operated remotely or in a automatic mode. The telescope has an optical design that more resembles that of a Schmidt camera, but has a 3-element lens to achieve a wide, corrected field of view.
The APT was developed by extensively modifying the optical and electronic s
The Picts were a confederation of peoples who lived in what is today eastern and northern Scotland during the Late Iron Age and Early Medieval periods. Where they lived and what their culture was like can be inferred from the geographical distribution of Brittonic place name elements and Pictish stones; the name Picts appears in written records from Late Antiquity to the 10th century, when they are thought to have merged with the Gaels. They lived to the north of the rivers Forth and Clyde, spoke the Pictish language, related to the Celtic Brittonic language spoken by the Britons who lived to the south of them. Picts are assumed to have been the descendants of the Caledonii and other tribes that were mentioned by Roman historians or on the world map of Ptolemy. Pictland called Pictavia by some sources merged with the Gaelic kingdom of Dál Riata to form the Kingdom of Alba. Alba expanded, absorbing the Brittonic kingdom of Strathclyde and Northumbrian Lothian, by the 11th century the Pictish identity had been subsumed into the "Scots" amalgamation of peoples.
Pictish society was typical of many Iron Age societies in northern Europe, having "wide connections and parallels" with neighbouring groups. Archaeology gives some impression of the society of the Picts. While little in the way of Pictish writing has survived, Pictish history since the late 6th century is known from a variety of sources, including Bede's Historia ecclesiastica gentis Anglorum, saints' lives such as that of Columba by Adomnán, various Irish annals; the term Pict is thought to have originated as a generic exonym used by the Romans in relation to people living north of the Forth–Clyde isthmus. The Latin word Picti first occurs in a panegyric written by Eumenius in AD 297 and is taken to mean "painted or tattooed people". Pict is Peohta in Old English, Pecht in Scots and Peithwyr in Welsh; some think. In writings from Ireland, the name Cruthin, Cruthni, Cruithni or Cruithini was used to refer both to the Picts and to another group of people who lived alongside the Ulaid in eastern Ulster.
It is accepted that this is derived from *Qritani, the Goidelic/Q-Celtic version of the Britonnic/P-Celtic *Pritani. From this came Britanni, the Roman name for those now called the Britons. What the Picts called themselves is unknown, it has been proposed that they called themselves Albidosi, a name found in the Chronicle of the Kings of Alba during the reign of Máel Coluim mac Domnaill, but this idea has been disputed. A unified "Pictish" identity may have consolidated with the Verturian hegemony established following the Battle of Dun Nechtain in 685 AD. A Pictish confederation was formed in Late Antiquity from a number of tribes—how and why is not known; some scholars have speculated that it was in response to the growth of the Roman Empire. The Chronicon Pictum, the Anglo-Saxon Chronicle and the early histographers such as Isidore of Seville, Bede, Geoffrey of Monmouth, etc. all present the Picts as conquerors of Alba from Scythia. However, little credence is now given to that view. Pictland had been described by Roman writers and geographers as the home of the Caledonii.
These Romans used other names to refer to tribes living in that area, including Verturiones and Venicones. But they may have heard these other names only second- or third-hand, from speakers of Brittonic or Gaulish languages, who may have used different names for the same group or groups. Pictish recorded history begins in the Dark Ages. At that time, the Gaels of Dál Riata controlled what is now Argyll, as part of a kingdom straddling the sea between Britain and Ireland; the Angles of Bernicia, which merged with Deira to form Northumbria, overwhelmed the adjacent British kingdoms, for much of the 7th century Northumbria was the most powerful kingdom in Britain. The Picts were tributary to Northumbria until the reign of Bridei mac Beli, when, in 685, the Anglians suffered a defeat at the Battle of Dun Nechtain that halted their northward expansion; the Northumbrians continued to dominate southern Scotland for the remainder of the Pictish period. Dál Riata was subject to the Pictish king Óengus mac Fergusa during his reign, though it had its own kings beginning in the 760s, does not appear to have recovered its political independence from the Picts.
A Pictish king, Caustantín mac Fergusa, placed his son Domnall on the throne of Dál Riata. Pictish attempts to achieve a similar dominance over the Britons of Alt Clut were not successful; the Viking Age brought great changes in Britain and Ireland, no less in Scotland than elsewhere, with the Vikings conquering and settling the islands and various mainland areas, including Caithness and Galloway. In the middle of the 9th century Ketil Flatnose is said to have founded the Kingdom of the Isles, governing many of these territories, by the end of that century the Vikings had destroyed the Kingdom of Northumbria weakened the Kingdom of Strathclyde, founded the Kingdom of York. In a major battle in 839, the Vikings killed the King of Fortriu, Eógan mac Óengusa, the King of Dál Riata Áed mac Boanta, many others. In the aftermath, in the 840s, Cínaed mac Ailpín became king of the Picts. During the reign of Cínaed's grandson, Caustantín mac Áeda, outsiders began to refer to the region as the Kingdom of Alba rather than the Kingdom of the Picts, but it is not known whether this was because a new kingdom was established or Alba was a closer
A horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body. The orbital period of the smaller body is nearly the same as for the larger body, its path appears to have a horseshoe shape as viewed from the larger object in a rotating reference frame; the loop is not closed but will drift forward or backward each time, so that the point it circles will appear to move smoothly along the larger body's orbit over a long period of time. When the object approaches the larger body at either end of its trajectory, its apparent direction changes. Over an entire cycle the center traces the outline of a horseshoe, with the larger body between the'horns'. Asteroids in horseshoe orbits with respect to Earth include 54509 YORP, 2002 AA29, 2010 SO16, 2015 SO2 and 2001 GO2. A broader definition includes 3753 Cruithne, which can be said to be in a compound and/or transition orbit, or 1998 UP1 and 2003 YN107. By 2016, 12 horseshoe librators of Earth have been discovered.
Saturn's moons Epimetheus and Janus occupy horseshoe orbits with respect to each other. The following explanation relates to an asteroid, in such an orbit around the Sun, is affected by the Earth; the asteroid is in the same solar orbit as Earth. Both take one year to orbit the Sun, it is necessary to grasp two rules of orbit dynamics: A body closer to the Sun completes an orbit more than a body further away. If a body accelerates along its orbit, its orbit moves outwards from the Sun. If it decelerates, the orbital radius decreases; the horseshoe orbit arises because the gravitational attraction of the Earth changes the shape of the elliptical orbit of the asteroid. The shape changes are small but result in significant changes relative to the Earth; the horseshoe becomes apparent only when mapping the movement of the asteroid relative to both the Sun and the Earth. The asteroid always orbits the Sun in the same direction. However, it goes through a cycle of catching up with the Earth and falling behind, so that its movement relative to both the Sun and the Earth traces a shape like the outline of a horseshoe.
Starting at point A, on the inner ring between L5 and Earth, the satellite is orbiting faster than the Earth and is on its way toward passing between the Earth and the Sun. But Earth's gravity exerts an outward accelerating force, pulling the satellite into a higher orbit which decreases its angular speed; when the satellite gets to point B, it is traveling at the same speed as Earth. Earth's gravity is still accelerating the satellite along the orbital path, continues to pull the satellite into a higher orbit. At Point C, the satellite reaches a high and slow enough orbit such that it starts to lag behind Earth, it spends the next century or more appearing to drift'backwards' around the orbit when viewed relative to the Earth. Its orbit around the Sun still takes only more than one Earth year. Given enough time, the Earth and the satellite will be on opposite sides of the Sun; the satellite comes around to point D where Earth's gravity is now reducing the satellite's orbital velocity. This causes it to fall into a lower orbit, which increases the angular speed of the satellite around the Sun.
This continues until point E where the satellite's orbit is now lower and faster than Earth's orbit, it begins moving out ahead of Earth. Over the next few centuries it completes its journey back to point A. On the longer term, asteroids can transfer between quasi-satellite orbits. Quasi-satellites aren't gravitationally bound to their planet, but appear to circle it in a retrograde direction as they circle the Sun with the same orbital period as the planet. By 2016, orbital calculations showed that four of Earth's horseshoe librators and all five of its known quasi-satellites transfer between horseshoe and quasi-satellite orbits. A somewhat different, but equivalent, view of the situation may be noted by considering conservation of energy, it is a theorem of classical mechanics that a body moving in a time-independent potential field will have its total energy, E = T + V, where E is total energy, T is kinetic energy and V is potential energy, negative. It is apparent since V = -GM/R near a gravitating body of mass M and orbital radius R, that seen from a stationary frame, V will be increasing for the region behind M, decreasing for the region in front of it.
However, orbits with lower total energy have shorter periods, so a body moving on the forward side of a planet will lose energy, fall into a shorter-period orbit, thus move away, or be "repelled" from it. Bodies moving on the trailing side of the planet will gain energy, rise to a higher, slower and thereby fall behind repelled, thus a small body can move back and forth between a leading and a trailing position, never approaching too close to the planet that dominates the region. See trojan. Figure 1 above shows shorter orbits around the Lagrangian points L4 and L5; these are called tadpole orbits and can be explained in a similar way, except that the asteroid's distance from the Earth does not oscillate as far as the L3 point on the other side of the Sun. As it moves closer to or farther from the Earth, the changing pull of Earth's gravitational field causes it to accelerate or decelerate, causing a change in its orbit known as libration. An example of a body in a tadpole orbit is Polydeuces, a small moon of Saturn which librates around the
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, is referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance, distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys and polar ice caps of Earth; the days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, of Valles Marineris, one of the largest canyons in the Solar System; the smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to a Mars trojan. There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, less than 1% of the Earth's, except at the lowest elevations for short periods; the two polar ice caps appear to be made of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars; the volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars can be seen from Earth with the naked eye, as can its reddish coloring, its apparent magnitude reaches −2.94, surpassed only by Jupiter, the Moon, the Sun.
Optical ground-based telescopes are limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earth's atmosphere. Mars is half the diameter of Earth with a surface area only less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity; the red-orange appearance of the Martian surface is caused by rust. It can look like butterscotch. Like Earth, Mars has differentiated into a dense metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometers, consisting of iron and nickel with about 16–17% sulfur; this iron sulfide core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, aluminum and potassium.
The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust averages 40 km. Mars is a terrestrial planet that consists of minerals containing silicon and oxygen and other elements that make up rock; the surface of Mars is composed of tholeiitic basalt, although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Localized concentrations of hematite and olivine have been found. Much of the surface is covered by finely grained iron oxide dust. Although Mars has no evidence of a structured global magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.
This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005, is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded, it is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine and sulphur, are much more common on Mars than Earth. After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is underlain by immense impact basins caused by those events.
There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km, or four times the size of the Moon's South Pole – Aitk
Chile the Republic of Chile, is a South American country occupying a long, narrow strip of land between the Andes to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, the Drake Passage in the far south. Chilean territory includes the Pacific islands of Juan Fernández, Salas y Gómez and Easter Island in Oceania. Chile claims about 1,250,000 square kilometres of Antarctica, although all claims are suspended under the Antarctic Treaty; the arid Atacama Desert in northern Chile contains great mineral wealth, principally copper. The small central area dominates in terms of population and agricultural resources, is the cultural and political center from which Chile expanded in the late 19th century when it incorporated its northern and southern regions. Southern Chile is rich in forests and grazing lands, features a string of volcanoes and lakes; the southern coast is a labyrinth of fjords, canals, twisting peninsulas, islands.
Spain conquered and colonized the region in the mid-16th century, replacing Inca rule in the north and centre, but failing to conquer the independent Mapuche who inhabited what is now south-central Chile. After declaring its independence from Spain in 1818, Chile emerged in the 1830s as a stable authoritarian republic. In the 19th century, Chile saw significant economic and territorial growth, ending Mapuche resistance in the 1880s and gaining its current northern territory in the War of the Pacific after defeating Peru and Bolivia. In the 1960s and 1970s, the country experienced severe left-right political polarization and turmoil; this development culminated with the 1973 Chilean coup d'état that overthrew Salvador Allende's democratically elected left-wing government and instituted a 16-year-long right-wing military dictatorship that left more than 3,000 people dead or missing. The regime, headed by Augusto Pinochet, ended in 1990 after it lost a referendum in 1988 and was succeeded by a center-left coalition which ruled through four presidencies until 2010.
The modern sovereign state of Chile is among South America's most economically and stable and prosperous nations, with a high-income economy and high living standards. It leads Latin American nations in rankings of human development, income per capita, state of peace, economic freedom, low perception of corruption, it ranks high regionally in sustainability of the state, democratic development. Chile is a member of the Organisation for Economic Co-operation and Development, joining in 2010, it has the lowest homicide rate in the Americas after Canada. Chile is a founding member of the United Nations, the Union of South American Nations and the Community of Latin American and Caribbean States. There are various theories about the origin of the word Chile. According to 17th-century Spanish chronicler Diego de Rosales, the Incas called the valley of the Aconcagua "Chili" by corruption of the name of a Picunche tribal chief called Tili, who ruled the area at the time of the Incan conquest in the 15th century.
Another theory points to the similarity of the valley of the Aconcagua with that of the Casma Valley in Peru, where there was a town and valley named Chili. Other theories say Chile may derive its name from a Native American word meaning either "ends of the earth" or "sea gulls". Another origin attributed to chilli is the onomatopoeic cheele-cheele—the Mapuche imitation of the warble of a bird locally known as trile; the Spanish conquistadors heard about this name from the Incas, the few survivors of Diego de Almagro's first Spanish expedition south from Peru in 1535–36 called themselves the "men of Chilli". Almagro is credited with the universalization of the name Chile, after naming the Mapocho valley as such; the older spelling "Chili" was in use in English until at least 1900 before switching to "Chile". Stone tool evidence indicates humans sporadically frequented the Monte Verde valley area as long as 18,500 years ago. About 10,000 years ago, migrating indigenous Peoples settled in fertile valleys and coastal areas of what is present-day Chile.
Settlement sites from early human habitation include Monte Verde, Cueva del Milodón and the Pali-Aike Crater's lava tube. The Incas extended their empire into what is now northern Chile, but the Mapuche resisted many attempts by the Inca Empire to subjugate them, despite their lack of state organization, they fought against his army. The result of the bloody three-day confrontation known as the Battle of the Maule was that the Inca conquest of the territories of Chile ended at the Maule river. In 1520, while attempting to circumnavigate the globe, Ferdinand Magellan discovered the southern passage now named after him thus becoming the first European to set foot on what is now Chile; the next Europeans to reach Chile were Diego de Almagro and his band of Spanish conquistadors, who came from Peru in 1535 seeking gold. The Spanish encountered various cultures that supported themselves principally through slash-and-burn agriculture and hunting; the conquest of Chile began in earnest in 1540 and was carried out by Pedro de Valdivia, one of Francisco Pizarro's lieutenants, who founded the city of Santiago on 12 February 1541.
Although the Spanish did not find the extensive gold and silver they sought, they recognize
In celestial mechanics, an orbital resonance occurs when orbiting bodies exert a regular, periodic gravitational influence on each other because their orbital periods are related by a ratio of small integers. Most this relationship is found for a pair of objects; the physical principle behind orbital resonance is similar in concept to pushing a child on a swing, where the orbit and the swing both have a natural frequency, the other body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances enhance the mutual gravitational influence of the bodies, i.e. their ability to alter or constrain each other's orbits. In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be stable and self-correcting, so that the bodies remain in resonance. Examples are the 1:2:4 resonance of Jupiter's moons Ganymede, Europa and Io, the 2:3 resonance between Pluto and Neptune.
Unstable resonances with Saturn's inner moons give rise to gaps in the rings of Saturn. The special case of 1:1 resonance between bodies with similar orbital radii causes large Solar System bodies to eject most other bodies sharing their orbits. A binary resonance ratio in this article should be interpreted as the ratio of number of orbits completed in the same time interval, rather than as the ratio of orbital periods, which would be the inverse ratio, thus the 2:3 ratio above means Pluto completes two orbits in the time it takes Neptune to complete three. In the case of resonance relationships among three or more bodies, either type of ratio may be used and the type of ratio will be specified. Since the discovery of Newton's law of universal gravitation in the 17th century, the stability of the Solar System has preoccupied many mathematicians, starting with Pierre-Simon Laplace; the stable orbits that arise in a two-body approximation ignore the influence of other bodies. The effect of these added interactions on the stability of the Solar System is small, but at first it was not known whether they might add up over longer periods to change the orbital parameters and lead to a different configuration, or whether some other stabilising effects might maintain the configuration of the orbits of the planets.
It was Laplace. Before Newton, there was consideration of ratios and proportions in orbital motions, in what was called "the music of the spheres", or Musica universalis. In general, an orbital resonance may involve any combination of the orbit parameters. Act on any time scale from short term, commensurable with the orbit periods, to secular, measured in 104 to 106 years. Lead to either long-term stabilization of the orbits or be the cause of their destabilization. A mean-motion orbital resonance occurs when two bodies have periods of revolution that are a simple integer ratio of each other. Depending on the details, this can either destabilize the orbit. Stabilization may occur when the two bodies move in such a synchronised fashion that they never approach. For instance: The orbits of Pluto and the plutinos are stable, despite crossing that of the much larger Neptune, because they are in a 2:3 resonance with it; the resonance ensures that, when they approach perihelion and Neptune's orbit, Neptune is distant.
Other Neptune-crossing bodies that were not in resonance were ejected from that region by strong perturbations due to Neptune. There are smaller but significant groups of resonant trans-Neptunian objects occupying the 1:1, 3:5, 4:7, 1:2 and 2:5 resonances, among others, with respect to Neptune. In the asteroid belt beyond 3.5 AU from the Sun, the 3:2, 4:3 and 1:1 resonances with Jupiter are populated by clumps of asteroids. Orbital resonances can destabilize one of the orbits; this process can be exploited to find energy-efficient ways of deorbiting spacecraft. For small bodies, destabilization is far more likely. For instance: In the asteroid belt within 3.5 AU from the Sun, the major mean-motion resonances with Jupiter are locations of gaps in the asteroid distribution, the Kirkwood gaps. Asteroids have been ejected from these empty lanes by repeated perturbations. However, there are still populations of asteroids temporarily present near these resonances. For example, asteroids of the Alinda family are in or close to the 3:1 resonance, with their orbital eccentricity increased by interactions with Jupiter until they have a close encounter with an inner planet that ejects them from the resonance.
In the rings of Saturn, the Cassini Division is a gap between the inner B Ring and the outer A Ring, cleared by a 2:1 resonance with the moon Mimas. In the rings of Saturn, the Encke and Keeler gaps within the A Ring are cleared by 1:1 resonances with the embedded moonlets Pan and Daphnis, respectively; the A Ring's outer edge is maintained by a destabilizing 7:6 resonance with the moon Janus. Most bodies that
European Southern Observatory
The European Southern Observatory, formally the European Organisation for Astronomical Research in the Southern Hemisphere, is a 16-nation intergovernmental research organization for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky; the organisation employs about 730 staff members and receives annual member state contributions of €162 million. Its observatories are located in northern Chile. ESO has operated some of the largest and most technologically advanced telescopes; these include the 3.6 m New Technology Telescope, an early pioneer in the use of active optics, the Very Large Telescope, which consists of four individual 8.2 m telescopes and four smaller auxiliary telescopes which can all work together or separately. The Atacama Large Millimeter Array observes the universe in the millimetre and submillimetre wavelength ranges, is the world's largest ground-based astronomy project to date, it was completed in March 2013 in an international collaboration by Europe, North America, East Asia and Chile.
Under construction is the Extremely Large Telescope. It will use a 39.3-metre-diameter segmented mirror, become the world's largest optical reflecting telescope when operational in 2024. Its light-gathering power will allow detailed studies of planets around other stars, the first objects in the universe, supermassive black holes, the nature and distribution of the dark matter and dark energy which dominate the universe. ESO's observing facilities have made astronomical discoveries and produced several astronomical catalogues, its findings include the discovery of the most distant gamma-ray burst and evidence for a black hole at the centre of the Milky Way. In 2004, the VLT allowed astronomers to obtain the first picture of an extrasolar planet orbiting a brown dwarf 173 light-years away; the High Accuracy Radial Velocity Planet Searcher instrument installed on the older ESO 3.6 m telescope led to the discovery of extrasolar planets, including Gliese 581c—one of the smallest planets seen outside the solar system.
The idea that European astronomers should establish a common large observatory was broached by Walter Baade and Jan Oort at the Leiden Observatory in the Netherlands in spring 1953. It was pursued by Oort, who gathered a group of astronomers in Leiden to consider it on June 21 that year. Thereafter, the subject was further discussed at the Groningen conference in the Netherlands. On January 26, 1954, an ESO declaration was signed by astronomers from six European countries expressing the wish that a joint European observatory be established in the southern hemisphere. At the time, all reflector telescopes with an aperture of 2 metres or more were located in the northern hemisphere; the decision to build the observatory in the southern hemisphere resulted from the necessity of observing the southern sky. Although it was planned to set up telescopes in South Africa, tests from 1955 to 1963 demonstrated that a site in the Andes was preferable. On November 15, 1963 Chile was chosen as the site for ESO's observatory.
The decision was preceded by the ESO Convention, signed 5 October 1962 by Belgium, France, the Netherlands and Sweden. Otto Heckmann was nominated as the organisation's first director general on 1 November 1962. A preliminary proposal for a convention of astronomy organisations in these five countries was drafted in 1954. Although some amendments were made in the initial document, the convention proceeded until 1960 when it was discussed during that year's committee meeting; the new draft was examined in detail, a council member of CERN highlighted the need for a convention between governments. The convention and government involvement became pressing due to rising costs of site-testing expeditions; the final 1962 version was adopted from the CERN convention, due to similarities between the organisations and the dual membership of some members. In 1966, the first ESO telescope at the La Silla site in Chile began operating; because CERN had sophisticated instrumentation, the astronomy organisation turned to the nuclear-research body for advice and a collaborative agreement between ESO and CERN was signed in 1970.
Several months ESO's telescope division moved into a CERN building in Geneva and ESO's Sky Atlas Laboratory was established on CERN property. ESO's European departments moved into the new ESO headquarters in Garching, Germany in 1980. Although ESO is headquartered in Germany, its telescopes and observatories are in northern Chile, where the organisation operates advanced ground-based astronomical facilities: La Silla, which hosts the New Technology Telescope Paranal, where the Very Large Telescope is located Llano de Chajnantor, which hosts the APEX submillimetre telescope and where ALMA, the Atacama Large Millimeter/submillimeter Array, is locatedThese are among the best locations for astronomical observations in the southern hemisphere. An ESO project is the Extremely Large Telescope, a 40-metre-class telescope based on a five-mirror design and the planned Overwhelmingly Large Telescope; the ELT will be the near-infrared telescope in the world. ESO began its design in early 2006, aimed to begin construction in 2012.
Construction work at the ELT site started in June 2014. As decided by the ESO council on 26 April 2010, a fou