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132-452: The Spektr module was originally developed as part of a top-secret military program code-named " Oktant ". It was planned to carry experiments with space-borne surveillance and test antimissile defense. The surveillance instruments were mounted on the exterior of the module opposite the docking port. Also in this location were two launchers for artificial targets. The heart of the Spektr payload

264-411: A = 313 Π 10800 {\displaystyle D_{a}={\frac {313\Pi }{10800}}} radians to arcsecs is given by: D a = 313 Π 10800 ⋅ 206265 = 1878 {\displaystyle D_{a}={\frac {313\Pi }{10800}}\cdot 206265=1878} . An example using a telescope with an aperture of 130 mm observing

396-515: A curved mirror in place of the objective lens, theory preceded practice. The theoretical basis for curved mirrors behaving similar to lenses was probably established by Alhazen , whose theories had been widely disseminated in Latin translations of his work. Soon after the invention of the refracting telescope, Galileo, Giovanni Francesco Sagredo , and others, spurred on by their knowledge that curved mirrors had similar properties to lenses, discussed

528-416: A focal ratio slower (bigger number) than f/12 is generally considered slow, and any telescope with a focal ratio faster (smaller number) than f/6, is considered fast. Faster systems often have more optical aberrations away from the center of the field of view and are generally more demanding of eyepiece designs than slower ones. A fast system is often desired for practical purposes in astrophotography with

660-618: A pupil diameter of 7 mm. Younger persons host larger diameters, typically said to be 9 mm, as the diameter of the pupil decreases with age. An example gathering power of an aperture with 254 mm compared to an adult pupil diameter being 7 mm is given by: P = ( D D p ) 2 = ( 254 7 ) 2 ≈ 1316.7 {\displaystyle P=\left({\frac {D}{D_{p}}}\right)^{2}=\left({\frac {254}{7}}\right)^{2}\approx 1316.7} Light-gathering power can be compared between telescopes by comparing

792-424: A "normal" or standard value of 7 mm for most adults aged 30–40, to 5–6 mm for retirees in their 60s and 70s. A lifetime spent exposed to chronically bright ambient light, such as sunlight reflected off of open fields of snow, or white-sand beaches, or cement, will tend to make individuals' pupils permanently smaller. Sunglasses greatly help, but once shrunk by long-time over-exposure to bright light, even

924-424: A computer ( smartphone , pad , or laptop) is required to make astronomical observations from the telescopes. The digital technology allows multiple images to be stacked while subtracting the noise component of the observation producing images of Messier objects and faint stars as dim as an apparent magnitude of 15 with consumer-grade equipment. The basic scheme is that the primary light-gathering element,

1056-404: A few weeks later by claims by Jacob Metius , and a third unknown applicant, that they also knew of this "art". Word of the invention spread fast and Galileo Galilei , on hearing of the device, was making his own improved designs within a year and was the first to publish astronomical results using a telescope. Galileo's telescope used a convex objective lens and a concave eye lens , a design

1188-400: A focus in a shorter distance. In astronomy, the f-number is commonly referred to as the focal ratio notated as N {\displaystyle N} . The focal ratio of a telescope is defined as the focal length f {\displaystyle f} of an objective divided by its diameter D {\displaystyle D} or by the diameter of an aperture stop in

1320-479: A half millennia . It began with the incipient unification of Nile Valley polities around 3100 BC, traditionally under Menes . The civilisation of ancient Egypt was characterised primarily by intensive agricultural use of the fertile Nile Valley; the use of the Nile itself for transportation; the development of writing systems – first hieroglyphs and then later hieratic and other derived scripts – and literature ;

1452-496: A large kingdom at three different times in history. These are called the Old (20th to 18th centuries BC), Middle (14th to 11th centuries BC), and Neo-Assyrian (9th to 7th centuries BC) kingdoms, or periods. Mitanni was a Hurrian empire in northern Mesopotamia founded around 1500 BC. The Mitanians conquered and controlled Assyria until the 14th century BC while contending with Egypt for control of parts of modern Syria. Its capital

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1584-406: A larger field of view. Design specifications relate to the characteristics of the telescope and how it performs optically. Several properties of the specifications may change with the equipment or accessories used with the telescope; such as Barlow lenses , star diagonals and eyepieces . These interchangeable accessories do not alter the specifications of the telescope, however they alter the way

1716-589: A later emperor, Darius the Great , expanded the empire to the Indus River , creating the largest empire in the world to that date. But Darius and his son Xerxes I failed to expand into Greece , with expeditions in 490 and 480 BC eventually failing. The Achaemenid dynasty and empire fell to Alexander the Great by 330 BC, and after Alexander's death, much of the area previously ruled by the Cyrus and his successors

1848-404: A limit related to something called the exit pupil . The exit pupil is the cylinder of light exiting the eyepiece and entering the pupil of the eye; hence the lower the magnification , the larger the exit pupil . It is the image of the shrunken sky-viewing aperture of the telescope, reduced by the magnification factor,   M   , {\displaystyle \ M\ ,} of

1980-402: A minimum and maximum. A wider field of view eyepiece may be used to keep the same eyepiece focal length whilst providing the same magnification through the telescope. For a good quality telescope operating in good atmospheric conditions, the maximum usable magnification is limited by diffraction. The visual magnification M {\displaystyle M} of the field of view through

2112-468: A more convenient viewing location, and in that case the image is erect, but still reversed left to right. In terrestrial telescopes such as spotting scopes , monoculars and binoculars , prisms (e.g., Porro prisms ) or a relay lens between objective and eyepiece are used to correct the image orientation. There are telescope designs that do not present an inverted image such as the Galilean refractor and

2244-399: A multitude of lenses that increase or decrease effective focal length. The quality of the image generally depends on the quality of the optics (lenses) and viewing conditions—not on magnification. Magnification itself is limited by optical characteristics. With any telescope or microscope, beyond a practical maximum magnification, the image looks bigger but shows no more detail. It occurs when

2376-451: A number of dynasties that peaked in power under the reign of Ashoka Maurya, one of India's most legendary and famous emperors. During the reign of Ashoka, the four dynasties of Chola , Chera , and Pandya were ruling in the South, while Devanampiya Tissa (250–210 BC) controlled Anuradhapura (now Sri Lanka ). These kingdoms, while not part of Ashoka's empire, were in friendly terms with

2508-522: A period often known as the Vedic period . Between 1500 and 500 BC these peoples spread throughout most of India and had begun to found small cities. Vedic society was characterized by the varna system which divided society into four broad castes, which were later elaborated. By the end of the Vedic period, this way of organizing society had become central to Indian society. Religion in the late Vedic period

2640-547: A survey of a given area, the field of view is just as important as raw light gathering power. Survey telescopes such as the Large Synoptic Survey Telescope try to maximize the product of mirror area and field of view (or etendue ) rather than raw light gathering ability alone. The magnification through a telescope makes an object appear larger while limiting the FOV. Magnification is often misleading as

2772-402: A telescope can be determined by the telescope's focal length f {\displaystyle f} divided by the eyepiece focal length f e {\displaystyle f_{e}} (or diameter). The maximum is limited by the focal length of the eyepiece . An example of visual magnification using a telescope with a 1200 mm focal length and 3 mm eyepiece

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2904-456: A tradition of bronze production and the manufacture of evermore refined bronze and iron objects, such as plows, axes and sickles with shaft holes, socketed arrows and spearheads and small ornamented items. By about 500 BCE, large and delicately decorated bronze drums of remarkable quality, weighing more than 70 kg (150 lb), were produced in the laborious lost-wax casting process. This industry of highly sophisticated metal processing

3036-528: Is Harappan, after the first of its cities to be excavated, Harappa in the Pakistani province of Punjab . Harappan civilization grew out of the earlier agricultural communities as they evolved into cities. These communities created and traded jewelry, figurines, and seals that appear widely scattered throughout Mesopotamia, Afghanistan, and Iran. Chickens were domesticated in addition to the earlier crops and animals. They developed their own writing system,

3168-493: Is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum , to create a magnified image for direct visual inspection, to make a photograph , or to collect data through electronic image sensors . There are three primary types of optical telescope: An optical telescope's ability to resolve small details is directly related to the diameter (or aperture ) of its objective (the primary lens or mirror that collects and focuses

3300-444: Is a time period from the beginning of writing and recorded human history through late antiquity . The span of recorded history is roughly 5,000 years, beginning with the development of Sumerian cuneiform script. Ancient history covers all continents inhabited by humans in the period 3000 BC – AD 500, ending with the expansion of Islam in late antiquity. The three-age system periodizes ancient history into

3432-425: Is given by where λ {\displaystyle \lambda } is the wavelength and D {\displaystyle D} is the aperture. For visible light ( λ {\displaystyle \lambda } = 550 nm) in the small-angle approximation , this equation can be rewritten: Here, α R {\displaystyle \alpha _{R}} denotes

3564-479: Is given by:   M m i n = D   d e p =   254   7 ≈ 36 ×   . {\displaystyle \ M_{\mathsf {min}}={\frac {D}{\ d_{\mathsf {ep}}}}={\frac {\ 254\ }{7}}\approx 36\!\times ~.} If the telescope happened to have a 1 200 mm focal length (   L   {\displaystyle \ L\ } ),

3696-463: Is given by: M = f f e = 1200 3 = 400 {\displaystyle M={\frac {f}{f_{e}}}={\frac {1200}{3}}=400} There are two issues constraining the lowest useful magnification on a telescope: Both constraints boil down to approximately the same rule: The magnification of the viewed image,   M   , {\displaystyle \ M\ ,} must be high enough to make

3828-477: Is given by: R = λ 10 6 = 550 10 6 = 0.00055 {\displaystyle R={\frac {\lambda }{10^{6}}}={\frac {550}{10^{6}}}=0.00055} . The constant Φ {\displaystyle \Phi } is derived from radians to the same unit as the object's apparent diameter ; where the Moon's apparent diameter of D

3960-431: Is more a discovery of optical craftsmen than an invention of a scientist. The lens and the properties of refracting and reflecting light had been known since antiquity , and theory on how they worked was developed by ancient Greek philosophers, preserved and expanded on in the medieval Islamic world , and had reached a significantly advanced state by the time of the telescope's invention in early modern Europe . But

4092-663: Is now called a Galilean telescope . Johannes Kepler proposed an improvement on the design that used a convex eyepiece , often called the Keplerian Telescope . The next big step in the development of refractors was the advent of the Achromatic lens in the early 18th century, which corrected the chromatic aberration in Keplerian telescopes up to that time—allowing for much shorter instruments with much larger objectives. For reflecting telescopes , which use

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4224-400: Is the ability of a telescope to collect a lot more light than the human eye. Its light-gathering power is probably its most important feature. The telescope acts as a light bucket , collecting all of the photons that come down on it from a far away object, where a larger bucket catches more photons resulting in more received light in a given time period, effectively brightening the image. This

4356-412: Is why the pupils of your eyes enlarge at night so that more light reaches the retinas. The gathering power P {\displaystyle P} compared against a human eye is the squared result of the division of the aperture D {\displaystyle D} over the observer's pupil diameter D p {\displaystyle D_{p}} , with an average adult having

4488-520: Is yet to be confirmed with extensive survey work. With the help of archaeological excavations mainly by Susan and Roderick McIntosh , the site is known to have been occupied from 250 BC to AD 900. The city is believed to have been abandoned and moved where the current city is located due to the spread of Islam and the building of the Great Mosque of Djenné . Previously, it was assumed that advanced trade networks and complex societies did not exist in

4620-569: The Chaldeans in 614 BC. The Achaemenid Empire was founded by Cyrus the Great , who first became king of the Persians, then conquered the Medes, Lydia , and Babylon by 539 BC. The empire built on earlier Mesopotamian systems of government to govern their large empire. By building roads, they improved both the ability to send governmental instructions throughout their lands as well as improving

4752-763: The Congo River and into the Great Lakes area. By AD 1000 these groups had spread throughout all of southern Africa south of the equator. Iron metallurgy and agriculture spread along with these peoples, with the cultivation of millet, oil palms, sorghum, and yams as well as the use of domesticated cattle, pigs, and sheep. These technologies helped increase population, and settled communities became common in sub-Saharan Africa except in deserts or heavy forests. Paleolithic tools have been discovered in India dating to 200,000 years ago, and Neolithic sites are known from near

4884-535: The Gregorian reflector . These are referred to as erecting telescopes . Many types of telescope fold or divert the optical path with secondary or tertiary mirrors. These may be integral part of the optical design ( Newtonian telescope , Cassegrain reflector or similar types), or may simply be used to place the eyepiece or detector at a more convenient position. Telescope designs may also use specially designed additional lenses or mirrors to improve image quality over

5016-681: The Indus Valley dating to around 8000 BC. Agriculture began in the Indus Valley around 7000 BC, and reached the Ganges Valley by 3000 BC. Barley , cotton , and wheat were grown and the population had domesticated cattle, goats, and sheep. The Indus Valley Civilisation developed around 3000 BC in the Indus and Ghaggar-Hakra river valleys of eastern Afghanistan , Pakistan, and western India. Another name for this civilisation

5148-495: The Indus Valley script , which is still mostly undeciphered. The exact structure of society and the way the cities were governed is not known. By about 1600 BC, the Indus Valley culture had abandoned many of their cities, including Mohenjo-Daro . The exact reason for this decline is not known. Indo-European speaking peoples began to spread into India about 1500 BC. The Rigveda , in Sanskrit , dates to this period and begins

5280-587: The Maccabean revolt led to independence during Hellenistic period until Roman conquest . Phoenicia was an ancient civilisation centered in the north of ancient Canaan , with its heartland along the coastal regions of modern-day Lebanon , Syria and Israel. Phoenician civilisation was an enterprising maritime trading culture that spread across the Mediterranean between the period of 1550 to 300 BC. One Phoenician colony, Carthage , ruled an empire in

5412-802: The Maritime Jade Road , a jade trade network, in Southeast Asia which existed in Taiwan and the Philippines for 3,000 years from 2000 BCE to 1000 CE. The trade was established by links between the indigenous peoples of Taiwan and the Philippines, and later included parts of Vietnam, Malaysia, Indonesia, Thailand, and other areas in Southeast Asia (known as the Sa Huynh - Kalanay Interaction Sphere). Lingling-o artifacts are one of

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5544-603: The Maurya Empire . An alliance existed between Devanampiya Tissa and Ashoka of India, who sent Buddhist missionaries to Sri Lanka. Most of North India was reunited under the Gupta Empire beginning under Chandragupta I around AD 320. Under his successors the empire spread to include much of India except for the Deccan Plateau and the very south of the peninsula. This was a period of relative peace, and

5676-778: The Nile Delta in the north, as far south as Jebel Barkal at the Fourth Cataract of the Nile. Extensions to the geographical range of ancient Egyptian civilisation included, at different times, areas of the southern Levant , the Eastern Desert and the Red Sea coastline, the Sinai Peninsula , and the Western Desert (focused on the several oases ). Ancient Egypt developed over at least three and

5808-688: The Old Kingdom , which saw pyramid building on a large scale. After 2100 BC, the Old Kingdom dissolved into smaller states during the First Intermediate Period , which lasted about 100 years. The Middle Kingdom began around 2000 BC with the reunification of Egypt under pharoes ruling from Thebes . The Middle Kingdom ended with the conquest of northern Egypt by the Hyksos around 1650 BC. The Hyksos were expelled from Egypt and

5940-827: The Pitcairns , the Kermadec Islands , and the Norfolk Islands were also formerly settled by Austronesians but later abandoned. There is also putative evidence, based in the spread of the sweet potato , that Austronesians may have reached South America from Polynesia, where they might have traded with the Indigenous peoples of the Americas . Austronesians established prehistoric maritime trade networks in Island Southeast Asia, including

6072-523: The Progress M-34 spacecraft crashed into Spektr while doing an experimental docking maneuver with the Kvant-1 module. The collision damaged one of Spektr's solar arrays and punctured the hull, causing a relatively slow leak. The crew had enough time to install a hatch cover and seal the module off to prevent depressurization of the entire Mir station. To seal the module, the crew had to remove

6204-845: The Seleucid Empire . Parthia had many wars with the Romans, but it was rebellions within the empire that ended it in the 3rd century AD. The Sasanian Empire began when the Parthian Empire ended in AD 224. Their rulers claimed the Achaemenids as ancestors and set up their capital at Ctesiphon in Mesopotamia. Their period of greatest military expansion occurred under Shapur I , who by the time of his death in AD 272 had defeated Roman imperial armies and set up buffer states between

6336-713: The Stone Age , the Bronze Age , and the Iron Age , with recorded history generally considered to begin with the Bronze Age. The start and end of the three ages vary between world regions. In many regions the Bronze Age is generally considered to begin a few centuries prior to 3000 BC, while the end of the Iron Age varies from the early first millennium BC in some regions to the late first millennium AD in others. During

6468-496: The Zapotec civilization . The ancient Near East is considered the cradle of civilization . It was the first to practice intensive year-round agriculture; created one of the first coherent writing systems , invented the potter's wheel and then the vehicular wheel , created the first centralized governments , law codes and empires, as well as displaying social stratification , slavery, and organized warfare. It began

6600-444: The areas A {\displaystyle A} of the two different apertures. As an example, the light-gathering power of a 10-meter telescope is 25x that of a 2-meter telescope: p = A 1 A 2 = π 5 2 π 1 2 = 25 {\displaystyle p={\frac {A_{1}}{A_{2}}}={\frac {\pi 5^{2}}{\pi 1^{2}}}=25} For

6732-431: The objective (1) (the convex lens or concave mirror used to gather the incoming light), focuses that light from the distant object (4) to a focal plane where it forms a real image (5). This image may be recorded or viewed through an eyepiece (2), which acts like a magnifying glass . The eye (3) then sees an inverted, magnified virtual image (6) of the object. Most telescope designs produce an inverted image at

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6864-506: The 19th century, long-lasting aluminum coatings in the 20th century, segmented mirrors to allow larger diameters, and active optics to compensate for gravitational deformation. A mid-20th century innovation was catadioptric telescopes such as the Schmidt camera , which uses both a lens (corrector plate) and mirror as primary optical elements, mainly used for wide field imaging without spherical aberration. The late 20th century has seen

6996-575: The Assyrians, who conquered Israel in 722 BC. The Neo-Babylonian Empire did the same to Judah in 586. After both conquests, the conquering forces deported many of the inhabitants to other regions of their respective empires. Following the fall of Babylon to the Persian Empire, Cyrus the Great allowed the rebuilding of the temple at Jerusalem , and some of the exiles from Judah returned to Judea , where they remained under Persian rule until

7128-650: The Egyptians as a possible challenge to their hegemony , but an ethnic group rather than an organised state. Israel had emerged by the middle of the 9th century BC, when the Assyrian King Shalmaneser III named " Ahab the Israelite" among his enemies at the battle of Qarqar (853). Judah emerged somewhat later than Israel, probably during the 9th century BC, but the subject is one of considerable controversy. Israel came into conflict with

7260-518: The Fertile Crescent, alongside the first evidence for agriculture. Other animals, such as pigs and poultry , were later domesticated and used as food sources. Cattle and water buffalo were domesticated around 7000 BC and horses , donkeys , and camels were domesticated by about 4000 BC. All of these animals were used not only for food, but to carry and pull people and loads, greatly increasing human ability to do work. The invention of

7392-613: The Gupta rulers generally left administration in local rulers. The Gupta Empire was weakened and ultimately ruined by the raids of Hunas (a branch of the Hephthalites emanating from Central Asia), and the empire broke up into smaller regional kingdoms by the end of the fifth century AD. India would remain fragmented into smaller states until the rise of the Mughal Empire in the 1500s. The Neolithic period of Southeast Asia

7524-889: The Malayan-Indonesian " thalassian " zone shared these characteristics with Indochinese polities like the Pyu city-states in the Irrawaddy River valley, the Văn Lang kingdom in the Red River Delta and Funan around the lower Mekong . Văn Lang, founded in the 7th century BCE, endured until 258 BCE under the Hồng Bàng dynasty , as part of the Đông Sơn culture that sustained a dense and organised population that produced an elaborate Bronze Age industry. Intensive wet-rice cultivation in an ideal climate enabled

7656-768: The Middle East. Egypt developed its own system of hieroglyphs by about 3200 BC. By 2800 BC the Indus Valley Civilization had developed its Indus script , which remains undeciphered. Chinese Characters were independently developed in China during the Shang dynasty in the form of the Oracle Bone Script dating to the period 1600 to 1100 BC. Writing in Mesoamerica dates to 600 BC with

7788-516: The Moon in a 550 nm wavelength , is given by: F = 2 R D ⋅ D o b ⋅ Φ D a = 2 ⋅ 0.00055 130 ⋅ 3474.2 ⋅ 206265 1878 ≈ 3.22 {\displaystyle F={\frac {{\frac {2R}{D}}\cdot D_{ob}\cdot \Phi }{D_{a}}}={\frac {{\frac {2\cdot 0.00055}{130}}\cdot 3474.2\cdot 206265}{1878}}\approx 3.22} The unit used in

7920-588: The Nubians had created a new kingdom further south, known as the Kingdom of Kush , centred on the upper Nile with a capital at Kerma . In the Egyptian New Kingdom period, Kush once more was conquered by Egypt. However, by 1100 BC a new kingdom of Kush had formed, with a capital at Napata . Nubian rulers conquered Egypt around 760 BC and retained control for about a century. The Kingdom of Aksum

8052-653: The Pacific Islands to successfully retain rice cultivation. Palau and Yap were settled by separate voyages by 1000 BCE. Another important migration branch was by the Lapita culture , which rapidly spread into the islands off the coast of northern New Guinea and into the Solomon Islands and other parts of coastal New Guinea and Island Melanesia by 1200 BCE. They reached the islands of Fiji , Samoa , and Tonga by around 900 to 800 BCE. This remained

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8184-401: The Sasanians and Roman Empires. After Shapur, the Sasanians were under more pressure from the Kushans to their east as well as the Roman then Byzantine Empire to its west. However, the Sasanians rebuilt and founded numerous cities and their merchants traveled widely and introduced crops such as sugar, rice, and cotton into the Iranian plateau. But in AD 651, the last Sassanid emperor was killed by

8316-447: The Spektr and Priroda modules in exchange for having 600 to 700 kg of US experiments installed. The Oktava military component was replaced with a conical mounting area for two additional solar arrays. The airlock for the Oktava targets to be used instead to expose experiments to the vacuum of space. Once in orbit, Spektr served as the living quarters for American astronauts until the collision in late June 1997. On June 25, 1997,

8448-411: The Western Mediterranean until being defeated by Rome in the Punic Wars . The Phoenicians invented the Phoenician alphabet , the forerunner of the modern alphabet still in use today. The history of Pre-Islamic Arabia before the rise of Islam in the AD 630s is not known in great detail. Archaeological exploration in the Arabian Peninsula has been sparse; indigenous written sources are limited to

8580-492: The ability of their military forces to be deployed rapidly. Increased trade and upgraded farming techniques increased wealth, but also exacerbated inequalities between social classes. The empire's location at the centre of trading networks spread its intellectual and philosophical ideas throughout a wide area, and its religion, while not itself spreading far, had an impact on later religions such as Christianity , Islam , and Judaism . Cyrus' son Cambyses II conquered Egypt, while

8712-433: The archipelago of the Philippines , intermingling with the earlier Australo-Melanesian population who had inhabited the islands since about 23,000 years earlier. Over the next thousand years, Austronesian peoples migrated southeast to the rest of the Philippines, and into the islands of the Celebes Sea and Borneo. From southwestern Borneo, Austronesians spread further west in a single migration event to both Sumatra and

8844-426: The bright cores of active galaxies . The focal length of an optical system is a measure of how strongly the system converges or diverges light . For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more strongly, bringing them to

8976-399: The cables that were routed through the (open) hatchway, including the power cables from Spektr's solar panels. An internal spacewalk in the Spektr module in August 1997 by cosmonauts Anatoly Solovyov and Pavel Vinogradov , from Soyuz TM-26 , succeeded in restoring these power connections by installing a modified hatch cover to allow the power cables to pass through the hatch when it was in

9108-406: The capital of the Akkadian Empire. Despite an extensive search, the precise site has never been found. Akkad reached the height of its power between about 2330 and 2150 BC, following the conquests of King Sargon of Akkad . Through the spread of Sargon's empire, the language of Akkad, known as Akkadian from the city, spread and replaced the Sumerian language in Mesopotamia and eventually by 1450 BC

9240-461: The captured light gets into the eye. The minimum   M m i n   {\displaystyle \ M_{\mathsf {min}}\ } can be calculated by dividing the telescope aperture   D   {\displaystyle \ D\ } over the largest tolerated exit pupil diameter   d e p   . {\displaystyle \ d_{\mathsf {ep}}~.} Decreasing

9372-407: The casting of iron with molds and then hammering it which enabled weapons and tools to be made stronger and also cheaper. Although chariots had been used previously, the use of spoked wheels allowed the chariots to be much lighter and more maneuverable. In 1274 BC the Hittites clashed with the Egyptians at the Battle of Kadesh , where both sides claimed victory. In 1207 the Hittite capital of Hattusa

9504-597: The closed position. In a second internal spacewalk in October they connected two of the panels to a computer system to allow the panels to be controlled remotely and align with the Sun. These modifications allowed power generation to return to approximately 70% of the pre-collision generation capability. Spektr was left depressurized and isolated from the remainder of the Mir complex. Optical telescope An optical telescope

9636-614: The coastal regions of southern Vietnam, becoming the ancestors of the speakers of the Malayic and Chamic branches of the Austronesian language family. Soon after reaching the Philippines, Austronesians colonized the Northern Mariana Islands by 1500 BCE or even earlier, becoming the first humans to reach Remote Oceania . The Chamorro migration was also unique in that it was the only Austronesian migration to

9768-402: The constant Φ {\displaystyle \Phi } all divided by the objects apparent diameter D a {\displaystyle D_{a}} . Resolving power R {\displaystyle R} is derived from the wavelength λ {\displaystyle {\lambda }} using the same unit as aperture; where 550 nm to mm

9900-496: The development of adaptive optics and space telescopes to overcome the problems of astronomical seeing . The electronics revolution of the early 21st century led to the development of computer-connected telescopes in the 2010s that allow non-professional skywatchers to observe stars and satellites using relatively low-cost equipment by taking advantage of digital astrophotographic techniques developed by professional astronomers over previous decades. An electronic connection to

10032-538: The empire was Aksum , now in northern Ethiopia. The Nok culture appeared in Nigeria around 1000 BC and mysteriously vanished around AD 200. The civilisation's social system is thought to have been highly advanced. The Nok civilisation was considered to be the earliest sub-Saharan producer of life-sized Terracotta which have been discovered by archaeologists. The Nok also used iron smelting that may have been independently developed. The civilisation of Djenné-Djenno

10164-498: The entire territory. Among large, thin-walled terracotta jars, ornamented and colorized cooking pots, glass items, jade earrings and metal objects were deposited near the rivers and along the coast. Around 3000 to 1500 BCE, a large-scale migration of Austronesians , known as the Austronesian expansion began from Taiwan . Population growth primarily fueled this migration. These first settlers settled in northern Luzon , in

10296-486: The expanding Islamic Arabs. The Hittites first came to Anatolia about 1900 BC and during the period 1600-1500 they expanded into Mesopotamia where they adopted the cuneiform script to their Indo-European language. By 1200 their empire stretched to Phoenicia and eastern Anatolia . They improved two earlier technologies from Mesopotamia and spread these new techniques widely – improved iron working and light chariots with spoked wheels in warfare. The Hittites introduced

10428-446: The eyepiece exit pupil,   d e p   , {\displaystyle \ d_{\mathsf {ep}}\ ,} no larger than the pupil of the observer's own eye. The formula for the eypiece exit pupil is where   D   {\displaystyle \ D\ } is the light-collecting diameter of the telescope's aperture. Dark-adapted pupil sizes range from 8–9 mm for young children, to

10560-439: The eyepiece-telescope combination: where   L   {\displaystyle \ L\ } is the focal length of the telescope and   ℓ   {\displaystyle \ \ell \ } is the focal length of the eyepiece. Ideally, the exit pupil of the eyepiece,   d e p   , {\displaystyle \ d_{\mathsf {ep}}\ ,} matches

10692-521: The farming communities to produce a regular crop surplus that was used by the ruling elite to raise, command and pay work forces for public construction and maintenance projects such as canals and fortifications. The earliest known evidence of copper and bronze production in Southeast Asia was found at Ban Chiang in north-east Thailand and among the Phùng Nguyên culture of northern Vietnam around 2000 BCE. The Đông Sơn culture established

10824-440: The finest detail the instrument can resolve is magnified to match the finest detail the eye can see. Magnification beyond this maximum is sometimes called empty magnification . To get the most detail out of a telescope, it is critical to choose the right magnification for the object being observed. Some objects appear best at low power, some at high power, and many at a moderate magnification. There are two values for magnification,

10956-459: The first practical reflecting telescopes, the Newtonian telescope , in 1668 although due to their difficulty of construction and the poor performance of the speculum metal mirrors used it took over 100 years for reflectors to become popular. Many of the advances in reflecting telescopes included the perfection of parabolic mirror fabrication in the 18th century, silver coated glass mirrors in

11088-405: The focal plane; these are referred to as inverting telescopes . In fact, the image is both turned upside down and reversed left to right, so that altogether it is rotated by 180 degrees from the object orientation. In astronomical telescopes the rotated view is normally not corrected, since it does not affect how the telescope is used. However, a mirror diagonal is often used to place the eyepiece in

11220-687: The furthest extent of the Austronesian expansion into Polynesia until around 700 CE, when there was another surge of island colonization. It reached the Cook Islands , Tahiti , and the Marquesas by 700 CE; Hawaii by 900 CE; Rapa Nui by 1000 CE; and New Zealand by 1200 CE. For a few centuries, the Polynesian islands were connected by bidirectional long-distance sailing, with the exception of Rapa Nui, which had limited further contact due to its isolated geographical location. Island groups like

11352-500: The idea of building a telescope using a mirror as the image forming objective. The potential advantages of using parabolic mirrors (primarily a reduction of spherical aberration with elimination of chromatic aberration ) led to several proposed designs for reflecting telescopes, the most notable of which was published in 1663 by James Gregory and came to be called the Gregorian telescope , but no working models were built. Isaac Newton has been generally credited with constructing

11484-413: The image by turbulence in the atmosphere ( atmospheric seeing ) and optical imperfections of the telescope, the angular resolution of an optical telescope is determined by the diameter of the primary mirror or lens gathering the light (also termed its "aperture"). The Rayleigh criterion for the resolution limit α R {\displaystyle \alpha _{R}} (in radians )

11616-555: The land was reunited in the New Kingdom around 1550 BC. This period lasted until about 1000 BC, and saw Egypt expand its borders into Palestine and Syria. The Third Intermediate Period was marked by the rule of priests as well as the conquest of Egypt by Nubian kings and then later Assyria, Persia, and Macedonians. The Ta-Seti kingdom in Nubia to the south of Egypt was conquered by Egyptian rulers around 3100 BC, but by 2500 BC

11748-409: The larger the aperture, the better the angular resolution. The resolution is not given by the maximum magnification (or "power") of a telescope. Telescopes marketed by giving high values of the maximum power often deliver poor images. For large ground-based telescopes, the resolution is limited by atmospheric seeing . This limit can be overcome by placing the telescopes above the atmosphere, e.g., on

11880-494: The light), and its light-gathering power is related to the area of the objective. The larger the objective, the more light the telescope collects and the finer detail it resolves. People use optical telescopes (including monoculars and binoculars ) for outdoor activities such as observational astronomy , ornithology , pilotage , hunting and reconnaissance , as well as indoor/semi-outdoor activities such as watching performance arts and spectator sports . The telescope

12012-528: The longest recommended eyepiece focal length (   ℓ   {\displaystyle \ \ell \ } ) would be   ℓ =   L   M ≈   1   200   m m   36 ≈ 33   m m   . {\displaystyle \ \ell ={\frac {\ L\ }{M}}\approx {\frac {\ 1\ 200{\mathsf {\ mm\ }}}{36}}\approx 33{\mathsf {\ mm}}~.} An eyepiece of

12144-405: The magnification past this limit will not increase brightness nor improve clarity: Beyond this limit there is no benefit from lower magnification. Likewise calculating the exit pupil   d e p   {\displaystyle \ d_{\mathsf {ep}}\ } is a division of the aperture diameter   D   {\displaystyle \ D\ } and

12276-467: The many inscriptions and coins from southern Arabia. Existing material consists primarily of written sources from other traditions (such as Egyptians, Greeks, Persians, Romans, etc.) and oral traditions later recorded by Islamic scholars. A number of small kingdoms existed in Arabia from around AD 100 to perhaps about AD 400. Carthage was founded around 814 BC by Phoenician settlers. Ancient Carthage

12408-626: The most significant step cited in the invention of the telescope was the development of lens manufacture for spectacles , first in Venice and Florence in the thirteenth century, and later in the spectacle making centers in both the Netherlands and Germany. It is in the Netherlands in 1608 where the first documents describing a refracting optical telescope surfaced in the form of a patent filed by spectacle maker Hans Lippershey , followed

12540-445: The object diameter results in the smallest resolvable features at that unit. In the above example they are approximated in kilometers resulting in the smallest resolvable Moon craters being 3.22 km in diameter. The Hubble Space Telescope has a primary mirror aperture of 2400 mm that provides a surface resolvability of Moon craters being 174.9 meters in diameter, or sunspots of 7365.2 km in diameter. Ignoring blurring of

12672-403: The optical power of the telescope, its characteristic is the most misunderstood term used to describe the observable world. At higher magnifications the image quality significantly reduces, usage of a Barlow lens increases the effective focal length of an optical system—multiplies image quality reduction. Similar minor effects may be present when using star diagonals , as light travels through

12804-442: The organisation of collective projects such as the pyramids ; trade with surrounding regions; and a polytheistic religious tradition that included elaborate funeral customs including mummification . Overseeing these activities were a socio-political and economic elite under the figure of a (semi)-divine ruler from a succession of ruling dynasties . Ancient Egyptian history is divided across various periods, beginning with

12936-461: The physical area that can be resolved. A familiar way to express the characteristic is the resolvable ability of features such as Moon craters or Sun spots. Expression using the formula is given by twice the resolving power R {\displaystyle R} over aperture diameter D {\displaystyle D} multiplied by the objects diameter D o b {\displaystyle D_{ob}} multiplied by

13068-472: The population to settle in one place instead of migrating after crops and herds. It also allowed for a much greater population density, and in turn required an extensive labour force and division of labour. This organization led to the necessity of record keeping and the development of writing. Babylonia was an Amorite state in lower Mesopotamia (modern southern Iraq ), with Babylon as its capital. Babylonia emerged when Hammurabi created an empire out of

13200-424: The pupil of the observer's eye: If the exit pupil from the eyepiece is larger than the pupil of individual observer's eye, some of the light delivered from the telescope will be cut off. If the eyepiece exit pupil is the same or smaller than the pupil of the observer's eye, then all of the light collected by the telescope aperture will enter the eye, with lower magnification producing a brighter image, as long as all of

13332-543: The purpose of gathering more photons in a given time period than a slower system, allowing time lapsed photography to process the result faster. Wide-field telescopes (such as astrographs ), are used to track satellites and asteroids , for cosmic-ray research, and for astronomical surveys of the sky. It is more difficult to reduce optical aberrations in telescopes with low f-ratio than in telescopes with larger f-ratio. The light-gathering power of an optical telescope, also referred to as light grasp or aperture gain,

13464-567: The region in the former savannah of the Sahara. Its inhabitants fished and grew millet. It has been found that the Soninke of the Mandé peoples were responsible for constructing such settlements. Around 300 BC, the region became more desiccated and the settlements began to decline, most likely relocating to Koumbi Saleh. From the type of architecture and pottery, it is believed that Tichit was related to

13596-634: The region until the arrival of traders from Southwest Asia . However, sites such as Djenné-Djenno disprove this, as these traditions in West Africa flourished long before. Towns similar to that at Djenne-Jeno also developed at the site of Dia, also in Mali along the Niger River , from around 900 BC. Dhar Tichitt and Oualata were prominent among the early urban centres, dated to 2000 BC, in present-day Mauritania. About 500 stone settlements littered

13728-452: The resolution limit in arcseconds and D {\displaystyle D} is in millimeters. In the ideal case, the two components of a double star system can be discerned even if separated by slightly less than α R {\displaystyle \alpha _{R}} . This is taken into account by the Dawes limit The equation shows that, all else being equal,

13860-415: The same apparent field-of-view but longer focal-length will deliver a wider true field of view, but dimmer image. If the telescope has a central obstruction (e.g. a Newtonian , Maksutov , or Schmidt–Cassegrain telescope ) it is also likely that the low magnification will make the obstruction come into focus enough to make a black spot in the middle of the image. Ancient history Ancient history

13992-588: The same time period. Cultivation of millet, rice , and legumes began around 7000 BC in China . Taro cultivation in New Guinea dates to about 7000 BC also with squash cultivation in Mesoamerica perhaps sharing that date. Animal domestication began with the domestication of dogs , which dates to at least 15,000 years ago, and perhaps even earlier. Sheep and goats were domesticated around 9000 BC in

14124-684: The same time, southeastern Europe and Siberia around 40,000 years ago, and Japan about 30,000 years ago. Humans migrated to the Americas about 15,000 years ago. Evidence for agriculture emerges in about 9000 BC in what is now eastern Turkey and spread through the Fertile Crescent . Settlement at Göbekli Tepe began around 9500 BC and may have the world's oldest temple. The Nile River Valley has evidence of sorghum and millet cultivation starting around 8000 BC and agricultural use of yams in Western Africa perhaps dates to

14256-471: The simple plough by 6000 BC further increased agricultural efficiency. Metal use in the form of hammered copper items predates the discovery of smelting of copper ores , which happened around 6000 BC in western Asia and independently in eastern Asia before 2000 BC. Gold and silver use dates to between 6000 and 5000 BC. Alloy metallurgy began with bronze in about 3500 BC in Mesopotamia and

14388-736: The study of the stars and the sciences of astronomy and mathematics. Mesopotamia is the site of some of the earliest known civilisations in the world. Agricultural communities emerged in the area with the Halaf culture around 8000 BC and continued to expand through the Ubaid period around 6000 BC. Cities began in the Uruk period (4000–3100 BC) and expanded during the Jemdet Nasr (3100–2900 BC) and Early Dynastic (2900–2350 BC) periods. The surplus of storable foodstuffs created by this economy allowed

14520-439: The subsequent Ghana Empire. Old Jenne (Djenne) began to be settled around 300 BC, producing iron and with sizeable population, evidenced in crowded cemeteries. The inhabitants and creators of these settlements during these periods are thought to have been ancestors of the Soninke people. Peoples speaking precursors to the modern-day Bantu languages began to spread throughout southern Africa, and by 2000 BC they were expanding past

14652-561: The summits of high mountains, on balloons and high-flying airplanes, or in space . Resolution limits can also be overcome by adaptive optics , speckle imaging or lucky imaging for ground-based telescopes. Recently, it has become practical to perform aperture synthesis with arrays of optical telescopes. Very high resolution images can be obtained with groups of widely spaced smaller telescopes, linked together by carefully controlled optical paths, but these interferometers can only be used for imaging bright objects such as stars or measuring

14784-756: The system. The focal length controls the field of view of the instrument and the scale of the image that is presented at the focal plane to an eyepiece , film plate, or CCD . An example of a telescope with a focal length of 1200 mm and aperture diameter of 254 mm is given by: N = f D = 1200 254 ≈ 4.7 {\displaystyle N={\frac {f}{D}}={\frac {1200}{254}}\approx 4.7} Numerically large Focal ratios are said to be long or slow . Small numbers are short or fast . There are no sharp lines for determining when to use these terms, and an individual may consider their own standards of determination. Among contemporary astronomical telescopes, any telescope with

14916-401: The telescope's properties function, typically magnification , apparent field of view (FOV) and actual field of view. The smallest resolvable surface area of an object, as seen through an optical telescope, is the limited physical area that can be resolved. It is analogous to angular resolution , but differs in definition: instead of separation ability between point-light sources it refers to

15048-524: The territories of the former kingdoms of Sumer and Akkad . The Neo-Babylonian Empire , or Chaldea , was Babylonia from the 7th and 6th centuries BC. Under the reign of Nebuchadnezzar II , it conquered Jerusalem . This empire also created the Hanging Gardens of Babylon and the still-surviving Ishtar Gate as architectural embellishments of its capital at Babylon. Akkad was a city and its surrounding region near Babylon. Akkad also became

15180-517: The time period of ancient history, the world population was already exponentially increasing due to the Neolithic Revolution , which was in full progress. While in 10,000 BC, the world population stood at 2 million, it rose to 45 million by 3000 BC. By the Iron Age in 1000 BC, the population had risen to 72 million. By the end of the ancient period in AD 500, the world population is thought to have stood at 209 million. In 10,500 years,

15312-568: The use of fire has been dated as early as 1.8 million years ago, a date which is contested, with generally accepted evidence for the controlled use of fire dating to 780,000 years ago. Actual use of hearths first appears 400,000 years ago. Dates for the emergence of Homo sapiens (modern humans) range from 250,000 to 160,000 years ago, with the varying dates being based on DNA studies and fossils respectively. Some 50,000 years ago, Homo sapiens migrated out of Africa . They reached Australia about 45,000 years ago, southwestern Europe about

15444-408: The use of opthamalogic drugs cannot restore lost pupil size. Most observers' eyes instantly respond to darkness by widening the pupil to almost its maximum, although complete adaption to night vision generally takes at least a half-hour. (There is usually a slight extra widening of the pupil the longer the pupil remains dilated / relaxed.) The improvement in brightness with reduced magnification has

15576-415: The visual magnification   M   {\displaystyle \ M\ } used. The minimum often may not be reachable with some telescopes, a telescope with a very long focal length may require a longer focal length eyepiece than is available. An example of the lowest usable magnification using a fairly common 10″ (254 mm) aperture and the standard adult 7 mm maximum exit pupil

15708-569: The world population increased by 100 times. Prehistory is the period before written history. Most of our knowledge of that period comes from the work of archaeologists. Prehistory is often known as the Stone Age , and is divided into the Paleolithic (earliest), Mesolithic , and Neolithic . The early human migrations in the Lower Paleolithic saw Homo erectus spread across Eurasia 1.8 million years ago. Evidence for

15840-540: Was Washukanni , whose precise location has not been determined by archaeologists. The Medes and Persians were peoples who had appeared in the Iranian plateau around 1500 BC. Both peoples spoke Indo-European languages and were mostly pastoralists with a tradition of horse archery. The Medes established their own Median Empire by the 6th century BC, having defeated the Neo-Assyrian Empire with

15972-535: Was a city-state that ruled an empire through alliances and trade influence that stretched throughout North Africa and modern Spain . At the height of the city's influence, its empire included most of the western Mediterranean. The empire was in a constant state of struggle with the Roman Republic , which led to a series of conflicts known as the Punic Wars . After the third and final Punic War , Carthage

16104-512: Was an experimental optical telescope code-named "Pion” ( Peony ). Instrument list: These experiments would have been a continuation of the research aboard a top-secret TKS-M module, which docked to Salyut 7 in 1985. However, with the end of the Cold War and the shrinking of Russia's space budget, the module was stuck on the ground. In the mid-1990s with the return of US-Russian cooperation in space, NASA agreed to provide funds to complete

16236-492: Was an important trading nation in northeastern Africa centered in present-day Eritrea and northern Ethiopia , it existed from approximately AD 100 to 940, growing from the Iron Age proto-Aksumite period around the 4th century BC to achieve prominence by the 1st century AD. The Kingdom of Aksum at its height by the early 6th-century AD extended through much of modern Ethiopia and across the Red Sea to Arabia. The capital city of

16368-445: Was characterized by several migrations into Mainland and Island Southeast Asia from southern China by Austronesian , Austroasiatic , Kra-Dai and Hmong-Mien -speakers. Territorial principalities in both Insular and Mainland Southeast Asia, characterized as "agrarian kingdoms", developed an economy by around 500 BCE based on surplus crop cultivation and moderate coastal trade of domestic natural products. Several states of

16500-541: Was destroyed and then occupied by Roman forces. Nearly all of the territory held by Carthage fell into Roman hands. Ancient Egypt was a long-lived civilisation geographically located in north-eastern Africa. It was concentrated along the middle to lower reaches of the Nile River, reaching its greatest extent during the 2nd millennium BC, which is referred to as the New Kingdom period. It reached broadly from

16632-455: Was developed independent of Chinese or Indian influence. Historians relate these achievements to the presence of organized, centralized and hierarchical communities and a large population. Between 1000 BCE and 100 CE, the Sa Huỳnh culture flourished along the south-central coast of Vietnam . Ceramic jar burial sites that included grave goods have been discovered at various sites along

16764-720: Was developed independently in China by 2000 BC. Pottery developed independently throughout the world, with fired pots appearing first among the Jomon of Japan and in West Africa at Mali . Sometime between 5000 and 4000 BC the potter's wheel was invented. By 3000 BC, the pottery wheel was adapted into wheeled vehicles which could be used to carry loads further and easier than with human or animal power alone. Writing developed separately in five different locations in human history: Mesopotamia, Egypt, India, China, and Mesoamerica. By 3400 BC, "proto-literate" cuneiform spread in

16896-421: Was evolving into Hinduism , which spread throughout Southeast Asia. Siddhartha Gautama , born around 560 BC in northern India, went on to found a new religion based on his ascetic life – Buddhism . This faith also spread throughout Eastern and Southeastern Asia after his death. This period also saw the composition of the epics Ramayana and Mahabharata . The kingdom of Magadha rose to prominence under

17028-524: Was located in the Niger River Valley in the country of Mali and is considered to be among the oldest urbanized centers and the best-known archaeology site in sub-Saharan Africa . This archaeological site is located about 3 kilometers (1.9 miles) away from the modern town and is believed to have been involved in long-distance trade and possibly the domestication of African rice. The site is believed to exceed 33 hectares (82 acres); however, this

17160-512: Was ruled by the Seleucid dynasty . Parthia was an Iranian civilisation situated in the northeastern part of modern Iran. Their power was based on a combination of military power based on heavy cavalry with a decentralised governing structure based on a federated system . The Parthian Empire was led by the Arsacid dynasty , which by around 155 BC under Mithradates I had mostly conquered

17292-682: Was sacked, ending the Hittite Empire . Israel and Judah were related Iron Age kingdoms of the ancient Levant and had existed during the Iron Ages and the Neo-Babylonian, Persian and Hellenistic periods. The name Israel first appears in the stele of the Egyptian pharaoh Merneptah around 1209 BC. This "Israel" was a cultural and probably political entity of the central highlands, well enough established to be perceived by

17424-634: Was the main language of diplomacy in the Near East. Assyria was originally a region on the Upper Tigris , where a small state was created in the 19th century BC. The capital was at Assur , which gave the state its name. Later, as a nation and empire that came to control all of the Fertile Crescent, Egypt and much of Anatolia , the term "Assyria proper" referred to roughly the northern half of Mesopotamia (the southern half being Babylonia), with Nineveh as its capital. The Assyrian kings controlled

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