cyanic-selkie/wikianc huggingface dataset:
Agbègbè Ìjọba Ìbílẹ̀ Oye
Agbègbè ìjọba ìbílẹ̀ Ọyẹ́ ń pín ààlà pẹ̀lú agbègbè ìjọba ìbílẹ̀ Ilejemeje sí apá Àríwa, Irepodun/Ifelodun sí apá Gúúsù,agbègbè Ìkọ̀lé sí apá ìlà-oòrùn àti agbègbè Ido/Osi sí apá Ìwọ̀-oòrùn.
KÒ sí ẹ̀yà kan ní agbègbè náà tó yàtọ̀ sí ẹ̀yà Yorùba. Gbogbo ará ìlú náà sì ń sọ èdè Yorùbá àti àwọn ẹ̀ka-èdè rẹ̀.
Jennifer Capriati
Jennifer Marie Capriati (ojoibi March 29, 1976, ni New York City) je agba tenis to je Eni Ipo Kinni Lagbaye tele.
Web browser
Web browser (ẹ̀rọ afọ̀nàhan Web, ètó ẹ̀rọ-ònkà ìsíwò ojúewé aláùntakùn).
A web browser is a software application which enables a user to display and interact with text, images, videos, music, games and other information typically located on a Web page at a website on the World Wide Web or a local area network. Text and images on a Web page can contain hyperlinks to other Web pages at the same or different website. Web browsers allow a user to quickly and easily access information provided on many Web pages at many websites by traversing these links. Web browsers format HTML information for display, so the appearance of a Web page may differ between browsers.
Some of the Web browsers currently available for personal computers include Internet Explorer, Mozilla Firefox, Safari, Netscape, Opera.[2], Avant Browser, Konqueror, Google Chrome, Flock, Arachne, Epiphany, K-Meleon and AOL Explorer. Web browsers are the most commonly used type of HTTP user agent. Although browsers are typically used to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or content in file systems. Contents [hide]
* 1 History * 2 Protocols and standards * 3 See also * 4 References
[edit] History
Main article: History of the web browser
The history of the web browser dates back to late 1980s when a variety technologies laid the foundation for the first web browser, the WorldWideWeb, by Tim Berners-Lee in 1991, which brought together a variety of existing and new software and hardware technologies.
Web browsers communicate with Web servers primarily using HTTP (hypertext transfer protocol) to fetch webpages. HTTP allows Web browsers to submit information to Web servers as well as fetch Web pages from them. The most commonly used HTTP is HTTP/1.1, which is fully defined in RFC 2616. HTTP/1.1 has its own required standards that Internet Explorer does not fully support, but most other current-generation Web browsers do.
STS-50
thumb|STS-50.
Agbègbè Ìjọba Ìbílẹ̀ Oyigbo
Agbegbe Ijoba Ibile Oyigbo je ijoba ibile ni Ipinle Rivers ni Naijiria. Ibujoko re wa ni Afam
Kadmium
Kadmium je ipilese elegbogi pelu ami-idamo Cd ati nomba atomu 48.
Àsìá ilẹ̀ Ántígúà àti Bàrbúdà
Àsìá ilẹ̀ Ántígúà àti Bàrbúdà
Funchal
Funchal je oluilu Madeira.
Lira Túrkì
thumb|Lira Turkey. je owonina ni orile-ede ni Europe.
São Gabriel
São Gabriel je ibile ilu ni ipinle Rio Grande do Sul, Brazil.
Ogun Abẹ́lé ilẹ̀ Lìbéríà
Ogun Abẹ́lé ilẹ̀ Lìbéríà le je:
Agbègbè Ìjọba Ìbílẹ̀ Paikoro
wa ni Naijiria
Agbègbè Ìjọba Ìbílẹ̀ Oyun
wa ni Naijiria
Àsìá ilẹ̀ Argẹntínà
Asà ilẹ̀ Argẹntínà
Dinar Sérbíà
thumb|Dinar Sebia. je owonina ni orile-ede ni Europe.
J. M. Coetzee
John Maxwell Coetzee (ojoibi 9 February 1940) je olukowe to gba Ebun Nobel ninu Litireso.
Franki Swítsàlandì
je owonina ni orile-ede ni Europe.
Umberto Eco
Umberto Eco,, (ojoibi Oṣù Kínní 5, 1932 - Oṣù Kejì 19, 2016) je olukowe ati amoye ara Italia to ko iwe aroso The Name of the Rose (Il nome della rosa, 1980).
Elfriede Jelinek
Elfriede Jelinek (ojoibi 20 October 1946) je olukowe ara Ostria to gba Ebun Nobel ninu Litireso ni 2004.
Ogun àgbáyé
Ogun àgbáyé ni a mo si ogun to kan ogunlogo awon orile-ede alagbara lagbaye, to si sele ni opo awon orílẹ̀ ati opolopo odun, to si fa iparun pupo.
Króna Fàróè
Àyọkà Ọ̀rọ̀ Àwòkà je owonina ni orile-ede ni Europe.
Agbègbè Ìjọba Ìbílẹ̀ Pankshin
Agbegbe Ijoba Ibile Pankshin je ijoba ibile ni Ipinle Plateau ni Naijiria. Ibujoko re wa ni Pankshin
John Cockcroft
John Douglas Cockcroft OM KCB CBE (27 May 1897 – 18 September 1967) je onimosayensi to gba Ebun Nobel ninu Fisiksi.
Alan S. Kaye
Alan S. Kaye
Kaye ti o je gbajugbaja onimo eda-ede ku ni 31/5/2007. Kaye ti sise ti o po lori ede Semitic. Ibi ti o ti n fi isinmi re se iwadii ni United Arab Emirate ni won ti ri i pe o ni kansa (Cancer) ni 1/5/2007 ti omo re, Jeremy Kaye, si gbe e wa si ile ni 22/5/2007.
Vilma Espin
Vilma Lucila Espín Guillois (tí a bí ní ọjọ́ keje oṣù kẹrin ọdún 1930 tí ó sì kú ní ọjọ́ kejìdínlógún oṣù kẹfà ọdún 2007) jẹ́ ọmọ ilẹ̀ Kuba bẹ́ẹ̀ sì ni ó tún jẹ́ ìyàwó Raul Kastro Ààrẹ ilẹ̀ Kuba. Ó kó ipa tí ó ṣe kókó nínú ìjà gbára ilé Cuba.
Harold Pinter
thumb|upright|Harold Pinter (1962) je olukowe to gba Ebun Nobel ninu Litireso.
Tsẹ́kì Olómìnira
thumb|[[Karlštejn|Karlštejn Castle in the Central Bohemian Region, founded in 1348 by Charles IV.]] thumb|[[Tábor, a town in the South Bohemian Region, founded in 1420 by the Hussites.]] thumb|[[Charles IV, Holy Roman Emperor|Charles IV, 1316 – 78, eleventh king of Bohemia. Charles IV was elected the Největší Čech (Greatest Czech) of all time. ]]
Kesium
Kesium tabi kaesium je apilese kemika pelu ami-idamo Cs ati nomba atomu 55.
Ernest Walton
je onimosayensi to gba Ebun Nobel ninu Fisiksi.
Àsìá ilẹ̀ Arméníà
je asia orile-ede Armenia.
Agbègbè Ìjọba Ìbílẹ̀ Patani
wa ni Naijiria
Àsìá ilẹ̀ Yerevan
thumb Àsìá ilẹ̀
Agbègbè Ìjọba Ìbílẹ̀ Pategi
wa ni Naijiria
Orhan Pamuk
thumb|right je olukowe to gba Ebun Nobel ninu Litireso.
Barium
Báríọ́mù jẹ́ ìpilẹ̀ṣẹ̀ kẹ́míkà. Ó ní àmì-ìdánimọ̀ Bá, nọ́mbà átọ́ọ́mù rẹ̀ jẹ́ mẹ́rìndínlọ́gọ́ta (56), nítorí òun ni ìpilẹ̀ṣẹ̀ karùn ún ní ipò kejì nínú kẹ́míkà atọ́ọ́mù.
Ponun Jersey
thumb|right|250px|1/13 shilling Ejò owo, 1851. je owonina ni orile-ede ni Europe.
Douala
Douala ni ilu titobijulo ni orile-ede Kameroon ati oluilu Littoral Province ni Kameroon.
Felix Bloch
je onimosayensi to gba Ebun Nobel ninu Fisiksi.
Àkójọ àwọn ogun abẹ́lé
Contemporary civil wars
The following civil wars are ongoing or ended in the past decade,. Some of them may be classified as insurrections, etc., rather than full civil wars, as they fade into the past.
Tẹ́lískópù Òfurufú Hubble
Tẹ́lískópù Òfurufú Hubble tabi Agbéwọ̀ọ́kán Òfurufú Hubble (Hubble Space Telescope; HST tabi TOH) je teliskopu ofurufu kan to je gbigbe lo sinu onaayipo pelu Oko Alobo kan ni 1990, to si wa nibe latigba na. O je teliskopu to ni enu-iwole imole 2.4 m, o si wa ni onaayipo isale Aye, awon irinse mererin pataki Hubble le sakiyesi ni itanka eti inuaro, alafojuri, ati eti inupupa. Teliskopu na je sisoloruko fun atorawo Edwin Hubble.
Ona-ayipo Hubble to wa niwaju ibi idilona ojuayika Aye gba laaye lati ya awon aworan to han kedere lai si ina eyin. Aworan Papa Ijin De le Hubble, fun apere lo je aworan afojuri ina to kunrere julo fun ohun to jinna to je yiya ni foto ni agbala aye. Opo awon akiyesi Hubble ti fa ojutu isoro ninu sayensi fisiksionirawo, bi sise bi agbala aye se unfe si gerege.
Bo tilejepe ki se teliskopu ofurufu akoko, Hubble je ikan ninu awon to tobijulo ati to se e mulo fun orisirisi ise, ati ohun iwadi to se pataki ati ohun ibasepo igboro fun itorawo. TOH je kiko latowo ile-ise eto ofurufu Amerika NASA, pelu ifikun latodo Ile-ise Ofurufu Europe, o si unje mimusise latowo Space Telescope Science Institute. Teliskopu na je ikan ninu awon Ibi Isakiyesi Gbangba ti NASA, lapapo mo Compton Gamma Ray Observatory, Chandra X-ray Observatory, ati Teliskopu Ofurufu Spitzer.
Awon teliskopu ofurufu je dida laba lati odun 1923. Owo fun iko Hubble bere sini je kikojo ni ewadun 1970s, pelu ireti pe yio gbera ni 1983, sugbon o ku seyin nitori isoro isise, inawo ati ijamba Challenger. Nigba to gbeyin gbera ni 1990, awon onimo sayensi ri pe jigi iwaju re ko duro daada, eyi fa ko mo sise boseye. Iranlose se atunse eyi ni 1993.
Hubble ni teliskopu kan soso to je sise lati se atunse re ninu ofurufu latowo awon arinlofurufu. Larin 1993 ati 2002, iranlose merin se atunse, isodotun ati won se idipo awon sistemu ninu teliskopu na; iranlose karun je fifagile fun abo leyin ijamba Columbia. Sugbon leyin iforowero igboro to waye, oludari NASA Mike Griffin fase si iranlose atunse to gbeyin, eyi waye ni 2009. Ireti ni pe teliskopu na yio sise titi di 2014 o kereju. Eyi ti yio ropo re ni Teliskopu Ofurufu James Webb (JWST), eyi yio gbera ni 2018 tabi leyin igba yi.
Ìdámọ̀ràn àtí àwọn asíwájú
Ni 1923, Hermann Oberth — to je gbigba bi baba ise roketi ayeodeoni, lapapo mo Robert H. Goddard ati Konstantin Tsiolkovsky — setewejade Die Rakete zu den Planetenräumen ("Roketi sinu Ofurufu Planeti"; "The Rocket into Planetary Space"), to fenu ba bawo ni teliskopu se le je mu jijulo sinu ona-ayika Aye pelu roketi.
Itan Teliskopu Ofurufu Hubble se wa seyin de odun 1946, nigbati atorawo Lyman Spitzer ko iwe-ayoka kan to unje "Astronomical advantages of an extraterrestrial observatory" (Awon anfani itorawo ibi-isakiyesi ojuorun). Ninu re, o jiroro nipa awon anfan pataki meji ti ibi-isakiyesi to budo si ofurufu ni lori awon teliskopu to budo si ori ile. Akoko, igbehan onigun (ijinna kekerejulo nibi ti awon ohunkan se le e damo) yio je sisaropin lasan latowo igedakoja, kaka ko je latowo iji ni oju-ayika, to unje ki awon irawo o tan yinrinyinrin, to je mimo bi iwo latowo awon atorawo. Lasiko na awon teliskopu ibudo ori ile igbana ni igbehan ti ko din ju 0.5–1.0 arcseconds lo, ti a ba fiwe mo igbehan 0.05 arcsec ti igedakoja saropin yio ni fun teliskopu pelu jigi ti idakoja re je 2.5 m. Ekeji, teliskopu ibudo ofurufu le sakiyesi imole oninupupa ati oninuaro, ti won le sonu soju-ayika fun teliskopu ibudo ori ile.
Itorawo ibudo ofurufu ti bere diedie leyin Ogun Agbaye 2k, bi awon onimo sayensi se lo awon igbedide to ti waye ninu oroiseona rọ́kẹ̀tì. Ìgbàjá-àwọ̀ onínúaró àkọ́kọ́ ti Òrùn jẹ́ rírí ní 1946, NASA sì ṣègbéra Orbiting Solar Observatory (OSO) láti gba àwọn ìgbàjá UV, ìtànká-X (X-ray), àti ìtànká gamma ní 1962. Tẹ́lískópù ọ̀nà-àyípo òrùn kan jẹ́ gbígbérá ní 1962 látọwọ́ Ilẹ̀ọba Aṣọ̀kan bíi apá ètò òfurufú Ariel, bẹ́ẹ̀sìni ní 1966 NASA ṣègbéra ìránlọṣe Orbiting Astronomical Observatory (OAO) àkọ́kọ́. Bátìrì OAO-1 kùnà lẹ̀yìn ọjọ́ mẹ́ta, èyí fi òpin sí ìránlọṣe náà. OAO-2 tó rọ́pò rẹ̀ ṣe àkíyèsí onínúaró àwọn ìràwọ̀ àti gáláksì láti ìgbà ìgbéra rẹ̀ ní 1968 títí di 1972, èyí pẹ́ ju ọdún kan tí wọ́n gbèrò fun lọ.
Àwọn ìránlọṣe OSO àti OAO fihàn bí àwọn àkíyèsí ibùdó òfurufú ṣe ṣe pàtàkì sí nínú ìtòràwọ̀, bó sì ṣe di 1968, NASA ṣàgbédìde àwọn ètò gidi fún tẹ́lískópù alátànpadà pẹ̀lú jígí tí ìdákọjá rẹ̀ jẹ́ 3 m, tó jẹ́ mímọ̀ nígbà náà bíi Large Orbiting Telescope tàbí Large Space Telescope (LST), tí yíò gbéra ní 1979. Awon eto yi tenumo bi o se se pataki fun awon iranlose itoju pelu awon eniyan lo si teliskopu na lati ri pe iru eto alewo na ni emi ojo pipe, besini igbedide lasiko kanna eto fun and the concurrent development of plans for the reusable oko alobo alatunmulo fihan pe oroiseona ti yio gba eyi laye ko ni pe waye.
Ìpèsè owó fún kíkọ́ rẹ̀
Ni 1974, Kongresi jawo inawo fun eto teliskopu na. Nitorie opo awon atorawo bere ipade pelu awon asoju ati alagba asofin lati ri pe owo ko ja lori igbedidide re. Nigbeyin Kongresi pinu lati da inawo re si abo.
Nitori aito owo lo fa ti European Space Agency se pinu lati pese owo ati irinse fun teliskopu na, ati batiri olorun ti yio fun ni agbara, ati awon osise lati sise lori teliskopu na ni Amerika, fun eyi won yio fun awon atorawo ara Europe ni 15% asiko isakiyesi lori teliskopu na. Nigbeyin Kongresi fi ase si ipese owo to to US$36,000,000 fun 1978, be sini iyaeto LST bere, pelu ero lati gbera ni 1983. Ni 1983 teliskopu na je sisoloruko fun Edwin Hubble, eni to sewari ikan ninu awon awari sayensi orundun 20k nigbato sawari pe agbala aye unfesi.
Ìkọ́ àti iṣẹ́ẹ̀rọ
Leyin ti iseowo Teliskopu Ofurufu na ti gba ase, ise bere kiakia lori re, o si je pinpin larin opo awon ile-ise. Marshall Space Flight Center (MSFC) lo gba ase lati daeto, sagbedide ati ko teliskopu na, nigbati Goddard Space Flight Center gba ase isejanu apapo awon irinse sayensi ati gbongan ibi ikojanu ori ile fun iranlose na. MSFC gbe ise fun ile-ise isiseiriran Perkin-Elmer lati daeto ati ko Optical Telescope Assembly (OTA) ati Fine Guidance Sensors fun teliskopu na. Lockheed gba ise lati ko ati searomo oko-ofurufu ti teliskopu na yio duro si.
Optical Telescope Assembly (OTA)
Fun iworan, TOH unlo Cassegrain reflector ti afowoda Ritchey-Chrétien, bo se je fun opo awon teliskopu isise miran. Afowoda yi, pelu jigi atenikun meji (hyperbolic mirrors), gbajumo fun iseaworan todara lori ibi iriran to fe gidi, pelu ainianfani pe awon bi awon jigi na se ri soro lati da ati danwo. Jigi ati sistemu onitiworan ti teliskopu na ni ni won unso bi yio se sise daradara si, be sini won je fifowoda ni iye pato. Awon teliskopu onitiworan saba ni jigi to ti je didan to ni isegeege bi ti idamewa ibuiruila itanmole afojuri, sugbon Teliskopu Ofurufu yi unje lilo fun isakiyesi lati itanmole afojuri de oninuawoaro (ibu-iruila kere) be sini o gbodo ni diffraction limited pato lati le lo gbogbo anfani ti ayiko ofurufu pese. Nitori eyi, jigi re gbodo je didan de isegeere 10 nanometers, bi tabi 1/65 ibu-iruila itanmole awopupa. Ni apa ibu-iruila togun, OTA na je fifowoda pelu pe IR re yio sise boseye daada — fun apere, awon jigi ni igbonasi toduro laimi (won si loworo, bi 15 °C). Eyi fa ala si ise Hubble bi teliskopu oninuawopupa.
Perkin-Elmer intended to use custom-built and extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape. However, in case their cutting-edge technology ran into difficulties, NASA demanded that PE sub-contract to Kodak to construct a back-up mirror using traditional mirror-polishing techniques. (The team of Kodak and Itek also bid on the original mirror polishing work. Their bid called for the two companies to double-check each other's work, which would have almost certainly caught the polishing error that later caused such problems. ) The Kodak mirror is now on permanent display at the Smithsonian Institution. An Itek mirror built as part of the effort is now used in the 2.4 m telescope at the Magdalena Ridge Observatory.
Construction of the Perkin-Elmer mirror began in 1979, starting with a blank manufactured by Corning from their ultra-low expansion glass. To keep the mirror's weight to a minimum it consisted of inch-thick top and bottom plates sandwiching a honeycomb lattice. Perkin-Elmer simulated microgravity by supporting the mirror on both sides with 138 rods that exerted varying amounts of force. This ensured that the mirror's final shape would be correct and to specification when finally deployed. Mirror polishing continued until May 1981. NASA reports at the time questioned Perkin-Elmer's managerial structure, and the polishing began to slip behind schedule and over budget. To save money, NASA halted work on the back-up mirror and put the launch date of the telescope back to October 1984. The mirror was completed by the end of 1981; it was washed using 2,400 gallons (9,100 L) of hot, deionized water and then received a reflective coating of aluminum 65 nm-thick and a protective coating of magnesium fluoride 25 nm-thick.
Doubts continued to be expressed about Perkin-Elmer's competence on a project of this importance, as their budget and timescale for producing the rest of the OTA continued to inflate. In response to a schedule described as "unsettled and changing daily", NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer's schedules continued to slip at a rate of about one month per quarter, and at times delays reached one day for each day of work. NASA was forced to postpone the launch date until March and then September 1986. By this time, the total project budget had risen to US$1.175 billion.
Spacecraft systems
The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge. It would have to withstand frequent passages from direct sunlight into the darkness of Earth's shadow, which would cause major changes in temperature, while being stable enough to allow extremely accurate pointing of the telescope. A shroud of multi-layer insulation keeps the temperature within the telescope stable, and surrounds a light aluminum shell in which the telescope and instruments sit. Within the shell, a graphite-epoxy frame keeps the working parts of the telescope firmly aligned. Because graphite composites are hygroscopic, there was a risk that water vapor absorbed by the truss while in Lockheed's clean room would later be expressed in the vacuum of space; the telescope's instruments would be covered in ice. To reduce that risk, a nitrogen gas purge was performed before launching the telescope into space.
While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA, Lockheed still experienced some budget and schedule slippage, and by the summer of 1985, construction of the spacecraft was 30% over budget and three months behind schedule. An MSFC report said that Lockheed tended to rely on NASA directions rather than take their own initiative in the construction.
Initial instruments
When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). WF/PC was a high-resolution imaging device primarily intended for optical observations. It was built by NASA's Jet Propulsion Laboratory, and incorporated a set of 48 filters isolating spectral lines of particular astrophysical interest. The instrument contained eight charge-coupled device (CCD) chips divided between two cameras, each using four CCDs. Each CCD has a resolution of 0.64 megapixels. The "wide field camera" (WFC) covered a large angular field at the expense of resolution, while the "planetary camera" (PC) took images at a longer effective focal length than the WF chips, giving it a greater magnification.
The final instrument was the HSP, designed and built at the University of Wisconsin–Madison. It was optimized for visible and ultraviolet light observations of variable stars and other astronomical objects varying in brightness. It could take up to 100,000 measurements per second with a photometric accuracy of about 2% or better.
HST's guidance system can also be used as a scientific instrument. Its three Fine Guidance Sensors (FGS) are primarily used to keep the telescope accurately pointed during an observation, but can also be used to carry out extremely accurate astrometry; measurements accurate to within 0.0003 arcseconds have been achieved.
Ground support
The Space Telescope Science Institute (STScI) is responsible for the scientific operation of the telescope and delivery of data products to astronomers. STScI is operated by the Association of Universities for Research in Astronomy (AURA) and is physically located in Baltimore, Maryland on the Homewood campus of Johns Hopkins University, one of the 33 US universities and seven international affiliates that make up the AURA consortium. STScI was established in 1981 after something of a power struggle between NASA and the scientific community at large. NASA had wanted to keep this function "in-house", but scientists wanted it to be based in an academic establishment. The Space Telescope European Coordinating Facility (ST-ECF), established at Garching bei München near Munich in 1984, provides similar support for European astronomers.
One rather complex task that falls to STScI is scheduling observations for the telescope. Hubble is in a low-Earth orbit so that it can be reached by the space shuttle for servicing missions, but this means that most astronomical targets are occulted by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the South Atlantic Anomaly due to elevated radiation levels, and there are also sizable exclusion zones around the Sun (precluding observations of Mercury), Moon and Earth. The solar avoidance angle is about 50°, which is specified to keep sunlight from illuminating any part of the OTA. Earth and Moon avoidance is to keep bright light out of the FGSs and to keep scattered light from entering the instruments. If the FGSs are turned off, however, the Moon and Earth can be observed. Earth observations were used very early in the program to generate flat-fields for the WFPC1 instrument. There is a so-called continuous viewing zone (CVZ), at roughly 90 degrees to the plane of Hubble's orbit, in which targets are not occulted for long periods. Due to the precession of the orbit, the location of the CVZ moves slowly over a period of eight weeks. Because the limb of the Earth is always within about 30° of regions within the CVZ, the brightness of scattered earthshine may be elevated for long periods during CVZ observations.
Because Hubble orbits in the upper atmosphere, its orbit changes over time in a way that is not accurately predictable. The density of the upper atmosphere varies according to many factors, and this means that Hubble's predicted position for six weeks' time could be in error by up to 4,000 km. Observation schedules are typically finalized only a few days in advance, as a longer lead time would mean there was a chance that the target would be unobservable by the time it was due to be observed.
Engineering support for HST is provided by NASA and contractor personnel at the Goddard Space Flight Center in Greenbelt, Maryland, 48 km south of the STScI. Hubble's operation is monitored 24 hours per day by four teams of flight controllers who make up Hubble's Flight Operations Team.
Challenger disaster, delays, and eventual launch
By early 1986, the planned launch date of October that year looked feasible, but the Challenger accident brought the U.S. space program to a halt, grounding the space shuttle fleet and forcing the launch of Hubble to be postponed for several years. The telescope had to be kept in a clean room, powered up and purged with nitrogen, until a launch could be rescheduled. This costly situation (about $6 million per month) pushed the overall costs of the project even higher. This delay did allow time for engineers to perform extensive tests, swap out a possibly failure-prone battery, and make other improvements. Furthermore, the ground software needed to control Hubble was not ready in 1986, and in fact was barely ready by the 1990 launch.
Eventually, following the resumption of shuttle flights in 1988, the launch of the telescope was scheduled for 1990. On April 24, 1990, shuttle mission STS-31 saw Discovery launch the telescope successfully into its planned orbit.
Flawed mirror
Within weeks of the launch of the telescope, the returned images indicated a serious problem with the optical system. Although the first images appeared to be sharper than those of ground-based telescopes, Hubble failed to achieve a final sharp focus and the best image quality obtained was drastically lower than expected. Images of point sources spread out over a radius of more than one arcsecond, instead of having a point spread function (PSF) concentrated within a circle 0.1 arcsec in diameter as had been specified in the design criteria.
Analysis of the flawed images showed that the cause of the problem was that the primary mirror had been ground to the wrong shape. Although it was probably the most precisely figured mirror ever made, with variations from the prescribed curve of only 10 nanometers, at the perimeter it was too flat by about 2,200 nanometers (2.2 micrometres). This difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edge of a mirror focuses on a different point from the light reflecting off its center.
The effect of the mirror flaw on scientific observations depended on the particular observation—the core of the aberrated PSF was sharp enough to permit high-resolution observations of bright objects, and spectroscopy was largely unaffected. However, the loss of light to the large, out of focus halo severely reduced the usefulness of the telescope for faint objects or high-contrast imaging. This meant that nearly all of the cosmological programs were essentially impossible, since they required observation of exceptionally faint objects. NASA and the telescope became the butt of many jokes, and the project was popularly regarded as a white elephant. (For instance, in the 1991 comedy The Naked Gun 2½: The Smell of Fear, the Hubble was pictured with theTitanic, the Hindenburg, and the Edsel). Nonetheless, during the first three years of the Hubble mission, before the optical corrections, the telescope still carried out a large number of productive observations. The error was well characterized and stable, enabling astronomers to optimize the results obtained using sophisticated image processing techniques such as deconvolution.
Origin of the problem
A commission headed by Lew Allen, director of the Jet Propulsion Laboratory, was established to determine how the error could have arisen. The Allen Commission found that the main null corrector, a testing device used to achieve a properly shaped non-spherical mirror, had been incorrectly assembled—one lens was wrongly spaced by 1.3 mm. During the initial grinding and polishing of the mirror, Perkin-Elmer analyzed its surface with two conventional null correctors. However, for the final manufacturing step (figuring), they switched to a custom-built null corrector, designed explicitly to meet very strict tolerances. Ironically, this device was mis-assembled, resulting in an extremely precise (but wrong) shape for the mirror. There was one final opportunity to catch the error, since a few of the final tests needed to use conventional null correctors for various technical reasons. These tests correctly indicated spherical aberration. However, the company ignored these results, as it believed they were less accurate than the primary device which reported that the mirror was perfectly figured.
The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction, due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer did not review or supervise the mirror construction adequately, did not assign its best optical scientists to the project (as it had for the prototype), and in particular did not involve the optical designers in the construction and verification of the mirror. While the commission heavily criticized Perkin-Elmer for these managerial failings, NASA was also criticized for not picking up on the quality control shortcomings, such as relying totally on test results from a single instrument.
Design of a solution
The design of the telescope had always incorporated servicing missions, and astronomers immediately began to seek potential solutions to the problem that could be applied at the first servicing mission, scheduled for 1993. While Kodak and Itek had each ground back-up mirrors for Hubble, it would have been impossible to replace the mirror in orbit, and too expensive and time-consuming to bring the telescope back to Earth for a refit. Instead, the fact that the mirror had been ground so precisely to the wrong shape led to the design of new optical components with exactly the same error but in the opposite sense, to be added to the telescope at the servicing mission, effectively acting as "spectacles" to correct the spherical aberration.
Because of the way the HST's instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera 2, already planned to replace the existing WF/PC, included relay mirrors to direct light onto the eight separate CCD chips making up its two cameras. An inverse error built into their surfaces could completely cancel the aberration of the primary. However, the other instruments lacked any intermediate surfaces that could be figured in this way, and so required an external correction device.
The Corrective Optics Space Telescope Axial Replacement (COSTAR) system was designed to correct the spherical aberration for light focused at the FOC, FOS, and GHRS. It consists of two mirrors in the light path with one ground to correct the aberration. To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed. By 2002, all of the original instruments requiring COSTAR had been replaced by instruments with their own corrective optics. COSTAR was removed and returned to Earth in 2009 where it is exhibited at the National Air and Space Museum. The area previously used by COSTAR is now occupied by the Cosmic Origins Spectrograph.
Ìránlọṣe Ìṣàtúnṣe 1
After the problems with Hubble's mirror came to light, the first servicing mission assumed a much greater importance, as the astronauts would have to carry out extensive work on the telescope to install the corrective optics. The seven astronauts selected for the mission were trained intensively in the use of the hundred or more specialized tools that would be needed. SM1 flew aboard Endeavour in December 1993, and involved installation of several instruments and other equipment over 10 days.
Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WFPC was replaced with the Wide Field and Planetary Camera 2 (WFPC2) with its internal optical correction system. In addition, the solar arrays and their drive electronics were replaced, as well as four of the gyroscopes used in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded, and the telescope's orbit was boosted.
On January 13, 1994, NASA declared the mission a complete success and showed the first of many much sharper images. At the time, the mission was one of the most complex ever undertaken, involving five lengthy periods of extra-vehicular activity, and its resounding success was an enormous boon for NASA, as well as for the astronomers who now had a fully capable space telescope.
Ìránlọṣe Ìṣàtúnṣe 2
Servicing Mission 2, flown by Discovery in February 1997, replaced the GHRS and the FOS with the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replaced an Engineering and Science Tape Recorder with a new Solid State Recorder, and repaired thermal insulation. NICMOS contained a heat sink of solid nitrogen to reduce the thermal noise from the instrument, but shortly after it was installed, an unexpected thermal expansion resulted in part of the heat sink coming into contact with an optical baffle. This led to an increased warming rate for the instrument and reduced its original expected lifetime of 4.5 years to about 2 years.
Ìránlọṣe Ìṣàtúnṣe 3A
Servicing Mission 3A, flown by Discovery, took place in December 1999, and was a split-off from Servicing Mission 3 after three of the six onboard gyroscopes had failed. A fourth failed a few weeks before the mission, rendering the telescope incapable of performing scientific observations. The mission replaced all six gyroscopes, replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets. The new computer is 20 times faster, with six times more memory, than the DF-224 it replaced. It increases throughput by moving some computing tasks from the ground to the spacecraft, and saves money by allowing the use of modern programming languages.
Ìránlọṣe Ìṣàtúnṣe 3B
Servicing Mission 3B flown by Columbia in March 2002 saw the installation of a new instrument, with the FOC (the last original instrument) being replaced by theAdvanced Camera for Surveys (ACS). This meant that COSTAR was no longer required, since all new instruments had built-in correction for the main mirror aberration. The mission also revived NICMOS and replaced the solar arrays for the second time, providing 30 percent more power.
Ìránlọṣe Ìṣàtúnṣe 4
Plans called for Hubble to be serviced in February 2005, but the Columbia disaster in 2003, in which Columbia disintegrated on re-entry into the atmosphere, had wide-ranging effects on the Hubble program. NASA Administrator Sean O'Keefe decided that all future shuttle missions had to be able to reach the safe haven of the International Space Station should in-flight problems develop. As no shuttles were capable of reaching both HST and the ISS during the same mission, future manned service missions were canceled. This decision was assailed by numerous astronomers, who felt that Hubble was valuable enough to merit the human risk. HST's planned successor, the James Webb Telescope, is not expected to launch until at least 2018. A gap in space-observing capabilities between a decommissioning of Hubble and the commissioning of a successor is of major concern to many astronomers, given the significant scientific impact of HST. The consideration that JWST will not be located in low Earth orbit, and therefore cannot be easily upgraded or repaired in the event of an early failure, only makes these concerns more acute. On the other hand, many astronomers felt strongly that the servicing of Hubble should not take place if the expense were to come from the JWST budget.
In January 2004, O'Keefe said he would review his decision to cancel the final servicing mission to HST due to public outcry and requests from Congress for NASA to look for a way to save it. The National Academy of Sciences convened an official panel, which recommended in July 2004 that the HST should be preserved despite the apparent risks. Their report urged "NASA should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope". In August 2004, O'Keefe asked Goddard Space Flight Center to prepare a detailed proposal for a robotic service mission. These plans were later canceled, the robotic mission being described as "not feasible". In late 2004, several Congressional members, led by Senator Barbara Mikulski, held public hearings and carried on a fight with much public support (including thousands of letters from school children across the country) to get the Bush Administration and NASA to reconsider the decision to drop plans for a Hubble rescue mission.
The nomination in April 2005 of a new NASA Administrator, Michael D. Griffin, changed the situation, as Griffin stated he would consider a manned servicing mission. Soon after his appointment Griffin authorized Goddard to proceed with preparations for a manned Hubble maintenance flight, saying he would make the final decision after the next two shuttle missions. In October 2006 Griffin gave the final go-ahead, and the 11-day mission by Atlantis was scheduled for October 2008. Hubble's main data-handling unit failed in September 2008, halting all reporting of scientific data until its back-up was brought online on October 25, 2008. Since a failure of the backup unit would leave the HST helpless, the service mission was postponed to incorporate a replacement for the primary unit. Servicing Mission 4, flown by Atlantis in May 2009, was the last scheduled shuttle mission for HST. SM4 installed the replacement data-handling unit, repaired the ACS and STIS systems, installed improved nickel hydrogen batteries, and replaced other components. SM4 also installed two new observation instruments—Wide Field Camera 3 (WTF3) and the Cosmic Origins Spectrograph(COS) —and the Soft Capture and Rendezvous System, which will enable the future rendezvous, capture, and safe disposal of Hubble by either a crewed or robotic mission. The work accomplished during SM4 is expected to render the telescope fully functioning at least into the year 2014, and perhaps longer.
Iṣẹ́ọwọ́ oníkókó
In the early 1980s, NASA and STScI convened four panels to discuss Key Projects. These were projects that were both scientifically important and would require significant telescope time, which would be explicitly dedicated to each project. This guaranteed that these particular projects would be completed early, in case the telescope failed sooner than expected. The panels identified three such projects: (1) a study of the nearby intergalactic medium using quasar absorption lines to determine the properties of the intergalactic medium and the gaseous content of galaxies and groups of galaxies; (2) a medium deep survey using the Wide Field Camera to take data whenever one of the other instruments was being used and (3) a project to determine the Hubble Constant within ten percent by reducing the errors, both external and internal, in the calibration of the distance scale.
Àwọn àwárí pàtàkì
The Hubble has helped to resolve some long-standing problems in astronomy, as well as turning up results that have required new theories to explain them. Among its primary mission targets was to measure distances to Cepheid variable stars more accurately than ever before, and thus constrain the value of the Hubble constant, the measure of the rate at which the universe is expanding, which is also related to its age. Before the launch of HST, estimates of the Hubble constant typically had errors of up to 50%, but Hubble measurements of Cepheid variables in the Virgo Cluster and other distant galaxy clusters provided a measured value with an accuracy of ±10%, which is consistent with other more accurate measurements made since Hubble's launch using other techniques.
While Hubble helped to refine estimates of the age of the universe, it also cast doubt on theories about its future. Astronomers from the High-z Supernova Search Team and the Supernova Cosmology Project used the telescope to observe distant supernovae and uncovered evidence that, far from decelerating under the influence of gravity, the expansion of the universe may in fact be accelerating. This acceleration was later measured more accurately by other ground-based and space-based telescopes, confirming Hubble's finding. The cause of this acceleration remains poorly understood; the most common cause attributed is dark energy.
The high-resolution spectra and images provided by the HST have been especially well-suited to establishing the prevalence of black holes in the nuclei of nearby galaxies. While it had been hypothesized in the early 1960s that black holes would be found at the centers of some galaxies, and work in the 1980s identified a number of good black hole candidates, it fell to work conducted with Hubble to show that black holes are probably common to the centers of all galaxies. The Hubble programs further established that the masses of the nuclear black holes and properties of the galaxies are closely related. The legacy of the Hubble programs on black holes in galaxies is thus to demonstrate a deep connection between galaxies and their central black holes.
The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 was fortuitously timed for astronomers, coming just a few months after Servicing Mission 1 had restored Hubble's optical performance. Hubble images of the planet were sharper than any taken since the passage of Voyager 2 in 1979, and were crucial in studying the dynamics of the collision of a comet with Jupiter, an event believed to occur once every few centuries.
Other major discoveries made using Hubble data include proto-planetary disks (proplyds) in the Orion Nebula; evidence for the presence of extrasolar planets around sun-like stars; and the optical counterparts of the still-mysterious gamma ray bursts. HST has also been used to study objects in the outer reaches of the Solar System, including the dwarf planets Pluto and Eris.
A unique legacy of Hubble are the Hubble Deep Field, Hubble Ultra-Deep Field, and Hubble Extreme Deep Field images, which utilized Hubble's unmatched sensitivity at visible wavelengths to create images of small patches of sky that are the deepest ever obtained at optical wavelengths. The images reveal galaxies billions of light years away, and have generated a wealth of scientific papers, providing a new window on the early Universe.
Ipa lórí ìtòràwọ̀
Many objective measures show the positive impact of Hubble data on astronomy. Over 9,000 papers based on Hubble data have been published in peer-reviewed journals, and countless more have appeared in conference proceedings. Looking at papers several years after their publication, about one-third of all astronomy papers have no citations, while only 2% of papers based on Hubble data have no citations. On average, a paper based on Hubble data receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year that receive the most citations, about 10% are based on Hubble data.
Although the HST has clearly helped astronomical research, its financial cost has been large. A study on the relative astronomical benefits of different sizes of telescopes found that while papers based on HST data generate 15 times as many citations as a 4 m ground-based telescope such as the William Herschel Telescope, the HST costs about 100 times as much to build and maintain.
Deciding between building ground- versus space-based telescopes is complex. Even before Hubble was launched, specialized ground-based techniques such as aperture masking interferometry had obtained higher-resolution optical and infrared images than Hubble would achieve, though restricted to targets about 108 times brighter than the faintest targets observed by Hubble. Since then, advances in adaptive optics have extended the high-resolution imaging capabilities of ground-based telescopes to the infrared imaging of faint objects. The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can only correct a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wide field. Only a small fraction of astronomical objects are accessible to high-resolution ground-based imaging; in contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are extremely faint.
Usage
Anyone can apply for time on the telescope; there are no restrictions on nationality or academic affiliation. Competition for time on the telescope is intense, and only about one-fifth of the proposals submitted in each cycle earn time on the schedule.
Calls for proposals are issued roughly annually, with time allocated for a cycle lasting about one year. Proposals are divided into several categories; 'general observer' proposals are the most common, covering routine observations. 'Snapshot observations' are those in which targets require only 45 minutes or less of telescope time, including overheads such as acquiring the target; snapshot observations are used to fill in gaps in the telescope schedule that cannot be filled by regular GO programs.
Astronomers may make 'Target of Opportunity' proposals, in which observations are scheduled if a transient event covered by the proposal occurs during the scheduling cycle. In addition, up to 10% of the telescope time is designated Director's Discretionary (DD) Time. Astronomers can apply to use DD time at any time of year, and it is typically awarded for study of unexpected transient phenomena such as supernovae.
Other uses of DD time have included the observations that led to the production of the Hubble Deep Field and Hubble Ultra Deep Field, and in the first four cycles of telescope time, observations carried out by amateur astronomers.
Amateur observations
The first director of STScI, Riccardo Giacconi, announced in 1986 that he intended to devote some of his Director Discretionary time to allowing amateur astronomers to use the telescope. The total time to be allocated was only a few hours per cycle, but excited great interest among amateur astronomers.
20th anniversary
The Hubble Telescope celebrated its 20th anniversary in space on April 22, 2010. To commemorate the occasion, NASA, ESA, and Space Telescope Institute (STScI) released an image from the Carina Nebula.
Transmission to Earth
Hubble data was initially stored on the spacecraft. When launched, the storage facilities were old-fashioned reel-to-reel tape recorders, but these were replaced by solid state data storage facilities during servicing missions 2 and 3A. About twice daily, the Hubble Space Telescope radios data to a satellite in the geosynchronous Tracking and Data Relay Satellite System, which then downlinks the science data to one of two 60-foot (18-meter) diameter high-gain microwave antennas located at the White Sands Test Facility in White Sands, New Mexico. From there they are sent to the Space Telescope Operations Control Center at Goddard Space Flight Center, and finally to the Space Telescope Science Institute for archiving. Each week, HST downlinks approximately 120 gigabytes of data.
Archives
All Hubble data is eventually made available via the archives at STScI, CADC and ESO. Data is usually proprietary—available only to the principal investigator (PI) and astronomers designated by the PI—for one year after being taken. The PI can apply to the director of the STScI to extend or reduce the proprietary period in some circumstances.
Observations made on Director's Discretionary Time are exempt from the proprietary period, and are released to the public immediately. Calibration data such as flat fields and dark frames are also publicly available straight away. All data in the archive is in the FITS format, which is suitable for astronomical analysis but not for public use. The Hubble Heritage Project processes and releases to the public a small selection of the most striking images in JPEG and TIFF formats.