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Astronomy n centerlineJoachim Wambsganssf Gravitational nquad Lensing in nquad Astronomy g Astrophysikalisches Institut Potsdam n centerlineAn der SternwartefJoachim 1 6 Wambsganss g 14482 Potsdam Gravitational Lensing in Astronomy n centerlineGermany f Astrophysikalisches InstitutJoachim Potsdam Wambsganssg jwambsganss at aip period de Astrophysikalisches Institut Potsdam n centerlinePublished 2f NovemberAn der Sternwarte 1 998 1 6 gAn der Sternwarte 1 6 open parenthesis Last Amended 31 August 200114482 closing Potsdam parenthesis n centerlineLiving Reviewsf14482 in Relativity Potsdam g Germany www period livingreviews period org slash Articlesjwambsganss slash Volume@ aip 1 . slash de 1 998 hyphen 12 wamb n centerlinePublished byfGermany the Max hypheng Planck hyphenPublished Institute 2 November for Gravitational 1 998 Physics A lbe r-t Einstein Institute comma Potsdam( Last comma Amended Germany 31 August 2001 ) n centerlineAbstract fjwambsganss $ @ $ aipLiving . de Reviewsg in Relativity Deflection of lightwww by gravity . livingreviews was predicted . org by General / Articles Relativity / Volume and 1 / 1 998 - 12 wamb n centerlineobservationallyf Published confirmedPublished in 2 1 November 9 1 9 by period the Max1 .. 998 In - Planck theg following - Institute decades for Gravitational comma various Physics as hyphen pects of the gravitational lens effectA lbe werer − exploredt Einstein theoretically Institute , Potsdam period .. , GermanyAmong n centerlinethem were :f ..( the Last possibility Amended of multiple 31 August or ring 2001 hyphenAbstract ) likeg images of background sources comma the use ofDeflection lensing as of a light gravitational by gravity telescope was predicted on very by General faint and Relativity and n centerlinedistant obj ectsf Living commaobservationally Reviews and the possibility in confirmed Relativity of in determining 1 9 1g 9 . 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Lookingperiod org at these slash telescope successes Inf o slash in on Copyright very faint slash period and g For permission to reproducethe the recent article past please we predict contact an livrev even more at aei luminous hyphen future potsdam for gravitational period mpg period de period n centerline f distant obj ects , and the possibilitylensing . of determining Hubble ' s constant with g circlecopyrt − c1998 Max - Planck - Gesellschaft and the authors . Further information on n centerlinecopyrightf l e n s i n is g given . nquad at httpIt : is / only / www relatively . l ivingreviews recently . org , n /quad Inf o( / after Copyright the discovery/ of the first g . For permission to reproduce the article please contact livrev @ aei - potsdam . mpg . de . n centerline f doubly imaged quasar in 1 9 79 ) , that gravitational lensing has became an g n centerline f observational science . Today lensing is a booming part of astrophysics . g n centerline f In addition to multiply − imaged quasars , a number of other aspects of g n centerline f lensing have been discovered : nquad For example , giant luminous arcs , quasar g n centerline f microlensing , nquad Einstein rings , nquad galactic microlensing events , nquad a r c l e t s , nquad and g n centerline fweak gravitational lensing . nquad At present , literally hundreds of individual g n centerline f gravitational lens phenomena are known . g n centerline fAlthough still in its childhood , lensing has established itself as a very g n centerline f useful astrophysical tool with some remarkable successes . nquad I t has con − g n centerline f tributed significant new results in areas as different as the cosmological g n centerline f distance scale , the large scale matter distribution in the universe , mass g n centerline fand mass distribution of galaxy clusters , the physics of quasars , dark mat − g n centerline f ter in galaxy halos , and galaxy structure . nquad Looking at these successes in g n centerline f the recent past we predict an even more luminous future for gravitational g n centerline f l e n s i n g . g nnoindent $ circlecopyrt −c 1 998 $ Max − Planck − Gesellschaft and the authors . Further information on copyright is given at http : / / www . l ivingreviews . org / Inf o / Copyright / . For permission to reproduce the article please contact livrev $ @ $ aei − potsdam . mpg . de . Article .. Amendments n centerline31 August 2001f A r .. t i Errata c l e nquad requestedAmendments by author andg minor editorial revision of reference list open parenthesis ref hyphen n beginerencef c numbers e n t e r g have changed closing parenthesis comma .. URLs 31updated August period 2001 nquad Errata requestedArticle by author Amendments and minor editorialCase 1 On author revision request of aLiving reference Reviews list article ( can ref be− amended to include errata Case 2 and small additions to ensure 31 August 2001 Errata requested by author and minor editorial revision of reference list ( thatnend thef c e most n t e r accurateg and up hyphen to hyphen date infor hyphen Case 3 mation possible is provided period For detailed ref - documentation of amendments comma Case 4 please go to the article s online version at Case 5 http : slash slash www period l nnoindent erence numbers have changed ) , nquad URLs ivingreviews perioderence org numbers slash Arti have c changed le s slash ) Vol , e URLs 1 slash updated 1 998 hyphen . 1 2 w m-a b slash period Case 6 Owing to the fact that aupdated Living Reviews . article can evolve over t ime comma we Case 7 recommend to cite the article as follows : Case 8 Wambsganss comma J period comma Case 9 Gravitational Lensing in Astronomy comma Case 10 Living Rev period Relativity comma 1 comman [ n l e f open t .quotedblleft parenthesis 1 998−quoteright closing parenthesis−quoteright comma− 1u 2− periodm−quotedblright open square bracket−hyphen OnlineOnauthorrequestan begin Articlef a l closing i g n eLivingReviews d squareg & bracket On articlecanbeamendedtoincludeerrata author request a Living Reviews article can be amended to include errata nn : cited on less date greater comma Case 11 http : slash slash www period livingreviews