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AstronomyWorkshop

• Howtouseyourtelescope• Telescopedesigns• Howtochoosetherighttelescopeforyou• Accessoriesandtheiruse• Whatyouneedtoobserveortakepictures• Howtouseaplanisphere• Whatisinthenightskyeachmonth

YourFirstTelescope

• Astronomyisan immenselyrewardingadventure fullofexplorationanddiscovery.Planets,stars,nebulaeandgalaxiesareawaitingtoinspireyou.Buyingyourfirsttelescopeisnotalwayseasy.We’lltakealookatthefourmostcommontype’softelescopesandhowtheyworktogiveyouabetterideaofwhatmaybebestforyou.

Whoinventedthetelescope?

• GalileoGalilei• SirIssacNewton• Copernicus• HansLipperhey

GalileoGalilei

Dateofbirth:1564-02-15Dateofdeath:1642-01-08Birthplace:Pisa,DuchyofFlorence,Italy

Historyofthetelescope• Intheearly1600’sDutchlensgrinderHansLipperhey,appliedtopatentadevicetomakedistantobjectsappearcloser.Thuswasborntherefractortelescope.

• In1609GalileoGalileiheardthisdevicewasrealanddecidedtoimproveonthedesign.Thefirstdeviceswereonlyabout3xpowerbutGalileo’searlyattemptsgave8xpowerviewing.ThisiswherethefirstrealevidenceofmountainousregionsonthemoonwasobservedandalsowasresponsiblefordiscoveringJupiter’sfourmoonsknowtodayastheGalileanMoons.

WhocannamethefourGalileanMoons?

TheFourGalileanMoons

• IO

• CALLISTO

• EUROPA

• GANYMEDE

Galileo’stelescopedesigndesigned8x,20xandfinally30xpower

Re-creationofGalileo’stelescope

Today’sTelescopeDesigns

Lightpaths/optics

• http://www.stargazing.net/naa/scope2.htm

Reflecting/Refractorlightpaths

Refractordesign(Galilean)

SirIsaacNewton

Newtonian(SirIssacNewton)Reflectordesign

JohnDobsonTheDobsonianDesign

JohnDobsonJohnDobson in2002.

Born JohnLowryDobsonSeptember14,1915Beijing, China

Died January15,2014 (aged 98)Burbank,California, U.S.

Nationality AmericanOccupation Vedantan

monk (1944−1967),lecturer/popularizerof amateurastronomy[1]

Known for Dobsoniantelescope, sidewalkastronomy

Today’sDobsonianReflector

Schmidt-CassegrainDesignCatadioptric

Verycompactdesignwithlongfocallength

Whatarethepro’s andcon’s ofeachtelescopedesign

• Refractor• Pro’s Classicdesign,Noobstructions,goodcontrast,Nocollimation(usually),Nothermaldegradation.Excellentforimaging

• Con’s Expensiveperaperture,Largerscopesverylong,Chromaticaberrationinlessexpensivemodels.

Newtonian /Dobsonian

• Pro’s Inexpensivetomanufacture,largestaperture,nochromaticaberration,variousdesignsavailable,Dobsoniandesignaswell.

• Con’s Requirescollimation,opendesignrequiresmaintenance,verylargetohandleonmounts,mustchoosefocuserbasedonobservingorimaging,coma(imaging)

SchmidtCassegrain

• Pro’s Verycompact,verypracticalhandling,portable,viewingisalwayscomfortable,veryflexiblewithaccessories,setsupveryquickly(forkmount)Con’sCanbeveryexpensive,longcoolingtime,largerprimarymirror,requirescollimation(notasmuchasNewtonian)

Accessories foryourOTA

Eyepieces,diagonals,finderscopes,solarfilters

StarDiagonals

RequiredforrefractorsandSCT’sforviewcomfort

Whatisastardiagonal?• Mirror(reflective)diagonals: Thesediagonals(oftencalledStar

diagonals)usea mirror setata45° angleinsidethediagonaltoturnthetelescope’simageata90° angletotherearcell.Mirrordiagonalsproduceanimageinthe eyepiece thatiscorrectlyorientedvertically,butisreversedleft-to-righthorizontally.Thiscausesimagereversal,theviewintheeyepieceisflippedleft-right.Themajoradvantagetomirrordiagonals isthattheycostlesstoproducetoahighdegreeofopticalaccuracy comparedtoaprismandthattheydonotintroduceanycolorerrorstotheimage. Themajordisadvantageofmirrordiagonalsisthatunlessthereflectivecoatingisproperlyappliedtheycanscatterlightrenderinglowerimagecontrastcomparedtoa90-degreeprism.Alsotheydeterioratewithageasthereflectivesurfaceoxidizes.ThenewerDielectricmirrorshavelargelysolvedthedeteriorationproblem,andifproperlymadetheDielectricmirrorsscatterlesslightcomparedtoconventionalmirrors.

Thepathoflight

Allowsmuchmorecomfortableviews

Flexiblediagonals

Finderscopes

Eyepieces• WhatTypeofTelescopeEyepieceShouldYouBuy?

Whatsortofeyepiece,then,shouldyouuse?Acasualinspectionofmostpublicationsadvertisingopticalaccessorieswillrevealaplethoraoftypes— almostasmanyvarietiesastelescopes,itseems!Choosingtherightoneforyoudependsonseveralfactors:theobjectsyouwishtoobserve;howtolerantyouareofopticalimperfections;whetheryouwantnarroworwidefieldsofview;whetherornotyouwearglasses;and(asalways)howmuchyouarepreparedtospend.

WhichOne?????

EyepieceDesigns

• EyepieceTypes• Somenames,like Ultrawide,giveacluetoaneyepiece'sprincipalcharacteristics.OthershaveclassicnameslikeKellner,Orthoscopic,Plössl,andErfle,ormorespecificmodernvariantslikeNagler andLanthanum. Opticalaberrations (deviationsfromthe"ideal"form)arebettercorrectedinsomedesignsthanothers,butlikeeverythinginlife,thehighertheprice,thebetterthequality.

Costeffectiveeyepieces

• Evenso,eyepieceswithdesirablecharacteristicsstillcanbeobtainedatreasonablecostonceyouknowwhattolookfor.Atthebudgetendofthemarket,three-element(meaningtheyhavethreelensesinside)eyepieceslabeledKellneror"MA"(modifiedachromat)canturninagoodperformancewithscopesoflongfocalratio,suchasSchmidtCassegrainsandtraditionalrefractors.Theydonotworkwellwithtelescopesofshortfocalratio.

MeadeMA(modifiedachromats)

KellnerThe3-elementKellnergivessharp,bright imagesatlowtomediumpowers.Bestusedonsmalltomedium-sizetelescopes,Kellners haveapparentfieldsaround40degrees�andgoodeyerelief,thoughshortathigherpowers.Good, low-costperformerdesign.

Intermediateeyepieces• Foroptically"fast"Newtoniansandthelike,betterresultswillbeobtainedwithfour-elementdesigns,suchastheslightlyout-of-fashionbutotherwisedesirableOrthoscopic,orthePlössl.Thelatterisagoodall-rounder,particularlywhenantireflectionmulticoated.APlösslcandeliverwell-corrected,widefieldsofviewwithgoodeyerelief—meaningtheeyecanbepositionedatacomfortabledistancebehindtherearlensandstillseethewholefieldofview. Itisworthpointingoutthatobserverswhowearglassestocorrectforsimplelong- orshort-sightedness(noastigmatism)don'tneedtousethematthetelescope;atwistofthefocuserwillremedythat.

Plossl

PlosslToday'smostpopulardesign, the4-elementPlossl providesexcellentimagequality,goodeyerelief,andanapparentfieldofviewaround50degress�.High-qualityPlossls exhibithighcontrastandpinpoint sharpnessout totheedge.Idealforallobserving targets.

Premium/widefieldeyepieces• High-powerlunarandplanetaryviewingentailstheuseofshort-focal-lengtheyepieces.Thishasspawnedthedevelopmentofsix- toeight-elementdesignsthatcombinecomfortableeyereliefandwideapparentfields.Theymayfeatureexoticrare-earthglasselementstoreduceopticalaberrationsstillfurther.ManyregardtheseLanthanumandUltrawidedesignsasthepinnacleofeyepieceevolution,butformanypeoplethepricewillbeabarrier— andtheirphysicalsizeandweightmaybeanissuefordelicatelybalancedsmallscopes.

PremiumWideAngle

UltrawideTypesVariousimproveddesigns incorporating 6to8lenselementsboastapparentfieldsupto85-100degrees� - sowideyouhavetomoveyoureyearound totakeinthewholepanorama.Lighttransmission isslightlydiminished, butotherwise theimagequalityintheseeyepiecesisveryhigh.Sotooistheirprice.

CoatingsonLenses• OpticalcoatingsinlensesarealmostalwaysmadeofMagnesium

Flouride(MgFL).Theyareappliedinavacuumchamber.Asingleopticalcoatingshouldhaveaverysubtlebluecolorwhenyoulookatthelenssurfaceatanangle.Multi-Coatswillhaveagreenorevenpurpletintwhenyouexaminethesurface.

• Inall,thereareseveralacceptedclassificationsforopticalcoatings:

• Coatedmeansthatatleastoneair-to-glasssurfaceintheopticalsystemhasanopticalcoating.

• FullyCoatedmeansthatallair-to-glasssurfacesintheopticalsystemhaveanopticalcoating.

• Multi-Coatedmeansthatatleastoneair-to-glasssurfaceinthesystemhasanopticalmulti-coat.Therestshouldhaveatleastasingleopticalcoating.

• FullyMulti-Coatedmeansthatallair-to-glasssurfacesinthesystemhavemutli-coatings.

BarlowLenses

WhiletheBarlowisnotstrictlyaneyepiece,anenormouslyvaluableaccessory.ABarlowisinsertedintothetelescope'sfocuserbeforetheeyepieceanddoubles(ortriples,insomeinstances)themagnification.Attheexpenseofasmalllossoflight,thisveryusefuldevicecandoubleyoureyepieceinvestmentbymakingeachperformattwopowers.Givesomethoughttostaggeringthefocallengthssothattheyarenotsimplemultiplesofoneanother:a10mmeyepiece islargelyredundantifyouusea20mmandaBarlow.

Barlowlenses

• BarlowsSaveYouMoneyUsedwitha2xbarlow,your40mmeyepieceeffectivelybecomesa20mmeyepiece.Inatelescopewitha1000mmfocallength,the40mmeyepieceyields25xmagnificationaloneand50xmagnificationwhenusedwitha2xbarlow.A10mmeyepieceyields100xaloneand200xwithabarlow.Soabarlowlensessentiallydoublesthenumberofeyepiecesinyourcollection-agreatmoney-savingstrategy.

Whatdothenumbersmeanonmytelescope?

•SpecificationsoftheFirstscope80EQRefractor:Aperture 80mmFocalLength900mmFocalRatiof/11ComputerControl- no1.25"Eyepieces:FocalLengths20mmand10mmMagnificationLevels:90xand45xFinderscope:StarPointerTripod:AluminiumadjustableMount:equatorialWeight:24lbs.MulticoatedopticsCanbeusedforbothterrestrialandastronomicalviewing

Aperture• Aperture80mm

Thediameteroftheobjectivelensis80mm,whichis3.1inches.

• Theobjectivelensisthelargelensthatcaptureslightandfocusesitintoanimage.Thebiggertheobjective,themorelightthetelescopecangatherwhichinturnmeansthatfainterobjectscanbeobserved.Thesizeoftheobjectivedetermineswhatmagnificationthetelescopecanachievewithoutlosingresolution.Aquickruleofthumbis50timesthediameteroftheobjectiveininches.So,youcouldreasonablyexpectthistelescopetomagnifyimages~150times(50x3.1)beforeresolutionisaffected.

FocalLength

• FocalLengthThefocallengthisthefocallengthoftheobjective;thedistanceneededbytheobjectivetobringallthelightcollectedtoafocus.Soforthistelescope,animageisformed900mmfromtheobjectivelens.Youwillneedthisnumberwhenyouareworkingoutmagnification - moreonthisunder eyepieces .

FocalRatio• FocalRatiof/11Sometimesknownasthef/number.Focalratiosarethefocallengthdividedbythediameter,henceforthistelescope:900mm̧ 80mm=11,writtenasf/11.

• Aquickruleofthumbis:f/10andhigher:smallerfieldofview;goodforlookingatthemoon,planetsanddoublestarsf/8:intermediateandgoodforgeneralallroundviewingf/6andbelow:widerfieldofview;goodfordeepskyobjects

MagnificationFormula• Magnification• Themagnificationofanastronomicaltelescopechangeswiththeeyepieceused.Itiscalculatedbydividingthefocallengthofthetelescope(usuallymarkedontheopticaltube)bythefocallengthoftheeyepiece (bothinmillimeters).Thus:

• TELESCOPEFOCALLENGTH/OCULARFOCALLENGTH=MAGNIFICATION

• Forexample,atelescopewitha1000mmfocallengthusinga10mmocularisoperatingat100xmagnification(1000/10=100).

FocalRatio(F5,F7,F10ect)• FocalRatio(f/stop)• Thefocalratio,orf/stop,ofanylenssystem(includingtelescopes),iscomputedbydividingthefocallengthbytheclearaperture(usuallyexpressedinmillimeters).Inotherwords,thefocalratioistheratioofthefocallengthandclearaperture.Thus:

• TELESCOPEFOCALLENGTH/CLEARAPERTURE=FOCALRATIO

• Forexample,atelescopewithafocallengthof1000mmanda100mm(4")clearaperturehasafocalratiooff/10(1000/100=10).

FieldofViewFOVinDegrees

Whatdothenumbersmean?

KnowtheNumbersWhenshopping forabinocular, buyerswillfindbinocularsarecategorizedbyasetofnumbers, suchas 7x35mm;read"sevenbythirty-fivemillimeters."Otherbinocularsmightrangefromatiny3x14mmtogiantbattleshipbinocularsthatare40x178mm.Thesetwonumbers representmagnificationandobjectivelensdiameter.Thesetwoaspectsareimportanttounderstandwhenselectingbinoculars.

Binoculars

Magnification:

Consider thisgeneralruleaboutoptics:lowmagnificationprovidesawidefieldofviewandiseasytoholdsteady.Soalthoughamagnificationof10,12orhigher isavailable,6,7,and8-powerbinocularsareeasiertouseandinmanycasesmorepractical.

LensDiameter:Thesecondnumber ina7x35mmpairofbinoculars indicatesthelensdiameter.Thelensdetermineshowmuchlightisgathered,andthereforedetermines thebrightnessofviewing. Thebigger thelensmeansthegreaterthelightcapacity,andthebrighter theview.However,thebigger lensmeansabiggerandbulkierbinocular.Generally,lensesbelow30mmaredefinedasminibinoculars.

BinocularTypes• Therearefourmaintypesofbinoculars:twotypesofstandardsizesandtwotypesof

smallersizes.Understanding thesemaintypeswillhelpbuyerstonarrowtheirsearchtothetypebinocular thatfitstheirneeds,budget,andpreference.

• MiniBinoculars• Thesearethesmallestcategoryofbinoculars.Asdiscussedabove,thesegenerallyinclude

objectivelensesnotlargerthanabout1inchindiameter,andtheyhavethestraight-lineroofprismdesign.Minibinocularsaredesignedspecificallyfortravel,andthereforearefoldable, lightweight, andhighlyversatile.Becauseoftheirrelativelysmallobjectivelenses,minibinocularsaregenerallynotintendedforhigh-resolutionactivities,suchasbirdwatching.

• Compactbinoculars areslightlylargerthanminibinoculars,butsmallerthanregular size.ThesebinocularsutilizethePorroprism,whichmakesthembulkierthanminibinoculars,buttheystillhaveanobjectivelensthatisthesamesizeastheminiversion.Compactbinocularsarepopular forsporting eventsorasageneral-purpose travelbinocular.Compactsprovideagoodtrade-offbetweenweight,performance,andcost.

• StandardPorroPrismBinoculars• Thisiswheremoststandardbinocularsfall.Thesehavealargerobjectivelens,andarea

generalbinocularforuseineverything fromsportingeventstohuntingand aremoderatelypricedandhighquality,availableinawiderangeofspecifications.

• Thestandard RoofPrismbinoculars areamoreprofessional-levelbinocularforadvancedapplications,suchasforseriousbirdwatchers. Thesebinocularshaveasleek,straight-linestyle,thefinestopticalglasses,andmulti-elementeyepieces.Theyprovideabright,sharp,andhigh-resolutionimagethatishigherqualitythanotherbinoculars.

Planispheres

NowtheHandsOn!!

FirstStep:AlignFinderScopewithMainScope

• Step1:Setupscope• Step2:RemoveCover(lol)• Step3:Chooseastilltarget(ifstarusePolaris)• Step4:Selectlowpowereyepiece• Step5:Pointscopeattarget(centerinFOV)• Step6:Usingfinder,centertargetwithknobs• Step7:Lookthrougheyepieceforaccuracy• Step8:Usehigherpowereyepieceandrepeat

AcclimateYourScope

Whyaremyviewsblurry?•TUBECURRENTTubecurrentsaretemporaryaberrationsthatcansometimesbeagreatproblem.Coolingdownatelescope(totheoutsidetemperature)beforeaviewing-sessionshouldnotleavemuchroomforthisproblem.Sometelescopes(closedCatadioptrics,SCT/MCT)sometimesneedalongcooldownorevendon’treachequilibriumduetoafastcoolingfromevening-temperaturetonight-temperature.

Collimation

BalanceYourScope

WhydoIneedtoBalance

• BalancingtheTelescope:

ToeliminatestressesontheEquatorialmountsandtoensuresmooth,judder-freemotionofthetelescopetheinstrumentneedstobebalancedaboutboththedeclinationandpolar(rightascension)axis.Thisisespeciallyimportantifyouproposetouseamotordriveforastrophotographyatafuturedate.