How to Use Your Telescope

8/3/2019 How to Use Your Telescope

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JUPITERBIGJUPE IS "THE EASIE.STPLANET TO SEE.--AWJAYSBRlGl- ITE.~THAN -I Y z MAG.tll$ FOU~ 8RIGmEST MOONSO f MA6.6 ~IUnLf B A c K A N Dt:O R TH ,CH AN 6IN G N I6 HT L Y

ONE OUT OF 15 STARS IS ADOUBLE OR MULTIPLE STARAND A60UT 500 OF THESEFROM 2. SECONDS TO I M IN UT EOFARc ~EPARATION CAN SE'S PL IT "W IT H S MA LL T E L E S C O P E S

PLANETARY NEBULAEPLANETARY NEBULAE ARI; SONAMED ONLY BECAUSE.T!-lEYARE ROUND II KE PLANtTS.'THE.Y ARE LUMINOUS GASCLOUDS AND ARE APART OF OUR. GALAXY

THE SUN INTERESilNG T l : L E ~ C O P OBJEC.T AT4011 ' TO 70" BUTYOU MUST US E A ~UN FILTH'!TO A,/OID SH~IOU~ I!'lJURyTO "'OUR EYE. T~E SUNSPOTS ARE E.ASY TO SEE

MAG.-OA(fylA)(.)SATURN

SATURN IS THE PI?E.1TIESTPLANn. THE RINGS Ae SEENPLAINL' l AT 40x ALTI-IOU6HINV IS IBLE lUlTH l)( BINOCULAJ i : .W IlH HIGHER POUlER Yo u M A 'l&. A e L E TO ~E E CA~5INI'~ O N I S I O N

MAG.-2;ERECr ~VIEW ~[ L

; ,?, c "THE MOON

MAGNITUDE -12 WHEN FULLIS 190,000 TIMES, BRIGH"TERTHAN F IR S T M A G NIT UD E S"TAIi?CRA'TER'TYCHO (TIE-CO) IS ONSOUTH SI DE - MOST PHO"T05AI


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HOW TO USE Y O U R T E L E S C O P E

ApPAIC!E.NT srz.a OF SOME POPULARSKY OBJECTS. DRAwINGS ARE SCALEDSO T~,AT SE.EN AT AVERAGE READINGDISTANCE. (10"), THE.Y ARE. SAMEDIAMET(R AS IN TELESCOPE AT 100){

LIKE A LOT of other hobbies, youcan go for star-gazing a little or

a lot, just as you like. Even with the smallesttelescope you have equipment far better thanthat used by Galileo some 360 years ago whenhe discovered planet Jupiter had four brightmoons, It take s the beginner about a year to be-come an expert star-gazer, In this time he getsover the idea that he is going to see huge fire-balls and other fantastic wonders, finding insteadan increasing enjoyment in his ability to use atelescope. Without leaving his backyard, he be-c~mes a sky explorer with the skill to guide thebig eye of his telescope to the most remotecorners of the sky.

For a starter, you will want to look at I'show"objects. Naturally, the moon and bright planetscome first. Then, in any star book or atlas, youwill find other showpieces ofthe sky: The Lagoonin Sagittarius; the double cluster in Perseus;M42, with the Trapezium set in its greenish glow;the blue-and-gold double star, Albireo; the star-dust glitter of M11; the double-double in Lyra;the ever-charming Seven Sisters; distant An-dromeda, the farthest you can see,

However, many sky objects can't be seen, andmany others are not seen as clearly as the be-ginner anticipates. Most beginners get a "fir atimpression" of the sky show from photographs,without realizing that these pictures are timeexposures. When a light strike s the camera filmit makes a bright spot; the longer the film isexposed, the bigger and brighter the spot be-comes. Sky photos represent a sincere effort toshow sky objects as they really are, but some ofthe effects have a strong el.ernerrt oftrick photo-

graphy. Don't expect to see most sky objectslike they are shown in photographs. There aresome exceptions--you can see the moon as bigand clear as any photo made from earth; Saturn,Jupiter and Venus all look better than theirpictures.

You may find the scaled sketche s below infor-mative. Look at them with one eye from a dis-tance of about 10 inches and you get the samesize effect obtained with a tele scope at 100x.Maybe you are surprised that Saturn and Marsare so small and the moon so big, Even scaleddrawings are not entirely realistic. M57, for ex-ample, looks like abig easy target but is actuallyquite difficult--close your eye nearly shut to re-duce the light and you will get the idea. Saturnfor all its apparent small size is bright and clearin any telescope at 40x or more and stands mag-nification beautifully, Mars is much more dif-ficult. Big objects are not lacking with nearly allof the open clusters and diffuse nebulae rangingfrom Jupiter to moon size or larger. The easiesttype of object to see is the open cluster; globu-lars are easily visible although you don't get sizeand detail like photographs. Planetaries and ex-ternal galaxies are dim, difficult. 100xis enoughpower for most objects and better seeing is amatter of a bigger diameter objective rather thanmere magnification. .

You should join a club or star-gazing groupto exchange ideas and talk shop- -group activitiesand showing the stars to others is half the fun.Dse your astro tele scope to see brilliant daytimeviews in amazing detail. Photography- -land orsky--is another popular hobby where the tele-scope adds new thrills.

Q : ~ ~ o0 QC(2)0,\ '",~' '"

MOON 01800 SECONDS . CI=: 9 INCHES DIA.

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VENUS SATURIII MARS MI'ZARr oiherobjects: '1(:

TAK TRUE I9N(i(/UIR JUPITEROIA.IN SEcoNOS NARc 40.0"POINT OFE TWOPLA~S .40DIVIDE BY 2. .2:0IlN$WcR ISSIZE IN INCHES

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..' . . . JUPITEIi: ANDMOONS (MOONS ATMAXIMV#/ o/STANU)


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Selecting YourTELESCOPE

A TELESCOPE is the kind of product where the biggest is thebest, What you have to do is weighsize against money--and al-ways with an eye on quality, Also youmust keep in mind thatwhile the big scope will let you see more, it is a bother to lugaround and set up, and is more affected by atmospheric condi-tions, It is assumed that youwantyour telescope to be portable,In such case, 6 inches is the accepted maximum size for a re-flector; 4 inches for a refractor. Larger telescopes up to 10inches for reflectors and 6 inches for refractors work wellsemi-portable, that is you have a permanent mount outdoorsand transport only the telescope, For serious star-gazing, a 3-inch refractor or a 4-1 j 4-.inch reflector are generally con-sidered minimum sizes, Both of these instruments have thesame focal length of 45 inches, giving 40 to 50xwith a low-power eyepiece, However, the 4-1j4-in. reflector hastwicethelight pickup power of a 3-inch. The next larger popular size ina reflector is the 6-inch, and this is twice as bright as the4-1 j 4-inch. Anything under 3 inches doesn't have the needed"light power" to show faint sky objects. Onthe other hand, the

smallest refractor, down to 1 in, aperture, will pro-vide a good view of the moon and bright planets. Intheory, a 3 in. mirror should perform as well as a.

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3 in. lens, but in actual practice the lens will in-variably show the best resolution despite the addedfault of a faint purple line around a star image.REFRACTOR vs REFLECTOR. You can read pageafter page comparing refractors andreflectors, butunless you have actual firsthand experience inusingtelescopes, suchinformation is oflittle actuaLvalue.The general situation is simply that refractors andreflectors are both good telescopes. Inch-for-inchof aperture, the refractor is generally rated a shadebetter because (1) it is more likely tobe in perfectalignment, (2) its closed tube means cleaner opticsand less air disturbance withinthe tube, (3)it can bemade nearly 100%glare-proof. Like adiamond, youmight say a refractor is forever.

The reflector has two big talking points: (1) itcosts only about one-third as muchas a refractor ofsimilar size, (2) it is 100%achromatic. Dollar-for-dollar. reflectors are considerably superior to re-fractors. The aluminized mirror will not last for-ever, but a good job with clear overcoating will last15years or more; repeated washings will graduallyremove the topcoat, andafter that the aluminumwillwear off the pinhole. Many pinholes will dim theimage but the picture will be as sharp as new.

Convenience of operation should always be con-sidered. For the most part, a refractor is a neck-breaker. This trouble can be eliminated by the useof a star diagonal, Fig. 4, toviewobjects high in thesky. For south sky objects, the reflector is verycomfortable to use, the eyepiece being just beloweye level, as can be seen in Fig. 1. It is somewhatless convenient for north sky objects unless the

@. GREGOR-IAN ... IS A POSITIVE PRO.JECTION.sYSTEOBJECTIVE(PRIMARY /VfIRIWR)

Ca..ss.Optks P~lfAARY SECOHDARYT..ue CASS. PA!?ABOt.Ol{) J /YPERBOLOIODAll-"IItK~ EL J . J PSOIa SPHERICAL ' .RITCHEY 1IYP~6t:Xi>fD I IYP1l80LOID

.-asiest -: build.. P": mirror CP.: 701'080%of RlI 'a ixX

PRIMARY MI RROR

PR IMARY M IRROR

CATAD IOPTRICS.YSTEM SCAA\IDT-GuseqrainH o w a R e f t e c t i n g T e l e s c o p e W o r k sThe basic reflecting telescope is the New-tonian with flat diagonal which serves todirect the image to the side ofthe main tubewhere it can be inspected with an eyepiece.

0 0 TI-II: EYEPIC MAGNIFIESTHE IMAGE MUCH TI-1 SAMEA S A WGNI~YING G l . . A S L OO KING AT A R EALOBJECT

~ A REAL IM AGE .IS FORME.DHE.RE~ Tl-lE DIAGONALDIVERTS THEL IG HT RAYSTOSIDEOFTUBE

IT] T HE M AIN M IR RORFOCUSES THELIGHT RAYS TOFORM ANIMAGE

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E VISUAL SIZE OF AN OBJECTDEPENDS ON THE ANGLE ITSUBTENDS AT THE EYE

tube can be rotated tomaintain ahorizontal positionof the eyepiece tube.COMPOUNDTELESCOPES. Twentyyears ago,buy-ing a telescope was pretty much a choice between arefractor and a simple Newtonian reflector. Todaythe compact compound telescope is pushing manyof the bulkier, heavier instruments out of the pic-ture. A compound telescope gets its name from thefact a second lens or mirror is used to magnify theimage produced bythe primary mirror or objective.The magnification of the secondary is in a rarigefrom about 4x to 6x. The optical theory involved issimple projection. The Gregorian, Fig. 6, usesprojection with a positive (concave) mirror. TheCassegrain, Fig. 7, makes use ofthe more compactprojection using a negative lens or mirror. Oncevery popular, the Gregorian is today a loner, beingbuilt now and then by amateurs but not at all bycommercial concerns despite goodfeatures ofeasy-to-fabricate optics and an erect image. This scopeis a little longer than the popular Cassegrain, butnot nearly so long as the standard Newtonian forthe same equivalent focal length.

Any optical system using two mirrors permitsthe correction for spherical aberration to be doneon one or both mirrors. This leads to a number ofpossible solutions for the Cassegrain, three of themore popular designs being as shown in Fig. 7. Ofthese, the Dall-Kirkham is most popular withamateur glass pushers because the optics are fairlyeasy to make--the secondary is a plain sphere,while the primary is an ellipsoid figured to about8 0 0 / 0 of the correction of a similar paraboloid. Thesimple rules for focal length and spacing are givenin the Edmund book, "All Ab~ut Telescopes." Youcan also buy readymade optics for various designs.

The top dogs in compounds are. the Cats. A Cattelescope is a catadioptric, whichmeans the optical

...,.-OBJECT

system combines a lens with a mirror. The lenscomponent is used only to correct spherical aber-ration; in other respects the designs are conven-tional Cassegrains. The twomost popular designsare the Maksutov-Cass and the Schmidt-Cass, asshown in Figs. 8 and 9. Both are also used astelephoto lenses.

All of the designs are shown as straight- shots,that is, you look right through the telescope at theobject. You can also use a star diagonal with mostdesigns for comfortable viewing of overhead ob-jects; a Penta prism is used with the Gregorian toretain the erect image. The various Cass designsare also made with non-perforated primary, thelight path being shunted to the side of the tube infront of the primary mirror; this is donewith a flatmirror in the same mann,er as the Newtonian.

Compound telescopes are lightweight, compactand powerful. AtypicaI5-in. instrument packs about50 inches equivalent focal length in atube less than12 inches long, and the whole outfit ontabletop forkmount weighs Iess than 10Iba, Themechanical workis usually excellent. Of course the price is up a bit,being some three to five times the cost of a con-ventional reflector. Apoor feature ofthe compoundtelescope is the large obstruction of the secondarywhich cuts off 10 to 2 5 0 / 0 of the light. Even worse isthe fact this "blind" spot tends to get into your eyewhen observing daytime objects. At night, youhaveblack- on-black and younever notice the blind spot--neither does a camera.OPTICAL QUALITY. This is where you have tode-pend on general specifications and advertiSingclaims unless you can personally inspect and testthe telescope. It is best not to believe everythingyou read because scope makers like soap makerscan make even the commonplace sound wonderfulThe usual tolerance for precision optics is 1/4-.

"!RUe FIELD

------~- .HEN YOuUS E ATELE~~OPE)ll- 1E O B JE .C T IV E LOOKS A , . . ,. I- lE06J ECT AT E.)(AClLY THE SAMEANGLE AS NAKED EYE ....

I ' , ~Ii 5XTELESCOPE \ ~~1\~VIRTUAL ,~ .. BUT YOUR E.YE~I IMAG~ SEES ,.14 IMAGE.\;' /~ OF THE OBJECT~ AT A MUCHGR.EATE.R ANGLE

H o w t h e T E L E S C O P EM A G N I F I E S6

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wave, which means the surface must not departmore than 5-1/2 millionths-of-an-inch from therequired shape. The required shape is (usually)a sphere for lenses; a parabola for concave mir-rors; a plane for diagonals. If the f/number of amirror is ff 1Oor higher, a good spherical figureis as close to being the perfect shape as a parab-oloid with 1/4-wave error. Sincethe spherical mir-ror can be gound and polished automatically bymachine methods, it eliminate s the expensive hand-figuring needed to obtain a perfect paraboloid orother aspheric (non-spherical) surface. One of thebest buys in mirror optics is the spherical 4-1/4-in. diameter mirror of 45 inches focal length. Thisis f/lO; with a goodspherical surface, it is as much"par-abolfzed" as a paraboloid with 1/4-wave toler-ance. Of course the spherical mirror itself is notfaultless. Most commercial mirrors will meet thespecified tolerance, but with the Foucault shadowtest the surface tends to show many small zonaldefects, commonly called "dog discuit." Needlessto say, a rough or dog-biscuit surface can spilla lot of light, which degrades the image by lower-ing the contrast.THE RAYLEIGH LIMIT. Even when an opticalsurface is made to quarter-wave tolerance, itdoes not comply with the quarter-wave toleranceof the Rayleigh limit. The Raleigh toleranceapplie s to the final eme,rgent wavefront. If thereis a shape or zonal error of 1/4-wave, the lightfalling on the mirror must cross this fault whenapproaching the glass, and again when departingfrom the glass. Hence, a 1!4-wave surface pro-duces a 1/2-wave wavefront, which is over theRayleigh limit. However, such a surface willusuallyperform close to perfect. Technically, to rate thequarter-wave Raleigh limit, the mirror surface it-self must be 1/8-wave. The Raleigh tolerance is arule-of-thumb, somewhat similar to the familiar.00l-inch applied to lathe work. In general theRaleigh tolerance is too easy for f/8 or higherf/numbers and too strict for the lower f/numbers of"fast" mirrors or lenses.

INSIDE FOCUS BEST FOCUS OUTSIDE FOCUS

BESTFOCUS

N G . - - - - - - .DIAGONALSILHOUETTENOT SJ./OWN

S P H f R tA 8 R R A@

THE BESTTELESCOPE. Youare right inthe grooveif you select either a 3-in. refractor or a 6-in. re-flector. If the pocketbook is thin, a 4-l/4-in. re-flector will let you see everything just as big, al-though not as bright as the 6-inch.

The mount should be an equatorial. This is builtto track the same paths as the grid of guide lines onstar atlas maps--you will find sky objects easierand faster with an equatorial. Setting circles arenot needed; neither do you need a clock drive, al-though it is a good idea to buy a mount for whichthese accessories are available. .If you have big eyes' for a cute compact com-

pound, just be sure you are buyinggoodoptics. Themechanical work on these high-priced gems isusually excellent, but the optics are not always asgood as the computer says they shouldbe. No doubtyou can understand that compounding the magnifi-cation of the primary mirror also compounds itsoptical faults. All compounds should be tested andcorrected as an assembly, with the final emergentwavefront to the usual lf4-wave or better.

GREE"';{ ONE. WAVE (A ) = .0000'2.2" (zzmillion1/'s)L/Gf.lT Y4 WAVE. (l-4). . ) = .0000055" (S~lni/ti()nihs)~; : -~---'----A ~-WAVE SHAPEEAAOR ON;~I --='"'--"_ S(JRFACECU:.4Nfl8 MIRROR ~ - - - - - - - - _ _ _- - - - - - ~ ~ ~ - = ~ ~~. .023"~ AtLOlUS A CONSIDERA8LE IIMOUIfT~. \ 0000055" OF SPHERICAL ABERRATIONY &-'- AT INFINITY FOC(fS

The usual tolerance for high-precision optics isone-quarter of the wavelength of light. This canbe applied directly to the surface shape ofa tele-scope mirror- -if no more than 1/4 wave from theideal parabolic shape, the mirror will performsatisfactorily. This is the Raleight limit. It iseasy to make when optics have a high f/number,but much more confining for lowf/numbers. Abovefig, a perfect spherical mirror will showlessS Athan a parabola with 1/ 4-wave er ror-, .

PrRMISSl6LES.A. TO! 4 - U J ( L I / ~ LIMITi2 .0014"f/ ~ .003i/4 .006fIb .012fie .01'3f/iO .035fIll. .050fIlS .079f/20 .141ALd7


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T E L E S C O P E P E R f U R D J N C DO&JECTIVE OIA. MAGNI FICAllON L IG - ....T RESOLUTIONINC": M M 3~1C 6" 10" 2.0" 30~ 40" 50" 60" CONlPAAAl'IVEFAIHTfST DAWES ' WOItKPER INCH PER INCH PER IrlCH PE~ INCII PER IMeH PER INC'" PER-INCH PE~INCH SCALE STAR LIMIT VALUI" 2. SMM .3 Y z C 6,c 10)( 20)1 30)( 40.K 50'" 60)< 9EYES S.8MAG. 4.5SEC.. S.Os1!4" l2. 4~]( ,~" 12" 25)( '38" SOi< 62,c 15)1. 14 9.3 36 6.4IY:i' 38 ;)( 9" IS,. 30)( 45" 60" '75)( 90" 20 9.7 3.0 5 . 3I~ ' 44 6" lOY," 17,c 35" 52" 7011 8 " ' ' ' 105" 28 10.0 2 . 6 4.62." S, . . , , , 12J( 2{J)C 40)( 60)( SO)( 100)( 120)( ~6 10.3 2.3 4.02Yi ' 64 9" 15)1 25" SOlC ,5" 100" 125x 150)( 56 10.8 1.8 3.2-3" 76 IOY:z ! laJ( 30" 60" 90lC 120)( 150x 180" 81 11.2 1.5 2."74" 101 14" 24)1 40" 80" 120lC 160)( 200" 2.40)( 144 11.8 1.1 2.04~' 108 15" 26" 4'3,c 85'1 128)( 1I0x 212" 255" 162 ".~ 1.0 I.~5" 121 18" 30){ SO" 100)( 150" 200" 2S0){ 300)( 22S' 12.3 .9 1.66" 152 21lC : : ; 6 1 < 601( 120" 180" 240'( 30011 36011 32.4 12., .8 1.38" 203 2.8lC 48" 80)( 160x 240)1. 320x 400" 480}< 5,6 13.3 .6 1.010" 2.54- 35" 60)( 100)( 2.00" 300)1. 400)( 500)( 600x 900 13.8 .5 .812" 305 42)( "72)1. 120)( 2.40)( 3601( 4801( 600" " ' 2 . 0 X 12.96 14.2- .4 .7

LOWEST BEST IOAL 6000 FOR 30TO 40> PEIl MAX. USEFUL /3IISEO 0'" 8A~0 011 !'lEEDSUSEFUL VISUAL FOR LAN. PL.ANETS, INCH IS NORMAL USEFUL ONLY OARK- ABILITY '~D~EN\ARK.S POwE~ IlCUiTY OBJECT.!J / I I I -08.JECT.S JlI-Po(u~. use' iJl-POUll FOR 1I0APTEC> OF/VAKEO SEING" SEEIN6... GIVES . ,.4/t1/1t1f ANOWIDE AND "'~2""M CLOSE tlNAIOEC> E:YET05E 4,.,0 POUIER. NEEDS7_EK. sxrr VIEWS GENERAL FoR PL.ANET )(IT fX)tlBLE EYE =1 MAG. 62 OF soy DEI( PE!


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T E L E S C O P EP E R F O R M A N C E

W n i l t t o R l p e o t i nATELESCOPE has three different kinds of power,which are (1)Magnifying power, (2) Light power (3)Resolving power. Beginners are most impressed bymagnifying power but light power and resolvingpower are more important. Resolving power ortheability of your scope to show a sharp image isreally the keyitem --it matters little howmuchmag-nifying power you have or howmuch light you haveif the image you see is soft and fuzzy.LIGHT POWER. Objective diameter alone deter-mines the light power of your telescope--the big-ger the lens or mirror, the more light it will pickup. Ifthe diameter of the eye is taken as about one-third inch and given a value of I, the comparativelight pickup will be as given in the table on oppositepage. The base for the "faintest star" isthe magni-tude the eye can see unaided, which is generallytaken as 6.2magnitude. Anydeparture from the baseshould be added or subtracted--if you can see toonly mag 5, you are 1.2 under the base and mustdeduct this amount from the rating ofanyobjective.

The telescope lets you see all stars brighter.With a 3-in. telescope, you will see 11thmagnitudestars as bright as 6th magnitude, while the mag 6stars will take on the appearance of l st magnitude,The explanation is simply the 5-magnitudes dif-ference between the naked eye value of 6.2 and the3-in. objective rating of 11.2.

THEDIFFRACTIONPATTERN. A star is very tinyin angular size, the largest being amere ,05 second,which is 1/20 of one secondofarc. No lens or mir-ror, eye or pinhole can form atrue image at such asmall angle. Instead, your eye or your telescope ob-jective will expand the angle to formaconsiderablylarger image, knownas adiffraction disk or pattern,as shown in Fig. 1.

The small table at the bottom ofopposite pageshows howthis applies tovarious objectives. Notice,for example, that a 3 in. objective will increase thetiny 1/20 second angle of a star to a full 3 seconds,a gain of about 60 times. Even with this boost, thediffraction disk is still very small--it does notcover even a single light cone in the retina of youreye. The situation is that even with a good amountof magnification, the light from a star triggers justone cone inyoureye;yourbraingetsthe impressionof one cone fully illuminated, and that is howbigthe star appears whether nakedeye or bytelescope.However, the distance between two stars can bemagnified as much as you like.RESOLVINGPOWER. One peculiar feature of thediffraction disk is that it becomes smaller as thesize of the objective is increased, Hence, you have 9

POINT(OBJ e.CT(A S _ T I I _ R _ ~ ----If-+-~

Q) THE IMAGE OF A STARISA OIFFRA(.TION 0151< .36"~ 2 .~o t Y e ' I041:*" 312.* 6'2.* 24" '/4" 1 . r 3 3lt 194*"WPOWE.R. I')~' 1.19" ' 1 9 " fO~2' ' ; 4 : ' - 1'28' 2 . - . 150ALL TYPES WILL 4L1.5 S.7)l 26 3 46 2 . . . , "WORK WELL IF .~ .ROPERLY MADE. 38.1 6.6)( 1.02:' ~O" r i o ' 120' 2'l3 ::;s ~'Z." Y s " 1 15' 2 ' / 7 - IIIWIDE IOIELD ANDLONG EYE RELIEFARE DESIRABLE ' ~ " ~., 8)( .85" 361' !.{" 1 6' 2 24 ?8" ' 1 6 " 1 3' 2 76FEATURES O~~~~~ 1 "1WITH ERFLE, I~" 1Ii' I" 0' 431( 'l," 56' 1.34 61"1PE 3) SYMMETRICAL 28.6 89)1 .76" 4o" 2 20MEOIUM I" 2504 10)( .68" 45", Y l s " 53' 134 15 48_ ' / e ' 50' I Y 2 . 49POWER '/8' 52" W' 48' IY z 55" ' 1 9 " 44' I Y 2 . 38RAMSDEN A , " ,O , :, _ u " ! .c ; ~ , :: ,S 22."2.. 1104>< .60" 11 13ARE ECONOMY CHOICEAND HAVE. SATIS- 4 " 19.1 13.3)< . 5 1 " ' 60" Y 2 O ' 40' 1)13 9 64" If II :Jl' I~ 27FACTORY EYE RELIE.F 1 1DOwN TO ABOUT ' 1 ' 2 " S I s ' , . . , . ;.L. KELLNE.R "T,(PE 15.~ 16)( .43" 72" !h " 3-;' I 6 ~3" 32' I 201 IS OFTEN U%.D J 24ALSO SYMMETRICAL ' / z " y~ 1 21' I 4 96"' Iltl 25' ~ 12OUe,LETS 12.1 20" .34" 90lf~ . C ; + - 4 3/8" 9.5" 26.1;>< .26" 1 2 0 1 1 ' ~ 20' % 2 '28" '1zI" 19' Y 2 . . ,POWER 5 " 1 . . . 145" ' . 4 e ' Y 2 - 154" Y l 6 ' 16' ' I : z . . 5BE LO W '/ ... "F.L. I" T IS 1 6 7 . 9 "32)( .2"2:' ., 16' IP..ESTTO USE ORTI>S 1 4 ' 1 5 9 " V 32O"THE~S WITt ! . 6.4 40)( .17"' l e o . , 13' ~ I 192" I f " 13' 3-MA)(. EYE RELIE.F. ?, LSIMPLE SINGLE 1 / 6 " 2 6 8 1 1 V c " !4 1/48 ~ENSES SOMET,,,,,E.s 4.2. 60" .11" 9' 0 269" 8' "2LISE!> 91illFOCALLENCTHDIVIDED ~ LINEAR DI,,)METER OF FIELD ~ 1.36 "IS LAR6ER THRIV @] AVERAGE VIEW OF MILKYWAY: STARS TO IItI'MF/C.FORINTO 10INCHES. "NAME AT FOCAL PLF/IVEOF E.YEPIEcE STF/NDARD I ~ ..FOCUSIIVC .3"_ 12.SMAG. FOR. 6"pOWER." IS (/':EOMORE,.SOME tVEDS BICCcR T(fBE. *Nor ACTt/ALLY OBTAINEDiHIlN TELESCOPEEYEPIEcES EYEPIECES WILL SHOWMORE f}S PER NOTE. aJ

power. The optics are usually good. You can take with agrain of salt the advertised claim that the focus stays wiresharp at all powers--you can usually sharpen it a littlewith conventional focusing.

Fig. 11 gives eyepiece data applied directly to two of themost popular backyard telescopes, which are the 3 in. re-fractor and the 6 in. reflector. Using modest power, eitherof these instruments will giveyouabasic M. of a little under50x and a top M. ofabout 100x.Be satisfied with this amountof power--the magic of a backyard telescope is that you cansee so far so beautifully at 50x. Higher powers are readilyobtained and they will let you see bigger, yes, but brighter,no, and sharper, no, no!THE BARLOW. You can get any M. you want with a Barlowlens, but it works best at about 2x visually and not over 5xphotographically. Fig, 16 gives exact spacing for Edmundproducts. The Barlow M. is applied as a divisor to the f.l.of any eyepiece you use-e-with 28mm eyepiece as shown inFig. 15, the equivalent f'.L, becomes 14mmwith 2x Barlowspacing. Another way of saying this is simply that a 2xBarlow setup will double the magnification.

~ 6 ) SPACIN(:,forEOMUNO SARL .Ow LE.N~ESP . L , Nt... . W2 . " 2" 1 . ' / 2 . " " 3" 3 > Y 2 . " q." 5"I.'~' A~ .58" .U" 1.014" I.IS" 1.23" 1.30" 1.38"1 A l ' e o . . .. . .. .81 1.13 2.60 3.1./6 1.f.32. 5.19 6.9218~' A~ .61 .92 . 1.10 {.2.3 1.30 1.31 1.46!Bl' &~ .92 1.83 1.1Ll 3.66 4.58 5 . 1 . 1 9 " . 3 , 2 .PRIMAlty '* ' 1.11" .81" ;70" 58" .50" . 4 - I . j " .35""I MAG E ~

A GOODWIN Act-roMo ,t , ~EDMUND Acnromot * for ,Mot. rp-pll

#ICTH Low

-FBJECT_IV_E~~~M-l'4--~-4f:1'-+--'PR IMARY'I _//MA6E, 11~ FORMeD e,\j

Bj~~ J M O : : ~ : :@1POSITIONOFI_ ... 8ur LeS~THANB ARL OW LENS ONE- F.L. OF BARi.OUtUl' ir

B A R l . . . ( ) U JLENS~ PRIMAR i="INALIMAG- ./IMAGEri'

2)(SETUP

B A R L D WLENS1.83"F.L.

2" w ith EOtiIIUND LENS1 7


18/37

THE BEGINNER should put in an hour or so ofpractice OIl land objects. Even though the image isupside down, you will gain valuable experience insetting up the telescope, focusing the eyepiece andother basic operations, all of which must be learnedby actual practice. Then, in the night sky, the beststarting sky is at dusk. This also of course is theonly time you can see Mercury or Venus as eveningstars.EYES MUSTBE DARK-ADAPTED. Ittakes at leastten minutes to dark-adapt your eyes and slight im-provement can be noted up to half-an-hour. If theweather outdoors is a bit chilly, you can get yournight eyes more comfortably by staying indoors withyour eyes closed or in a dark room. Meanwhile, youhave already setup the telescope and it too is under-going a slight change in adapting to the weather. Ifyou want to look at maps or notes outdoors, use alamp or flashlight covered with red or brown paperor a red filter.EYE POSITION. Your eye must not touch the eyepiecebut at the same time it must be centered on the em-ergent light beam. This is impossible to do whenyour eyes are not dark-adapted. After you get yournight eyes, you will note that the sky as seen in thetelescope is not really black but a rather bright,luminous gray. Given this target, your eye willautomatically center on the eyepiece. Obviously, alow-power eyepiece is easier to use because it hasa bigger exit pupil. If desired, you can cup yourhand around the eyepiece to serve as a guide untilyou get your eye centered on the light beam.IF YOUWEARGLASSES. Take them off if you arefar sighted. Your unaided eyes will then see distantobjects clearly, while the removalof the glasses willlet you crowd the eyepiece when necessary. Myopeshave a different problem: if you remove your glassesyou lose your eyes for distant objects. The best

practical solution here is to keep your glasses on anduse only eyepieces with long eye relief of 1/2 inchor more. Note, however, that even with eyepieceshaving short eye relief, a long eye position meansonly that you lose field.FOCUSING. There is no such thing as exact focus-ing of a telescope. What happens is that the imageforms at a very pre.cise and exact image plane, butyou can see the image at various settings of the eye-piece because the eye can adjust for either long orshort focus. The best general practice is to focus"long". This is done by extending the eyepiece alittle more than necessary and then focusing in justenough to get a sharp image. The "long" focuscauses your eye to focus as for a distant object--the most comfortable position. If you focus to themaximum "in" position which yet retains a sharpimage, the eye accommodates as for a close object.This position gives slightly greater magnification butis somewhat more tiring. In actual practice, youwill use both the long and short focus since frequentchanges will allow you to see clearer without eyefatigue. Also, as a matter of fact, objects low inthe sky require a slightly different focus then ob-jects at the zenith; a bright object like the moonmayrequire different focusing than a dim nebula. Exactfocus on star objects is simply a matter of obtainingthe smallest possible star image.

Out-of-focus focusing is sometimes useful. Forexample, if the f inder telescope is set slightly out-side focus, the star images will be big and easilyseen; you can even make fine crosshairs visible inthis manner. Colored doubles are sometimes seenbetter slightly outside focus although too much ofthis tends to dilute the colors rather than improvethem.AVERTED VISION. On luminous objects> you canincrease visual acuity by one or two magnitudes byusing averted vision. The idea is to get the target

Five i'AA6NITUDES= 100 7/MES

"\ \ \ 1 //1 / EACH MA6Nlruo STEP L.IMIT FOR-.-, /S"'T Il MAGN' TUD ~(PMttJ9",,6I,,Cl-.._"~ A E IS A DIFFERENCE IN 1- C ,;: / ' 8RI6I1T/VESS OF2~ rIMES 0 000 ; ,h231B . COVNTIeY 00 0 1 1 ~ 1118192D re IVI4KEO EYE LIMlr- CITY EI>';IO~'O 0 0 9 II 1 '2 13 14 I~ LI4V~ FOR8~ll. l@e91 3 011 l_ _2S!!LSIRIUS IS 8~ L V R P ~ 6 7 16 .06.0 I IBRIGI4TEST 080p ic ll- ~ 5 I .4 L.JMIT FORJ ~ "'-.i. .L.MLrMAG. -1.6 I C O J I 0 ! > < ' s CJ 2..3 6 ,.5 3 TELUCOPE ~N .eas.a:o I 40 16~Tt6~ITUDE~ -2 ~~, 251 100 8RIGHTttESS O'FfE~ENCE BY MAGNITUDESSCALE. /"",1,85' A'ii.iieN! J : : ONE MAGNITUOe. = 2.5TIMES SIX MAGNITUOE~= 2.51 TIMES

/ FINO OIEFERENCE BETWEENA 4t" TWO MAGNITUDES: 6.3TIMES S E . V E N MAGNITUDES=6 3 1 TItHESRELATIVE M116. STA2 AIVD A STAR OE 9th MA6.BRIGHTNESS SOLUiION: 9-4:: 5 MAG!>.DIFFERENCE 1HREEMAGNITUDES= 15.8TIMES(ElIeSTMAGNITUD FIi'OMTIiBU: 5MAGS.DII=F. = 100 FOURMAGNITUOES=39.81IMESSTAR RAT[) 100) 7JlEI?EEOR: 9,h MAG. IS /00 TIMES EIIIIVTR

tIGHT MAGNITUDES: IS8S TIMESNINEMAGNITUDES: ~981m;,esTE.NMAGNITUDES: 10000 TItHES

1 8


19/37

~OIf'V'I'\~. ~ t : t ~ V \ i \bIllM~A,.. Lljbt1 "1 \ \ \ \ \ VV\~~- i ! vS G i h , , (> . r w ' jr - o u . " > l 1 !

L A _ 1 / \ CifT Xo 'o j ~ c . , ."' ~'55 4111\f: 7M{/l\ 0 r: (j,~? II

0.'("'(.


20/37

~J~11'-STARS SI-IINE l.IJIT~ A FAIRL'fSTEAD'f ' LlGI-IT (TllEIJ~ISSTEAt)Y)_ _ _ _ _ _ _ _ - , \ ~ . - eta ('I)3./\ "5.04.3

kbCilal>.---1-

. l.UI4EN YOU CAN'T SE.E ;3 .Y2.MAG.STARS, SUC+-I A$ ME.GI2E.Z.(INO/CATES SKY /S NOT CLEIlR, A.S_FROM (!t.O(!DS,.sA1Q{i, FOG OR IIIlZE)

YOU CAN SEe MAG. 5 STARSNAKED EYE, SUCH AS Eta..ANt> "Theta. IN Tf. lE LITTLEDI PPE.R (71-1AIR IS CLEAR) ... I-IEAiED ~OOFTOPS

object in the center of the field, and then instead ofiooking directly at it, direct your. gaze a little to oneside. This technique is especially useful for starclusters. The center of your eye sees the sharpest,but the outer portion is more sensitive to light andmovement.

It is easy to demonstrate that any portable tele-scope vibrates by tapping your finger gently on thefocusing tube. The image will immediately gointo anelliptical or figure-eight movement--really quitepretty although not what you want. Do this with abright star near the horizon and off-focus the imagea little- -you will see a flaming pinwheel shootingoff red and green sparks!IBRATIONOF MOUNT. At 50x or less, a sturdy

mount can be pushed around without disturbing theimage- +you can do continuous tracking, manually.Light-duty mounts will show s


21/37

.. . . ..; ~ , . ; h o w t o : .F I N 0 ~: ' { \ ~ ~ ~ ' B ; S ~ Y ; , . O , b j ; e : c~ ~ ;M11- OPE" CLUSTER

MANY TINY STARS'GIVE B GLOWING-EFFECT. EASY,OSEE/IIITH 3TO 6"AT40x

-'I,aUATOR

.\__ _ _ _ _ _STAR WOPPIN6,,' FROM PILOT STAR,ALTAIR, TO MilCHART IS SHOWN ERECT FORE.RECTII'IG- FINDEE' SHOULDBE TuRNEO UPSIDE POWIYFOR II'IVERTING FINDE!?

_ I r : : t ~ i - - ; - " ' h --"S"-,O",U,,,-,--TH,-,---- +. -" " 1 9h

J-- ---- (-\~---r- \!/I\. TRUE FIELD ANG~ _"/),FIELD)OF VIEW

VARIOUS methods are used in locating sky objectswith a telescope, ranging from coarse naked-eyesighting to precise pin-poiriting with the use of set-ting circles. All methods require a good mount--it must not vibrate unduly, it must "stay put" atany position and it must work smoothly on bothaxes. Other requirements are a planisphere and astar atlas. The planisphere is used to determinethe general aspect of the sky; the atlas then suppliesthe detail maps. Don't expect to find sky objectsby random sweeping- -you must know exactly whatyou are looking for and how to get there,STAR HOPPING. This is the finding method mostused by beginners. The idea is that you hop froma bright star you know to another star you know,etc. , and in this way reach your target, which maybe invisible to the naked eye. An important part ofthis technique is careful plotting of the course on astar atlas. Make a "field plotter" of clear plasticas shown in drawing, scaled to the degree markswhich you will find at the edge of all atlas maps .If you don't know the field of your finder, find it bythe method shown in boxed drawing below.

Now, let's plot the route to a typical telescopeobject, such as M 11. Altair will be your pilotstar or starting point. Note in drawing that a 6-degree finder field will take in the two guard stars,which will make identification positive when youlocate Altair in the sky. Move the field plotter,keeping Altair in field but stretching out to anotherstar along the route. This will be Mu, as shown.Keeping Mu in the field, you can reach Delta.From Delta to Lambda you will have a little bit ofblind hop, but it will not be hard to pick up thecurved string of stars ending at the top of Scutum(SKYOU -turn) , the Shield. Be low Eta and Beta inScutum you will find three faint stars, and abouthalf degree east and south is M 1I.Note that the general direction of your route iswest and south. The drawing shows the stars asthey appear in a naked-eye view facing south. Ifyour finder is the usual inverting type, all this willbe upside down. Hence, turn the drawing (or atlas)upside down and it will then agree with the view youwill see later in the eyepiece of the finder. Mem-orize each step of the route; call out each star by

.,.", .. """"

FIELD OF A TELESCO PEA STAR ON OR NEAR nl EEQUATOR MOVES WESTWARDAT THE RATE. OF FI FTEENOEGREES PER HOUR

RYALS 10IN 4 MI",UTE.SOR IS' IN IMINUTE.By TI~ING THE PAS.SAGE

OF THE STAR ACROS~ THEI=IELO OF VIEW, YOU CANDETERMINE TilE. ANGULARF"IELO OF THE. TELE.SCOPE.

He re 'S th e I d . e a . ~

THEN: DI\lIDE TIME INMINUTES BV 4 TO GETFIELD IN DEGRe.E.SE I . 1 APPRO"., ,:~

OR: MULTPLYTME INMINUTES BY IS"TO GETFIELD IN MINUTES4.5" 15"::.6,.5'

oR JO 'Y2IGH,. ANY Eq,UATORIAL .sTAR2 0


22/37

a Y 2 . E.ASTONPOLAR AlClS

OEiC.4S"O:Z'

STe PPI NG.-OFFTH E DISTANCE

SECoND POSITION ......- ......\v /,o " " ,I \.' II J\ I4/Vy STAlh /NEAR ,~- ......

1)(; OF;:-IELO

3 NORTi4ON DEC.,A)(IS

CYGNUSr.NOR7HE~N CROSS)

,;, R\GHT ANGLE SUJEEP - DENEB TOM39 ;;.

IS F O R L P ~ A T H E G R E E K A L P I - I A 6 E T(ALPHA) (BETA)A a. ALPI-IA AL-fu.h I I. IOTA l. - OH-tu.h P p RHO Row (VOVI?BOAr)a ~ BETA BAY- tu.h K K KAPPA CAP-u.h t: a : SIGMA S16- rnuhr r & AMMA GAM - uh 1\ A . LAMBDA LAM- d.uh T r TAU Taw6 is DELTA DELL-tu.h M p.. MU Mew or Moo Y u UPSILON UP-sih-IonE . [,E EPSILON E.PP-sih Lon. N 71 NU N ew or Noo ' " Pt-II FieZ ~ Z.ETA Z.AY-Luh - ~ XI Zi ( " ' 0 7 Z SOVNo) X X . CHI KieH > t E.TA AY-tu.h 0 0 OMICRON"bHM-ihkra.wn 'If If PSI Sie (sieh)e B THETA 'THAY-iLlh 1 1 " 7T P I Pie n w OME.6A Oh- ME -gu.h+LlKE Ome/efj Omnibus

2 1

name. Careful attention to the atlas plotting willmake the actual finding of M 11 a fairly simplematter. Itwill show as a misty patch of light inthe finder, while the telescope will resolve it intoa myriad of tiny sparklers.RIGHT ANGLE SWEEP. With an equatorial mountthere are just two possible movements: (0 Anymovement on the declination axis will follow ameridian, (2) any polar axis movement describes acircle around the pole. These movements are atright angles and correspond to the grid o f linesshown on all atlas maps. In making a right anglesweep you first locate a pilot star and from thisstep off the required number of degrees in two sep-arate movements, measuring the distance by thefield of a low-power eyepiece. The finder is notused.

M 39 is shown as a target object, with Denebthe pilot star. You will need a little cardboardscale, marked to atlas scale. This serves tomeasure angular distances in both declination andright ascension. The scaling is not exact on most

maps, especially for the crosswise R. A. distance,but is accurate enough for the purpose. As shownin the drawing, M 39 is 3 degrees north of Deneband 8-1 /2 degrees east. A low-power eyepiecewith a field of about 1-1/6 degrees (the average)is convenient for stepping off the distance, theslightly larger field eliminating the need of mea-suring exactly to the edge of eyepiece field.

Make the declination sweep first. You will beable to see many faint stars not shown on the atlasand these serve as spacing guides--you pick upany star at one side of the field and then move thetelescope to put it at the opposite side--that's onefield or 1 degree. After completing the declinationstep, lock the declination shaft. Step off 8-1/2fields to the east, moving only on the polar axis.This should bring you to M 39. If not in the field,sweep cautiously in the immediate ar-ea-e-M 39 isjust a bright splash of stars and is not outstandingagainst the rich background of the Milky Way.

In any right-angle sweep, it will be apparentyou have a choice of two routes. Sometimes a con-venient bright star will simplify the whole operation,


23/37

as with M39, the alternate route shownhas a turningpoint at Rho, eliminating the need of measuring theangular distance. While in the Cygnus area, starsDeneb and Delta provide a convenient check forthealignment of your mounting to the pole--you shouldbe able to sweep from one star to the other withpolar axis movement only. The separation of 10degrees can be used to check atlas scale and alsoyour own ability to step off the distance with eye-piece field.SWEEPING IN SAGITTARIUS.The Sagittarius re-gion was Messier's favorite hunting ground andmore than a quarter of his popular list can be foundin this richly- spangled area of the sky. Sagittariusis especially goodfor measured right-angle sweeps,using reddish, third magnitude Lambda as a pilotstar, as shown in map above. A little triangle ofstars directly under Lambda will make identifica-tion positive. If you put Lambda at the edge of alow-power field you can pick up a faint glow at theopposite edge of field. This. is the globular cluster,M28, of seventh magnitude. Abrighter globular isM22, which tops the famous M13 cluster in stze-

~-----+GMlOMEGA ORHORSESHOE NE81/LAMOVEMeNT ON

__ ~"". POLAR Aj/{/J' .M~ --- -r;r----- ---6561

@3

If you move 1 degree north from Lambda indeclination and then' sweep to the west in R.A., youwill not fail to pick up M8, the popular Lagoonnebula. It is unfortunate this splendid object mustbe viewed under the luminous skies of summer,since even this small amount of light destroys thenebulosity which forms the lagoon, leaving only afair star cluster. View this on a really dark nightabout midnight and you will understand how it gotits name-c-It does indeed resemble a misty lakedotted about with lights.

There are many fine openclusters inSagittarius,all easily located with measured sweeps fromLambda. M25andM23are popular low-power fields;M24packs about fifty stars in a tiny 4-minute fieldand needs a 3 to6-inch objective andmedium, powerfor good resolution although the bright glowofaboutfifth magnitude is easily seen with the smallesttelescope or binoculars. Sagittarius offers a goodtest sweep from Zeta to Delta of nearly an exactnine degrees separation and on nearly the sameparallel of declination. Zeta is a fine double (mags.3.4 and 3.6) but the separationoflessthan 1 secondputs it beyondthe range ofmost portable telescopes.

2 2


24/37

H o w t o u s eS E T T I N G C I R C L E SSETTING CIRCLES can be purchased singly or inpairs in paper, plastic or metal in sizes from 3 in.to 8 in. for portable telescopes. The declinationcircle is the easiest to use and is often used alone,as shown by the example on this page.

A paper circle should be mounted on plywoodwhich is then bored to fit over the shaft. Theaddition of a pipe flange hub as shown in drawingsis optional. The circle is mounted between collarswith a leather or rubber washer on each side; thisprovides enough tension so that the circle moveswhen the telescope is moved in declination, but thefitting is loose enough to slip-turn the circle byhand as needed for setting. The index is fixed andmay be single-ended. Usually you will have thetelescope on the east side of a German equatorialmount--the single index should be positioned toread comfortably from this position.

The manner ofusing the declination circle shouldbe apparent from the example on this page. Youlocate a star of known declination in the center ofthe telescope field, and then slip-turn the circle toread the known declination of your pilot star. Youcan then move the telescope to anydesired parallelof declination, reading the declination from thecircle. In most cases you will have to do a littleblind sweeping in R.A. after getting to the requireddeclination. One adjustment of the circle to a pilotstars serves for a whole evening of star-gazing,but if you move from east to west of pedestal, or,if you move to 'a new sky area at some distance,it is best to reset the declination. This resettingis needed only tocorrect a rough setting to the pole,where you may be off several degrees.THE HOURCIRCLE. Given a choice of a fixed ormoving index, you will invariably selectthe fixedindex for the simple reason it is always in the sameplace. However, ifyou select a fixed index for thehour circle, you have unwittingly gotten yourselfinto something of a me ss, With the fixed index, youcan read only HourAngleonanykind of hour circle,that is you can read any number of hours east orwest from your meridian. To apply this system toa sky object, you must knowthe R.A. of the object

MOUtn ' IWITHfLOORr:LAN6~~ULLSIZE

2 3


25/37

INSTALLATION OF HOUR CIRCLEcorr-oor A CLOCK; THECIRCLE CAN BE ;:IT EITHEREND OF THE POL;:IRSHAFT flOUSING

IfNUTMUSTBETI6IIT

,",OUR CIRCLE WITHDJtfU~D CLOCK DRIVE

and you must know Sidereal Time at the moment,Then, subtracting the smaller quantity from thelarger, you get the hour angle of the sky object,which is west if sidereal time is greater or eastif R,A. is greater.

This cumbersome and confusing method hasbeen inflicted on amateurs for many years indozens of telescope books--all because somebodylong ago made an apparent logical choice inselecting a fixed index. Now the hour circle on aportable telescope is not all that big that it istiresome to follow amoving indexaround the circle.Ifwith a moving index you use a 24-hour scale withthe hours increasing counterclockwise, you have asimple and convenient system of direct indexingin. R.A. This eliminates both sidereal time and theannoying numerical computations. Direct indexing

FIRST: LEVEL THE{ECL..INA710N SHAFT

SEcOND: LOOS.!N SET SCREWIN SHAFT COLLAR_____ AND SET INDEX'INVERTlC;:IL POSI7'lONG )

5ETTIN6 TI-IE HOURc .. RCLE N DEl(works best with a clock drive, but it can also beused without a clock. Either way, it is much easierthan setting to hour angle. Ifyou want to use thismethod, make sure the hour circle is 24-hr., in-creasing counterclockwise, Aclockwise sequence ofhours is still found on many hour circles; as a'matter of fact, some commercial telescopes stilluse the hour angle method.INDEXMUSTBE SECURE. Youwill need adouble-ended index to read the circle withtelescope eithereast or west of pedestal. Without a clock, you caninstall the hour circle at either end of the polarshaft, Fig. 5. Sincethe indexmoves, the circle itselfis fixed, and this is usually done with a mountinghub and a setscrew, as in Fig. 6. The general ideais that while the circle is fixed, you must be ableto slip-turn it for setting, The index itself is madesolid on the polar shaft--it moves when the tele-scope moves, but it is non-slip, a part of the polarshaft. This, too, is mounted with a setscrew butwith. the difference the setting is permanent whenonce made, To get the proper setting, youlevel thedeclination shaft, Fig. 7, and then set the index topoint at a right angle to the declination shaft. Inother words, the index points up to your meridian.In this position, it will point to the same R.A. asthe telescope itself.If you are using a clock drive, the hour circleis a slip-fit on a hub permanently attached to theworm gear. The double-ended indexis permanentlyattached to the extension of the polar shaft, Fig. 8.The setting is the same as before- -pointing upwhen the declination shaft is level. On the Edmunddrive, the holding nut must be made very secure;Edmund engineers have wisely made this a self-locking nut but since it jams against aplain threadedcollar, the net holding power is just onenut jammedtightly against another. This will hold if the nut ismade up tight; lock the polar shaft with the lockknob provided, and then make the nut as tight as youcan. On the Edmund drive, the nut is solely tofasten the index andthe clutch backstop collar to thepolar shaft extension; the tension on the clutch is

2 4


26/37

.SIDE.RE.AL TIME..... (IT IS /0 O'CLOCK10 9 Bur YouNEEO Nor< 9 KNOw THIS). .

' l f H E HOUR CIRCLE. IS IN ANY CHANCEPOSITION. THE MOVING INDEX POINT.sIN S AM E . DIRECTION AS TELE.SCOPE.T# INDEX SETTING IS ~ PERIWINEIVTf)D./VSTMNT SEEOPPOSITE PAGE

*~\\;: BRIGHT~TAR AT \R A 1 11 .3 0""

@ o"tt ~~LIP-TURN T ~ E . HOUR CIRCLE TOPUT R .A .OF PILOT S TAR (1Ih30m)IN LI NE WITI-l TI-lE INDEX'.NOTE THE HOUR CIRCLE NOWMATCflS 711ESKY CLOCK

done entirely with the two thumb screws provided.DIRECT INDEXING.Ifyouare onclockdrive, directindexing is as simple as the setting in declination.First, you point the telescope at any bright starwhose R.A. is known to you, Fig. 10. Put this starin the center of the field. Then, slip-turn the circleto put the R.A. of your pilot star in line with theindex, as shown in Fig. 11. You can index directlyto the R.A. of any sky object you want to find, andyou can keep doing this all night without furtheradjustment. You must, of course, also make theheeded movement in declination, setting the decli-

DIRECT INDEXiNG IN R.A .I

~ 1(PO INT THE. TELESCOPE. AT ANYBRIG~T STAR WHOSE R.A. ISKNOwN TO YOU. CENTER HIE~TAR IN FI E.LD OF EYEPIEC.E.R.A. OF STARSHOwN IS Ilh 30"'"

10

@() N DE-X DIRECTLY TO THE. ?TARYOU WAN T TO F= IND (8h 10m INDRAWING ) . IF ON CLOCK ORIVE) YO(/CAN CONTIN ( /c [ )I R CT /NJ))(INGTOOTH E~ SK Y OE VC TS AS LONGIJS'/l)(/UK

nation pointer to the knowndeclination ofthe object.Usually the declination movement is made first.DIRECT INDEXINGWITHOUTACLOCK. The onlycomplication here is that the grid of hour circleson the celestial sphere is constantly drifting to thewest. This means that after setting tothe R.A. of thesky object by direct indexing, you must make asmall additional westerly movement in R.A., equalto the elapsed time since you set the hour circle.Whenthe time lapse becomes excessive, you simplyreset the hour circle to a convenient pilot star. andthen continue as before.

2 5


27/37

M /-~--tRCtJRY C < SUPERIOR' ORBITOFB/?IGHTEST...,. CONJUNCTION -, INNER" ' * " Pf_ANETI I \ (MU?C//RIiIVO VENtI' ",\\~/ \ 1%:":\~~ i~I~\t ICREIITST ~ / (iIeEATt:rEA$TI?H ~ WPSrtRtVEION6ATION ~ ELON6liTION, INFERIOR. /,~ C 'O ....JUMCTIO!:!-- ,BRI6HTEST\"'_-~- rt"A)(IMUM~"~J < L O " " " O " I- - , _ _ -O!iU3IT OP';;! ~EARrll

C D

uis

ASPECTS ANO PHASES 01=AN INHER PLANET

NINEPLANETSmake up the solar system but onlyVenus, Mars, Jupiter and Saturn rate as ideal tele-scope objects. Fig. 1 shows all ofthe bright planetsas they might appear in the sky. Ifyou are good atvisualizing, try this: Face south. Turn the drawingupside downand put a straightedge (ruler) connect-ing earth and sun. This is your horizon--turn thepage as needed to make it level. Now, keeping theimaginary horizon level, rotate the drawing slowlyin a clockwise direction, withthe earth as pivot. Youwill notice that little Mercury is seen briefly afterthe sun sets; Jupiter and Saturn are prominent inthe night sky; Mars will rise in the east and Venuswill be seen as a morning star before the rotatingdiagram shows the sun coming over the horizon.

follows the order of orbit travel, that is, from su-perior conjunction to eastern elongation toinferiorconjunction to western elongation. Any angle eastor west of the sun is an elongation. You can seefrom Fig. 4 that if the planet is east of the sun, itwill appear as an evening star after the sun hasset, Fig. 3.

Like the moon, the inner planets showvaryingamounts of illuminated surface. Venus is mostbrilliant at the crescent phase, being then near-lysix times larger in angular diameter than when atsuperior conjunction. Mercury is brightest be-tween greatest elongation and superior conjunction.Nearer, larger and brighter, Venus far outclassesMercury as a telescope object. Thirty-six dayseither way from new, she is at her brightest, aglowing crescent outshining Sirius a dozen timesand of an apparent size when viewed at 40x equalto the moon as seen withnaked eye. Mercury shouldbe viewed at greatest elongation in order to obtaina iihigh" sky position. Even so, he is hard to see,being lost behind trees and rooftops surroundingthe average backyard telescope.

THE INNER PLANETS. Mercury and Venus areconveniently classified as inner planets becausethey are inside the orbit of the earth. Both are inthe daytime sky every day of the year becauseMercury can never get more than 28 degrees ortwo hours from the sun; Venus, three hours. Inthe circular race around the sun, the planets arenow abreast, now lagging behind or pulling aheadin relation to the earth. Certain of these positionsor aspects are named and should be learned. Fig.2 shows the aspects of an inner planet; the cycle

THE OUTER PLANETS. The aspects of an outerplanet are shown in Fig. 5. Here, opposition isthe aspect of greatest interest since it is at oppo-

2 6


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1975MA _ , ., .. t: J t6~-- . .. .. ..R J . . . . . \ '0 -..1988I 1 I I ; , ~%-'i21f"I '~RTH '11/ \",J, __)._ ''y,/19CJa. ~Bt\ ~ ///11\\\~ 1 t\ \ EARTH ~90" / ;'

\ EASTERN AY SKY

w . QUADRATUREPt..ANT RISES AT/IIIIONI6I1T AND IS'ONMERIDIAN ATSUNRISE

OPPOSITIONPLANET RISESAS "THESUN SErS 1'1/110SVISIBLE ALL NIGHT

CYCLE 01= ASPECTS OF AN OUTE.R PLANET (MARS, .JUPITER, SATVRN)

sHion that the planet is nearest the earth and at itsbiggest and brightest best. Oppositionmeans simplythat the planet is opposite the sun.Whenyou have anouter planet rising in the east just as the sun sets,you knowthat the planet is inopposition and ideallyplaced for observation. The other aspects are read-ily determined by the location of the planet in re-gard to the sun, Fig. 6.MARS.Opposition distances are not uniform,notablyin the case of Mars, Fig. 8, where it can be seenthat 1971was the last favorable opposition and 1988will be the next. This best-to-best cycle runs 15 or17 years. At a favorable opposition, Mars is bothbig and bright at about 24 second of arc and -2.5magnitude, He does not fade a whole lot in the op-positions on either side of a favorable one. Theminimum planet disk of about 14 seconds at a poor~opposition is still big enough for a nice view. Atconjunction, Mars fades to 2nd magnitude; with along synodic period of over two years, he is brightone year dim the next. Unlike cloudy Venus, Marshas a fairly clear atmosphere and shows amaze ofsurface detail, most of which is beyondthe range ofearth-based telescopes, large or small. In1965the

Mariner flyby produced photos taken at 6200miles.These reveal detail never seen before--even theexperts were surprised tofindMars heavily crater-ed very much like the moon. Needless to say, youwon't see craters with a small telescope. ButMarsis always a nice object at opposition just on thebasis of color and brilliance. Dark areas canbe de-tected with even a 2-inch at 50xbut it takes at least5 in. aperture and 200 to 300xto define these withany measure of clarity.JUPITER. Big Jupiter is the most consistent per-former of the bright planets; he is never under 30seconds in angular diameter, Fig. 7, which is big-ger than Mars at his best. Even the four brightsatellites are 5th and 6th magnitude, easily seenwith binoculars. Fig. 9is a sketch viewof the satel-lites in orbit, but our actual viewisnearly edge-onso that the moons merely shuttle back and forth. Asatellite in transit is difficult to see because it is abright object seen against a bright surface. It ismuch easier to see a shadow transit, which is ablack dot on a bright surface. A random view willusually show all four bright moons. From the dataon satellites you can see that the maximum true

2 7


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O~ [)ISTAHtEMIUIONS OFII1I/.S PERIOD OF ~ITAL MA6HITUOE AH6UlM DIAMlTEIl SUITA8LEPLANET IN f'rom SUN from EARn-l REVOWTlOfoI EO SECOI'IDS 01=ARC T E l . S C . O P f/VIILES MAx. MEAN OTtiERMIL~S MAX. MIN. MA'I.. MIN. S ID E R E A l S Y N O D IC PE.RSEC. MAx. MEAN MIN. POwE.ftMERCURY tI 2,~00 43.3 26.6 136 SO ae 116 29.1 -1.9 -1.1 +0.2- 12.9" 6.," 4.1" 40-120DAYS DAYS ' NEAR s . c . Ne,qRS.C. AV.G..VENUS 9 '7,600 61.6 66."7 161 2S 2'2.5 594 21."7 -4.4 -4 -3.3 64.0 16.0 9.9 20-120DAYS' O A Y s CRESCHTV. v.E. 1'14I1RS.C.EARTH E B 7)913 94.4 91.3 - - 365 - 18.S' - - - - - - -Oll' l:rN\A~S c f 4;lOO 154.1 1'29.3 24a 35 1.9 leo 15.0 -2.8 -1.8 +2- '2.5'.1 6.1 3.5 100-300YRS. 1JAY$ AV. OPP. CONJ. IIIJUPITER ~ 86,800 506:7 459.9 600 367 11.9 399 8.1 -'2.5 -2.2. -1.4 49.8 31.9 30.S 20-300YRS. DAYS 1111.oPP. CONJ.SA'TUtz,.., h lID71,500 936 837 1028 144 29.5 3 , a 6.0 -0.4 +0.0 +0.9 [ID20.5 11.3 14.1 40-300I[J110,000 YRS. OIlvs AV.OPP. IIIIVCU~S 1[J49."2. 41.S 35'2-\1~ANUS 0 2.9,400 1861 1699 1960 1606 84- 310 4.2 +5.1 tITTlE CIIIINGE 4.2- 3.~ 3.4 IlNYYRS'. DA' /SNEPTU'-'E W 28,000 2811 2710 2910 U,77 165 361 3.4 +"7.6 Ll7Ti.E CIlIll'lGE 2.4 2.3 2.2... / JNVYRS. ClAYSPLUTO E 3,600 4600 2160 4100 2610 249 361 3.0 +14 L.1"7TlCHIlI'ICE O.W 0.2 0.16 NEEDSYRS'. DIIYS IOINCI{

lI D BALL ~ RING SYWODIC PERIOD: TIME BETUIUN s.c.,.....SVPERIOR. CONJVNCT/ONSIDEREAL PERIOD: rIME TO MAKE St/CCESS'IVG SIMILAR ASPGCT.S' ... Et;>t/IJL70 AV.6. .. .AVERA61i CREATES'T ELONC.4T10NONE REVOLUrlON AROVNO SUN ... PLANETS oNE "LAP "INRACE aor E.4R7}/ AROVNO S'VI'I A V. O PP . .4I/ERA GE ORMEAN OPPOS'1710N''YEAR.'' IN TERMS OF EARTH TIME [i] SeE FIG. 8OR OPPOSlilON oIAMETEI


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O B S E R V I N G T B E S U NTHE SAFE and sane way to observe the sun is byprojection. Equipment for this can be homemadeas shown by the simple ideas on this page, or youcan buy a commercial camera holder made for thispurpose, such as Edmund No.70,162whichincludesa sun screen.

The general idea is that you place awhite card-board screen 5 or 6 inches behind the eyepiece.You can hold this by hand ifdesired. Then, extend-ing the eyepiece just a trifle you will form animage of the sun on the card. Of course the tele-scope must be pointing at the sun, and the way youdo this is by watching the shadow of the telescopetube on the ground.

You can also calculate in advance how muchprojection you can handle with your ownequipment.Projection M. of lOx is a good starter. Table 1shows how this is applied to various eyepieces.If, say, your eyepiece 5/8 inch focal length, theeyepiece to screen distance at lOxwill be nearly7 inches. You can accommodate this much throwin a cereal box, as shown in Fig. 1. Then, Table2 will showyou the size of the sun image. Assum-ing a 30 in. f.l. objective at lOx,the sun image willbe 2~3/4 inch diameter. While small, this will bebright even on an open screen and it is big enoughto show sun spots. Higher M. means the image willbe less bright; over 20xyou will need a closed boxor an opaque cloth to keep outside light off thescreen. Never view the sun directly with any tele-scope or binoculars unless the instrument is fittedwith approved equipment to protect your eyes.

~;:SUN PR.OJec.TION DATA ; f ~ '~ .CAUTIOH: INrNSE HEAT CAN DAMAGE

CEMENTED EYEPIECE LENSES =us RAMSOENOR HlIY6ENS, ESPECIALLY lUI/EN (j)SlIN ISBRI6I1T, asa)OBJECTIVE IS OVER 3"O!AMTOl

TASLE 1 - EVEPIECE TO SCREEN OISTANCE (THROW)PROJECTION EYEPIGE FOCAL LEH6TtIMAG. '4" '/~" S i s " 3/4" "/S" , . . I~"S" I~" .3" 3~" 4Yz" 5~" 6" 7~"10" 2~ SY2 6~ 8X, 9-% /I 13~1 5 1 C 4 8 9 Y t : ! 12 13S 16 20-20" 5%; lOY:.. 13 ISJ:, /8~ 21 26~30" 7~ IS92 19y" 23J4 27 3/ 38~40" 10/4 20!t2. 25a .30~ 35~ 41 51Y4SO" 12* 25Y2 31* 38~ 44~ 5/ 63.J4*WlJ"L s s u : C.Q'iEgBiLL I2tiJLJtlEYR ee SlIIV'

OAT BOX ORSIMILAR-/4"DIA."7"

THREE S.IMPLE SETUPSFOR VIEWIN6 THE .sUNBY P~OJE('TION

TABLE 2. - DIAMETE.R OF SUN IMAGEOBJ1:CTIVE:::: PROJECTED .MAGeF . L . S" 10. IS~ 20~ 301( 40" 50"20" .180" '1'8" 1'~6' 2''4;'' 3 S " 5 ' h 6 ' 7%" 9"" ' . . .271 I~ 2 % . 4116 5?16 8Y s /O~ /3Yf640" .361 /9;'6 3% S?16 7 Y 4 10rs 14fi 187;64S" .405 2 4~6 6'46 B Y e 12.%, /6J16 20Y..,48" .432- 2 Y s 4fi6 6fi 8% /3 /7Y4 2/%SO" .4S/ 2.~ 4Y2. 6~ 9 /3Y2 /8 22~60" .541 2~6 5~6 8 ' 4 3 /0* 1674- 21f8 27..,0" .63/ 3 Y a 6t6 9}i /2% /9 2S~ 3112

2 9


31/37

MIZAR- AN EASYDoUBLE AT 43"ApPA~/Ifr SE.MRATltJl'I=14 ~43602"= /0'

NORTH

1/'----" ' .MAG. 5 L62"._L7/>'~MA6.S

IZA~ A - MAG.2.4B MI~"Ii'4//~.~.V AU:OR(80)

NO~H

_/1I8OVT 6' ElELP" ~" ,JS ...Q /'4YSMALL PAIlT OF

FULL FIELO "~ ~v(III",} DRAGO f' \POPU LAFt LOuJ- 1 1 1 EtaminPOWER DOUBL.E. ~ MII6.ZA tJrtJJJgeEA~'I'WITI-I 1" OR MORE

SOUTH

2.2.. ( .> ---I;.. MAGS.S.I-S.4I3~2I.'MAGS5./-6 .;.- ~

-'\ 0

E(E"sJlo,,) LYRATilE FAMOUS DOUBLEDOUBLE. NE.EDSHIGH POWe.R

A80vTS' FIELP., IS ABOUt; HALFFIELD OF~'::type. AT 192> ' 2.=-96 ~.f/=f/8 )f.2 =f(16 ~ A~PTER~ @ (Blk.TNITEPladi"c)EITHE.R POS/7IVIE 2" noAJE~IO&l r----,ORNEGATIVE SySTEM r-.u "I .,./S 5U-S(JPPORTING EYEPIECe

IN TELESCOPEFOCtJSING TtJBE/

required distance beyond the focusing tube. Sadjusted, the telescope is still useable visually.AFOCAL SYSTEM. This is popular because itcabe done with any camera and any telescope, alsoit covers 35mm film right tothe corners. Howeveryou need an extra piece of equipment to hold thcamera, as can be seen in Fig. 8. The spacing between telescope and camera should be such as tput the exit pupil ofthe telescope at or near the irisdiaphragm of the camera, Fig. 9. Usually this iabout right if the eyepiece is nearly incontact witthe camera.

The best way to obtain additional power is byusing a slightly longer camera lens. For exampleif you use a 3-in. camera lens, the equivalent focalength of Fig. 9 example is increased to129 inchesPOSITIVE PROJECTION. This is a simple pro-jection system using the eyepiece of the telescope.The camera lens is not used. The object to be pro-jected is the image formed by the telescope. Thprojection magnification is determined bydistancesA and B in Fig. 10 which is a typical setup usingthe 1-1/4 inch Edmund Erfle eyepiece and itsadapter. Youhave to make your ownadapter for thecoupling to camera; this canbe seen inFig. 11. Theyepiece specified has a focusing sleeve which cabe used to obtain more or lesspower. Actual focusing is done by the rack-and-pinion ofthe telescope.

Any eyepiece canbeused. Obviously, the shorterfocal lengths will make upmore compactly for anspecified amount of projection M., but best opticaperformance is usually obtained with focal lengthsof 1 in. or more. Short f'.L, camera lenses are some-times used, usually with the lens facing toward thefilm since this is the greater of the two conjugatedistances. However, many lenses workequallywelfacing either direction.NEGATIVEPROJECTION. This is done withaneg-ative lens and is better known as aBarlow system.Again, the camera lens is not used. The negative(Barlow) lens intercepts the primary light cone andprojects it a greater distance to form an enlargedimage. The Barlow is the most compact ofall pro-jection andtelephoto systems; this is apparent fromFig. 13 which is a typical system working at 2.3xprojection M.--compare withthe 2xpositive systemin Fig. 10 which is drawn to same scale. Like thepositive projection system, the Barlow is free-standing in any telescope.

Most Barlow lenses are made for visual use anthey work best photographically at 2xormore, i.e.,you should not use less than 2x projection M. Thspacing is the same as for eye use, as shown opage 17. An extension tube can be used for morepower with either a positive or negative projectionsystem--if made one f.l. of the eyepiece or Barlowused, it will increase the projection M. exactly lx,

3 4


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M W MOON IS ,1'1I.JNEWIT!' SuN AtiONOTrUN I I 'NI&IffSKY rfew Cfl[SCEHTAPPEAgs BRIEFLYIIFTE~ Sf.JtltillS SET

TargetM O O NPRIME target for telescope obser-vers everywhere, the moon at acomparatively near 240,000 milesshows amazing detail in even thesmallest telescope. Over 100, 000objects are shown on maps andphotos, and the beauty of the wholething is that with a good 3-inch tel-. escope you can see everything asclear as the very finest photos.

Any and all powers can be used.Since the moon is about 30 minutesof arc in angular diameter, the max-imum power which will show thewhole surface is about 90x. Thesmallest crater you can hope to seeis two times Dawes Limit. Thus, a3-inch telescope can show cratersas small as 3 miles diameter.Twice this (6 miles} is a moreprac-tical working value. Much smallerdetail can be detected when in thefor m of a line; you will h a v e notrouble seeing The Straight Wall.

REMARKS2 A ROCKY PLATEAU 1$ BRIGHTESTTHE. MOON

ARlnILLUS(air-is-TILL-us) CRATE.R 35 oo: ONE. as: T!olE BE.ST-I=ORME.D C.RA'ERS INA MAGNIFICE.NT MOUNTAIN SE.TTING

20 DIA.FINE. E.XAMPLE OF A RINGE.D PLAIN CRATER.MAN'f BRIGHT RAYS IN IMME.D/ATE VICIN ITY1 56 DIA.

3 "~IMALDI (gri- M4LL - di) DARKEST SPOT ON T~ E. MOONttVGINUS (h-ih.-JINE-;us) 401A. SMALL

CRATEFl SPLIT BY A GREATCLE.FT C.AN BE SE.EN IN SMALL IE

4 PeTAVIus (pek -lAVE-lit. -us) E,ASY OBJE.C.T WHE.N MOON IS NE.W CRESCENT.MOUNTAIN AT C.e.NTE ~ WITH CLE.FT E.)l.TE.NDIN6S2 PITON (PIE-tun.) B~IGHT HIGH PEAK WHICH CASTS A LONGSHADOW WI-lE.N ON TERMINATOR2 PLATO (PLAY- toe)

....EO PtA'''-IO 'TO('O

C.RATER* STO so CRAMILES DIAMETEIC VPTOMAINl'f'PESQF CRATE


37/37

'""= Thqta.-two IS AC4-~WIOE DOuBLEb ~L '.-.. ,'/V~S2~--------- ./ '~0'o ~ .

DARK SA'\(7h~Fish'sMo(/th

" ' / " 0 , < Thl'1a--one (fi)d THE TRAPEZIUM, INVERTED VIEW AS SEEN IN TELESCOPE

DOUBLE STARS

selected SKY OB JECTSR _ A_ DE .C . REMARKS

UlI-IITE AND YEL.-WIIT.

IN BR:IC.HT AREA OF 1'114-2..SEE:DIAGRAMPRETTY YEUOW PAl R. BOTtiHA"E FAINT COMPANIONS

'"/ (G(J.m__ ) DELPI-lINUS61-CYGN us,P o (Mu.j CYGNUSTMfTAAPU.IUM IS S E .EN P LA IN LY

IN 6" A T,S Ox _ /)/A6RAM SHOUIS_Af}f}JfL % 7I1EAI?4 y~USEEAT sox. ~ (Zeta-) AQUARI US

OPEN CLUSTERSNGC i S 2 . -ANOI i !OME .DA 8S 10 Nice 6ROUPOFABOUr"10 SrARSf: AeoUT 80 athto I:~ll,MAG- STARS.5" 30'. . 1030'

10 20' '' A MA$S'OF STARS OF A SQUAMSO-MONOCE.~OS 10 10'M46- PUPPIS II 24' MANYTIN'(M2.5-SAGlnA~IUS 8 45'

II

1"2. '3 '-3'< f O . E " ~ - 14 14'. AS"TEROPE.~~-TA/~~-J>eeCELAEI'Io ...seh-I..EE-nOe 13.6 10 'ELECTRA ....eh _LEK-fr4 4.0MAIA ....... MY- uh . 4.3 6.6 14 9 BLA'Z.E ATME ROPE ...MAttE -m,-pee 4.4 6 . ; 'rAY(;'ETA ... f . 4 J r _IJ-aJ>-frIh 5.\ -14 e;, Pl.E lO.NE .plee-OH-nee !..8 l5TLAS..... AT-lus I 14

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How to Use Your Telescope