Exploring the Night Sky October 28, 2009 1
Exploring the Night Sky Course Outline Session 1 OC lodge - Ron Presentation: Orientation to the Night Sky Viewing: Naked eye Session 2 OC Lodge John Presentation: The Solar System Viewing: more naked eye, binoculars/telescopes for moon, planets Assistance with personal telescopes Session 3 - OC Lodge Ron Presentation: Telescopes and Binoculars Introduction to Deep Sky Objects Viewing: More naked eye, binoculars, some telescope Assistance with personal telescopes 2
Presented by Ron Olson October 28, 2009 3
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Topics Binoculars Labeling Advantages and disadvantages Telescopes Basic Types Basic Parameters Selection Criteria Example Costs and Features Powers of a Telescope More Telescope Parameters 5
Binocular labeling Example Magnification 7 35 Diameter of objective lens in mm 6
Binoculars Advantages Low cost, portable, easy to locate objects Large Field of View (e.g. 5 ) 5 to see all of larger objects 10 X 50 good choice Disadvantages Limited capability to view faint objects Large apertures (> 50mm) difficult to hold steady Can use tripod Image stabilized expensive 7
Telescope basic types Refractors Reflectors Catadioptrics (Hybrids) Basic Parameters Diameter of objective lens (D o ) (= aperture) Focal Length (F( o ) 8
Basic Telescope Parameters Eyepiece Refractor Objective lens light D o F o light F o is the focal length D o is the diameter of the objective lens (aperture) 9
Refractor 10
Basic Telescope Parameters Reflector light Diagonal mirror Objective mirror D o light Eyepiece F o F o is the focal length D o is the diameter of the objective mirror (aperture) 11
Newtonian Reflector 12
Telescope basic types Refractors Reflectors Newtonian Dobsonian Catadioptrics (Hybrids) Schmidt-Cassegrain ACF Advanced Coma Free Optical System EdgeHD Optical System 13
Basic Telescope Parameters Schmidt-Cassegrain light Secondary mirror Objective mirror Corrector lens D o light F o Eyepiece F o is the focal length D o is the diameter of the objective mirror (aperture) 14
Schmidt Cassegrain 15
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Schmidt Cassegrain Advanced Coma Free 17
Telescope Selection Criteria Portability Purpose Cost Features 18
Portability Consider Size Weight Set-up time Difficulty < 8 8 easy 8 medium > 8 8 medium/hard The best telescope for you is the one you will actually use! 19
Purpose Solar System Bright objects smaller aperture Deep Sky Objects Larger aperture Detail Larger aperture, quality refractor Manual vs Automated Alignment, Locating Objects (GoTo( GoTo), Tracking Objects Astrophotography Tracking stability 20
Cost Lincoln Hills Astronomy Group Aperture (light gathering power) Bigger more expensive Detail More detail more expensive Automation Alignment, tracking, GoTo more expensive Tracking Stability Stability more expensive 21
Cost Lincoln Hills Astronomy Group Type less to more expensive Low quality refractor Dobsonian reflector Newtonian reflector Schmidt Cassegrain High quality refractors 22
Features GoTo Capability Computer Control 23
Alignment Location, Level, and North Alignment Manual Automatic GPS Star Alignment Methods 1-Star or 2-2 Star Any three bright celestial objects Celestron SkyAlign No stars fully automatic Meade Lightswitch 24
DS-2090AT 2090AT-LNT 3 in Refractor $300 Meade DS-2114ATS 2114ATS-LNT 4.5 in Reflector $330 ATS Auto Align LNT Level North Technology DS-2130ATS 2130ATS-LNT 5 in Reflector $350 25
4 SE Makutsov $500 5 SE SCT $700 6 SE SCT $800 Celestron NexStar 8 SE SCT $1200 26
ETX 80 ETX 90 ETX 125 3 in Refractor 3.5 in Mak $250 $600 Meade 5 in Mak $900 ETX-LS 6 in SCT $1300 27
Meade LX90-ACF $2000 Meade LX200-ACF $2600 GPS XLT 8 in Celestron CPC $2000 28
Powers of a Telescope Magnification Resolution Light Gathering 29 1
Telescope Parts Eyepiece Lenses Focal Length (F e ) Apparent Field of View (AFOV or AF) More Telescope Parameters Magnification (M) Resolving Power (RP) True Field of View (FOV or TF) Light Gathering Power (LGP) 30
Telescope magnification Focal Length (objective) Magnificat ion = = Focal Length (eyepiece) F F o e Example: M = F o /F e = 2000 mm / 20 mm = 100X Shorter eyepiece higher magnification 31
Practical Limit for Magnification 50 x aperture (D( o ) inches Example: 50 x 3 inches = 150X 34
Resolving Power (RP) How close in angular separation can two objects be and still be distinguished as two objects? The larger the diameter of the telescope (D),( the better its resolving power (Note: the lower RP is, the better the resolving power): 35
Field of View 1 1 0.5 FOV 1.5 FOV 37
Telescope Field of view Apparent FOV AF True FOV = = Magnification M Apparent FOV is built into the eyepiece Example: TF = AF /M = 50 / / 40X = 1.2 The higher the magnification, the smaller the field of view 38
Light Gathering Power Function of size (diameter) of objective lens or mirror (D o ) Determined by surface area of the lens or mirror LGP = Surface Area (larger scope) Surface Area (smaller scope) = Diameter (larger scope) Diameter (smaller scope) 2 Example: LGP = (200 mm/50 mm) 2 = (4) 2 = 16X Larger objective lens = more light gathering power 39
Telescope magnification Magnificat ion = Telescope Field of view Focal Length (objective) Focal Length (eyepiece) Apparent FOV AF True FOV = = Magnification M Light Gathering Power LGP Diameter (larger scope) Diameter (smaller scope) Maximum Practical Magnification = MPM= 50 D 0 (in inches) 2 Remember D 0 is the same as the aperture!