Exercise IE Essentials of a Telescope

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Exercise IEEssentials of a Telescope

• Begin
• Look at Cameras brought in by students
• Talk about telescope basics and set up Celestron
  telescope
• Topics
• Focal length (F), magnification (M), light
  gathering power (L.G.P.), angular resolution (a),
  chromatic aberration
• Results
• Determine M, L.G.P., and resolving power of
  several telescope configurations

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Exercise IETelescopes

• Telescope basic types
• Binoculars
• Refractors
• Reflectors Newtonian, Cassegrain
• Hybrids Schmidt-Cassegrain
• Basic Parameters
• Diameter of objective lens (Do)
• Focal Length (Fo) on white board
• Use lens/mirror demo equipment.

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Binoculars

• Binocular labeling
• Binocular Advantages
• Low cost, portable
• Large Field of View (e.g. 5) to see all of
  larger objects

Example
Magnification ?
?Diameter of objective lens in mm
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Telescopes

• Basic Telescope Parameters
• Refractor
• Fo is the focal length
• Do is the diameter of the objective lens
  (aperture)

Objective lens
Eyepiece
light
Do
light
Fo
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Telescopes

• Basic Telescope Parameters
• Reflector
• Fo is the focal length
• Do is the diameter of the objective mirror
  (aperture)

Objective mirror
light
Diagonal mirror
Do
light
Fo
Eyepiece
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Telescopes

• Basic Telescope Parameters
• Schmidt-Cassegrain
• Fo is the focal length
• Do is the diameter of the objective mirror
  (aperture)

Objective mirror
Secondary mirror
light
Corrector lens
light
Fo
Eyepiece
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Exercise IETelescopes

• Stats of the Celestron (C-8) Telescopes
• Objective Diameter Do 200 mm
• Focal Length of Objective Fo 2000 mm
• Telrad
• Three eyepieces characterized by their focal
  length (Ex 40 mm)

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Exercise IETelescopes

• Telescope magnification

Example M Fo /Fe 2000 mm / 40 mm 50X
50 X 40 mm eyepiece 100 X 20 mm
eyepiece 250 X 8 mm eyepiece
Higher Magnification
Shorter Eyepiece
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Magnification
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Empty magnification
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Exercise IETelescopes

• Procedure
• Determine the magnification (M ) of a telescope
  by using the following
• where Fo is the focal length of the objective
  (the telescope) and Fe is the focal length of the
  eyepiece.
• Magnification is a unitless number

Eq. 1
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Exercise IETelescopes

• Light Gathering Power
• Function of size (diameter) of objective lens
  (Do)
• Determined by surface area of the lens
• Area of circle p(radius2)

Example
LGP (200 mm/50 mm)2 (4)2 16X
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Light gathering power
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Exercise IETelescopes

• Other Things
• The light gathering power (L.G.P.) is a
  comparison between two telescopes collecting
  area
• where D1 and D2 are the diameters of the
  larger and smaller objective, respectively
• The focal ratio (f/ratio) is simply the focal
  length of the lens or mirror divided by
  its diameter

Eq. 2
Eq. 3
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Exercise IETelescopes

• Angular Measurement
• Units
• degrees () arc minutes (') arc seconds (?)
• Angular Unit Conversion
• 1 degree () 60 arc minutes (')
• 1 minute (') 60 arc seconds(?)
• 1 degree () 60 x 60 3600 arc seconds (?)

7b
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Exercise IETelescopes

• Other Things
• The angular resolution (a) or resolving power of
  a telescope (observing at visible wavelengths)
• where D is the diameter of the objective
  measured in millimeters and a is measured in arc
  seconds.

Eq. 4
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Resolving power
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Other Slides
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The Lens Maker Equation
F
O
I
Lens
or
where I is the image distance
and O is the object distance.
Both I and O are measured from the lens or
mirror.
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Another Question

• Suppose you have an optical bench, with a lens
  and a light source and a screen as shown below.
  The Objects light passes through a Lens of focal
  length F and makes an Image on the screen, with
  the distances between the Object and Lens and the
  Image and Lens given below . Using the Lens
  Makers Equation, calculate the focal length of
  the Lens.

45 mm
screen
Object
Image
Lens
85 mm
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Exercise IEObserving Objectives

• Tonight at the observing site (if possible)
• Find 10 stars which do not appear on Star Chart A
• Set up telescopes and Find the 5 Deep Sky Objects
  you selected, use finder charts youve created
  from TheSky
• Keep reading the textbook (Chapters 1, 2)

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The End
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Exercise IECelestial Tools

• Hertzsprung-Russell (HR) Diagram
• Plot Luminosity vs. Temperature and what do you
  get?
• Luminosity ? Absolute Magnitude
• Temperature ? color or spectral class

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Exercise IECelestial Tools

• Hertzsprung-Russell (HR) Diagram
• Plot Luminosity vs. Temperature and what do you
  get?
• Luminosity ? Absolute Magnitude
• Temperature ? color or spectral class
• Luminosity Classes
• Some spectral classes can be found in multiple
  locations on HR diagram
• Roman number used to distinguish location on HR
  diag.
• V Main Sequence
• IV Sub-giants III Giants
• II Bright Giants I Supergiants (Ia Ib)

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An H-R diagram
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Schmidt-Cassegrain focal arrangement
Corrector Plate