Download Telescopes - Fort Lewis College

Charles Hakes
Fort Lewis College
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Chapter 3
Telescopes
The Tools of Astronomy
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Fort Lewis College
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Hotel Mauna Kea

http://www.youtube.com/watch?v=XPdTlHK1h_0
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Fort Lewis College
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Outline
• Grades posted
• Test Friday
• Don’t forget your red scantron sheets
• #2 pencil(s).
• Calculator (no phone calculators)
• Optical Telescopes
• Refractors
• Reflectors
• Others
• Other Wavelengths
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Fort Lewis College
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Review
• What was the most important thing you
learned?
• the speed of light, x-ray, gamma rays... is all
the same. (~= 3.00x108 m/s)
• wavelength x frequency = velocity
• frequency = 1/period
• Electromagnetic waves don’t need anything to
move in.
• There are far more types of invisible “light”
than there are visible
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Fort Lewis College
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The Speed of Light
299,792.458 km/sec
(~= 3.00x108 m/s)
It’s not just a good idea.
It’s the law!
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Fort Lewis College
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Figure 2.8
Electromagnetic Spectrum
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Fort Lewis College
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Which is correct
A)
B)
C)
D)
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Fort Lewis College
period * frequency = wavelength
velocity / period = wavelength
velocity * frequency = wavelength
velocity * period = wavelength
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Which is correct
A)
B)
C)
D)
Charles Hakes
Fort Lewis College
period * frequency = wavelength
velocity / period = wavelength
velocity * frequency = wavelength
velocity * period = wavelength
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Which list is in the correct order of electromagnetic
radiation frequency, going from lowest to highest?
A) infrared, ultraviolet, gamma, radio
B) gamma, x-ray, ultraviolet, visible
C) radio, infrared, visible, ultraviolet
D) radio, x-ray, ultraviolet, visible
E) red, violet, blue, green
Charles Hakes
Fort Lewis College
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Which list is in the correct order of electromagnetic
radiation frequency, going from lowest to highest?
A) infrared, ultraviolet, gamma, radio
B) gamma, x-ray, ultraviolet, visible
C) radio, infrared, visible, ultraviolet
D) radio, x-ray, ultraviolet, visible
E) red, violet, blue, green
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Fort Lewis College
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Discussion/Exercise
• What is the wavelength of a microwave
oven at 2.45 GHz?
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Fort Lewis College
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What is the wavelength of a
microwave oven at 2.45 GHz?
A)
B)
C)
D)
7.35x1017 m
0.735 m
122 m
0.122 m
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Fort Lewis College
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Chapter 3
Hubble Space Telescope and VLT
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Fort Lewis College
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Figure 3.6bc
Palomar Telescope
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Fort Lewis College
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Figure 3.8
Mauna Kea Observatory
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Fort Lewis College
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Figure 3.9
VLT Observatory
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Fort Lewis College
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Figure 3.X
FLC Observatory
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Fort Lewis College
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Figure 3.X
FLC Observatory
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Fort Lewis College
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Telescopes
• What is a telescope?
• What does it do for you?
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Fort Lewis College
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Telescopes
• A telescope is a “light bucket” - it
gathers photons.
• A telescope is an imaging device - it
focuses the photons.
• It also magnifies, but this is less important.
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Fort Lewis College
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Figure 3.1
Reflecting Mirror
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Fort Lewis College
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Figure 3.3
Image Formation
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Fort Lewis College
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Types of Telescopes
• Refractor
• Galilean
• Achromatic
• Apochromatic
• Reflector
• Newtonian
• Cassegrain
• Catadioptric
• Schmidt Cassegrain
• Maksutov Cassegrain
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Fort Lewis College
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Figure 3.4
Reflectors and Refractors
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Fort Lewis College
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Refractors
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Fort Lewis College
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Figure 3.2
Refracting Lens
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Fort Lewis College
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Figure 2.7
Visible Spectrum
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Fort Lewis College
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Refractors
• Galilean • Uses one positive and one negative lens.
• No longer made. (except for toys = “pirate”
telescope)
• Very narrow field of view
• Achromatic
• Apochromatic
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Fort Lewis College
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Refractors
• Achromatic
•
•
•
•
Most common type of small telescope today.
The “objective” lens has two different types of glass.
Red light and green light can focus in the same spot.
Often have a “purple haze” on bright objects.
• Apochromatic
• Uses exotic glass or more than two lens elements.
• Gets three of more colors to focus together - no more
purple haze
• Expensive.
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Fort Lewis College
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Demonstration
• Making a refractor telescope
• Objective
• Eyepiece
• Mount
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Fort Lewis College
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Reflectors
• Newtonian
• Parabolic mirror
• Several places possible to focus the light.
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Fort Lewis College
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Figure 3.5
Reflecting Telescopes
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Fort Lewis College
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Reflectors
• Assembly Demonstration
• Advantages
• can make mirrors bigger (can support them
from the back)
• Reflection only on surface (colors focus
together)
• Only need one optical surface (lenses require
at least two)
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Fort Lewis College
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Telescopes
• Building your own telescope can be very
fun and rewarding.
• You cannot build a telescope as cheaply
as you can buy one.
• Be sure to get good eyepieces. Half the
imaging device is the eyepiece. Some
can be expensive, however.
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Fort Lewis College
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Telescopes
• No telescope is good at all things.
• Know what you want to observe.
• The best telescope is the one that gets
used the most.
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Fort Lewis College
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Useful Parameters
• Focal ratio (focal length/diameter)
• Magnification (FL/fl)
• maximum 50x/inch rule of thumb
• or… 300x max (from the atmosphere)
• Exit pupil (diameter/magnification)
• 7mm max
• 0.5mm min
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Fort Lewis College
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Figure 3.7
Sensitivity
•Size does matter
•Bigger is better!
(diameter, that is)
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Fort Lewis College
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Figure 3.6a
Palomar Telescope
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Fort Lewis College
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Figure 3.6bc
Palomar Telescope
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Fort Lewis College
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Figure 3.8
Mauna Kea Observatory
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Fort Lewis College
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Figure 3.9
VLT Observatory
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Fort Lewis College
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Telescope size
• Light gathering ability is proportional to the area of
the objective.
• This means it is proportional to the diameter squared.
• 8” telescope gathers 4 times the light of a 4” telescope.
( 8”x8”=64 sq in, 4”x4”=16 sq in )
• Photographic exposures would be 1/4 as long on the 8”
as they would be on the 4”
• Similarly, an 8” telescope gathers 1/4 as much light as a
16” telescope.
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Fort Lewis College
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Size Example - Binoculars
• 10x50 binoculars
• “10” means • “50” means -
• How much more light can they gather than
your naked eye?
• eyes ~7mm diameter
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Fort Lewis College
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Size Example - Binoculars
• 10x50 binoculars
• “10” means - magnification
• “50” means -
• How much more light can they gather than
your naked eye?
• eyes ~7mm diameter
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Fort Lewis College
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Size Example - Binoculars
• 10x50 binoculars
• “10” means - magnification
• “50” means - diameter in mm
• How much more light can they gather than
your naked eye?
• eyes ~7mm diameter
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Fort Lewis College
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Size Example - Binoculars
• 10x50 binoculars ~50x area of pupil.
• To get another 50x light gathering power,
you would need ~14” diameter telescope!
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Fort Lewis College
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A 5 meter (diameter) telescope
A) gathers 5 times as much light as a 1 m telescope
B) gathers 1/2 as much light as a 10 m telescope
C) gathers 4 times as much light as a 2.5 m telescope
D) gathers 5/2 as much light as a 2 m telescope
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Fort Lewis College
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A 2 meter telescope takes a picture of a
galaxy in 10 minutes.
How long will it take to make the same
exposure using a 1 meter telescope?
A) 5 minutes
B) 2.5 minutes
C) 20 minutes
D) 40 minutes
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Fort Lewis College
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Figure 3.10
Resolution
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Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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