Transcript Light, radiation, telescopes

Light, radiation,
telescopes
Tools of the trade
 Electromagnetic
Radiation from
distant sources
 Telescopes
 Detectors
 Computers
 Lots of hard work
Electromagnetic Radiation
Characterized by
 Wavelength
 Frequency
 All types travel at
same speed…
 300,000 km/s = c

f c
f = frequency
 = wavlength
c = speed of light
Electromagnetic spectrum
Click on images to go to Physics 2000 site!
Lower frequency waves are caused by oscillating charges
What frequency do electrons in your car antenna oscillate at?
Telescopes and detectors
 First
detector:
 The Eye
The Bending of Light
Focus – to bend all light waves coming from the same
direction to a single point
Light rays which come from different directions converge
at different points to form an image.
Angular Resolution
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The ability to
separate two objects.
The angle between
two objects decreases
as your distance to
them increases.
The smallest angle at
which you can
distinguish two
objects is your
angular resolution.
Types of Telescopes
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What’s the difference between a
refracting telescope and a reflecting
telescope?
What are the two most important
properties of a telescope?
Refractor
Yerkes 40-inch telescope; largest refractor in the world
Reflecting Telescope
Lick Observatory 2.4 m
Planet Finder
Gemini 8 m telescope Hawaii
Different Reflector designs
Best type to buy?
 Dobsonian!
 Most
Bang for buck
 Large aperature
 Relatively light
 Relatively cheap
 Easy to maneuver
 Easy to fix
College scopes
 14”
Schmidt Cassegrain
 Corrector plate
 Compact design
 Tracking
 Not cheap
Build your own scope?
 Chabot
Science Center Telescope
makers workshop:
 http://www.chabotspace.org/visit/tel
escopeworkshop.asp
Space telescopes

1.
2.
Why
bother?
To improve
resolving
power
(seeing)
Observe non
visible
wavelengths
Seeing
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Due to turbulence in
atmosphere
Limits resolving power to size
of seeing disk
About ½ arc second maximum
for “normal” observing (no
adaptive optics)
With no atmosphere, seeing is
about .01 arc seconds for 10 m
telescope


D
 =wavelength, D = Diameter of objective (mirror)
Seeing Disks of Binary Stars
above are what
two binary stars
separated by 1
degree would look
like if
photographed by
Different sized
telescopes…largest
on left, smallest on
right. Hubble
images on right
More Hubble images
 .1
arc second Seeing!
Spitzer IR telescope
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85 cm aperture
Trails earth in
orbit
Cooled
Wavelength
between 3 – 180
microns
Multi-wavelength images
 Combine
light from visible and IR
telescopes!
How to improve Resolving power
 At
1m, telescopes on ground are
already “diffraction limited” by size of
seeing disk
 So…Build bigger telescope in space
 Or correct for atmospheric distortion
 Use adaptive optics
Next Generation

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James
Web
space
telescope
6.5 meter
Aperture
Launch
2011
Note
large sun
shield
Adaptive optics
 Taking
out the twinkle!
Image of a star
“dancing” on detector
due to motion of air
Laser Guide star system
 Laser
“scintillates”
atoms in
ionosphere
 Optical system
brings artificial
star into focus.
other wavelength astronomy
 Radio
Astronomy
 Uses much larger aperatures—why?
 Ultraviolet, X-Ray, Gamma Ray
In future
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Gigantic Earth
based optical
telescopes with
adaptive optics
systems
More
Interferometers