AST 103
Telescopes
Prof. Ken Nagamine
UNLV
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Telescopes
• The best observing
sites are atop remote
mountains
Calm, High, Dark, Dry
Mauna Kea, Hawaii
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A telescopes is a tool used to gather
light from objects in the universe
There are two different types of telescopes
• A refracting telescope: focuses light
with glass lenses
• A reflecting telescope: focuses light
with mirrors
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A refracting telescope uses a lens
to focus incoming light
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Refraction
• Refraction is the
bending of light
when it passes
from one
substance into
another
• Your eye uses
refraction to
focus light
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Focusing Light
• Refraction can cause parallel light rays to
converge to a focus
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Refracting Telescope
• Refracting
telescopes need
to be very long,
with large, heavy
lenses
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Reflecting Telescope
• Reflecting telescopes can have much greater
diameters
• Most modern telescopes are reflectors
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Reflecting telescopes use mirrors to
focus incoming starlight
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Mirrors in Reflecting Telescopes
Twin Keck telescopes on
Mauna Kea in Hawaii
Segmented 10-meter mirror of
a Keck telescope
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Many big telescopes!!
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Three main functions of
a telescope
• gather light – (bigger IS better) –
makes objects appear brighter
Telescopes with a larger collecting area can gather
a greater amount of light in a shorter time.
• see fine detail (resolution)
Telescopes that are larger are capable of
taking images with greater detail.
• magnify
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A larger objective
lens provides a
brighter (not
bigger) image
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But visible light is just
one part of spectrum
Astronomers are interested
in the entire spectrum of
light!
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Astronomers use different instruments to look at light
of different wavelengths - sometimes, we even have to
go above Earth’s atmosphere.
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Quiz
Which of the following wavelengths can be
observed easily by a telescope located on
Earth’s surface?
a) gamma ray
b) X-ray
c) ultraviolet
d) radio
e) all of the above wavelengths
f) none of the above wavelengths
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IR & UV Telescopes
SOFIA (IR)
GALEX
(UV)
Spitzer (IR)
• Infrared and ultraviolet-light telescopes operate
like visible-light telescopes but need to be above
atmosphere to see all IR and UV wavelengths
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Radio wavelength observations are
possible from Earth’s surface
Green Bank
(west virginia)
Arecibo, Puerto Rico
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The Very Large Array (VLA) in New Mexico
Interferometer
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High above
Earth’s
atmosphere, the
Hubble Space
Telescope
provides
stunning details
about the
universe
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Earth’s atmosphere hinders astronomical research
Image of stars taken
with a telescope on the
Earth’s surface
Same picture taken with
Hubble Space Telescope
high above Earth’s blurring
atmosphere
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Lecture-Tutorial (LT):
Telescopes (pp. 49-51)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
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•
•
one another.
Come to a consensus answer you both agree
on.
If you get stuck or are not sure of your answer,
ask another group.
If you get really stuck or don’t understand what
the LT is asking, ask for help.
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Quiz
Which of the following wavelengths of
light emitted by the Sun is most effectively
blocked by Earth’s atmosphere?
a) visible
b) radio
c) infrared
d) gamma
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Quiz
Imagine that you are the head of a funding
agency that can afford to build one telescope.
Which of the following proposed telescopes
would be best to support?
a) a radio telescope in orbit around Earth
b) an ultraviolet telescope in orbit around Earth
c) an X-ray telescope located in New Mexico
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Quiz
The Hubble Space Telescope obtains
higher resolution images than most
ground-based telescopes because it is
a) larger.
b) closer to stars.
c) above Earth’s atmosphere.
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