Transcript Foundation 1 - Discovering Astronomy

Chapter 6:
Telescopes – Portals of
Discovery
Visible light is only one
type of electromagnetic
radiation emitted by stars
Each type of EM radiation
travels at exactly the same
speed - the speed of light!
Not all EM radiation can penetrate Earth’s atmosphere.
Different types of EM radiation require
different types of telescopes
• A refracting telescope uses a lens to concentrate
•
incoming light
A reflecting telescope uses mirrors to
concentrate incoming starlight
Refracting Telescope
• Refracting
telescopes need to
be very long,
with large, heavy
lenses.
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A refracting
telescope uses a
lens to
concentrate
incoming light
Similar to a
magnifying glass
A larger objective
lens provides a
brighter (not
bigger) image
lenses
reverse
images
Three main functions of a telescope
• brighten
(called light collecting area)
• see fine detail
(called angular resolution)
and least important,
• magnify
magnification = (objective lens focal length / eyepiece lens focal
length)
Refracting telescopes have drawbacks
• Spherical aberration
• Chromatic aberration
Special achromatic compound lenses and lens
coatings can often fix this aberration
Refracting telescopes have drawbacks
• Spherical aberration
• Chromatic aberration
• Sagging due to gravity
distorting the lens
• Unwanted refractions
• opaque to certain
wavelengths of light
Reflecting Telescope
• Reflecting telescopes can have much greater diameters.
• Most modern telescopes are reflectors.
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Designs for Reflecting Telescopes
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Mirrors in Reflecting Telescopes
Pick-up
images.
Twin Keck telescopes on
Mauna Kea in Hawaii
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Segmented 10-meter mirror of a
Keck telescope
Astronomer’s face two major obstacles
in observing the stars
• Light Pollution from Cities
• Effects of Twinkling from Earth’s atmosphere
Light Pollution
• Scattering of human-made light in the atmosphere is
a growing problem for astronomy.
Tucson, Arizona in 1959 and 1980
Twinkling and Turbulence
Bright star viewed with groundbased telescope
Same star viewed with Hubble
Space Telescope
• Turbulent air flow in Earth's atmosphere distorts our view,
causing stars to appear to twinkle.
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Rapid changes in the density of
Earth’s atmosphere cause passing
starlight to quickly change direction,
making stars appear to twinkle.
Advanced technology is spawning a new
generation of equipment to view the universe
• CCDs (charge-coupled devices)
• Large telescopes on remote mountain tops
– Mauna Kea in Hawaii
– Cerro Pachon in Chile
• Adaptive Optics to counteract the blurring of Earth’s
•
atmosphere
Orbiting space observatories
A Charge-Coupled Device (CCD)
Ordinary Photographs vs. CCDs
Matching 10-m, multiple mirror
Keck Telescopes in Hawaii with
adaptive optics
Adaptive Optics
Without adaptive optics
With adaptive optics
• Rapidly changing the shape of a telescope's mirror compensates for some
of the effects of turbulence.
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Calm, High, Dark, Dry
• The best
observing sites
are atop
remote
mountains.
Summit of Mauna Kea, Hawaii
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High above
Earth’s
atmosphere, the
Hubble Space
Telescope
provides stunning
details about the
universe
Observations at wavelengths other than visible light
are revealing previously invisible sights
Visible light image
radio wavelength image
Radio wavelength observations are
possible from Earth’s surface
Radio Telescopes
• A radio
telescope is
like a giant
mirror that
reflects radio
waves to a
focus.
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Infrared and Ultraviolet Telescopes
SOFIA
Spitzer
• Infrared and ultraviolet light telescopes operate like visiblelight telescopes but need to be above atmosphere to see all
wavelengths.
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X-Ray Telescopes
• Focusing of X-rays requires special mirrors.
• Mirrors are arranged to focus X-ray photons through grazing
bounces off the surface.
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Gamma-Ray Telescopes
• Gamma-ray
telescopes also need
to be in space.
• Focusing gamma
rays is extremely
difficult.
Fermi Gamma-Ray Observatory
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Interferometry
• Interferometery is a
technique for
linking two or more
telescopes so that
they have the
angular resolution
of a single large
one.
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The Very Large Array (VLA) in New Mexico
Observations at other wavelengths are revealing
previously invisible sights
UV
infrared
Ordinary
visible
Map of
Orion
region
The Future of Telescopes?
• Telescopes at Lagrange Points
• Telescopes on other planets/moons
• A large telescope to take over for Hubble on the
•
•
•
Moon’s polar region
Better telescopes on Earth, larger, coupled
Gravity wave detectors
Improved optics…..