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Telescopes and the Atmosphere
• Our goals for learning
• How does Earth’s atmosphere affect ground-based observations?
• Why do we put telescopes into space?
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How does Earth’s atmosphere affect ground-based observations?
• The best sites for astronomical observing are those that avoid the worst problems caused by the atmosphere.
• Light pollution
• Turbulence
• atmospheric losses – (clouds, wavelength absorptions)
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1) Light Pollution• Scattering of human-made light in the atmosphere
is a growing problem for astronomy
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2) Twinkling and TurbulenceTurbulent air flow in Earth’s atmosphere distorts our view, causing stars to appear to twinkle
Star viewed with ground-based telescope
Same star viewed with Hubble Space Telescope
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Adaptive OpticsRapidly changing the shape of a telescope’s mirror
compensates for some of the effects of turbulence
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Adaptive OpticsThe light’s wave peaks do not interfere with each
other so badly, so the result is increased resolution
Without adaptive optics With adaptive optics
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• The best ground-based sites for astronomical observing are– Calm (not too windy)– High (less atmosphere to see through)– Dark (far from city lights)– Dry (few cloudy nights)
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Calm, High, Dark, Dry
• The best observing sites are atop remote mountains, in deserts
Summit of Mauna Kea, Hawaii
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3) Transmission in Atmosphere
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3) Transmission in Atmosphere
• Only radio and visible light pass easily through Earth’s atmosphere
• We need telescopes in space to observe other forms
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What have learned?• How does Earth’s atmosphere affect
ground-based observations?– Telescope sites are chosen to minimize
the problems of light pollution, atmospheric turbulence, and bad weather.
• Why do we put telescopes into space?– Forms of light other than radio and visible
do not pass through Earth’s atmosphere.– Also, much sharper images are possible
because there is no turbulence.
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A team of astronomers wants to build an x-ray telescope on a high mountain (10
km above sea level). Will this work?
A.Yes, we already have telescopes like this
B.Yes it's the 1st of its kind
C. No it's too hard to put telescopes on mountains
D.No x rays don't penetrate the atmopshere
Thought Question
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Eyes & Cameras: Everyday Light Sensors
• Our goals for learning
• How can we observe nonvisible light?
• How can multiple telescopes work together?
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How can we observe nonvisible light?
• A standard satellite dish is essentially a telescope for observing radio waves
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Radio Telescopes
• A radio telescope is like a giant mirror that reflects radio waves to a focus
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How can multiple telescopes work together?
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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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Interferometry
• Easiest to do with radio telescopes
• Now becoming possible with infrared and visible-light telescopes
Very Large Array (VLA)
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Allen Telescope Array, CA
• 48 radio linked telescopes, more are planned
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Other wavelengths: IR, Microwave
• To detect other wavelengths, instruments need to be above most of the atmosphere.
SOFIA Balloons, used for measuring Cosmic rays, CMB and nutrinos
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Space telescopes and Spacecraft
• Clearer view (space telescopes)• Closer view (spacecraft)
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Other wavelengths: UV & IR
• Infrared and ultraviolet-light telescopes operate like visible-light telescopes but need to be above atmosphere to see all IR and UV wavelengths
GALEX Spitzer
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High Energy Telescopes
• X-ray and Gamma ray telescopes also need to be above the atmosphere
Chandra (X-rays) Compton Observatory(Gamma rays)
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Chandra X-Ray Telescope
• 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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X-rays, Chandra Visible, Hubble IR, Spitzer
M51 in Multiple WavelengthsThe data from different spacecraft can be combined to
produce simultaneous multi-wavelength images
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1960s - Present: Spacecraft!
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Exploration Strategy
1. Initial Reconnaissance - a) Earth-based Observation - b) Fly- by mission.
2. Exploration phase - a) Planetary orbiter. - b) Surface landers.
3. Intensive Study - a) rovers - b) sample return - c) manned exploration
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Current Vital Statistics Reconnaissance Exploration Intensive Study
Observation Fly-by Orbiter Lander/Probe
Rover Sample Return
Manned
Mercury Yes Yes In flight In flight
Venus Yes Yes Yes Yes
Moon Yes Yes Yes Yes Yes Yes Yes
Mars Yes Yes Yes Yes Yes proposed
Jupiter Yes Yes Yes Yes
Saturn Yes Yes Yes Yes/Titan
Uranus Yes Yes
Neptune Yes Yes
Pluto Yes In flight
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Spacecraft
• Each mission has identified goals appropriate to what we want to know about a specific world.
• The answers we want each require specific types of data.
• The spacecraft carries instruments tailored to take that data and send it back to Earth for analysis
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Instrument Purpose Result UsefulnessCameras
(often in IR)Take pictures maps Discover what’s on the
surface
Spectrometers Remote chemical analysis
Spectra Discover some of surface composition.
Neutron detectors ” Neutron maps find near surface water
Lander instrument package (various)
Measure surface conditions
Temps, wind speed, images
Discover what’s it like on the surface
Sample return Discover what ground is made of
Age dating, chemical analysis
Find the age & composition of key areas of the world
Radio/plasma Science packages
Measures behavior of electrical fields
Dust distribution in a system
Understand upper atm. & ring systems
Magnetometer Measures Magnetic fields
Magnetic map Data sets are combined to discover what the interior of the world is like.Altimeter Measures heights Height map
Doppler shift of spacecraft
spacecraft movement in relation
the planet
Find high-mass areas causing extra gravity