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Unformatted text preview: Light: The Cosmic Messenger
How does light tell us the
speed of a distant object? The Doppler Effect Doppler Shifts
REDSHIFT Hearing the Doppler effect
Cause of the Doppler effect BLUESHIFT Moving AWAY
“Redder” Moving TOWARD
“Bluer” Doppler effect for light No moving or moving ACROSS No shift Doppler Effect & Relative Motion
V=0 (or across)
Wavelength V>0 (away)
V>>0 Measuring Redshift
Measuring Velocity V<0 (towards)
V<<0 1 Doppler Effect Summary Telescopes Motion to or away from an observer causes a a
shift in the observed wavelength of light.
Motion towards you -> “blueshift” = shorter
Motion away from you -> “redshift” = longer
Motion across the sky -> no shifts.
Size of the wavelength shift measures speed. Advantages over eyes
How do telescopes help us
learn about the Universe? Bigger is better
1. Larger light-collecting area
2. Better angular resolution • Bigger (more sensitive, more accurate)
• Can add cameras, CCDS
• Can “see” more of the electromagnetic
spectrum 1. Light Collecting Area
• Larger is better.
• “Size” = diameter = d
• Area is proportional to d2 :
• 2x diameter means 4x area
• 10-meter has 4x more area than a 5-meter 2 2. Angular Resolution
• Units of
e.g. 1’ (eye),
0.05” (HST) Resolution
Diameter Bigger diameter ->
Better resolution A star as seen by
the Hubble Space
A* B* Where would you put your large telescope? The Biggest Optical Telescope
Keck I and
10 meters in
Mauna Kea, Hawaii 3 Basic Telescope Design Basic Telescope Design • Reflecting: mirrors
• Refracting: lenses • Reflecting: mirrors
• Refracting: lenses • Nearly all
are reflecting • Nearly all
are reflecting Basic Telescope Design
• Reflecting: mirrors
• Refracting: lenses
• Nearly all
are reflecting Why put telescopes in space? Want one?
• Buy binoculars first (e.g. 7x35) - you get
much more for the same money.
• Ignore magnification (sales pitch!)
• Notice: aperture size, optical quality,
• “Go-to” capability.
• Consumer research: Astronomy, Sky &
Tel, Mercury. Astronomy clubs. Atmospheric Effects
• Light Pollution
• Turbulence causes twinkling - blurs
• High dry places best.
• Above atmosphere even better. 4 Turbulence
view. View from
atmosphere Atmospheric Absorption View from
Hubble Infrared Telescopes • Atmosphere absorbs X-ray, UV, some
infrared (Figure 5.24) Spitzer Infrared observatory detects “ warm” regions in space 5 X-ray Telescopes
• Must be in space
• Focusing X-rays
is like focusing
focus the light. Chandra X-ray Observatory observes energetic
phenomena. How does technology
revolutionize astronomy? Correcting
optics Adaptive Optics Adaptive Optics 6 Radio Telescopes
Allows small telescopes to work together to obtain the
angular resolution of a large telescope. VLA
New Mexico Very Large Array (VLA) : 40 km “telescope” MSU’s telescope: SOAR
telescope MSU has 12% of all of the
nights (40/year) & built the
Spartan IR camera 7 SOAR telescope mirror is 4.1 meters.
The SOAR site is dark, high, calm, and dry.
Chileʼs Atacama desert 8 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.
- Fall '08