# Download Wave: a disturbance which carries energy through a material or

Survey

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Hubble Space Telescope wikipedia, lookup

Arecibo Observatory wikipedia, lookup

James Webb Space Telescope wikipedia, lookup

Spitzer Space Telescope wikipedia, lookup

International Ultraviolet Explorer wikipedia, lookup

XMM-Newton wikipedia, lookup

CfA 1.2 m Millimeter-Wave Telescope wikipedia, lookup

Optical telescope wikipedia, lookup

Very Large Telescope wikipedia, lookup

Reflecting telescope wikipedia, lookup

Transcript
```Chapter 6: Light and Telescopes
Wave: a disturbance which carries energy through a material or
through empty space.
Often a regular series of disturbances
Wavelength (λ ): distance between successive crests
Frequency (f ): rate at which crests pass a fixed point
Energy Flux: rate at which the wave carries energy through a given
area, Intensity
a1c6:1
Electromagnetic Waves
Electric and Magnetic disturbance
[fig 6.2, em_plane_polarization1.avi]
wave speed: 3x108 m/s
=186,000 miles per second
= speed of light (c)
Ey
Bz
x
Electromagnetic Flux
energy per area = ‘brightness’
Flux-distance-energy relationship: Inverse Square Law
[figure 6-3 ,inverse_square_law.mov]
Intensity decreases with distance in a particular way (mathematically)
F=
E
4πd 2
a1c6:2
Wavelength and frequency
λf=c
[wave1.gif ]
higher frequency shorter wavelength
spectrum : different frequencies [Figure 6-5]
Doppler Effect: moving wave source’s motion affects received
frequency
[tuning fork demonstration, Figure 6-6, doppler_shift_interacti.swf]
∆λ =
λ 0vr
c
“red” shift
= lower frequency/longer wavelength
= moving away
“blue” shift
= higher frequency/shorter
wavelength
= moving towards
a1c6:3
Photons: particles of light
light comes in “quanta” (or packets) of energy = photons
photoelectric effect: an experiment whose results are inconsistent with the wave nature
of light [figure 6.7]
photon energy depends upon frequency [fig 6.8]
E=hf
higher f higher E lower λ
a1c6:4
Light “rays” [ http://www.falstad.com/ripple/, optical disk demos]
i
r
Reflection (light rays bounce) [Fig 6-9]
i
Refraction (light rays bend) [Fig 6-11,12]
index of refraction n = c/v
= the optical “thickness” of a material
r
also
Diffraction: light (as a wave) bends around corners
Dispersion: light rays separated according to wavelength (color)
prism [Fig 6-13]
a1c6:5
Optical Telescopes
Refractor: objective is a lens
Lens [demonstration optical disk, fig 6.15,16]
focal point
focal length
focal point
focal length
a1c6:6
Optical Telescopes
Reflector: objective is a mirror
Mirror [demonstration optical disk, fig 6.18]
focal point
focal length
focal point
focal length
a1c6:7
Forming an Image [figure 6-19]
Focal Plane: where lens or mirror forms image
Brightness of an image depends upon:
•Light-gathering power of objective (area A)
•Size of image (focal length f )
~(Diameter/f)2
f-number is the “speed” of a lens or mirror = f/D
smaller f-number → more light → shorter exposure
Resolution: ability to resolve fine detail [figure 6.20, resolver.avi]
Diffraction: light (as a wave) bends around corners
→ smallest resolvable angle
θ = 250,000 λ/D
resolution depends upon wavelength! [resolver_wavelength.avi]
Magnification: angular size of image/angular size of object
m = fp/fe
[figure 6-21]
a1c6:8
Detectors: beyond the human eye (requirements for: sensitivity,
non-visible wavelengths, numerical measurements, permanent
record)
Photography: Telescope acts as a camera
Photometer: measures brightness of an object
CCDs (Charge Coupled Devices): digital electronic
imaging, very sensitive [fig6-22, 23 A=photo B=CCD of same field]
Spectroscopy: light is dispersed according to wavelength
[grating demonstration, suna.jpg (sun's spectrum in detail)]
Spectrograph: also known as a Spectrometer, a device
that measures spectra [figure 6-24]
a1c6:9
Telescopes
Large Refractors: largely pre 1900
40 inch (1 m) Yerkes Observatory [fig 6.25]
Large Reflectors
Mount Wilson (1.5 m in 1908, 2.5 m in 1917)
Mount Palomar (5m in 1948)
Mauna Kea (10-m Keck) telescope
[fig 6.26]
uses Adaptive Optics to improve seeing
seeing: blurring of an image because of atmospheric turbulence
[laser demonstration]
[06ex1.jpg, 06ex2.jpg, fig 6.31 (same telescope w/wout adaptive optics)]
Very Large Telescope (VLT) in Chile [figure 6-27]
a1c6:10
Observatories
Transmission through earth’s atmosphere depends upon wavelength [Fig 6-29]
Light Pollution [figure 6.30]
Optical Observatories [fig 6.32(Kitt Peak), fig 6.33 (Chile) fig 6.34 Hawaii]
Radio Telescopes: larger wavelengths = more resolution problems
Large Dishes (arecibo [fig 6.40])
increased resolution using interferometry (arrays)
VLA ~ 27 km [fig 6.41]
VLBA ~ continental USA [Figure 6-42])
[fig 6.44 length scale of resolvable objects at distance of moon by A:Arecibo B:VLA C:VLBA]
Space Observatories
Hubble Space Telescope [Figure 6-35,36]
James Webb Telescope (2013) Hubble's successor (visible & infrared)
Spitzer Space Telescope (Space Infrared Telescope Facility) [fig 6.37]
International Ultraviolet Explorer (1978 -1996)
Einstein X-Ray Observatory(1970's), Chandra (1999-) [fig 6.38,39]
Compton Gamma Ray observatory (1991-2000)
Planes, Rockets, Balloons: means to get above some of the atmosphere
a1c6:11
```
Related documents