![Page 1: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/1.jpg)
Chapter 5Telescopes: “light bucket”
![Page 2: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/2.jpg)
Telescopes have three functions
1.Gather as much light as possible:
LGP ∝ Area = πR2 Why?
UV IR
Ene
rgy
Out
put
Wavelength
![Page 3: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/3.jpg)
The light gathering power is proportional to
the area
![Page 4: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/4.jpg)
Telescopes have three functions
2. Resolve objects: Θ = 0.25 (λ/D)Why?In astronomy, we are always concerned with angular measurement
“close together” means “separated by a small angle on the sky,”
angular resolution is the factor that determines our ability to see fine structure
![Page 5: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/5.jpg)
Telescopes have three functions
3. Magnify EXTENDED objects. Why?
Extended objects: The most surprising property is that extended objects do not get brighter in a scope.
Also the contrast does not change (actually it only can get worse).
The only thing that changes is that the object itself gets bigger by magnification
![Page 6: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/6.jpg)
Reflection is the
bouncing of light off a surface
![Page 7: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/7.jpg)
How do we see an object
Light rays coming from one point of an object are focused at one point at the back of your eye
(retina).
Different points from an object are focused at different points of your retina.
So we see an image of the object produced by the lense in our eyes at the back of our eye.
![Page 8: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/8.jpg)
A telescope is not a microscope• Microscope’s function is magnification
• Telescope’s function is gathering as much light as possible: Large lenses
• Large lenses do not result in larger magnification
![Page 9: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/9.jpg)
The refracting telescope uses two lenses.
Where is the image of the star?
Light Bending
![Page 10: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/10.jpg)
Problem with refraction
Different color light is refracted at different angles, causing a distortion of the image
![Page 11: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/11.jpg)
Refractors suffer from Chromatic Aberration
![Page 12: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/12.jpg)
Dispersive refraction leads to chromatic aberration:
More on chromatic aberration
CLL: Diffraction Rings
![Page 13: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/13.jpg)
Chromatic Aberration
![Page 14: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/14.jpg)
Images can be formed through reflection or refraction
Reflecting mirror
![Page 15: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/15.jpg)
Image formation
Where do you stand to observe the object?
What’s the problem with that?
How to overcome the problem?
![Page 16: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/16.jpg)
Types of reflecting telescopes:
To get around the blocking of light when you stand in the focal plane, different telescope types were invented
![Page 17: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/17.jpg)
Do reflecting optical devices suffer from chromatic aberration
A) Yes, different color light reflects at different angles and therefore focuses at different points.
B) No, different color light reflects always at the same angle as it incidents, causing no chromatic aberration.
![Page 18: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/18.jpg)
But: Spherical mirrors suffer from Spherical
Aberration
Parallel light from different locations of the mirror is not exactly focused at one point
![Page 19: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/19.jpg)
Spherical aberration
can be eliminated
by a parabolic shape or a corrector
plate
CLL: Focus of a Cassegrain reflector
![Page 20: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/20.jpg)
![Page 21: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/21.jpg)
Optical TelescopesThe Keck telescope, a modern research telescope:
![Page 22: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/22.jpg)
Optical Telescopes
The Hubble Space Telescope has a variety of detectors:
![Page 23: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/23.jpg)
Discovery 5-1: The Hubble Space Telescope
The Hubble Space Telescope’s main mirror is 2.4 m in diameter and is designed for visible, infrared, and ultraviolet radiation
![Page 24: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/24.jpg)
Discovery 5-1: The Hubble Space Telescope
Here we compare the best ground-based image of M100, on the left, with the Hubble image on the right
![Page 25: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/25.jpg)
In astronomy, we are always concerned with angular measurement
“close together” means “separated by a small angle on the sky,”
angular resolution is the factor that determines our ability to see fine structure
Protractor-string Example
![Page 26: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/26.jpg)
Light-gathering power: Improves detail
Brightness proportional to square of radius of mirror
Below: (b) was taken with a telescope twice the size of (a)
Telescope Size
![Page 27: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/27.jpg)
Resolving power: When better, can distinguish objects that are closer together
Resolution is proportional to wavelength and inversely proportional to telescope size—bigger is better!
Telescope Size
![Page 28: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/28.jpg)
Resolution
Want to resolve objects which are close
together.
Objects that are close together are
separated by a smaller angle than objects
that are at the same distance but further
apart.
Θ = 2.06 X 105 (λ/D)
Smaller the better
![Page 29: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/29.jpg)
How to improve the resolution?• A) Increase the size of the mirror• B) Decrease the size of the mirror• C) Use light with smaller wavelength• D) Use light with larger wavelength
Smaller the better
For comparison, the angular resolution of the human eye in the middle of the visual range is about 0.5'.
![Page 30: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/30.jpg)
What limits a telescope’s resolution?
One important factor is diffraction, the tendency of light, and all other waves to bend around corners
Diffraction introduces a certain “fuzziness,” or loss of resolution
![Page 31: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/31.jpg)
Effect of improving resolution:
(a) 10′; (b) 1′; (c) 5″; (d) 1″
5.2 Telescope Size
![Page 32: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/32.jpg)
Image acquisition: Charge-coupled devices (CCDs) are electronic devices, can be quickly read out and reset
5.3 Images and Detectors
![Page 33: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/33.jpg)
5.3 Images and Detectors
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation
![Page 34: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/34.jpg)
Image processing by computers can sharpen images
5.3 Images and Detectors
![Page 35: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/35.jpg)
Atmospheric blurring: Due to air movements5.4 High-Resolution Astronomy
![Page 36: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/36.jpg)
“Seeing”
![Page 37: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/37.jpg)
Solutions:
• Put telescopes on mountaintops, especially in deserts
• Put telescopes in space
5.4 High-Resolution Astronomy
![Page 38: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/38.jpg)
Active optics: Control mirrors based on temperature and orientation
5.4 High-Resolution Astronomy
![Page 39: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/39.jpg)
Adaptive optics: Track atmospheric changes with laser; adjust mirrors in real time
5.4 High-Resolution Astronomy
![Page 40: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/40.jpg)
5.4 High-Resolution Astronomy
These images show the improvements possible with adaptive optics:
![Page 41: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/41.jpg)
Radio telescopes:
• Similar to optical reflecting telescopes
• Prime focus
• Less sensitive to imperfections (due to longer wavelength); can be made very large
5.5 Radio Astronomy
![Page 42: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/42.jpg)
Largest radio telescope: 300-m dish at Arecibo
5.5 Radio Astronomy
![Page 43: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/43.jpg)
Longer wavelength means poor angular resolution
Advantages of radio astronomy:
• Can observe 24 hours a day
• Clouds, rain, and snow don’t interfere
• Observations at an entirely different frequency; get totally different information
5.5 Radio Astronomy
![Page 44: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/44.jpg)
Interferometry:
• Combine information from several widely spread radio telescopes as if they came from a single dish
• Resolution will be that of dish whose diameter = largest separation between dishes
5.6 Interferometry
![Page 45: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/45.jpg)
5.6 Interferometry
Interferometry involves combining signals from two receivers; the amount of interference depends on the direction of the signal
![Page 46: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/46.jpg)
Can get radio images whose resolution is close to optical
Interferometry can also be done with visible light but is much more difficult due to shorter wavelengths
5.6 Interferometry
![Page 47: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/47.jpg)
Infrared radiation can image where visible radiation is blocked; generally can use optical telescope mirrors and lenses
5.7 Space-Based Astronomy
![Page 48: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/48.jpg)
Infrared telescopes can also be in space; the image on the left is from the Infrared Astronomy Satellite
5.7 Space-Based Astronomy
![Page 49: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/49.jpg)
The Spitzer Space Telescope, an infrared telescope, is in orbit around the Sun. These are some of its images.
5.7 Space-Based Astronomy
![Page 50: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/50.jpg)
Ultraviolet observing must be done in space, as the atmosphere absorbs almost all ultraviolet rays.
5.7 Space-Based Astronomy
![Page 51: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/51.jpg)
X-rays and gamma rays will not reflect off mirrors as other wavelengths do; need new techniques
X-rays will reflect at a very shallow angle and can therefore be focused
5.7 Space-Based Astronomy
![Page 52: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/52.jpg)
X-ray image of supernova remnant
5.7 Space-Based Astronomy
![Page 53: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/53.jpg)
Gamma rays cannot be focused at all; images are therefore coarse
5.7 Space-Based Astronomy
![Page 54: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/54.jpg)
Much can be learned from observing the same astronomical object at many wavelengths. Here, the Milky Way:
5.8 Full-Spectrum Coverage
![Page 55: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/55.jpg)
• Refracting telescopes make images with a lens
• Reflecting telescopes with a mirror
• Modern research telescopes are all reflectors
• CCDs are used for data collection
• Data can be formed into image, analyzed spectroscopically, or used to measure intensity
• Large telescopes gather much more light, allowing study of very faint sources
• Large telescopes also have better resolution
Summary of Chapter 5
![Page 56: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/56.jpg)
• Resolution of ground-based optical telescopes is limited by atmospheric effects
• Resolution of radio or space-based telescopes is limited by diffraction
• Active and adaptive optics can minimize atmospheric effects
• Radio telescopes need large collection area; diffraction limited
• Interferometry can greatly improve resolution
Summary of Chapter 5 (cont.)
![Page 57: Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?](https://reader035.vdocuments.site/reader035/viewer/2022062314/56649e025503460f94aeceb8/html5/thumbnails/57.jpg)
• Infrared and ultraviolet telescopes are similar to optical
• Ultraviolet telescopes must be above atmosphere
• X-rays can be focused, but very differently than visible light
• Gamma rays can be detected but not imaged
Summary of Chapter 5 (cont.)