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Copyright © 2010 Pearson Education, Inc. Chapter 3 Telescopes

Copyright © 2010 Pearson Education, Inc. Telescopes

Copyright © 2010 Pearson Education, Inc. Chapter 3 Optical Telescopes Telescope Size High-Resolution Astronomy Radio Astronomy Other Astronomies

Copyright © 2010 Pearson Education, Inc. Images can be formed through reflection or refraction. Reflecting mirror Optical Telescopes Collect a large amount of light

Copyright © 2010 Pearson Education, Inc. Refracting lens Optical Telescopes

Copyright © 2010 Pearson Education, Inc. Optical Telescopes Image formation

Copyright © 2010 Pearson Education, Inc. Reflecting and refracting telescopes Optical Telescopes

Copyright © 2010 Pearson Education, Inc. Modern telescopes are all reflectors: Light traveling through lens is refracted differently depending on wavelength. Some light traveling through lens is absorbed. Large lens can be very heavy, and can only be supported at edge. Lens needs two optically acceptable surfaces, mirror only needs one. Optical Telescopes

Copyright © 2010 Pearson Education, Inc. Chromatic aberration

Copyright © 2010 Pearson Education, Inc. Types of reflecting telescopes Optical Telescopes

Question 1 Modern telescopes use mirrors rather than lenses for all of these reasons EXCEPT a) light passing through lenses can be absorbed or scattered. b) large lenses can be very heavy. c) large lenses are more difficult to make. d) mirrors can be computer controlled to improve resolution. e) reflecting telescopes aren’t affected by the atmosphere as much.

Question 1 Modern telescopes use mirrors rather than lenses for all of these reasons EXCEPT a) light passing through lenses can be absorbed or scattered. b) large lenses can be very heavy. c) large lenses are more difficult to make. d) mirrors can be computer controlled to improve resolution. e) reflecting telescopes aren’t affected by the atmosphere as much. Reflecting instruments like the KECK telescopes can be made larger, and more capable, than refractors.

Copyright © 2010 Pearson Education, Inc. Optical Telescopes Details of the Keck telescope

Copyright © 2010 Pearson Education, Inc. Image acquisition: Charge- coupled devices (CCDs) are electronic devices, can be quickly read out and reset. Optical Telescopes

Copyright © 2010 Pearson Education, Inc. CCD Camera Sensor

a) they don’t require chemical development. b) digital data is easily stored & transmitted. c) CCDs are more light sensitive than film. d) CCD images can be developed faster. e) All of the above are true. An advantage of CCDs over photographic film is Question 2

a) they don’t require chemical development. b) digital data is easily stored & transmitted. c) CCDs are more light sensitive than film. d) CCD images can be developed faster. e) All of the above are true. An advantage of CCDs over photographic film is Question 2

Copyright © 2010 Pearson Education, Inc. Image processing by computers can sharpen images. Optical Telescopes

Copyright © 2010 Pearson Education, Inc. Ground Based Telescope

Copyright © 2010 Pearson Education, Inc. Early HST

Copyright © 2010 Pearson Education, Inc. Computer Enhanced HST

Copyright © 2010 Pearson Education, Inc. Later HST

Copyright © 2010 Pearson Education, Inc. The Hubble Space Telescope has several instruments. The Hubble Space Telescope

Copyright © 2010 Pearson Education, Inc. Resolution achievable by the Hubble Space Telescope limited by optics and not atmosphere The Hubble Space Telescope Ground Based – M100

Copyright © 2010 Pearson Education, Inc.

Light-gathering power: Improves detail Brightness proportional to square of radius of mirror The figure, part (b) was taken with a telescope twice the size of (a) Telescope Size Area =  R 2 R=1 R=2

Copyright © 2010 Pearson Education, Inc. Multiple telescopes: Mauna Kea Telescope Size

Copyright © 2010 Pearson Education, Inc. Telescope Size The VLT (Very Large Telescope), Atacama, Chile

a) bend around corners and edges. b) separate into its component colors. c) bend through a lens. d) disperse within a prism. e) reflect off a mirror. Diffraction is the tendency of light to Question 3

a) bend around corners and edges. b) separate into its component colors. c) bend through a lens. d) disperse within a prism. e) reflect off a mirror. Diffraction is the tendency of light to Question 3 Diffraction affects all telescopes and limits the sharpness of all images.

Copyright © 2010 Pearson Education, Inc. Resolving power: Ability to distinguish objects that are close together. Resolution is proportional to wavelength and inversely proportional to telescope size. Telescope Size

Question 4 Resolution is improved by using a) larger telescopes & longer wavelengths. b) infrared light. c) larger telescopes & shorter wavelengths. d) lower frequency light. e) visible light.

Question 4 Resolution is improved by using a) larger telescopes & longer wavelengths. b) infrared light. c) larger telescopes & shorter wavelengths. d) lower frequency light. e) visible light. Diffraction limits resolution; larger telescopes and shorter-wave light produces sharper images. 10’1”

Copyright © 2010 Pearson Education, Inc. Effect of improving resolution: (a) 10′; (b) 1′; (c) 5″; (d) 1″ Telescope Size

a) the quality of the telescope’s optics. b) the transparency of a telescope’s lens. c) the sharpness of vision of your eyes. d) the image quality due to air stability. e) the sky’s clarity & absence of clouds. Seeing in astronomy is a measurement of Question 5

Seeing in astronomy is a measurement of Question 5 “Good Seeing” occurs when the atmosphere is clear and the air is still. Turbulent air produces “poor seeing,” and fuzzier images. a) the quality of the telescope’s optics. b) the transparency of a telescope’s lens. c) the sharpness of vision of your eyes. d) the image quality due to air stability. e) the sky’s clarity & absence of clouds. Point images of a star Smeared overall image of star

Question 6 Adaptive optics refers to a) making telescopes larger or smaller. b) reducing atmospheric blurring using computer control. c) collecting different kinds of light with one type of telescope. d) using multiple linked telescopes.

Question 6 Adaptive optics refers to a) making telescopes larger or smaller. b) reducing atmospheric blurring using computer control. c) collecting different kinds of light with one type of telescope. d) using multiple linked telescopes. Shaping a mirror in “real time” can dramatically improve resolution. Cluster R136

Copyright © 2010 Pearson Education, Inc. Atmospheric blurring due to air movements High-Resolution Astronomy

Copyright © 2010 Pearson Education, Inc. Solutions: Put telescopes on mountaintops, especially in deserts. Put telescopes in space. Active (adaptive) optics – control mirrors based on temperature and orientation. High-Resolution Astronomy

Copyright © 2010 Pearson Education, Inc. Solutions: Without active (adaptive) optics a 1m telescope is limited to about 2’ With active (adaptive) optics the same 1m telescope could approach 0.1”. High-Resolution Astronomy

Copyright © 2010 Pearson Education, Inc. Radio telescopes: Similar to optical reflecting telescopes Prime focus Less sensitive to imperfections (due to longer wavelength); can be made very large Radio Astronomy 105 m Green Bank, WV

Radio dishes are large because Question 7 a)radio photons don’t carry much energy. b)they are painted white. c) they are cheap to make. d) they are can operate during the day.

Radio dishes are large in order to Question 7 Resolution is worse with long-wave light, so radio telescopes must be large to compensate. a)radio photons don’t carry much energy. b)they are painted white. c) they are cheap to make. d) they are can operate during the day.

Copyright © 2010 Pearson Education, Inc. Largest radio telescope: 300-m dish at Arecibo Radio Astronomy

Question 8 Radio telescopes are useful because a) observations can be made day & night. b) we can see objects that don’t emit visible light. c) radio waves are not blocked by interstellar dust. d) they can be linked to form interferometers. e) All of the above are true.

Question 8 Radio telescopes are useful because a) observations can be made day & night. b) we can see objects that don’t emit visible light. c) radio waves are not blocked by interstellar dust. d) they can be linked to form interferometers. e) All of the above are true. The Very Large Array links separate radio telescopes to create much better resolution.

Copyright © 2010 Pearson Education, Inc. Longer wavelength means poorer 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. Radio Astronomy Centaurus A

Copyright © 2010 Pearson Education, Inc. Interferometry: Combines information from several widely spread radio telescopes as if it came from a single dish. Resolution will be that of dish whose diameter = largest separation between dishes. Radio Astronomy

Copyright © 2010 Pearson Education, Inc. Radio Astronomy Interferometry requires preserving the phase relationship between waves over the distance between individual telescopes.

Copyright © 2010 Pearson Education, Inc. Can get radio images whose resolution is close to optical. Radio Astronomy M51 VLA 4 m Kitt Peak

Copyright © 2010 Pearson Education, Inc. Radio Astronomy Interferometry can also be done with visible light, but much harder due to shorter wavelengths. CHARA 1 m at Mount Wilson, CA

Copyright © 2010 Pearson Education, Inc. Infrared radiation can image where visible radiation is blocked; generally can use optical telescope mirrors and lenses. Other Astronomies Orion Nebula

Question 9 Infrared telescopes are very useful for observing a) pulsars & black holes. b) from locations on the ground. c) hot stars & intergalactic gas. d) neutron stars. e) cool stars & star-forming regions.

Question 9 Infrared telescopes are very useful for observing a) pulsars & black holes. b) from locations on the ground. c) hot stars & intergalactic gas. d) neutron stars. e) cool stars & star-forming regions. Infrared images of star-forming “nurseries” can reveal objects still shrouded in cocoons of gas and dust.

Copyright © 2010 Pearson Education, Inc. Infrared telescopes can also be in space or flown on balloons. Other Astronomies

Copyright © 2010 Pearson Education, Inc. Ultraviolet images (a)The Cygnus loop supernova remnant (b) M81 Other Astronomies

Copyright © 2010 Pearson Education, Inc. 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. Other Astronomies

Copyright © 2010 Pearson Education, Inc. X-ray image of supernova remnant Cassiopeia A Other Astronomies Cas A

Copyright © 2010 Pearson Education, Inc. Gamma rays cannot be focused at all; images are therefore coarse. Other Astronomies Galaxy 3C279

Copyright © 2010 Pearson Education, Inc. Much can be learned from observing the same astronomical object at many wavelengths. Here, the Milky Way. Other Astronomies

Copyright © 2010 Pearson Education, Inc. RADIO

Copyright © 2010 Pearson Education, Inc. INFRARED

Copyright © 2010 Pearson Education, Inc. VISIBLE

Copyright © 2010 Pearson Education, Inc. X-RAY

Copyright © 2010 Pearson Education, Inc. GAMMA-RAY

Question 10 The Hubble Space Telescope (HST) offers sharper images than ground telescopes primarily because a) HST is closer to planets & stars. b) HST uses a larger primary mirror. c) it gathers X-ray light. d) HST orbits above the atmosphere. e) it stays on the nighttime side of Earth.

Question 10 The Hubble Space Telescope (HST) offers sharper images than ground telescopes primarily because a) HST is closer to planets & stars. b) HST uses a larger primary mirror. c) it gathers X-ray light. d) HST orbits above the atmosphere. e) it stays on the nighttime side of Earth. HST orbits less than 400 miles above Earth – not much closer to stars & planets! But it can gather UV, visible, and IR light, unaffected by Earth’s atmosphere.

Example Exam Questions One advantage of the Hubble Space telescope over ground based ones is that A. it can better focus x-ray images. B. in orbit, it can operate close to its diffraction limit at visible wavelengths. C. it is larger than any Earth-based scopes. D. its adaptive optics controls atmospheric blurring better. E. it can make better observations of the ozone layer.

What problem does adaptive optics correct? A. defects in the optics of the telescope, such as the original Hubble mirror B. turbulence in the earth's atmosphere which creates twinkling C. the opacity of the earth's atmosphere to some wavelengths of light D. chromatic aberration due to use of only a single lens objective E. the light pollution of urban areas

An emission line results from an electron falling from a higher to lower energy orbital around its atomic nucleus. A. True B. False

The angular resolution of an 8 inch diameter telescope is _______ greater than that of a 2 inch diameter telescope. A. 2× B. 4× C. 8× D. 9× E. 16×

The larger the red shift, the faster the distant galaxy is rushing toward us. A. True B. False

Changing the electric field will have no effect on the magnetic fields of a body. A. True B. False

Doubling the temperature of a black body will double the total energy it radiates. A. True B. False

Copyright © 2010 Pearson Education, Inc. Refracting telescopes make images with a lens. Reflecting telescopes make images 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 3

Copyright © 2010 Pearson Education, Inc. 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 is limited. Interferometry can greatly improve resolution. Summary of Chapter 3, cont.

Copyright © 2010 Pearson Education, Inc. 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 3, cont.