Chapter 3

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

D) turbulence in the Earthʹs atmosphere that creates twinkling

7) A Newtonian reflector needs no secondary mirror.

False

8) The Hubble Space Telescope gives us its best resolution with X-rays.

False

12) Mt. Palomarʹs 200ʺ Hale telescope is the largest reflector now in service.

True

14) The 400ʺ Keck reflector can see objects 100 times fainter than the 40ʺ Yerkes lens.

True

15) Radio telescopes have poorer angular resolution than optical telescopes because radio waves have a much longer wavelength than optical waves.

True

17) Stars do not twinkle; the instability of the atmosphere causes this effect.

True

20) Optical telescopes are usually used only at night, but radio telescopes can be used day or night.

True

25) Due to our ozone layer, ultraviolet astronomy must be done from space.

True

4) All optical telescopes will bring the light from a star to a focus.

True

5) A telescope design that uses a lens and no mirrors is a refractor.

True

6) CCD detectors gather light 10-20 times faster than the most sensitive photographic film.

True

9) The Cassegrain reflector needs a primary concave main mirror and a smaller, convex secondary mirror to reflect light back through a hole in the primary.

True

44) What is true of radio telescopes? A) They have poorer angular resolution than a refractor of the same size. B) They have better angular resolution than a reflector. C) They are the smallest, most compact telescopes. D) They can only be used above the atmosphere. E) They are most sensitive to the opacity of the ozone layer.

A) They have poorer angular resolution than a refractor of the same size.

35) Adding a secondary concave lens of carefully chosen different glass to the primary lens on a refractor allows A) chromatic aberration to be reduced. B) X-rays to be focused. C) effects of atmospheric turbulence to be reduced. D) greater magnification. E) more light to be gathered.

A) chromatic aberration to be reduced.

33) The primary purpose of a telescope is to A) collect a large amount of light and bring it into focus. B) magnify distant objects. C) separate light into its component wavelengths. D) make distant objects appear nearby. E) measure the brightness of stars very accurately.

A) collect a large amount of light and bring it into focus.

34) A major advantage of a Newtonian reflector over a refractor is A) its compact size. B) the elimination of chromatic aberration. C) there are only two lenses to grind. D) the central hole in the mirror is smaller. E) the elimination of the secondary mirror.

A) its compact size.

29) Which type of telescope has the simplest light path? A) prime focus reflector B) single lens refractor C) achromatic refractor D) Newtonian reflector E) Cassegrain reflector

A) prime focus reflector

45) The Arecibo radio telescope is laid out like which optical telescope design? A) prime focus reflector B) Newtonian reflector C) Cassegrain reflector D) Coude reflector E) grazing incidence reflector

A) prime focus reflector

42) Green light has a shorter wavelength than orange light. In a 5 inch telescope, green light will A) provide better angular resolution than orange light. B) come to the same exact focus as orange light. C) provide worse angular resolution than orange light. D) allow dimmer stars to be observed. E) reduce the effects of atmospheric turbulence.

A) provide better angular resolution than orange light

38) The amount of diffraction and thus the resolution of the telescope depends upon A) the wavelength used and the size of the main telescope objective lens or mirror. B) the design of the telescope. C) whether the telescope is a reflector or refractor. D) the brightness of the object. E) the size and sensitivity of the CCD chip used for imaging.

A) the wavelength used and the size of the main telescope objective lens or mirror.

32) The most important advantage of CCDs over film is that A) they record much more light in a given exposure time. B) their images do not have to be developed as film does. C) they record colors better than film can. D) they can cover larger areas of the sky than film can. E) their images never fade, as film can.

A) they record much more light in a given exposure time.

47) Compared to optical telescopes, radio telescopes are built large because A) theyʹre less expensive to make than optical telescopes. B) radio waves have very long wavelengths. C) atmospheric turbulence is more of a problem. D) radio sources are harder to find. E) radio waves are absorbed by the atmosphere.

A) theyʹre less expensive to make than optical telescopes.

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

B) 4

41) What is the light-gathering power of an 8 inch telescope compared to a 4 inch telescope? A) 2 times better B) 4 times better C) 8 times better D) 16 times better E) 32 times better

B) 4 times better

50) Which of the following is currently supplying high resolution X-ray images from space? A) ROSAT B) Chandra C) Einstein D) HEAO-2 E) COBE

B) Chandra

30) Which of the following is NOT a reason to use a reflecting telescope rather than a refractor? A) Lenses are subject to chromatic aberration. B) Lenses are harder to focus than mirrors. C) Lenses absorb light, while mirrors do not. D) Heavy lenses, which can only be supported at their edges, tend to deform under their own weight. E) A lens must have two precision surfaces; a mirror needs only one.

B) Lenses are harder to focus than mirrors

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

B) it can better focus X-ray images

39) What is the resolution of a telescope? A) its ability to see very faint objects B) its ability to distinguish two adjacent objects close together in the sky C) its ability to make distant objects appear much closer to us D) its ability to separate light into its component colors for analysis E) its ability to focus more than just visible light for imaging

B) its ability to distinguish two adjacent objects close together in the sky

40) Compared to a 5 inch prime focus reflector, a 5 inch Newtonian reflector will A) have more light gathering power. B) have the same light gathering power. C) be easier to build. D) have more chromatic aberration. E) have a larger hole in the center of its mirror.

C) be easier to build.

31) What problem do refractor telescopes have that reflectors donʹt? A) diffraction limited resolution B) light loss from secondary elements C) chromatic aberration D) atmospheric blurring E) bad seeing

C) chromatic aberration

49) The design of modern X-ray telescopes depends on A) lenses made of germanium. B) the prime focus design, with mirrors made of iron. C) grazing incidence optics. D) achromatic lenses to keep the X-rays in focus E) the Cassegrain design, with mirrors made of lead.

C) grazing incidence optics.

46) In astronomy, an interferometer can be used to A) yield better seeing conditions with optical telescopes. B) decrease the effects of light pollution in getting darker sky backgrounds. C) improve the angular resolution of radio telescopes. D) increase the sensitivity of infrared telescopes to longer wavelengths. E) speed up the processing of CCD images.

C) improve the angular resolution of radio telescopes.

36) It is diffraction that limits the ________ of a telescope of a given objective diameter. A) magnification B) light grasp C) resolution D) aperture E) interference

C) resolution

10) Photography with film is still the preferred way of capturing fine detail in the faintest, most distant galaxies.

False

13) A telescope with an 8-inch mirror will collect twice as much light as one with a 4-inch mirror.

False

16) All modern large optical telescopes are refractors.

False

18) The opacity of the atmosphere is partially corrected via adaptive optics.

False

19) In the future, adaptive optics will greatly enhance the resolution of the Hubble Space Telescope.

False

2) Galileo is credited with designing the first reflector telescope.

False

21) The Earthʹs atmosphere is the major factor limiting the use of ground-based radio telescopes.

False

22) Optical interferometry is more in use than radio interferometry.

False

23) Radio astronomy can only be done from up in space, due to our ionosphere.

False

24) Like radio and optical astronomy, infrared astronomy is easily done with ground-based telescopes.

False

26) The mirrors for X-ray telescopes are the same shape as those of optical reflectors.

False

27) The Compton GRO was the first telescope used for our exploration of high-energy astronomy.

False

28) Galaxies look the same whether viewed in visible or X-ray wavelengths.

False

3) Chromatic aberration affects reflector telescopes.

False

11) The light-gathering ability of a telescope is most dependent on the diameter of its primary objective.

True

1) The simplest reflector telescope design is the prime focus reflector.

True

CQ3 Diffraction is the tendency of light to 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.

a) bend around corners and edges

CQ6 Radio dishes are large in order to a) improve angular resolution. b) give greater magnification. c) increase the range of waves they can collect. d) detect shorter waves than optical telescopes for superior resolution.

a) improve angular resolution.

CQ7 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.

b) reducing atmospheric blurring using computer control.

CQ4 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.

c) larger telescopes & shorter wavelengths

CQ10 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.

d) HST orbits above the atmosphere

CQ2 Seeing in astronomy is a measurement of 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.

d) the image quality due to air stability.

CQ5 An advantage of CCDs over photographic film is 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.

e) All of the above are true.

CQ8 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.

e) All of the above are true.

CQ9 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

e) cool stars & star-forming regions

CQ1 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.

e) reflecting telescopes aren't affected by the atmosphere as much