Deck 4: Telescopes: the Tools of Astronomy

Question 1

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

Answer 1

True

Question 2

Chromatic aberration affects reflector telescopes.

Answer 2

False

Question 3

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

Answer 3

False

Question 4

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

Question 5

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

Question 6

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

Question 7

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

Question 8

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

Question 9

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

Question 10

A Newtonian reflector needs no secondary mirror.

Question 11

The simplest reflector telescope design is the prime focus reflector.

Question 12

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

Question 13

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

Question 14

Mt. Palomar's 200" Hale telescope is the largest reflector now in service.

Question 15

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

Question 16

Galileo is credited with designing the first reflector telescope.

Question 17

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

Question 18

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

Question 19

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.

Question 20

All modern large optical telescopes are refractors.

Question 21

The primary purpose of a telescope is to

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

Question 22

The Earth's atmosphere is the major factor limiting the use of ground- based radio telescopes.

Question 23

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

Question 24

It is diffraction that limits the _ _ of a telescope of a given objective diameter.

A) aperture
B) magnification
C) resolution
D) interference
E) light grasp

Question 25

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

Question 26

The most important advantage of CCDs over film is that

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

Question 27

The amount of diffraction and thus the resolution of the telescope depends upon

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

Question 28

Compared to a 5- inch prime focus reflector, a 5- inch Newtonian reflector will

A) have the same light gathering power.
B) have more light gathering power.
C) have more chromatic aberration.
D) have a larger hole in the center of its mirror.
E) be easier to build.

Question 29

Which of the following is NOT a reason to use a reflecting telescope rather than a refractor?

A) Lenses absorb light, while mirrors do not.
B) Lenses are subject to chromatic aberration.
C) Heavy lenses, which can only be supported at their edges, tend to deform under their own weight.
D) A lens must have two precision surfaces; a mirror needs only one.
E) Lenses are harder to focus than mirrors.

Question 30

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

Question 31

The angular resolution of an 8 inch diameter telescope is times greater than that of a 2 inch diameter telescope.

A) 9
B) 16
C) 4
D) 2
E) 8

Question 32

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) more light to be gathered.
D) greater magnification.
E) effects of atmospheric turbulence to be reduced.

Question 33

Which type of telescope has the simplest light path?

A) achromatic refractor
B) prime focus reflector
C) Cassegrain reflector
D) single lens refractor
E) Newtonian reflector

Question 34

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

Question 35

Optical interferometry is more in use than radio interferometry.

Question 36

What problem do refractor telescopes have that reflectors don't?

A) light loss from secondary elements
B) bad seeing
C) diffraction limited resolution
D) atmospheric blurring
E) chromatic aberration

Question 37

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

Question 38

What is the resolution of a telescope?

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

Question 39

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

Question 40

A major advantage of a Newtonian reflector over a refractor is

A) the elimination of chromatic aberration.
B) the central hole in the mirror is smaller.
C) its compact size.
D) there are only two lenses to grind.
E) the elimination of the secondary mirror.

Question 41

What problem does adaptive optics correct?

A) the opacity of the Earth's atmosphere to some wavelengths of light
B) turbulence in the Earth's atmosphere that creates twinkling
C) defects in the optics of the telescope, such as the original Hubble mirror
D) the light pollution of urban areas
E) chromatic aberration due to use of only a single lens objective

Question 42

What is true of radio telescopes?

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

Question 43

The twinkling of starlight and the focusing of images by lenses are both due to of light.

A) refraction
B) reflection
C) transmission
D) polarization
E) aberration

Question 44

The design of modern X- ray telescopes depends on

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

Question 45

The focus reflector needs only a single optical surface to form images.

Question 46

Compared to optical telescopes, radio telescopes are built large because

A) radio waves are absorbed by the atmosphere.
B) they're less expensive to make than optical telescopes.
C) radio waves have very long wavelengths.
D) atmospheric turbulence is more of a problem.
E) radio sources are harder to find.

Question 47

A mirror must be in shape to reflect the light back to a focus.

Question 48

Grazing incidence optics are critical to focusing

A) infrared radiation.
B) radio waves.
C) X- rays.
D) ultraviolet light.
E) gamma rays.

Question 49

An advantage a reflector has over a refractor is the elimination of .

Question 50

In astronomy, an interferometer can be used to

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

Question 51

To a large degree, the has replaced photographic film for astronomical imaging.

Question 52

The large reflector, the 10 m Keck, gathers _ _ light than the 1.0 m Yerkes refractor.

A) an equal amount of
B) 100 times less
C) 10 times more
D) 100 times more
E) 10 times less

Question 53

The Arecibo radio telescope is laid out like which optical telescope design?

A) Cassegrain reflector
B) Newtonian reflector
C) grazing incidence reflector
D) prime focus reflector
E) Coude reflector

Question 54

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) reduce the effects of atmospheric turbulence.
D) provide worse angular resolution than orange light.
E) allow dimmer stars to be observed.

Question 55

The Space Telescope still gives us the highest resolution optical images.

A) Einstein
B) Kepler
C) Chandra
D) Hubble
E) Fermi

Question 56

Which of the following is currently supplying high resolution X- ray images from space?

A) COBE
B) ROSAT
C) Chandra
D) HEAO- 2
E) Einstein

Question 57

What is the light- gathering power of an 8- inch telescope compared to a 4- inch telescope?

A) 32 times better
B) 2 times better
C) 16 times better
D) 8 times better
E) 4 times better

Question 58

optics deform the shape of the mirror to compensate for the turbulence in the atmosphere and yield a close to diffraction- limited image.

A) CCD
B) Parabolic
C) Coherent
D) Collimating
E) Adaptive

Question 59

One advantage of the Hubble Space Telescope over ground based ones is that

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

Question 60

The separation of red and blue light in single- lens telescopes is called aberration.

Question 61

When used in a single instrument to greatly enhance its resolution, the four separate mirrors of the VLT act as a(n) .

Question 62

In general, as a telescope's diameter increases, its angular resolution _.

Question 63

The ability of a telescope to separate two closely spaced stars is called _.

Question 64

Name two advantages of larger telescopes over smaller ones.

Question 65

You are a novice telescope builder. Should you attempt a 6" Newtonian or Cassegrain reflector first? Why?

Question 66

With a prime focus reflector, why is digital imaging much easier than using an eyepiece for visual work?

Question 67

Name the four types of reflector designs.

Question 68

optics greatly reduces the effect of atmospheric turbulence by deforming the shape of the mirror by computer control.

Question 69

A lens must be _ in shape to focus the transmitted light.

Question 70

Contrast image formation in reflectors and refractors.

Question 71

There are ground- based telescopes much larger than Hubble, yet the HST still reveals the faintest objects yet seen. Explain.

Question 72

Which type of reflector telescope would be the easiest to construct, and why?

Question 73

What are two advantages of CCDs over photographic films for astronomy?

Question 74

If the _ is good, the atmosphere is stable, and image quality is sharp.

Question 75

Contrast the main mirrors of Newtonian and Cassegrain designs.

Question 76

In design, most radio telescopes, like Arecibo, are .

Question 77

How does the placement of the eyepiece with Newtonian and Cassegrain reflectors differ?

Question 78

Why is it easier to travel to a remote viewing site with an 8" Cassegrain than an 8" Newtonian reflector?

Question 79

Using _ _ incidence optics, the Chandra is the X- ray equivalent of the HST.

Question 80

The light- gathering power of a telescope varies with the of the diameter of the lens or mirror.