Deck 5: Telescopes

Question 1

If your pupils have a diameter of about 5 mm, about how many times more light gathering power does a telescope with a diameter of about 20 cm (8 inches) have than your pupils?

A) 4 times
B) 16 times
C) 40 times
D) 160 times
E) 1,600 times

Answer 1

1,600 times

Question 2

The two most important properties of any telescope are

A) the light-gathering power and the length of the tube.
B) the length of the tube and the magnification.
C) the magnification and the light-gathering power.
D) the resolving power and the magnification.
E) the light-gathering power and the resolving power.

Answer 2

the light-gathering power and the resolving power.

Question 3

A pencil inside a water glass appears to be bent because of

A) reflection of light.
B) refraction of light.
C) diffraction of light.
D) None of these choices are correct.

Answer 3

refraction of light.

Question 4

What is a disadvantage of using a single large lens in a telescope?

A) Large lenses are expensive to fabricate.
B) A lens has to be supported only at its edges, so the lens can sag in the middle.
C) Different colors of white light on passing through a lens focus at different points and result in a blurred image.
D) Some lens materials completely absorb short wavelengths.
E) All of these choices are correct.

Question 5

Carl has a 5-inch refracting telescope, and Jim has a 3-inch reflecting telescope. Whose telescope has a higher light-gathering power?

A) Carl's, because lenses gather more light.
B) Jim's, because mirrors gather more light.
C) Carl's, because the larger the diameter, the more light to be collected.
D) Jim's, because the smaller the diameter, the more light to be collected.

Question 6

If a 3-meter diameter telescope is doubled in size, then its new light collecting power would

A) not change.
B) double.
C) increase by a factor of four.
D) reduce by half.

Question 7

How do astronomers calculate a telescope's light collecting area (A)? (where r = radius of the telescope's mirror or lens)

A) A = 2?r
B) A = ?r2
C) A = 4?r2
D) A = 4/3 ?r3

Question 8

Telescope A has a mirror twice the diameter of telescope B's mirror. How does A's light-gathering power compare to B's?

A) A gathers 1/2 the light that B does.
B) A gathers twice the light that B does.
C) A gathers 4 times the light that B does.
D) A gathers 1/4th as much light as B does.

Question 9

How does the light-gathering power of a telescope affect the ability to see faint objects?

A) Faint objects are brighter if the telescope can gather a lot of light.
B) Faint objects appear larger when viewed through a large-diameter telescope.
C) Faint objects do not twinkle if the telescope can gather a lot of light.
D) Faint objects are clearer (better resolved) if the telescope can gather a lot of light.

Question 10

What is the difference between a reflecting and a refracting telescope?

A) A reflecting telescope uses a lens to focus light; a refracting telescope uses a mirror.
B) A reflecting telescope uses a mirror to focus light; a refracting telescope uses a lens.
C) Both use a mirror to focus light, but a reflecting telescope uses mirrors elsewhere to bend light.
D) There is no difference. "Refracting" is an outmoded way of saying "reflecting."

Question 11

Light travels _________ in water than in air.

A) faster
B) slower
C) at the same speed
D) perpendicular to

Question 12

Astronomy's largest optical telescopes are ____.

A) reflectors
B) refractors
C) diffractors
D) deflectors

Question 13

Chromatic aberration creates images fringed with color when using which kind of telescope?

A) reflector
B) refractor
C) radio
D) interferometer
E) adaptive optic

Question 14

When light passes through a transparent material, different wavelengths (colors) of light are refracted by differing amounts. This effect is called ____.

A) reflection
B) diffraction
C) dispersion
D) aberration
E) scintillation

Question 15

Which of these is a reason for using mirrors rather than lenses in telescopes?

A) Lenses are more expensive to make than mirrors.
B) Most transparent materials focus light of different colors to different spots.
C) Lenses can only be supported by their edges, making them sag in the middle (mirrors can be supported from behind).
D) All of these choices are correct.

Question 16

Using ___________, scientists can use a few smaller telescopes to take images with the same resolution as a much larger telescope.

A) satellite telescopes
B) charge-coupled devices (CCDs)
C) interferometry
D) adaptive optics

Question 17

To double the resolving power of a telescope, you must _________.

A) increase the diameter by a factor of two
B) increase the collecting area by a factor of two
C) decrease the diameter by half
D) decrease the collecting area by half

Question 18

Ignoring the effects of the atmosphere, what is the theoretical resolution of an 8-inch telescope (about 20 cm) if you are looking at visible light with a wavelength of about 500 nm?

A) about half an arc second
B) about half a degree
C) about 1/100 of an arc second
D) about 25 arc seconds

Question 19

The resolving power of a telescope is affected by the property of light called

A) refraction.
B) diffraction.
C) reflection.
D) seeing.
E) attenuation.

Question 20

The ability of a telescope to show two very close objects separately is called its ________.

A) light-gathering power
B) resolving power
C) magnification
D) focal length

Question 21

Tom has a 4-inch refracting telescope, and Steve has a 3-inch reflecting telescope. Whose telescope has a higher resolving power?

A) Tom's, because lenses are more efficient in showing the objects separately.
B) Steve's, because mirrors are more efficient in showing the objects separately.
C) Tom's, because the larger the diameter, the better the resolution.
D) Steve's, because the smaller the diameter, the better the resolution.

Question 22

______ is the most important quality of an astronomical telescope.

A) Magnification
B) Resolving power
C) Ability to see at night
D) Rigidity

Question 23

A telescope's resolving power measures its ability to see

A) fainter sources.
B) more distant sources.
C) finer details in sources.
D) larger sources.

Question 24

One way to increase the resolving power of a telescope is to

A) make its mirror bigger.
B) make its mirror smaller.
C) replace its mirror with a lens of the same diameter.
D) observe objects using longer wavelengths.

Question 25

In a telescope, diffraction creates _______________.

A) bright and clear images
B) images fringed with color
C) images with faint ripples
D) washed out images

Question 26

"Spikes" seen in images of stars are caused by ______________.

A) diffraction from the telescope support structures
B) dispersion from the telescope's primary lens
C) deflection from the inner surfaces of the telescope
D) disruption from nearby light sources

Question 27

What process limits a telescope's resolving power?

A) reflection
B) refraction
C) diffraction
D) distraction

Question 28

A telescope with a large-diameter aperture or mirror will __________.

A) collect a lot of light and have high resolution
B) collect less light, but have higher resolution
C) collect a lot of light, but have poor resolution
D) collect less light, and have poor resolution

Question 29

Why use an interferometer?

A) Its two widely spaced mirrors act like one giant telescope with increased collecting area.
B) Its two widely spaced mirrors act like one giant telescope with increased resolving power.
C) By putting one mirror above the other you can make the instrument much smaller.
D) It can detect light at wavelengths not available to single telescopes.

Question 30

A warm dust cloud in which stars are forming would be best observed with a(n) _________ telescope.

A) radio
B) gamma-ray
C) infrared
D) optical (visible light)

Question 31

A galaxy with almost no starlight but plenty of cool clouds of hydrogen gas would be best observed with a(n) _________ telescope.

A) X-ray
B) radio
C) infrared
D) optical (visible-light)

Question 32

In a false color image,

A) only one color is used.
B) color information from optical telescopes is combined with information from a non-visible wavelength telescope to make the image.
C) stars appear black and the background appears white.
D) colors can represent photon energies or the intensity of electromagnetic radiation.

Question 33

Which is the most efficient means of recording light?

A) photographic films
B) photomultiplier tubes
C) charge-coupled device (CCD)
D) the human eye

Question 34

Which of the following is an inherent disadvantage of radio telescopes?

A) Radio telescopes cannot detect visible light.
B) Radio telescopes have low magnification.
C) Radio signals are very weak, and their photons do not penetrate the atmosphere easily.
D) The long wavelength of radio waves results in lower resolving power, compared to other telescopes of the same size.
E) They only work at night.

Question 35

What does CCD stand for?

A) charge-coupled device
B) cosmic-ray channel detector
C) charge collecting device
D) channel-coupled detector

Question 36

How is a CCD better than film for astronomical imaging?

A) CCDs are much more sensitive to light than film.
B) Film images require developing, CCD images do not.
C) It is more difficult to enhance the contrast and clarity with film images.
D) All of these choices are correct.

Question 37

What technique does a radio telescope use to focus incoming light?

A) reflection
B) refraction
C) diffraction
D) dispersion

Question 38

Which of the following astronomical objects emit radiation mostly at non-visible wavelengths?

A) dust clouds in space
B) hot gas surrounding black holes
C) cold interstellar gas clouds
D) All of these choices are correct.

Question 39

An interstellar dust cloud may be very cold. What kind of telescope would we use to observe it at its strongest wavelength?

A) a ground-based infrared telescope
B) a ground-based X-ray telescope
C) a space-based ultraviolet telescope
D) a ground-based visible-light telescope
E) None of these choices are correct.

Question 40

The accretion disk of a black hole is typically very hot.What kind of telescope would we use to observe it at its strongest wavelength?

A) a ground-based X-ray telescope
B) a space-based X-ray telescope
C) a ground-based gamma-ray telescope
D) a space-based radio telescope
E) None of these choices are correct.

Question 41

Radio telescopes allow us to observe objects that are too cold to emit strongly in the visible part of the spectrum.Astronomers still use images of these object for study.What kind of images are these?

A) artist's renditions
B) false-color images
C) black-and-white images
D) holographic images
E) Astronomers do not use images to study radio objects.

Question 42

The best site for placing an X-ray telescope is _________.

A) a mountaintop
B) a valley
C) near an ocean
D) a desert
E) above Earth's atmosphere

Question 43

An interstellar gas is emitting 10-centimeter wavelength radiation, and a nearby star is emitting 10-micrometer wavelength radiation. Which of these can you observe through an Earth-based telescope?

A) the interstellar gas
B) the star
C) Both interstellar gas and the star.
D) None of these choices are correct.

Question 44

X-rays are blocked by ________ and _________ present in Earth's atmosphere.

A) water molecules; carbon dioxide
B) ozone; oxygen
C) nitrogen; helium
D) electric charges; clouds

Question 45

Which space telescope is observing X-rays?

A) the Hubble Space Telescope (HST)
B) the Chandra Observatory
C) the Spitzer Space Telescope
D) the Extreme Ultraviolet Explorer (EUVE)

Question 46

Which of the following telescopes is most suitable for observing cool gas clouds?

A) X-ray telescope
B) radio telescope
C) visible-light telescope
D) All of these choices are correct.
E) Cool gas clouds cannot be observed by telescopes.

Question 47

Do astronomers use ground-based X-ray telescopes?

A) Yes, because they can penetrate gas clouds.
B) No, because no astronomical objects emit X-rays.
C) No, because X-rays cannot get through Earth's atmosphere.
D) No, because astronomers have not yet devised detectors for X-rays.

Question 48

Why must radio telescopes have very large dishes?

A) A large mirror is necessary to resolve radio-emitting images.
B) Radio-emitting objects are very far from Earth, and so are very dim.
C) Large radio telescopes are easier to repair than small instruments.
D) The large dish is to compensate for atmospheric absorption of radio waves.
E) Size is immaterial to quality observations.

Question 49

Ground-based observations can be made easily in the ____ part(s) of the spectrum.

A) radio and visible
B) ultraviolet and visible
C) radio and ultraviolet
D) infrared

Question 50

One of the biggest problems for ground-based astronomy today is

A) all the best mountains already have telescopes on them.
B) atmospheric pollution has significantly worsened the seeing.
C) space-based observatories are making most of the observations.
D) light pollution makes it difficult to observe faint objects.

Question 51

Why does the Sun look flattened near the horizon?

A) The Sun's light is reflected off the horizon, making the Sun appear compressed.
B) Earth's dense atmosphere compresses the gaseous Sun.
C) The larger refraction near the horizon lifts the lower edge of the Sun more than the upper edge and makes the Sun look flattened.
D) The Sun is cooler on the horizon, so it looks flattened.

Question 52

Why does the Moon appear bigger near the horizon?

A) due to an optical illusion
B) due to refraction
C) due to reflection
D) due to the compression produced by Earth's atmosphere

Question 53

What is "seeing"?

A) the ability of a telescope to show two very close objects separately
B) the capacity of a telescope to gather more light
C) the ability of a telescope to see in the night
D) the distortion of an image due to an atmospheric turbulence

Question 54

The best site for placing a ground-based optical telescope is _________.

A) a mountaintop
B) a valley
C) in an urban setting
D) in a location that has few sunny days throughout the year

Question 55

Why do stars twinkle?

A) due to rapid changes occurring on their surfaces
B) due to their movement across the sky
C) due to the refraction caused by atmospheric irregularities
D) due to imperfections in the human eye

Question 56

Why does the useful resolving power of a ground-based telescope not match its theoretical value?

A) Mirrors can't be built accurately enough.
B) The atmosphere blurs the image, decreasing the resolving power.
C) Mirrors cannot collect enough light to reach their theoretical expectations.
D) The theoretical value can only be reached when there is a Full Moon.

Question 57

On some telescopes, actuators on the mirror change its shape to match distortions in the atmosphere. What is this technique called?

A) actuary observing
B) interferometry
C) refraction
D) adaptive optics

Question 58

Which of the following is a reason to build an observatory in space?

A) They are much less expensive than ground-based observatories.
B) They can last forever.
C) to avoid atmospheric blurring
D) There is no good reason to build a space-based observatory.

Question 59

What causes the image of a star to "twinkle" or scintillate?

A) irregularities in the density of layers of Earth's atmosphere, rapidly refracting the light
B) the flickering fusion process in the stars
C) a purely physiological reaction in the eye
D) None of these choices are correct.

Question 60

Why are remote sites chosen for ground-based telescopes?

A) Populated areas produce light pollution that degrades the quality of observations.
B) Deserts and mountaintops tend to be cloud-free, making observations convenient.
C) Mountaintops allow astronomers to avoid morning hazes.
D) Remote areas have less interference from power lines and other sources of noise.
E) All of these choices are correct.

Question 61

The collision of two neutron stars might be detected as what?

A) an atmospheric window
B) a nebula.
C) an emission-line spectrum.
D) a gamma-ray burst.
E) All of these choices are correct.

Question 62

In a reflecting telescope, the secondary mirror causes a hole in the center of the image.

Question 63

To double the light-gathering power of a telescope, we need to double the diameter.

Question 64

The design of radio telescopes is very similar to the design of refracting telescopes.

Question 65

The effect of tripling the size of a telescope's primary mirror is to triple its resolving power.

Question 66

An optical telescope is able to resolve blue objects better than red objects.

Question 67

CCDs are widely used in astronomy because the images are easily manipulated in computers, but photographic film is actually more sensitive to photons.

Question 68

Radio telescopes on Earth can only make observations at night.

Question 69

The Hubble Telescope gets much clearer images of astronomical objects than ground-based telescopes because it has a much larger mirror than ground-based telescopes.

Question 70

The Hubble Space Telescope only detects visible light.

Question 71

Gamma-ray telescopes, such as the Fermi Gamma Ray Space Telescope, are launched into space because they are dangerous to operate on Earth.