Deck 5: The Tools of the Astronomer

Question 1

The highest spatial resolution images that we have of many planets' surfaces come from the Hubble Space Telescope.

Answer 1

False

Question 2

The light-gathering power of a 4-m telescope is __________ than that of a 2-m telescope.

A) 8 times larger
B) 4 times larger
C) 16 times smaller
D) 2 times smaller

Answer 2

4 times larger

Question 3

Radio telescopes are often used in interferometric arrays to increase light gathering power.

Answer 3

False

Question 4

Which telescope would collect 100 times more light than a 1-m telescope?

A) 100-m telescope
B) 50-m telescope
C) 30-m telescope
D) 10-m telescope

Question 5

One of the reasons why the Hubble Space Telescope has better spatial resolution than a 4-m ground-based telescope is that it has a larger mirror.

Question 6

How faint an object we can see with our eyes is limited only by the integration time of our eye (how often it processes input).

Question 7

The 305-m Arecibo radio telescope has a resolution that is no better than that of the human eye.

Question 8

The telescope was invented by

A) Galileo Galilei,an Italian inventor.
B) Hans Lippershey,an eyeglass maker in the Netherlands.
C) Gote Reber,a German cabinetmaker.
D) Tycho Brahe,a Danish astronomer.

Question 9

Understanding the results of high-energy collisions between elementary particles can give astronomers insight into conditions that were present during the earliest moments of the universe.

Question 10

The image quality of most optical telescopes is limited by differential atmospheric refraction experienced by light as it passes through the Earth's atmosphere.

Question 11

Unlike gravity waves,neutrinos are relatively easy to detect.

Question 12

The path of red light is deflected by a larger angle than blue light when passing through a glass prism.

Question 13

The dispersing element in a spectrograph could be a prism or a diffraction grating.

Question 14

Which of the following was NOT discovered by Galileo using a telescope?

A) The Moon has a heavily cratered surface.
B) Jupiter has four moons that orbit around it.
C) Mars has a polar ice cap similar to the Earth.
D) The planet Venus went through phases similar to those of the Moon.

Question 15

Hans Lippershey invented the telescope in the early 1600s.

Question 16

Chromatic aberration is a problem that limits the image quality of reflecting telescopes.

Question 17

How does the resolution of a telescope depend on its focal length?

A) The longer the focal length,the better the resolution.
B) The longer the focal length,the worse the resolution.
C) There is no relation between resolution and focal length.

Question 18

Astronomers usually study distant objects by looking at them directly through the eyepiece of
a telescope.

Question 19

In the past,astronomers have placed telescopes in highflying aircraft in an effort to rise above the water vapor in the Earth's atmosphere.

Question 20

Only point sources look both closer and brighter when viewed through a telescope.

Question 21

The angular resolution of a ground-based telescope (without adaptive optics)is usually

A) 30 arcsec.
B) 1 arcmin.
C) 1 arcsec.
D) 30 arcmin.

Question 22

A grating is able to spread white light out into a spectrum of colors based on the property of

A) reflection.
B) refraction.
C) dispersion.
D) interference.

Question 23

Before CCDs were invented,what was the device most commonly used for imaging with optical telescopes?

A) Polaroid cameras
B) photographic glass plates
C) high-speed film
D) video cameras

Question 24

An object sits at the focal point of a parabolic mirror.At what distance from the mirror will its image be created?

A) It will be imaged at half the focal length.
B) It will be imaged at the focal length.
C) It will be imaged at twice the focal length.
D) No image will be created (the beams would be reflected parallel to each other).

Question 25

How much fainter are the faintest stars you can see with a 10-inch telescope and a CCD camera that can integrate for 10 minutes compared to what you can see with your naked eye?

A) 30 billion times fainter
B) 30 thousand times fainter
C) 30 million times fainter
D) 30 trillion times fainter

Question 26

Photography provides an improvement over naked-eye observations because

A) it is possible to observe a larger field of view with photographic plates.
B) the quantum efficiency is higher for photographic plates.
C) the image resolution is much better for photographic plates.
D) it is possible to detect fainter objects with the use of photographic plates.

Question 27

Why can a compound lens combat a refracting telescope's chromatic aberration?

A) Red light is absorbed by a larger amount than blue light.
B) Red light is refracted by a larger amount than blue light.
C) Blue light is refracted by a larger amount than red light.
D) Blue light is absorbed by a larger amount than red light.

Question 28

The diffraction limit of a 4-m telescope is __________ than that of a 2-m telescope.

A) 2 times larger
B) 4 times larger
C) 2 times smaller
D) 4 times smaller

Question 29

Cameras that use adaptive optics provide higher spatial resolution images primarily because

A) they operate above the Earth's atmosphere.
B) they capture infrared light,which has a longer wavelength than visible light.
C) deformable mirrors are used to correct the blurring due to the Earth's atmosphere.
D) composite lenses correct for chromatic aberration.

Question 30

The part of the human eye that acts as the detector is the

A) retina.
B) pupil.
C) rods.
D) cones.

Question 31

Large reflecting telescopes have mirrors that are __________ in shape.

A) spherical
B) parabolic
C) hyperbolic
D) cylindrical

Question 32

The major advantage CCDs have over other imaging techniques is that

A) they have a higher quantum efficiency.
B) they have a linear response to light.
C) they yield output in digital format.
D) they operate at visible and near-infrared wavelengths.
E) All of the above are true.

Question 33

Why do reflecting telescopes usually have a secondary mirror in addition to a primary mirror?

A) To increase the light gathering power
B) To make the telescope shorter
C) To increase the focal length
D) To combat chromatic aberration

Question 34

As a beam of light travels from one medium to another,the change in direction of the beam of light depends on

A) the wavelength of the light.
B) the index of refraction of the medium through which it is traveling.
C) the index of refraction of the medium into which it is moving.
D) All of the above

Question 35

One reason to prefer a reflecting over a refracting telescope is its

A) lack of chromatic aberration.
B) shorter length for the same aperture size.
C) lighter weight for larger apertures.
D) All of the above are valid reasons.

Question 36

The angular resolution of a ground-based telescope is usually set by

A) diffraction.
B) refraction.
C) the focal length.
D) atmospheric seeing.

Question 37

According to the law of reflection,if a beam of light strikes a flat mirror at an angle of 30° relative to a plane perpendicular to the surface of the mirror,at what angle will it reflect,relative to a plane perpendicular to the surface of the mirror?

A) 0°
B) 30°
C) 60°
D) 120°

Question 38

The angular resolution of the largest single-dish radio telescope in the United States,the 300-ft Green Bank Telescope,is __________ when it operates at a wavelength of 20 cm.

A) 0.12°
B) 0.12 arcmin
C) 0.12 arcsec
D) 12 arcsec

Question 39

A beam of light passes from air to water at an incident angle of 40°,relative to a plane perpendicular to the boundary between the two.At what angle will it emerge into the water,relative to a plane perpendicular to the boundary?

A) Less than 40°
B) Exactly 40°
C) More than 40°
D) There is not enough information to answer the question.

Question 40

A prism is able to spread white light out into a spectrum of colors based on the property of

A) reflection.
B) refraction.
C) dispersion.
D) interference.

Question 41

The 305-m Arecibo radio telescope in Puerto Rico has a resolution that is closest to that of

A) the Hubble Space Telescope (0.1 arcsec).
B) a human eye (1 arcmin).
C) the Chandra X-ray Telescope (0.5 arcsec).
D) a 1-m optical telescope (1 arcsec).

Question 42

In 2008,the Cassini spacecraft made a flyby of Enceladus,one of the icy moons of Saturn.If the spacecraft's high resolution camera had an angular resolution of 3 arcsec,and it flew at an altitude of 23 km above Enceladus' surface,how large an object could be resolved on the surface?

A) 3 m
B) 30 cm
C) 4 cm
D) 40 m

Question 43

The SETI project's Allen Telescope Array will have 350 radio dishes,each with an individual diameter of 6 m,spread out over a circle whose diameter is 1 km.What would this array's spatial resolution be when it operates at 6,000 MHz?

A) 10 arcsec
B) 0.10 arcsec
C) 10 arcmin
D) 1.0 arcmin

Question 44

Arrays of radio telescopes can produce much better resolution than single-dish telescopes because they work based on the principle of

A) reflection.
B) refraction.
C) diffraction.
D) interference.

Question 45

Explain why stars twinkle when viewed from the ground.Would they twinkle if viewed from outer space?

Question 46

Particle accelerators that smash atoms or particles together at high speeds,such as Fermilab or CERN,are important tools used for simulating conditions in

A) the early universe.
B) the solar wind.
C) brown dwarf stars.
D) planetary nebula.

Question 47

What is the diffraction limit of a 4-m telescope observing at a wavelength of 650 nm?

Question 48

When we determine the angular resolution of an interferometric array of radio telescopes using the formula ,the variable D stands for the

A) diameter of the telescopes.
B) separation between the telescopes.
C) number of telescopes.
D) focal length of the telescopes.

Question 49

The Voyager I spacecraft is currently 16.5 billion km from Earth and heading out of our Solar System.How long does it take radio messages from Voyager I to reach us?

A) 1.5 days
B) 15 hours
C) 1.5 weeks
D) 15 minutes

Question 50

Why do reflecting telescopes use curved mirrors instead of flat mirrors?

Question 51

Explain why the largest telescopes are not refracting telescopes.

Question 52

What is the angular resolution of a 1-m,ground-based,optical telescope that observes at a wavelength of 600 nm compared to that of a 300-ft,single dish radio telescope that observes at a wavelength of 21 cm?

Question 53

Which of the following causes the biggest problem in detecting infrared photons from an astronomical object?

A) Smog
B) Carbon dioxide
C) Water vapor
D) Light pollution

Question 54

Which of the following celestial bodies has yet to be observed by spacecraft that have flown by them?

A) Uranus
B) Venus
C) Pluto
D) Neptune

Question 55

Ultraviolet radiation is hard to observe primarily because

A) the Earth's atmosphere easily absorbs it.
B) no space-based telescopes operate at ultraviolet wavelengths.
C) only the lowest mass stars emit ultraviolet light.
D) very few objects emit at ultraviolet wavelengths.

Question 56

Explain why chromatic aberration is a problem for refracting mirrors but not reflecting mirrors.

Question 57

Compare the light-gathering power of the human eye to that of a 10-inch telescope.

Question 58

Samples of which celestial object(s)have been brought back to Earth to be studied in detail?

A) a comet
B) the solar wind
C) the Moon
D) all of the above

Question 59

The two Keck 10-m telescopes,separated by a distance of 85 m,can operate as an interferometer.What is its resolution when it observes in the infrared at a wavelength of 2 microns?

A) 0.01 arcsec
B) 0.006 arcsec
C) 0.05 arcsec
D) 0.2 arcsec

Question 60

Neutrino detectors typically capture one out of every __________ neutrinos that pass through them.

A) 10
B) (one million)
C) (one trillion)
D) (10 billion trillion)

Question 61

Discuss two advantages of flyby missions over orbiters in exploring planets and moons in the Solar System.

Question 62

Discuss two tools that modern astronomers use to explore the cosmos that are different from traditional optical telescopes,and give an example of how and why each is used.

Question 63

Explain how adaptive optics help compensate for atmospheric seeing.

Question 64

Explain three major advantages of CCDs over other imaging techniques.

Question 65

What are gravity waves? Have astronomers been able to detect them yet?

Question 66

In 2009,the Cassini spacecraft made repeated orbits around Titan,Saturn's largest moon.If this spacecraft orbited at an altitude of 1,000 km above Titan's surface,and its high resolution camera had an angular resolution of 3 arcsec,how large an object could be resolved on Titan's surface?

Question 67

Calculate the resolution of an interferometric array consisting of five 10-m radio telescopes,each located 1,000 meters apart from each other and observing a distant object at a wavelength of 21 cm.

Question 68

Compare the brightness of the faintest objects you can see with your naked eye,which has an aperture of approximately 1 cm,an integration time of 100 ms,and a quantum efficiency of 10 percent,to the faintest objects you can see in a CCD image taken with a 1-m telescope.Assume the CCD has a quantum efficiency of 80 percent,and the image has an integration time of 10 minutes.