Deck 6: The Tools of the Astronomer

Question 1

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.
E) A compound lens cannot combat chromatic aberration.

Answer 1

Blue light is refracted by a larger amount than red light.

Question 2

Point sources look brighter when viewed through a telescope.

Answer 2

True

Question 3

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

Answer 3

True

Question 4

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 5

Why can you see fainter stars with an 8-inch telescope than you can see with your naked eye?

A) The telescope collects light over a larger area.
B) The telescope magnifies the field of view.
C) The telescope collects light over a wider range of wavelength than your eye.
D) The telescope has a wider field of view.
E) The telescope has a longer integration time than your eyes.

Question 6

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

Question 7

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

Question 8

Unlike photons, neutrinos are relatively easy to detect.

Question 9

The aperture of a telescope partially or totally determines its:

A) focal length and magnification
B) light-gathering power
C) focal length
D) light-gathering power and magnification
E) light-gathering power and diffraction limit

Question 10

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
E) Johannes Kepler, a German astronomer

Question 11

Large reflecting telescopes have mirrors that are _________ in shape.

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

Question 12

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

Question 13

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

Question 14

Hans Lippershey invented the telescope in the early 1600s.

Question 15

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

A) its lack of chromatic aberration
B) its shorter length for the same aperture size
C) there is no aperture limit
D) its lighter weight for larger apertures
E) all of the above are valid reasons

Question 16

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

A) 100-meter telescope
B) 80-meter telescope
C) 50-meter telescope
D) 30-meter telescope
E) 10-meter telescope

Question 17

The highest spatial resolution images that we have of many planets' surfaces were obtained with the Hubble Space Telescope.

Question 18

The magnification of a telescope depends on the focal length of the telescope and:

A) the size of the aperture
B) the type of telescope (refracting vs. reflecting)
C) the wavelengths being observed
D) the focal length of the eyepiece
E) the angular resolution of the telescope

Question 19

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 goes through phases similar to those of the Moon.
E) The Milky Way is a collection of countless numbers of individual stars.

Question 20

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 21

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) 1 arcsec
D) 10 arcmin
E) 1.0 arcmin

Question 22

In practice, the smallest angular size that one can resolve with a 10-inch telescope is governed by the:

A) blurring caused by the Earth's atmosphere
B) diffraction limit of the telescope
C) size of the primary mirror
D) motion of the night sky
E) magnification of the telescope

Question 23

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

A) 30 arcsec
B) 1 arcmin
C) 10 arcsec
D) 1 arcsec
E) 30 arcmin

Question 24

Which of the following phenomena is shown in the figure below?

A) reflection
B) chromatic aberration
C) diffraction
D) magnification
E) interference

Question 25

Which of the following phenomena is shown in the figure below?

A) reflection
B) refraction
C) magnification
D) diffraction
E) interference

Question 26

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

A) reflection
B) refraction
C) magnification
D) resolution
E) aberration

Question 27

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 magnification
D) to increase the focal length
E) to combat chromatic aberration

Question 28

Which of the following phenomena is shown in the figure below?

A) reflection
B) refraction
C) magnification
D) diffraction
E) interference

Question 29

Chromatic aberration results from:

A) blue light being reflected more than red light
B) red light being reflected more than blue light
C) red light being refracted more than blue light
D) blue light being refracted more than red light
E) a lens being polished incorrectly

Question 30

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).
E) The image is created on the other side of the mirror.

Question 31

Grote Reber conducted the first radio survey of the sky in the 1930s and 1940s with his 9-meter diameter radio telescope. Why did his telescope need to be so large?

A) He needed a large light-collecting area because radio sources are notoriously dim.
B) He needed better angular resolution to identify sources because radio waves are so long.
C) He needed a higher magnification to identify sources because radio sources are quite small.
D) He needed a longer focal length since radio sources are so far away.
E) He needed a shorter focal length since radio sources are so far away.

Question 32

Which property of light is responsible for chromatic aberration?

A) reflection
B) interference
C) dispersion
D) diffraction
E) magnification

Question 33

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 34

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) 90°
E) 120°

Question 35

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

A) 0.01 arcsec
B) 0.005 arcsec
C) 0.4 arsec
D) 0.06 arcsec
E) 0.2 arcsec

Question 36

The diffraction limit of a 4-meter telescope is _________ than that of a 2-meter telescope.

A) two times larger
B) four times larger
C) four times smaller
D) two times smaller
E) It depends on the type of telescope.

Question 37

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 outgoing medium
C) the index of refraction of the incoming medium
D) the angle of incidence
E) all of the above

Question 38

The angular resolution of the largest single-dish radio telescope in the United States, the 100-m Green Bank Telescope, is _________ when it operates at a wavelength of 20 cm.

A) 41 arcmin
B) 6.8 arcmin
C) 4.1 arcmin
D) 6.8 arcsec
E) 4.1 arcsec

Question 39

Which of the following phenomena is shown in the figure below?

A) reflection
B) chromatic aberration
C) diffraction
D) magnification
E) interference

Question 40

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) The beam of light does not emerge from the water.
E) There is not enough information to answer the question.

Question 41

Which of the following phenomena is shown in the figure below?

A) reflection
B) refraction
C) chromatic aberration
D) magnification
E) interference

Question 42

Water vapor in Earth's atmosphere primarily easily absorbs which type of photons?

A) radio
B) infrared
C) visible
D) ultraviolet
E) X-ray

Question 43

Most modern spectrographs use a _________ to disperse the light from an object.

A) spherical mirror
B) lens
C) glass prism
D) diffraction grating
E) parabolic mirror

Question 44

Typically, video is shot using 24 to 30 frames per second (one frame each 33 to 42 ms). If a filmmaker shot new experimental video at 100 frames per second (one frame each 1 ms), how would it look during playback to the human eye?

A) It would look like the video was being fast-forwarded.
B) It would look like the video was about the same as normal video.
C) It would look like the video was being played back in slow motion.
D) It would look like a slideshow, a series of pictures on the screen each for a perceptible amount of time.
E) It would look like the video was about the same speed as normal video, but blurry.

Question 45

What property of light allows a grating to disperse the light from an object into a spectrum?

A) interference
B) reflection
C) refraction
D) aberration
E) magnification

Question 46

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

A) Polaroid cameras
B) photographic glass plates
C) 35-mm film
D) high-speed film
E) video cameras

Question 47

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 48

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
E) the Earth emits too much ultraviolet background light

Question 49

The first astronomical radio source ever observed was:

A) the Andromeda Galaxy
B) the galactic center, in the constellation Sagittarius
C) thunderstorms
D) the Earth
E) Jupiter

Question 50

You are observing the Andromeda Galaxy using both photographic plates and a CCD. If you double the exposure time for both detectors, you:

A) double the amount of light collected on both the photographic plate and the CCD
B) double the amount of light collected on the CCD, but the photographic plate collects less
C) double the amount of light collected on the photographic plate, but the CCD collects less
D) double the amount of light collected on the photographic plate, but the CCD collects more
E) collect less than twice the amount of light on both the photographic plate and the CCD

Question 51

What part(s) of the human eye is responsible for detecting light?

A) cornea
B) lens
C) pupil
D) rods and cones
E) iris

Question 52

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) dispersion
D) diffraction
E) interference

Question 53

The 305-meter 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-meter optical telescope (1 arcsec)
E) one of the 10-meter Keck telescopes (0.0133 arcsec)

Question 54

NASA's Kuiper Airborne Observatory and SOFIA are two examples of telescopes placed in high-flying aircraft. Why would astronomers put telescopes in airplanes?

A) to get the telescopes closer to the stars
B) to get the telescopes away from the light-pollution of cities
C) to get the telescopes above the majority of the water vapor in the earth's atmosphere
D) to be able to observe one object for more than 24 hours without stopping.
E) to allow the telescopes to observe the full spectrum of light

Question 55

When we determine the angular resolution of an interferometric array of radio telescopes using the formula $\theta$ $\infty$ $\lambda$ /D, the variable D stands for the:

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

Question 56

Which of the following is NOT a reason to put a telescope in space?

A) to observe at wavelengths blocked by the Earth's atmosphere
B) to avoid light pollution on Earth
C) to avoid weather on Earth
D) to avoid atmospheric distortion
E) to get closer to the stars

Question 57

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
E) they simulate a much larger telescope

Question 58

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
E) the integration time is much shorter with the use of photographic plates

Question 59

If we could increase the quantum efficiency of the human eye, it would:

A) allow humans to see a larger range of wavelengths
B) allow humans to see better at night, or other low-light conditions
C) increase the resolution of the human eye
D) decrease the resolution of the human eye
E) not make a difference in the sight of the human eye

Question 60

Astronomers can use ground-based telescopes to observe in the majority of which of the following parts of the electromagnetic spectrum?

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

Question 61

How much larger is the light-gathering power of a 10-inch telescope than the human eye?

Question 62

Remote sensing instruments have been used to:

A) map surfaces hidden beneath thick atmospheres
B) measure the composition of atmospheres
C) identify geological features
D) watch weather patterns develop
E) all of the above

Question 63

High-speed computers have become one of an astronomer's most important tools. Which of the following does NOT require the use of a high-speed computer?

A) analyzing images taken with very large CCDs
B) generating and testing theoretical models
C) moving a telescope from object to object
D) studying the evolution of astronomical objects or systems over time
E) correcting for atmospheric distortion

Question 64

Which of the following cannot be directly detected using a telescope?

A) X-rays
B) visible light
C) infrared light
D) neutrinos
E) ultraviolet light

Question 65

Explain why the largest telescopes are not refracting telescopes.

Question 66

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

A) 10
B) 10⁶ (one million)
C) 10⁹ (one billion)
D) 10¹² (one trillion)
E) 10²² (10 billion trillion)

Question 67

Telescopes and satellites such as COBE, WMAP, and Planck are designed to detect microwave radiation emitted by:

A) galaxies
B) black holes
C) planets
D) the Big Bang
E) stars

Question 68

Landers, rovers, and/or atmospheric probes have visited which object(s) listed below in an effort to gain new information about our Solar System?

A) Jupiter
B) Titan, Saturn's moon
C) Mars
D) Eros, an asteroid
E) all of the above

Question 69

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

Question 70

Label the eyepiece, primary mirror, secondary mirror, focus, and focal length of the telescope below.

Question 71

The Voyager I spacecraft is currently 18 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) 1.7 days
B) 17 hours
C) 17 days
D) 17 weeks
E) 17 minutes

Question 72

What type of waves have NOT yet been directly detected by astronomers?

A) sound waves
B) gravitational waves
C) X-ray waves
D) gamma-ray waves
E) pressure waves

Question 73

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) an asteroid
D) the Moon
E) all of the above

Question 74

Which of the following is the biggest disadvantage of putting a telescope in space?

A) Astronomers don't have as much control in choosing what to observe.
B) Astronomers have to wait until the telescopes come back to Earth to get their images.
C) Space telescopes can only observe in certain parts of the electromagnetic spectrum.
D) Space telescopes don't last long before they fall back down to Earth.
E) Space telescopes are much more expensive than similar ground-based telescopes.

Question 75

Label the eyepiece, lens, focus, and focal length of the telescope below.

Question 76

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's surface, how large an object could be resolved on the surface?

A) 3 m
B) 30 cm
C) 30 km
D) 5 cm
E) 50 m

Question 77

Explain the difference between dispersion and diffraction. How can both phenomena be used to create a spectrum?

Question 78

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

A) the early universe
B) the solar wind
C) red giants
D) brown dwarf stars
E) planetary nebula

Question 79

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

Question 80

Explain what happens when white light is refracted by a prism.