Deck 5: Telescopes: The Tools of Astronomy

Question 1

One reason for building telescopes on mountain tops is that they improve seeing by reducing the amount of air above the observer.

Answer 1

True

Question 2

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

Answer 2

True

Question 3

The primary purpose of an astronomical telescope is to magnify the images of distant objects,making them appear closer.

Answer 3

False

Question 4

Absorption of light passing through the glass is a bigger problem for Cassegrain reflectors than achromatic refractors.

Question 5

Optical interferometry is more in use than radio interferometry.

Question 6

In addition to visible light,Hubble can do some work in the infrared and ultraviolet portions of the spectrum.

Question 7

All radio telescopes are reflectors in design.

Question 8

Chromatic aberration affects refractor and reflector telescopes equally,unless they have very long focal lengths.

Question 9

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

Question 10

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

Question 11

The simplest scope design,by Isaac Newton,uses only a primary mirror.

Question 12

A convex lens is thinnest in its center; it refracts light to a focus,while a convex mirror reflects it to the focus instead.

Question 13

You could more easily resolve a close double star with a blue filter than with a red one.

Question 14

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

Question 15

The Schmidt corrector plate largely cures spherical aberration,giving a wide,flat field of view.

Question 16

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

Question 17

It is much easier to build large reflectors than large refractors.

Question 18

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

Question 19

Hubble Space Telescope is still the largest scope ever built.

Question 20

To reach the Cassegrain focus,a hole must be cut in the center of the primary mirror.

Question 21

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.

Question 22

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

Question 23

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) will have more chromatic aberration.
E) will have a larger hole in the center of its mirror.

Question 24

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.

Question 25

The process occurring when photons bounce off a polished surface is called:

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

Question 26

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

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

Question 27

The amount of diffraction,and thus the resolution of the scope,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.

Question 28

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

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

Question 29

What is the primary purpose of an astronomical telescope?

A) to magnify and make distant objects appear closer
B) to separate light into its component colors
C) to measure the intensity of light very accurately
D) to access wavelengths that we cannot see visually
E) to collect a lot of light and bring it to a focus

Question 30

Which design has a convex primary mirror and flat secondary mirror,with the eyepiece located on the top side of the telescope tube?

A) refractor
B) Newtonian reflector
C) Cassegrain reflector
D) prime focus reflector
E) interferometer

Question 31

Which design is subject to chromatic aberration?

A) refractor
B) prime focus reflector
C) Newtonian reflector
D) Cassegrain reflector
E) Gregorian reflector

Question 32

It is diffraction that limits the ________ of a telescope's objective.

A) magnification
B) resolution
C) light grasp
D) wavelengths
E) frequencies

Question 33

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

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

Question 34

This design involves only one optical surface,a concave mirror.

A) prime focus reflector
B) Newtonian reflector
C) Cassegrain reflector
D) Gregorian reflector
E) refractor

Question 35

What type of telescope is the Subaru telescope (shown below)?

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

Question 36

The convex secondary mirror in this design focuses light down through a hole cut in the concave primary mirror.

A) refractor
B) prime focus reflector
C) Newtonian reflector
D) Cassegrain reflector
E) interferometer

Question 37

What is the resolving power of the telescope?

A) the ability to make distant objects appear closer
B) the ability to collect a lot of light
C) the ability to detect very faint objects
D) the ability to distinguish adjacent objects in the sky
E) the ability to separate light into its component colors

Question 38

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

Question 39

The tendency of a wave to bend as it passes from one transparent medium to another is called:

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

Question 40

Why are most large telescopes reflectors,not refractors?

A) Large lenses deform under their own weight, but mirrors can be supported.
B) Large mirrors need only one optical surface, achromats four surfaces to grind.
C) Reflectors do not suffer from chromatic aberration like refractors do.
D) Large, very clear lenses are harder to cast than more tolerant mirror blanks.
E) All of the above are correct.

Question 41

Diffraction is the tendency of light to:

A) spread around corners.
B) separate into its component colors.
C) bend through a lens.
D) disperse within a prism.
E) reflect off a mirror.

Question 42

What are two advantages of large scopes over smaller ones?

A) Large scopes have a larger field of view and sharper focus.
B) Large scopes are not subject to atmospheric turbulence and opacity like smaller ones.
C) Large scopes are easier to mount and control than small ones.
D) Large telescope have more light grasp and better resolution.
E) Large telescopes give higher magnification and are easier to build.

Question 43

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.

Question 44

How much better resolution would a 60 mm objective lens have than your eye's 6 mm exit pupil?

A) 6 times
B) 10 times
C) 16 times
D) 60 times
E) 100 times

Question 45

Which of these devices helps correct coma in fast reflectors?

A) Cassegrain secondary mirror
B) star diagonal
C) achromatic doublet
D) Schmidt corrector plate
E) Newtonian secondary mirror

Question 46

What type of telescope is the Hubble Space Telescope?

A) refractor
B) prime focus
C) Newtonian
D) Cassegrain
E) Nasmyth/Coude

Question 47

What problem is adaptive optics designed to correct?

A) the opacity of the Earth's atmosphere
B) defects in the optical figuring, such as with the adaptive optics on HST
C) slight tracking errors in trying to compensate for our unsteady rotation
D) the effects of atmospheric turbulence
E) the absorption of ultraviolet by the ozone layer

Question 48

A mountain top is an especially good site for infrared telescopes since:

A) there you are closer to celestial objects.
B) you are above most of the carbon dioxide and water vapor in the atmosphere.
C) the cold weather helps the sensitivity of infrared detectors.
D) less air above means better seeing in many cases.
E) All of the above are factors.

Question 49

Which method of astronomical measurement is the precise measurement of brightness?

A) spectroscopy
B) photography
C) astrometry
D) photometry
E) interferometry

Question 50

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 Earth's atmosphere to some wavelengths of light
C) the light pollution of urban areas
D) turbulence in the Earth's atmosphere which creates twinkling
E) chromatic aberration due to use of only a single lens objective

Question 51

The amount of diffraction a telescope creates depends upon:

A) whether the telescope is a refractor or a reflector.
B) the wavelength and the diameter of the telescope objective.
C) the magnification of the eyepiece.
D) the types of glass used in the achromat.
E) the transparency of the atmosphere.

Question 52

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.

Question 53

What is "seeing"?

A) a measure of the quality of the telescope's optics
B) a measure of the transparency of the scope's objective lens
C) a measurement of the sharpness of vision of the astronomer's eyes
D) a measurement of the image quality due to air stability
E) a measurement of clarity and absence of clouds

Question 54

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

A) it is larger than any Earth-based scopes.
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.

Question 55

Refractor telescopes suffer from this separation of light into its component colors.

A) limited diffraction
B) spherical aberration
C) chromatic aberration
D) bad seeing
E) refraction

Question 56

What is true of radio telescopes?

A) They have poorer angular resolution than a refractor.
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.

Question 57

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

Question 58

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

Question 59

Which of the following is a problem inherent in all large radio telescopes?

A) They are badly affected by poor seeing and atmospheric turbulence.
B) The lightest breeze shakes them, making the observations blurry.
C) Their waves are blocked by water vapor, so they must be located in deserts.
D) Radio waves have long wavelengths, so radio telescopes have poor resolution.
E) The dust clouds in the Milky Way block almost all wavelengths except light.

Question 60

A telescope with a 60 mm objective lens collects how many times as much light as does your eye's 6 mm exit pupil?

A) 5 times
B) 10 times
C) 25 times
D) 100 times
E) 250 times

Question 61

Compared to optical telescopes,radio telescopes are built large because:

A) they're less expensive to make than optical telescopes.
B) radio photons don't carry much energy.
C) atmospheric turbulence is more of a problem.
D) radio sources are harder to find.
E) radio waves are absorbed by the atmosphere.

Question 62

The name of the Infrared Orbiting Observatory launched in 2003 is the:

A) Hubble Space Telescope.
B) Compton Observatory.
C) Spitzer Space Telescope.
D) Chandra Orbiting Telescope.
E) Newton Imaging System.

Question 63

The Atacama Large Millimeter Array achieves exceptional resolution by using exceptionally:

A) large radio antennas in a fixed array.
B) large radio antennas in a mobile array.
C) many radio antennas in a fixed array.
D) many radio antennas in a mobile array.
E) many portions of the electromagnetic spectrum.

Question 64

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

Question 65

Which of the following greatly improves the angular resolution of radio maps?

A) Schmidt corrector plates
B) more sensitive spectrometers
C) switching from film to CCD imaging
D) use of interferometers
E) chilling the infrared detectors

Question 66

In which part of the electromagnetic spectrum have astronomers been unable to get any information?

A) gamma rays
B) X-rays
C) ultraviolet
D) microwaves
E) We now can access information in all spectral lengths.

Question 67

The detectors on the Spitzer Space Telescope were cooled to near absolute zero in order to:

A) allow the electronics in these instruments to operate most efficiently.
B) keep the telescope more nearly stationary.
C) prevent the infrared radiation from the instruments interfering with the infrared signals from space.
D) improve the angular resolution of the telescope.

Question 68

The Chandra X-ray telescope must use:

A) a lens of fluorite.
B) grazing incidence optics to focus the short wavelengths.
C) a Newtonian reflecting design to avoid chromatic aberration.
D) X-ray film instead of CCDs for imaging.
E) a Schmidt corrector plate to avoid spherical aberration.

Question 69

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

Question 70

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

Question 71

Very accurate measurements of stellar brightnesses and sudden changes are made with a ________.

Question 72

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.

Question 73

Radio dishes are large in order to:

A) attract funding from NASA and the NSF.
B) give greater magnification.
C) increase their angular resolution and collect the very weak radio photons.
D) increase the range of waves they can collect.
E) detect shorter waves than optical telescopes for superior resolution.

Question 74

This design combines the radiation from two different telescopes to greatly enhance resolution via computer synthesis.

A) Cassegrain reflector
B) Newtonian reflector
C) prime focus reflector
D) refractor
E) interferometer

Question 75

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.

Question 76

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

Question 77

The ________ is a measure of the stability of the atmosphere,usually degraded by turbulent currents in the air.

Question 78

Because of ________,images in small telescopes are more blurred than with larger objectives.

Question 79

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

Question 80

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