Astronomy Chapter 5

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

True

True or False All radio telescopes are reflectors in design

True

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

True

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

True

True or False It is much easier to build large reflectors than large refractors.

True

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

True

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

True

True or False Telescopes on Earth that use adaptive optics can have better angular resolution than the Hubble Space Telescope.

True

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

True

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

True

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

True

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

True

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

False

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

False

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

False

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

False

True or False Hubble Space Telescope is still the largest scope ever built.

False

True or False Optical interferometry is more in use than radio interferometry.

False

True or False The James Webb Space Telescope is designed to observe object primarily using ultraviolet light.

False

True or False The largest refracting telescope can collect more light than the largest reflecting telescope.

False

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

False

True or False The simplest reflecting telescope design, by Isaac Newton, uses only a primary mirror.

False

Why are most large telescopes reflectors, not refractors? a) Large lenses deform under their own weight, but mirrors can be supported. b) Large, very clear lenses are harder to cast than more tolerant mirror blanks. c) Large mirrors need only one optical surface, achromats four surfaces to grind. d) Reflectors do not suffer from chromatic aberration like refractors do. e) All of the above are correct.

E) All of the above are correct

What is the main reason that ultraviolet astronomy must be done in space? a) Earth's atmosphere absorbs most ultraviolet wavelengths. b) to collect more visible light without loss because it's very dark in orbit c) to prevent competing countries from reaching them d) to provide a stable platform for imaging

a) Earth's atmosphere absorbs most ultraviolet wavelengths

Which of the following is NOT a difference between the operation of a radio telescope and that of an optical reflecting telescope? a) Optical reflectors can detect the entire visible range of wavelengths simultaneously, whereas radio telescopes can detect only a small band of wavelengths at one time. b) Optical reflectors must have smooth surfaces for reflecting visible light, whereas radio telescope dishes don't. c) Optical reflecting telescopes can only observe interstellar objects during the night, whereas radio telescopes can also observe them during the day. d) Optical reflectors can have their detector placed at the prime focus, whereas radio telescopes never do.

a) Optical reflectors can have their detector placed at the prime focus, whereas radio telescopes never do.

Which of the following statements about the use of infrared telescopes is true? a) The detector and telescope must be cooled to very low temperatures. b) The sky conditions must be exceptionally free of dust and haze. c) They can only be used from space. d) The mirror surface can be composed of wire mesh. e) They must be placed at low elevations, not on a mountaintop.

a) The detector and telescope must be cooled to very low temperatures

Which of the following is an advantage the Hubble Space Telescope has over ground-based telescopes? a) There is no blurring due to the atmosphere. b) Being weightless in space, it can utilize the largest mirror ever built. c) It is always in darkness. d) It has a better view of celestial objects because it is closer to them.

a) There is no blurring due to the atmosphere

The best frequency range in which to study the hot (million-kelvin) gas found among the galaxies in the Virgo galaxy cluster would be in the following region of the electromagnetic spectrum: a) X-ray. b) radio. c) infrared. d) gamma-ray.

a) X-ray.

If you want to make a very dim object appear much brighter in an image photographed through a telescope, which of the following factors are important? a) the diameter of each telescope. b) the electrical power supplied to each telescope. c) the distance between telescopes. d) the number of telescopes in a given area.

a) diameter of the telescope and the length of the exposure

Astronomers use the term "seeing" to describe the ____________. a) effects of atmospheric turbulence b) sensitivity of an astronomer's eyes c) optical quality of a telescope d) amount of light gathered by a telescope e) size of a telescope eyepiece

a) effects of atmospheric turbulence

Radio dishes are large in order to: a) increase their angular resolution and collect the very weak radio photons. b) attract funding from NASA and the NSF. c) detect shorter waves than optical telescopes for superior resolution. d) increase the range of waves they can collect. e) give greater magnification.

a) increase their angular resolution and collect the very weak radio photons.

Chromatic aberration in lenses is a result of which wave property of light? a) refraction b) diffraction c) interference d) polarization

a) refraction

The image shown in Figure 5.12 in the textbook ("Resolution") is sharpest when the ratio of wavelength to telescope size is a) small. b) large. c) close to unity. d) none of these.

a) small

A major advantage of a Newtonian reflector over a refractor is: a) the elimination of chromatic aberration. b) there are only two lenses to grind. c) its compact size. d) the central hole in the mirror is smaller. e) the elimination of the secondary mirror.

a) the elimination of chromatic aberration

The amount of diffraction a telescope creates depends upon a) the wavelength and the diameter of the telescope objective. b) the transparency of the atmosphere. c) the types of glass used in the achromat. d) the magnification of the eyepiece. e) whether the telescope is a refractor or a reflector.

a) the wavelength and the diameter of the telescope objective

The angular resolution of an 8-inch diameter telescope is ________ better than that of a 2-inch diameter telescope a) 16 times b) 4 times c) 9 times d) 2 times e) 8 times

b) 4 times

Which of the following telescopes does (did) NOT observe infrared light? a) Herschel b) Chandra c) James Webb d) Hubble e) Spitzer

b) Chandra

What are two advantages of large scopes over smaller ones? a) Large scopes are not subject to atmospheric turbulence and opacity like smaller ones. b) Large telescope have more light grasp and better resolution. c) Large scopes have a larger field of view and sharper focus. d) Large telescopes give higher magnification and are easier to build. e) Large scopes are easier to mount and control than small ones.

b) Large telescope have more light grasp and better resolution.

A small telescope has ________ angular resolution when compared to a large telescope. a) smaller b) larger c) the same d) brighter e) chromatic

b) Larger

Explain two reasons why astronomers are continually building larger and larger telescopes a) Larger telescope mirrors have a larger surface area and can therefore collect more light, which contributes to better angular resolution. Also, larger telescope mirrors produce more scattering of light due to diffraction, which makes faint objects bright enough to detect. b) Larger telescope mirrors have a larger surface area and can therefore collect more light, which makes faint objects bright enough to detect. Also, larger telescope mirrors produce less scattering of light due to diffraction, which contributes to better angular resolution. c) Larger telescope mirrors have a larger surface area and can therefore collect more light, which makes faint objects bright enough to detect. Also, larger telescope mirrors produce more scattering of light due to diffraction, which contributes to better angular resolution. d) Larger telescope mirrors have a larger surface area and can therefore collect more light, which contributes to better angular resolution. Also, larger telescope mirrors produce less scattering of light due to diffraction, which makes faint objects bright enough to detect.

b) Larger telescope mirrors have a larger surface area and can therefore collect more light, which makes faint objects bright enough to detect. Also, larger telescope mirrors produce less scattering of light due to diffraction, which contributes to better angular resolution.

Which design has a convex primary mirror and flat secondary mirror, with the eyepiece located on the top side of the telescope tube? a) interferometer b) Newtonian reflector c) prime focus reflector d) Cassegrain reflector e) refractor

b) Newtonian reflector

Refractor telescopes suffer from this separation of light into its component colors. a) limited diffraction b) chromatic aberration c) refraction d) bad seeing e) spherical aberration

b) chromatic aberration

What problem do refractor telescopes have that reflectors don't? a) diffraction limited resolution b) chromatic aberration c) light loss from secondary elements d) bad seeing e) spherical aberration

b) chromatic aberration

This design combines the radiation from two different telescopes to greatly enhance resolution via computer synthesis. a) refractor b) interferometer c) Newtonian reflector d) prime focus reflector e) Cassegrain reflector

b) interferometer

The main reason that most professional research telescopes are reflectors is that a) they do not suffer from the effects of seeing. b) large mirrors are easier to build than large lenses. c) their images are inverted. d) mirrors produce sharper images than lenses do.

b) large mirrors are easier to build than large lenses.

In both reflecting and refracting telescopes, the main role that an eyepiece plays is to a) collect more light. b) magnify the image. c) correct the colors of the image. e) turn the image right side up.

b) magnify the image.

The Arecibo radio telescope is laid out like which optical telescope design? a) Coude reflector b) prime focus reflector c) grazing incidence reflector d) Cassegrain reflector e) Newtonian reflector

b) prime focus reflector

The primary reason professional observatories are built on the highest mountaintops is to a) improve chromatic aberration. b) reduce atmospheric blurring. c) get away from city lights. d) be above the rain clouds.

b) reduce atmospheric blurring.

Computers are used to sharpen images collected by telescopes by a) increasing resolution. b) reducing the noise in observations. c) reducing diffraction. d) reducing chromatic aberration. e) producing false color images.

b) reducing the noise in observations.

How much better resolution would a 60 mm objective lens have than your eye's 6 mm exit pupil? a) 100 times b) 16 times c) 10 times d) 6 times e) 60 times

c) 10 times

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) 10 times b) 25 times c) 100 times d) 250 times e) 5 times

c) 100 times

What is the light-gathering power of an 8-inch telescope compared to a 4-inch telescope? a) 2× better b) 8× better c) 4× better d) 16× better e) 32× better

c) 4× better

What type of telescope is the Hubble Space Telescope? a) Newtonian b) Nasmyth/Coude c) Cassegrain d) prime focus e) refractor

c) Cassegrain

Which of the following is a problem inherent in all large radio telescopes? a) The dust clouds in the Milky Way block almost all wavelengths except light. b) The lightest breeze shakes them, making the observations blurry. c) Radio waves have long wavelengths, so radio telescopes have poor resolution. d) They are badly affected by poor seeing and atmospheric turbulence. e) Their waves are blocked by water vapor, so they must be located in deserts.

c) Radio waves have long wavelengths, so radio telescopes have poor resolution.

What is meant in astronomy by the phrase "active optics"? a) The optical elements of a telescope are placed on vibration-free mounts to compensate for ground motion. b) The optical elements of a telescope are actively heated to maintain the proper temperature. Slow modifications are made to the pointing controls of a telescope to keep it pointed toward the target object. c) Rapid modifications are made to the tilt and location of the elements of a telescope to correct for the effects of atmospheric and instrumental distortion. d) The mirrors and eyepiece of a large telescope are spring-loaded to allow them to return quickly to a known position.

c) Rapid modifications are made to the tilt and location of the elements of a telescope to correct for the effects of atmospheric and instrumental distortion.

What is true of radio telescopes? a) They are most sensitive to the opacity of the ozone layer. b) They can only be used above the atmosphere. c) They have poorer angular resolution than a refractor. d) They have better angular resolution than a reflector. e) They are the smallest, most compact telescopes.

c) They have poorer angular resolution than a refractor.

What is "seeing"? a) a measurement of clarity and absence of clouds b) a measure of the transparency of the scope's objective lens c) a measurement of the image quality due to air stability d) a measure of the quality of the telescope's optics e) a measurement of the sharpness of vision of the astronomer's eyes

c) a measurement of the image quality due to air stability

The Chandra X-ray Observatory must use: a) a Schmidt corrector plate to avoid spherical aberration. b) X-ray photographic plates instead of CCDs for imaging. c) grazing incidence optics to focus the short wavelengths. d) a Newtonian reflecting design to avoid chromatic aberration. e) a lens of fluorite.

c) grazing incidence optics to focus the short wavelengths.

The design of modern X-ray telescopes depends on: a) lenses made of germanium. b) achromatic lenses to keep the X-rays in focus. c) grazing incidence optics. d) the prime focus design, with mirrors made of iron. e) the Cassegrain design, with mirrors made of lead.

c) grazing incidence optics.

Compared to a 5-inch prime focus reflector, a 5-inch Newtonian reflector will a) will have a larger hole in the center of its mirror. b) have more light gathering power. c) have the same light gathering power. d) will have more chromatic aberration. e) be easier to build.

c) have the same light gathering power

In astronomy, an interferometer can be used to: a) speed up the processing of CCD images. b) yield better seeing conditions with optical telescopes. c) improve the angular resolution of radio telescopes. d) decrease the effects of light pollution in getting darker sky backgrounds. e) increase the sensitivity of infrared telescopes to longer wavelengths.

c) improve the angular resolution of radio telescopes.

The Atacama Large Millimeter Array achieves exceptional resolution by using exceptionally: a) many portions of the electromagnetic spectrum. b) many radio antennas in a fixed array. c) many radio antennas in a mobile array. d) large radio antennas in a mobile array. e) large radio antennas in a fixed array.

c) many radio antennas in a mobile array.

If telescope mirrors could be made of odd sizes, the one with the most light-gathering power would be a) square with 1-m sides. b) triangle with 1-m sides. c) rectangle with two 1-m sides and two 2-m sides. d) circle 1 m in -diameter.

c) rectangle with two 1-m sides and two 2-m sides.

The thickest lenses deflect and bend light a) the fastest. b) the slowest. c) the most. d) the least.

c) the most

Radio telescopes have poorer angular resolution than optical telescopes because: a) radio telescopes often use multiple telescopes to make observations. b) the reflecting surfaces in radio telescopes have holes in them. c) the wavelength of radio waves is longer than that of visible light. d) radio is distorted more by Earth's atmosphere than visible light is. e) Radio telescopes actually have better resolution than optical telescopes.

c) the wavelength of radio waves is longer than that of visible light.

The amount of diffraction, and thus the resolution of the scope, depends upon: a) the design of the telescope. b) the brightness of the object. c) the wavelength used and the size of the main telescope objective lens or mirror. d) whether the telescope is a reflector or refractor. e) the size and sensitivity of the CCD chip used for imaging.

c) the wavelength used and the size of the main telescope objective lens or mirror

What is the primary purpose of an astronomical telescope? a) to magnify and make distant objects appear closer b) to access wavelengths that we cannot see visually c) to collect a lot of light and bring it to a focus d) to measure the intensity of light very accurately e) to separate light into its component colors

c) to collect a lot of light and bring it to a focus

What problem does adaptive optics correct? a) the opacity of the Earth's atmosphere to some wavelengths of light b) the light pollution of urban areas c) turbulence in the Earth's atmosphere which creates twinkling d) defects in the optics of the telescope, such as the original Hubble mirror e) chromatic aberration due to use of only a single lens objective

c) turbulence in the Earth's atmosphere which creates twinkling

Which of the following greatly improves the angular resolution of radio maps? a) chilling the infrared detectors b) more sensitive spectrometers c) use of interferometers d) switching from photographic plates to CCD imaging e) Schmidt corrector plates

c) use of interferometers

The Spitzer Space Telescope (SST) is stationed far from Earth because a) the telescope is sensitive to electromagnetic interference from terrestrial radio stations. b) this increases the telescope's field of view. c) doing so avoids the obscuring effects of Earth's atmosphere. d) Earth is a heat source and the telescope must be kept very cool.

d) Earth is a heat source and the telescope must be kept very cool.

What is image processing? a) the process used to make radio maps of the sky b) the process that takes place during the time a telescope is obtaining an image c) the procedure used in photography to develop film or photographic plates d) computer processing of electronic images to correct for defects and remove noise

d) computer processing of electronic images to correct for defects and remove noise

Which method of astronomical measurement is the precise measurement of brightness? a) spectroscopy b) interferometry c) astrometry d) photometry e) photography

d) photometry

Green light has a shorter wavelength than orange light. In a 5-inch telescope, green light will: a) come to the same exact focus as orange light. allow dimmer stars to be observed. b) reduce the effects of atmospheric turbulence. c) provide worse angular resolution than orange light. d) provide better angular resolution than orange light.

d) provide better angular resolution than orange light.

Compared to optical telescopes, radio telescopes are built large because: a) radio sources are harder to find. b) they're less expensive to make than optical telescopes. c) atmospheric turbulence is more of a problem. d) radio photons don't carry much energy. e) radio waves are absorbed by the atmosphere.

d) radio photons don't carry much energy.

As telescopes become larger and larger, astronomers favor ________. a) refracting telescopes, in part because as light bounces off of mirrors, some of it is absorbed; this doesn't happen with lenses b) reflecting telescopes, in part because the angular resolution of refractors is limited by diffraction whereas the angular resolution of reflectors is not c) refracting telescopes, in part because lenses are easier than mirrors to shape and polish accurately d) reflecting telescopes, in part because large lenses and mirrors sag under their own weight, and it is easier to support a mirror along its entire back side than it is to support a lens only around its edge

d) reflecting telescopes, in part because large lenses and mirrors sag under their own weight, and it is easier to support a mirror along its entire back side than it is to support a lens only around its edge

The process occurring when photons bounce off a polished surface is called: a) interference. b) refraction. c) dispersion. d) reflection. e) diffraction.

d) reflection

Compared with radio telescopes, optical telescopes can a) penetrate interstellar dust. b) see through clouds. c) be used during the daytime. d) resolve finer detail.

d) resolve finer detail.

Diffraction is the tendency of light to: a) bend through a lens. b) disperse within a prism. c) separate into its component colors. d) spread around corners. e) reflect off a mirror.

d) spread around corners.

What problem is adaptive optics designed to correct? a) defects in the optical figuring, such as with the adaptive optics on HST b) the absorption of ultraviolet by the ozone layer c) the opacity of the Earth's atmosphere d) the effects of atmospheric turbulence e) slight tracking errors in trying to compensate for our unsteady rotation

d) the effects of atmospheric turbulence

The James Webb Space Telescope is different than other space telescopes because it a) observes infrared light. b) is launched on a rocket. c) is more compact. d) uses a segmented mirror. e) is closer to the Sun.

d) uses a segmented mirror.

A mountain top is an especially good site for infrared telescopes since: a) the cold weather helps the sensitivity of infrared detectors. b) you are above most of the carbon dioxide and water vapor in the atmosphere. c) there you are closer to celestial objects. d) less air above means better seeing in many cases. e) All of the above are factors

e) All of the above are factors

The convex secondary mirror in this design focuses light down through a hole cut in the concave primary mirror. a) interferometer b) refractor c) Newtonian reflector d) prime focus reflector e) Cassegrain reflector

e) Cassegrain reflector

Which of the following is currently supplying high resolution X-ray images from space? a) HEAO-2 b) Einstein c) COBE d) ROSAT e) Chandra

e) Chandra

Which of the following telescopes observes the highest energy photons? a) James Webb b) Chandra c) Hubble d) ALMA e) Fermi

e) Fermi

Which of these devices helps correct coma in fast reflectors? a) achromatic doublet b) Newtonian secondary mirror c) Cassegrain secondary mirror d) star diagonal e) Schmidt corrector plate

e) Schmidt corrector plate

The name of the Infrared Orbiting Observatory launched in 2003 is the: a) Newton Imaging System. b) Compton Observatory. c) Chandra Orbiting Telescope. d) Hubble Space Telescope. e) Spitzer Space Telescope.

e) Spitzer Space Telescope.

In which part of the electromagnetic spectrum have astronomers been unable to get any information? a) gamma rays b) ultraviolet c) X-rays d) microwaves e) We now can access information in all spectral lengths.

e) We now can access information in all spectral lengths.

The primary purpose of a telescope is to: a) make distant objects appear nearby. b) separate light into its component wavelengths. c) measure the brightness of stars very accurately. d) magnify distant objects. e) collect a large amount of light and bring it into focus.

e) collect a large amount of light and bring it into focus

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 make better observations of the ozone layer. c) it can better focus X-ray images. d) its adaptive optics controls atmospheric blurring better. e) in orbit, it can operate close to its diffraction limit at visible wavelengths.

e) in orbit, it can operate close to its diffraction limit at visible wavelengths.

What is the resolution of a telescope? a) its ability to separate light into its component colors for analysis b) its ability to distinguish two adjacent objects close together in the sky c) its ability to focus more than just visible light for imaging d) its ability to make distant objects appear much closer to us e) its ability to see very faint objects

e) its ability to distinguish two adjacent objects close together in the sky

Radio telescopes would NOT represent a good choice for astronomical study of which of the following types of object? a) nebulae b) the center of the Milky Way c) radar studies of planets d) other galaxies e) ordinary stars

e) ordinary stars

This design involves only one optical surface, a concave mirror. a) refractor b) Newtonian reflector c) Cassegrain reflector d) prime focus reflector e) Gregorian reflector

e) prime focus reflector

Which type of telescope has the simplest light path? a) Cassegrain reflector b) Newtonian reflector c) single lens refractor d) achromatic refractor e) prime focus reflector

e) prime focus reflector

The tendency of a wave to bend as it passes from one transparent medium to another is called: a) diffraction. b) dispersion. c) interference. d) reflection. e) refraction.

e) refraction

Which design is subject to chromatic aberration? a) prime focus reflector b) Gregorian reflector c) Newtonian reflector d) Cassegrain reflector e) refractor

e) refractor

It is diffraction that limits the ________ of a telescope's objective a) wavelengths b) frequencies c) light grasp d) magnification e) resolution

e) resolution

What is the resolving power of the telescope? a) the ability to detect very faint objects b) the ability to separate light into its component colors c) the ability to make distant objects appear closer d) the ability to collect a lot of light e) the ability to distinguish adjacent objects in the sky

e) the ability to distinguish adjacent objects in the sky

The best way to study warm (1000 K) young stars forming behind an interstellar dust cloud would be to use a) blue light. b) ultraviolet light. c) X-rays. d) infrared light.

infrared light.

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) improve the angular resolution of the telescope. c) keep the telescope more nearly stationary. d) prevent the infrared radiation from the instruments interfering with the infrared signals from space.

prevent the infrared radiation from the instruments interfering with the infrared signals from space.

When multiple radio telescopes are used for interferometry, resolving power is most improved by increasing

the distance between telescopes.