Chap 6

Which of the following statements about light focusing is not true?
A) In a healthy eye, light is focused on the retina.
B) Film should be placed at the focal plane in a camera.
C) If you try to look at an image that is not formed at the focal plane, it will be blurry.
D) The focal plane of a reflecting telescope is always located within a few inches of the primary
mirror.
E) Light can be focused with a lens or a mirror.

The focal plane of a reflecting telescope is always located within a few inches of the primary
mirror.

Suppose the angular separation of two stars is smaller than the angular resolution of your eyes.
How will the stars appear to your eyes?
A) You will not be able to see these two stars at all.
B) The two stars will look like a single point of light.
C) The two stars will appear to be touching, looking rather like a small dumbbell.
D) You will see two distinct stars.
E) You will see only the larger of the two stars, not the smaller one.

The two stars will look like a single point of light.

Which of the following is a principal advantage of CCDs over photographic film?
A) CCDs allow long exposures (e.g., minutes or hours), and film does not.
B) CCDs can record the colors of astronomical objects accurately, while film cannot.
C) CCDs capture a much higher percentage of the incoming photons than does film.
D) Images recorded with CCDs never require any image processing, while images recorded by
film often do.
E) CCDs can be attached to modern telescopes more easily than cameras.

CCDs capture a much higher percentage of the incoming photons than does film.

Order the following in order of increasing efficiency of detecting photons of visible light.
A) eye, photographic film, CCD
B) photographic film, CCD, eye
C) CCD, eye, photographic film
D) CCD, photographic film, eye
E) eye, CCD, photographic film

eye, photographic film, CCD

What is meant by spectral resolution?
A) It is a measure of how much energy an object emits in different parts of the electromagnetic
spectrum.
B) It is a measure of how close two spectral lines can be distinguished.
C) It is a measure of how close two point sources can be distinguished.
D) It is the same as angular resolution when applied to telescopes operating at different
wavelengths.

It is a measure of how close two spectral lines can be distinguished.

Which of the following studies is best suited to a time monitoring experiment?
A) studying how different stars differ in their chemical compositions
B) studying whether a particular star's brightness is steady or variable
C) determining the age of the solar system
D) measuring the rotation rate of a distant star
E) estimating the time since the Big Bang

studying whether a particular star's brightness is steady or variable

Which of the following is always true about images captured with X-ray telescopes?
A) They are always very pretty.
B) They are always displayed with the highest possible angular resolution.
C) They are always useful for seeing through things.
D) They are always displayed in false color.
E) They are always displayed with north pointing upward in the images.

They are always displayed in false color.

What do astronomers mean by light pollution?
A) Light pollution refers to pollution caused by light industry as opposed to heavy industry.
B) Light pollution refers to harmful gases emitted by common street lights.
C) Light pollution refers to light used for human activities that brightens the sky and hinders
astronomical observations.
D) Light pollution refers to the lights that must be used inside major observatories and that make
it difficult for astronomers' eyes to adapt to darkness.
E) Light pollution is another name for sunlight, which makes it impossible to see stars in the daytime

Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations.

What causes stars to twinkle?
A) It is intrinsic to the stars–their brightness varies as they expand and contract.
B) variations in the absorption of the atmosphere
C) variable absorption by interstellar gas along the line of sight to the star
D) bending of light rays by turbulent layers in the atmosphere
E) the inability of the human eye to see faint objects

bending of light rays by turbulent layers in the atmosphere

Which of the following wavelength regions cannot be studied with telescopes on the ground?
A) radio waves
B) ultraviolet
C) X rays
D) both B and C
E) both A and C

both B and C

Telescopes operating at this wavelength must be cooled to observe faint astronomical objects.
A) radio
B) extreme infrared
C) visible
D) X-ray
E) gamma-ray

extreme infrared

At which wavelength range is there no current or planned space observatory?
A) radio
B) infrared
C) visible
D) X-ray
E) gamma-ray

radio

In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate?
A) radio
B) infrared
C) visible
D) ultraviolet
E) X-ray

radio

What does the technique of interferometry allow?
A) It allows two or more telescopes to obtain a total light-collecting area much larger than the
total light-collecting area of the individual telescopes.
B) It allows two or more telescopes to obtain the angular resolution of a single telescope much
larger than any of the individual telescopes.
C) It allows us to determine the chemical composition of stars.
D) It allows astronomers to make astronomical observations without interference from light
pollution.
E) It allows the same telescope to make images with both radio waves and visible light.

It allows two or more telescopes to obtain the angular resolution of a single telescope much larger than any of the individual telescopes.

Which of the following best describes what we mean by the focal plane of a telescope?
A) It is the upper surface of the telescope's primary lens or mirror.
B) It is the place where, if we mounted film or an electronic detector, we could get a clear (not
blurry) image of an object viewed through the telescope.
C) It is the lower surface of the telescope's primary lens or mirror.
D) It is the surface of the lens on the eyepiece, through which you would look to see objects in
the telescope's field of view.

It is the place where, if we mounted film or an electronic detector, we could get a clear (not blurry) image of an object viewed through the telescope.

What does angular resolution measure?
A) the angular size of the smallest features that the telescope can see
B) the brightness of an image
C) the size of an image
D) the number of electromagnetic waves captured by an image

the angular size of the smallest features that the telescope can see

What is the angular resolution of the human eye?
A) about 1 degree
B) about 1 arcsecond (1/3600 of a degree)
C) about 1 arcminute, or 1/60 of a degree
D) about 1 milliarcsecond

about 1 arcminute, or 1/60 of a degree

What is a CCD?
A) It is an electronic detector that can be used in place of photographic film for making images.
B) It is an abbreviation for the world's largest operating telescope.
C) It refers to any kind of instrument that can be hooked up to a telescope.
D) It is a unit used by astronomers to measure angular resolution.

It is an electronic detector that can be used in place of photographic film for making images.

Which of the following is always true about images captured with X-ray telescopes?
A) They are always shown with colors that are not the true colors of the objects that were
photographed.
B) They always are made with adaptive optics.
C) They show us light with extremely long wavelengths compared to the wavelengths of visible
light.
D) They always have very high angular resolution.
E) They are always very pretty.

They are always shown with colors that are not the true colors of the objects that were photographed.

What do astronomers mean by light pollution?
A) Light pollution is a type of air pollution created by lightweight gases such as hydrogen and
helium.
B) Light pollution is light from human sources that makes it difficult to see the stars at night.
C) Light pollution means contamination of light caused by chemicals in the Earth's atmosphere.
D) Light pollution is a term used to describe the appearance of the sky in regions that are
crowded with stars.

Light pollution is light from human sources that makes it difficult to see the stars at night.

Which of the following effects is caused by atmospheric turbulence?
A) twinkling of stars
B) light pollution
C) magnification of images
D) diffraction of light

twinkling of stars

Which of the following wavelength regions can be studied with telescopes on the ground?
A) radio, visible, and very limited portions of the infrared and ultraviolet regions
B) all light with wavelengths longer than ultraviolet wavelengths
C) all light with wavelengths shorter than infrared wavelengths
D) infrared, visible, and ultraviolet light

radio, visible, and very limited portions of the infrared and ultraviolet regions

Which of the following best describes the principle advantage of CCDs over photographic film?
A) CCDs allow long exposures (e.g., minutes or hours) and film does not.
B) CCDs capture a much higher percentage of the incoming photons than film.
C) CCDs can record the colors of astronomical objects accurately while film cannot.
D) CCDs can be attached to modern telescopes more easily than can photographic film.

CCDs capture a much higher percentage of the incoming photons than film

How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
A) The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
B) The 8-meter telescope has 4 times the light-collecting area of the 2-meter telescope.
C) The 8-meter telescope has 8 times the light-collecting area of the 2-meter telescope.
D) The answer cannot be determined from the information given in the question.

The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.

Which of the following best describes the development of astronomical telescopes over the past 60 years?
A) Over the 60-year period, telescopes have gradually gotten bigger and more powerful.
B) Although there have been advances in cameras and computing power, telescopes themselves
have not changed much in the last 60 years.
C) The world's most powerful telescope remained the same for most of this period, but in the
past 20 years many new and more powerful telescopes have been built.
D) The only major change in telescope power has occurred because of our ability to launch
telescopes into space rather than operating them only from the ground.

The world's most powerful telescope remained the same for most of this period, but in the
past 20 years many new and more powerful telescopes have been built.

Which of the following best describes why radio telescopes are generally much larger in size
than telescopes designed to collect visible light?
A) Getting an image of the same angular resolution requires a much larger telescope for radio
waves than for visible light.
B) Radio telescopes are designed to collect sound rather than light.
C) It is because radio telescopes are used in the daytime and visible light telescopes are used at
night.
D) Objects that emit radio waves are always much larger than objects that emit visible light, and
therefore require larger telescopes.

Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.

Consider two future observatories in space. Observatory X consists of a single 50-meter
telescope. Observatory Y is an interferometer consisting of five 10-meter telescopes, spread out
over a region 100 meters across. Which observatory can detect dimmer stars, and which one can
see more detail in its images? (Assume all else is equal, such as quality of optics, types of
instruments, and so on.)
A) Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.
B) Observatory Y can detect dimmer stars and Observatory X reveals more detail in images.
C) Observatory X both detects dimmer stars and reveals more detail in images.
D) Observatory Y both detects dimmer stars and reveals more detail in images.

Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.

Which of the following is not a major reason why astronomers would like an observatory on
the far side of the Moon?
A) Telescopes on the Moon could see objects in all parts of the sky equally well, whereas
telescopes on Earth can see only portions of the sky that depend on their latitude.
B) Radio astronomy would be advantageous on the Moon because human radio transmissions are
less likely to cause interference, especially on the far side of the Moon.
C) It would be possible to put telescopes for ultraviolet and X-ray astronomy on the surface,
unlike the case on the surface of the Earth.
D) Telescopes on the Moon could observe stars even when it is daytime on the Moon.

Telescopes on the Moon could see objects in all parts of the sky equally well, whereas telescopes on Earth can see only portions of the sky that depend on their latitude.

Which of the following studies is best suited to astronomical observations that fall into the
category called timing?
A) studying how different planets differ in their surface compositions
B) studying how a star's brightness varies over a period of 3 years
C) measuring the rotation rate of a distant star
D) determining the age of the solar system

studying how a star's brightness varies over a period of 3 years

What is the purpose of adaptive optics?
A) It reduces blurring caused by atmospheric turbulence for telescopes on the ground.
B) It allows several small telescopes to work together like a single larger telescope.
C) It is a special technology that allows the Hubble Space Telescope to adapt to study many
different types of astronomical objects.
D) It allows ground-based telescopes to observe ultraviolet light that normally does not penetrate the atmosphere

It reduces blurring caused by atmospheric turbulence for telescopes on the ground.