Conceptual Quiz  Chapter 6
Part A
Suppose you have two small photographs of the Moon. Although both look the same at small size, when you blow them up to poster size one of them still looks sharp while the other one becomes fuzzy (grainy) looking. Which of the following statements is true?
Hint A.1
Study Section 6.2.
ANSWER:

Both photographs have the same angular resolution, because they are both photographs of the same object. Both photographs have the same angular resolution, because they were both printed at the same sizes in each case. The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy. The one that looks fuzzy at large size has better angular resolution (smaller) than the one that looks sharp.
Part B
Suppose that the angular separation of two stars is 0.1 arcseconds, and you photograph them with a telescope that has an angular resolution of 1 arcsecond. How will the stars appear in the photograph?
Hint B.1
Study Section 6.2.
ANSWER:

Since their angular separation is smaller than the telescope's angular resolution, your photograph will seem to show only one star rather than two. The two stars will appear to be touching, looking rather like a small dumbbell. You will see two distinct stars in your photograph, separated from one another by a distance of 1 arcsecond. Since their angular separation is smaller than the telescope's angular resolution, you will not be able to see these stars at all in your photograph.
Part C
Suppose you point your telescope at a distant object. Which of the following is NOT an advantage of taking a photograph of the object through the telescope as compared to just looking at the object through the telescope?
Hint C.1
Study Section 6.2.
ANSWER:

The photograph will have far better angular resolution than you can see with your eye. If taken with a camera with a sensitive detector such as a CCD, the photograph can capture a much larger percentage of the incoming photons than can your eye. By using a long exposure time, the photograph can allow you to see objects that would be too dim to see with your eye. The photograph provides a more reliable record of what is seen through the telescope than can a drawing made by eye.
Part D
Which of the following best describes the principle advantage of CCDs over photographic film?
Hint D.1
Study Section 6.1.
ANSWER:

CCDs capture a much higher percentage of the incoming photons than film. CCDs can record the colors of astronomical objects accurately while film cannot. CCDs can be attached to modern telescopes more easily than can photographic film. CCDs allow long exposures (e.g., minutes or hours) and film does not.
Part E
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
Hint E.1
Study Section 6.2.
ANSWER:

The answer cannot be determined from the information given in the question. The 8-meter telescope has 4 times the light-collecting area of the 2-meter telescope. The 8-meter telescope has 8 times the light-collecting area of the 2-meter telescope. The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
Part F
Which of the following best describes the development of astronomical telescopes over the past 60 years?
Hint F.1
Study Section 6.2.
ANSWER:

Over the 60-year period, telescopes have gradually gotten bigger and more powerful. The world's most powerful telescope remained the same for most of this period, but in the past 15 years many new and more powerful telescopes have been built. 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. Although there have been advances in cameras and computing power, telescopes themselves have not changed much in the last 60 years.
Part G
Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?
Hint G.1
Study Section 6.2.
ANSWER:

Radio telescopes are designed to collect sound rather than light. 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. It is because radio telescopes are used in the daytime and visible light telescopes are used at night.
Part H
Which of the following studies is best suited to astronomical observations that fall into the category called timing?
Hint H.1
Study Section 6.2.
ANSWER:

Determining the age of the solar system. Measuring the rotation rate of a distant star. Studying how different planets differ in their surface compositions. Studying how a star's brightness varies over a period of 3 years.
Part I
Which of the following is NOT a reason why telescopes tend to be built on mountaintops that are relatively far from cities and are in regions with dry climates?
Hint I.1
Study Section 6.3.
ANSWER:

Mountaintops far from cities are generally subject to less light pollution than locations nearer to cities. Dry regions mean less rain and clouds, and mountaintops in dry regions may even allow some infrared observations. The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping. Being on a high mountain top means being relatively high in the atmosphere, which tends to limit turbulence.
Part J
The stars in our sky twinkle in brightness and color because of ______.
Hint J.1
Study Section 6.3.
ANSWER:

the bubbling and boiling of gases on the surfaces of stars. turbulence in the Earth's atmosphere. rapid changes in the brightnesses and colors of stars caused by changes in their spectra. light pollution.
Part K
Which of the following is NOT an advantage of the Hubble Space Telescope over ground-based telescopes?
Hint K.1
Study Section 6.3.
ANSWER:

It can observe infrared and ultraviolet light, as well as visible light. It is closer to the stars. Stars do not twinkle when observed from space. It never has to close because of cloudy skies.
Part L
The Chandra X-ray Observatory must operate in space because:
Hint L.1
Study Section 6.3.
ANSWER:

X-ray telescopes require the use of grazing incidence mirrors. X rays do not penetrate Earth's atmosphere. X rays are too dangerous to be allowed on the ground. It was built by NASA.
Part M
Which of the following telescopes would benefit most from adaptive optics?
Hint M.1
Study Section 6.3.
ANSWER:

The Chandra X-ray Observatory. The Hubble Space telescope. The Arecibo radio telescope in Puerto Rico. The Keck I telescope on Mauna Kea.
Part N
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.)
Hint N.1
Study Section 6.4.
ANSWER:

Both observatories have the same capabilities, but Observatory Y would be cheaper to build. Observatory X can detect dimmer stars and Observatory Y reveals more detail in images. Observatory X both detects dimmer stars and reveals more detail in images. Observatory Y both detects dimmer stars and reveals more detail in images. Observatory Y can detect dimmer stars and Observatory X reveals more detail in images.
Part O
Which of the following is NOT a major reason why astronomers would like an observatory on the far side of the Moon?
Hint O.1
Study Section 6.4.
ANSWER:

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. Telescopes on the Moon could observe stars even when it is daytime on the Moon. 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. 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.