Chapter 6
Currently, the largest optical telescope mirrors have a diameter of?
10 meters
Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope?
A refracting telescope uses a transparent glass lens to focus light while a reflecting telescope uses a mirror to focus light.
Which of the following best describes why radio telescopes are generally much larger in size than telescopes designed to collect visible light?
Getting an image of the same angular resolution requires a much larger telescope for radio waves than for visible light.
Which of the following is a principal advantage of CCDs over photographic film?
CCDs capture a much higher percentage of the incoming photons than does film.
Which of the following best describes the principle advantage of CCDs over photographic film?
CCDs capture a much higher percentage of the incoming photons than film.
The largest effective telescope, created by radio interferometry, is the size of
Earth
What is the purpose of interferometry?
It allows two or more small telescopes to achieve the angular resolution of a much larger telescope.
What does the technique of interferometry allow?
It allows two or more telescopes to obtain the angular resolution of a single telescope much larger than any of the individual telescopes.
What is meant by spectral resolution?
It is a measure of how close two spectral lines can be distinguished
What is a CCD?
It is an electronic detector that can be used in place of photographic film for making images.
Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?
It is closer to the stars.
What do we mean by the diffraction limit of a telescope?
It is the angular resolution the telescope could achieve if nothing besides the size of its light-collecting area affected the quality of its images.
What do we mean by the diffraction limit of a telescope?
It is the best angular resolution the telescope could achieve with perfect optical quality and in the absence of atmospheric distortion.
Which of the following best describes what we mean by the focal plane of a telescope?
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 is the purpose of adaptive optics?
It reduces blurring caused by atmospheric turbulence for telescopes on the ground.
What do astronomers mean by light pollution?
Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations.
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.)
Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.
Why do astronomers need different telescope designs to observe across the electromagnetic spectrum?
Photons of different energy behave differently and require different collection strategies.
Which of the following statements best describes the two principal advantages of telescopes over eyes?
Telescopes can collect far more light with far better angular resolution.
Which of the following statements best describes the two principle advantages of telescopes over eyes?
Telescopes can collect far more light with far better angular resolution.
Which of the following is nota major reason why astronomers would like an observatory on the far side of 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.
How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?
The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope.
Which of the following telescopes would benefit most from adaptive optics?
The Keck I Telescope on Mauna Kea.
Which of the following statements about light focusing is not true?
The focal plane of a reflecting telescope is always located within a few inches of the primary mirror.
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?
The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy.
The angular separation of two stars is 0.1 arcseconds and you photograph themwith a telescope that has an angular resolution of 1 arcsecond. What will you see?
The photo will seem to show only one star rather than two.
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?
The photograph will have far better angular resolution than you can see with your eye.
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?
The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping.
Suppose the angular separation of two stars is smaller than the angular resolution of your eyes. How will the stars appear to your eyes?
The two stars will look like a single point of light.
Which of the following best describes the development of astronomical telescopes over the past 60 years?
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 is always true about images captured with X-ray telescopes?
They are always displayed in false color.
The Chandra X-Ray Observatory must operate in space because
X rays do not penetrate Earth's atmosphere.
What is an artificial star?
a point of light in Earth's atmosphere created by a laser for the purpose of monitoring atmospheric fluctuations
What is the angular resolution of the human eye?
about 1 arcminute, or 1/60 of a degree D) about 1 milliarcsecond
What causes stars to twinkle?
bending of light rays by turbulent layers in the atmosphere
Which of the following wavelength regions cannot be studied with telescopes on the ground?
both B (ultraviolet) and C (x-ray)
Telescopes operating at this wavelength must be cooled to observe faint astronomical objects.
extreme infrared
Order the following in order of increasing efficiency of detecting photons of visible light.
eye, photographic film, CCD
Which of the following is not one of the three main categories of observation generally used by astronomers?
filtering to look at just a single color from an object
Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have?
high spectral resolution
At which wavelength range is there no current or planned space observatory?
radio
In what part of the electromagnetic spectrum do the biggest telescopes on Earth operate?
radio
In what wavelength range was interferometry first routinely used?
radio
Which of the following wavelength regions can be studied with telescopes on the ground?
radio, visible, and very limited portions of the infrared and ultraviolet regions
Which of the following studies is best suited to astronomical observations that fall into the category called timing?
studying how a star's brightness varies over a period of 3 years
Which of the following studies is best suited to a time monitoring experiment?
studying whether a particular star's brightness is steady or variable
What does angular resolution measure?
the angular size of the smallest features that the telescope can see
Which of the following could not be measured by an observation that uses only imaging?
the rate at which a variable star brightens and dims
Which of the following could not be determined by an observation that uses only spectroscopy?
the size of a distant galaxy
Which of the following is not a good reason to place observatories on remote mountain tops?
to be able to observe at radio wavelengths
What is the purpose of adaptive optics?
to eliminate the distorting effects of atmospheric turbulence for telescopes on the ground
The stars in our sky twinkle in brightness and color because of
turbulence in the Earth's atmosphere.
Which of the following effects is caused by atmospheric turbulence?
twinkling of stars