Chapter 5

25 July 2022
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question
What is the primary purpose of an astronomical telescope?
answer
to collect a lot of light and bring it to a focus
question
Why are most large telescopes reflectors, not refractors?
answer
A. Reflectors do not suffer from chromatic aberration like refractors do. B. Large mirrors need only one optical surface, achromats four surfaces to grind. C. Large lenses deform under their own weight, but mirrors can be supported. D. Large, very clear lenses are harder to cast than more tolerant mirror blanks
question
Which design has a convex primary mirror and flat secondary mirror, with the eyepiece located on the top side of the telescope tube?
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Newtonian reflector
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The convex secondary mirror in this design focuses light down through a hole cut in the concave primary mirror.
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Cassegrain reflector
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The amount of diffraction, and thus the resolution of the scope, depends upon:
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the wavelength used and the size of the main telescope objective lens or mirror.
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The angular resolution of an 8-inch diameter telescope is ________ greater than that of a 2-inch diameter telescope.
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4 times
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t is diffraction that limits the ________ of a telescope's objective.
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resolution
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What is the resolution of a telescope?
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its ability to distinguish two adjacent objects close together in the sky
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What type of telescope is the Subaru telescope (shown below)?
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Cassegrain reflector
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What is the resolving power of the telescope?
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the ability to distinguish adjacent objects in the sky
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What is the light-gathering power of an 8-inch telescope compared to a 4-inch telescope?
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4Γ— better
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The process occurring when photons bounce off a polished surface is called:
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reflection.
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Compared to a 5-inch prime focus reflector, a 5-inch Newtonian reflector will:
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have the same light gathering power.
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Which method of astronomical measurement is the precise measurement of brightness?
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photometry
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A telescope with a 60 mm objective lens collects how many times as much light as does your eye's 6 mm exit pupil?
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100 times
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How much better resolution would a 60 mm objective lens have than your eye's 6 mm exit pupil?
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10x
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Diffraction is the tendency of light to:
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spread around corners.
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It is diffraction that limits the ________ of a telescope of a given objective diameter.
answer
resolution
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What are two advantages of large scopes over smaller ones?
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Large telescope have more light grasp and better resolution.
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The amount of diffraction a telescope creates depends upon:
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the wavelength and the diameter of the telescope objective.
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What type of telescope is the Hubble Space Telescope?
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Cassegrain
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The most important advantage of CCDs over film is that:
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they record much more light in a given exposure time.
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Which type of telescope has the simplest light path?
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prime focus reflector
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Refractor telescopes suffer from this separation of light into its component colors.
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chromatic aberration
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One advantage of the Hubble Space telescope over ground based ones is that:
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in orbit, it can operate close to its diffraction limit at visible wavelengths.
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in orbit, it can operate close to its diffraction limit at visible wavelengths.
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Schmidt corrector plate
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Green light has a shorter wavelength than orange light. In a 5-inch telescope, green light will:
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provide better angular resolution than orange light.
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What is "seeing"?
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a measurement of the image quality due to air stability
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A mountain top is an especially good site for infrared telescopes since:
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A. there you are closer to celestial objects. B. you are above most of the carbon dioxide and water vapor in the atmosphere. C. less air above means better seeing in many cases. D. the cold weather helps the sensitivity of infrared detectors.
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What problem does adaptive optics correct?
answer
turbulence in the Earth's atmosphere which creates twinkling
question
The Arecibo radio telescope is laid out like which optical telescope design?
answer
prime focus reflector
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What is true of radio telescopes?
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They have poorer angular resolution than a refractor.
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Which design is subject to chromatic aberration?
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refractor
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Which of the following is a problem inherent in all large radio telescopes?
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Radio waves have long wavelengths, so radio telescopes have poor resolution.
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Radio dishes are large in order to:
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increase their angular resolution and collect the very weak radio photons.
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In astronomy, an interferometer can be used to:
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improve the angular resolution of radio telescopes.
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This design combines the radiation from two different telescopes to greatly enhance resolution via computer synthesis.
answer
interferometer
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Which of the following greatly improves the angular resolution of radio maps?
answer
use of interferometers
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In which part of the electromagnetic spectrum have astronomers been unable to get any information?
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We now can access information in all spectral lengths.
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The design of modern X-ray telescopes depends on:
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grazing incidence optics.
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What problem do refractor telescopes have that reflectors don't?
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chromatic aberration
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This design involves only one optical surface, a concave mirror.
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prime focus reflector
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A major advantage of a Newtonian reflector over a refractor is:
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the elimination of chromatic aberration.
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Optical interferometry is more in use than radio interferometry.
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False
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A convex lens is thinnest in its center; it refracts light to a focus, while a convex mirror reflects it to the focus instead.
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False
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To reach the Cassegrain focus, a hole must be cut in the center of the primary mirror.
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True
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The light gathering ability of a telescope is most dependent on the diameter of its primary objective.
answer
True