The Tools of Astronomy Answer Key

Astronomy Telescopes: The Tools of Astronomy True/False Questions 1) It is much easier to build large reflectors than large refractors. Answer: TRUE 2) Chromatic aberration affects refractor and reflector telescopes equally, unless they have very long focal lengths. 3) The largest refracting telescope can collect more light than the largest reflecting telescope. Answer: FALSE 4) The primary purpose of an astronomical telescope is to magnify the images of distant objects, making them appear closer. Answer: FALSE 5) A convex lens is thinnest in its center; it refracts light to a focus, while a convex mirror reflects it to the focus instead. Answer: FALSE 6) Absorption of light passing through the glass is a bigger problem for Cassegrain reflectors than achromatic refractors. Answer: FALSE 7) To reach the Cassegrain focus, a hole must be cut in the center of the primary mirror. Answer: TRUE 8) The simplest reflecting telescope design, by Isaac Newton, uses only a primary mirror. Answer: FALSE 9) The light gathering ability of a telescope is most dependent on the diameter of its primary objective. Answer: TRUE 10) Hubble Space Telescope is still the largest scope ever built. Answer: FALSE 11) The Schmidt corrector plate largely cures spherical aberration, giving a wide, flat field of view. Answer: TRUE 12) You could more easily resolve a close double star with a blue filter than with a red one. Answer: TRUE 13) One reason for building telescopes on mountain tops is that they improve seeing by reducing the amount of air above the observer. Answer: TRUE 14) Telescopes on Earth that use adaptive optics can have better angular resolution than the Hubble Space Telescope. Answer: TRUE 15) Optical telescopes are usually used only at night, but radio telescopes can be used day or night. Answer: TRUE 16) Radio telescopes have poorer angular resolution than optical telescopes because radio waves have a much longer wavelength than optical waves. Answer: TRUE 17) All radio telescopes are reflectors in design. Answer: TRUE 18) Optical interferometry is more in use than radio interferometry. Answer: FALSE 19) In addition to visible light, Hubble can do some work in the infrared and ultraviolet portions of the spectrum. Answer: TRUE 20) The James Webb Space Telescope is designed to observe object primarily using ultraviolet light. Answer: FALSE 21) Due to our ozone layer, ultraviolet astronomy must be done from space. Answer: TRUE 22) Galaxies look the same whether viewed in visible or X-ray wavelengths. Answer: FALSE 5.2 Multiple Choice Questions 1) What is the primary purpose of an astronomical telescope? A) to magnify and make distant objects appear closer B) to separate light into its component colors C) to measure the intensity of light very accurately D) to access wavelengths that we cannot see visually E) to collect a lot of light and bring it to a focus Answer: E 2) The process occurring when photons bounce off a polished surface is called: A) diffraction. B) refraction. C) reflection. D) dispersion. E) interference. Answer: C 3) Which type of telescope has the simplest light path? A) prime focus reflector B) single lens refractor C) achromatic refractor D) Newtonian reflector E) Cassegrain reflector Answer: A 4) Which design is subject to chromatic aberration? A) refractor B) prime focus reflector C) Newtonian reflector D) Cassegrain reflector E) Gregorian reflector Answer: A 5) The tendency of a wave to bend as it passes from one transparent medium to another is called: A) reflection. B) dispersion. C) refraction. D) diffraction. E) interference. Answer: C 6) The primary purpose of a telescope is to: A) collect a large amount of light and bring it into focus. B) magnify distant objects. C) separate light into its component wavelengths. D) make distant objects appear nearby. E) measure the brightness of stars very accurately. Answer: A 7) What problem do refractor telescopes have that reflectors don't? A) diffraction limited resolution B) light loss from secondary elements C) chromatic aberration D) spherical aberration E) bad seeing Answer: C 8) This design involves only one optical surface, a concave mirror. A) prime focus reflector B) Newtonian reflector C) Cassegrain reflector D) Gregorian reflector E) refractor Answer: A 9) A major advantage of a Newtonian reflector over a refractor is: A) its compact size. B) the elimination of chromatic aberration. C) there are only two lenses to grind. D) the central hole in the mirror is smaller. E) the elimination of the secondary mirror. Answer: B 10) Why are most large telescopes reflectors, not refractors? A) Large lenses deform under their own weight, but mirrors can be supported. B) Large mirrors need only one optical surface, achromats four surfaces to grind. C) Reflectors do not suffer from chromatic aberration like refractors do. D) Large, very clear lenses are harder to cast than more tolerant mirror blanks. E) All of the above are correct. Answer: E 11) Which design has a convex primary mirror and flat secondary mirror, with the eyepiece located on the top side of the telescope tube? A) refractor B) Newtonian reflector C) Cassegrain reflector D) prime focus reflector E) interferometer Answer: B 12) The convex secondary mirror in this design focuses light down through a hole cut in the concave primary mirror. A) refractor B) prime focus reflector C) Newtonian reflector D) Cassegrain reflector E) interferometer Answer: D 13) In both reflecting and refracting telescopes, the main role that an eyepiece plays is to: A) collect more light. B) turn the image right side up. C) correct the colors of the image. D) magnify the image. Answer: D 14) The amount of diffraction, and thus the resolution of the scope, depends upon: A) the wavelength used and the size of the main telescope objective lens or mirror. B) the design of the telescope. C) whether the telescope is a reflector or refractor. D) the brightness of the object. E) the size and sensitivity of the CCD chip used for imaging. Answer: A 15) The angular resolution of an 8-inch diameter telescope is ________ greater than that of a 2inch diameter telescope. A) 2 times B) 4 times C) 8 times D) 9 times E) 16 times Answer: B 16) It is diffraction that limits the ________ of a telescope's objective. A) magnification B) resolution C) light grasp D) wavelengths E) frequencies Answer: B 17) What is the resolution of a telescope? A) its ability to see very faint objects B) its ability to distinguish two adjacent objects close together in the sky C) its ability to make distant objects appear much closer to us D) its ability to separate light into its component colors for analysis E) its ability to focus more than just visible light for imaging Answer: B 18) What type of telescope is the Subaru telescope (shown below)? A) prime focus reflector B) single lens refractor C) achromatic refractor D) Newtonian reflector E) Cassegrain reflector Answer: E 19) What is the resolving power of the telescope? A) the ability to make distant objects appear closer B) the ability to collect a lot of light C) the ability to detect very faint objects D) the ability to distinguish adjacent objects in the sky E) the ability to separate light into its component colors Answer: D 20) What is the light-gathering power of an 8-inch telescope compared to a 4-inch telescope? A) 2 times better B) 4 times better C) 8 times better D) 16 times better E) 32 times better Answer: B 21) Compared to a 5-inch prime focus reflector, a 5-inch Newtonian reflector will: A) have more light gathering power. B) have the same light gathering power. C) be easier to build. D) have more chromatic aberration. E) have a larger hole in the center of its mirror. Answer: B 22) Which method of astronomical measurement is the precise measurement of brightness? A) spectroscopy B) photography C) astrometry D) photometry E) interferometry Answer: D 23) 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) 5 times B) 10 times C) 25 times D) 100 times E) 250 times Answer: D 24) How much better resolution would a 60 mm objective lens have than your eye's 6 mm exit pupil? A) 6 times B) 10 times C) 16 times D) 60 times E) 100 times Answer: B 25) Diffraction is the tendency of light to: A) spread around corners. B) separate into its component colors. C) bend through a lens. D) disperse within a prism. E) reflect off a mirror. Answer: A 26) A small telescope has ________ angular resolution when compared to a large telescope. A) smaller B) larger C) the same D) chromatic E) brighter Answer: B 27) What are two advantages of large telescopes over smaller ones? A) Large telescopes have a larger field of view and sharper focus. B) Large telescopes are not subject to atmospheric turbulence and opacity like smaller ones. C) Large telescopes are easier to mount and control than small ones. D) Large telescopes have more light grasp and better resolution. E) Large telescopes give higher magnification and are easier to build. Answer: D 28) The amount of diffraction a telescope creates depends upon: A) whether the telescope is a refractor or a reflector. B) the wavelength and the diameter of the telescope objective. C) the magnification of the eyepiece. D) the types of glass used in the achromat. E) the transparency of the atmosphere. Answer: B 29) What type of telescope is the Hubble Space Telescope? A) refractor B) prime focus C) Newtonian D) Cassegrain E) Nasmyth/Coude Answer: D 30) Refractor telescopes suffer from this separation of light into its component colors. A) limited diffraction B) spherical aberration C) chromatic aberration D) bad seeing E) refraction Answer: C 31) 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 better focus X-ray images. C) it can make better observations of the ozone layer. D) its adaptive optics controls atmospheric blurring better. E) in orbit, it can operate close to its diffraction limit at visible wavelengths. Answer: E 32) Which of these devices helps correct coma in fast reflectors? A) Cassegrain secondary mirror B) star diagonal C) achromatic doublet D) Schmidt corrector plate E) Newtonian secondary mirror Answer: D 33) Computers are used to sharpen images collected by telescopes by A) producing false color images. B) increasing resolution. C) reducing diffraction. D) reducing chromatic aberration. E) reducing the noise in observations. Answer: E 34) Green light has a shorter wavelength than orange light. In a 5-inch telescope, green light will: A) provide better angular resolution than orange light. B) come to the same exact focus as orange light. C) provide worse angular resolution than orange light. D) allow dimmer stars to be observed. E) reduce the effects of atmospheric turbulence. Answer: A