Chapter 6
Telescopes and Our Insight into the Cosmos
1. The telescopic observation confirming the heliocentric model of the solar system was:
A. sunspots.
B. stellar parallax.
C. Jupiter's four moons.
D. the discovery of Uranus.
2. The telescope function that is NOT directly dependent on the size of the objective is:
A. resolving power.
B. magnification.
C. light-gathering power.
D. none of these.
3. Astronomers wish to build larger and larger telescopes because larger telescopes:
A. allow fainter objects to be seen.
B. allow more detail to be seen or photographed.
C. give higher magnification of the image.
D. both (A) and (B).
4. Which of the following is NOT an advantage of the Newtonian reflecting telescope over the
refractor telescope?
A. It can be made larger.
B. It is generally less expensive.
C. It has a more convenient observing position.
D. Reflectors have no chromatic aberration.
5. Which of these is NOT an advantage of radio telescopes over optical telescopes?
A. They can be used in cloudy weather.
B. They have greater resolution for similar size collectors.
C. They allow us to study objects optically invisible.
D. They are easier to construct than large optical telescopes.
6. The essential difference between infrared and optical telescopes is:
A. the type of detector used.
B. the shape of the mirror or reflector.
C. the use of carbon dioxide as an absorber in infrared telescopes.
D. the longer focal length to accommodate the longer infrared waves.
7. What is the MOST important function of the telescope?
A. Magnification
B. Resolution
C. Light collection
D. Dispersion
8. Astronomers have constructed radio interferometers mainly to:
A. force the development of supercomputers.
B. increase their resolving power.
C. increase the light-gathering power.
D. increase the magnification.
9. Given that the magnification of a telescope is the ratio of the focal length of its objective, divided
by the focal length of its eyepiece, find the magnification of a Celestron C-8 (focal length = 2,000
mm) when used with a 40 mm eyepiece.
A. 20 x
B. 50 x
C. 80 x
D. 125 x
10. The resolution of the telescope is proportional to its diameter. How much better is the resolution
of the 50 mm objective lens in a pair of 7 x 50 binoculars than the 7 mm exit pupil of the human
eye?
A. 4 times sharper
B. 7 times sharper
C. 25 times sharper
D. 50 times sharper
11. The light grasp of a lens (its light collecting ability) depends on its surface area. How much
fainter stars would 7 x 50 binoculars (50 mm diameter objective lenses) show compared to the 7
mm exit pupil of your eye?
A. about 5 times fainter
B. about 10 times fainter
C. about 50 times fainter
D. over 100 times fainter
12. Which type of telescope collects light with a convex lens?
A. Refractor
B. Newtonian Reflector
C. Cassegrain Reflector
D. Gregorian Reflector
13-15. Match the telescope type with its description:
A. Simple Refractor
B. Newtonian Reflector
C. Cassegrain Reflector
13. Uses a flat secondary mirror to focus light to front side of telescope tube
14. Uses convex secondary mirror to focus light back behind the main mirror
15. Uses only a convex lens to focus light
16. The type of telescope using a concave primary mirror and a flat secondary mirror, tilted at a 45
degree angle to the main mirror, is a:
A. newtonian reflector.
B. achromatic refractor.
C. cassegrain reflector.
D. gregorian refractor.
17. The most complicated commercial design listed below is the:
A. simple refractor.
B. newtonian reflector.
C. cassegrain reflector.
D. achromatic refractor.
18. If a 60 mm refractor has an f/15 lens, the focal length will be:
A. 4 mm.
B. 90 mm.
C. 600 mm.
D. 900 mm.
19. A 60 mm refractor has a focal length of 800 mm and comes with eyepieces of focal lengths of
20 mm, 10 mm, and 5 mm. What should be the advertised magnifications?
A. 50 x, 100 x, 200 x
B. 120 x, 60 x, 30 x
C. 40 x, 80 x, 160 x
D. 1200 x, 600 x, 300 x
20. In 1994, the largest operational optical telescope was the:
A. Palomar in California.
B. Hubble in orbit.
C. Keck in Hawaii.
D. VLA in New Mexico.
21. In which two spectral regions are ground based observations MOST useful?
A. microwave and ultraviolet
B. optical and X-ray
C. radio and optical
D. ultraviolet and infrared
22. Which is NOT an advantage of infrared astronomy?
A. It is less hindered by interstellar dust than optical astronomy.
B. It is less hindered by terrestrial clouds than optical astronomy.
C. it is capable of detecting cooler sources than optical astronomy.
D. Both A and C are correct.
23. Which type of detector is most useful on the Hubble Space Telescope?
A. photographic emulsion
B. visual observers
C. charge coupled devices
D. bolometers
24. The HST is used at a variety of wavelengths; which would give the best resolution?
A. ultraviolet
B. red light
C. yellow light
D. infrared waves
ESSAYS
1. Name three advantages the Hubble Space Telescope has over any telescope observing from the
surface of the earth.
2. Describe why CCD imaging is rapidly replacing photography in much research.
3. Briefly describe why radio telescopes must be so much larger than optical ones for the same
angular resolution.
4. Explain why the Hubble Space Telescope actually gives better resolution than larger ground
based optical telescopes.
5. Compare the temperatures of objects observed with infrared telescopes with those seen in optical
ones.
6. Compare the temperatures of objects observed via X-ray observatories in orbit versus those of
optically visible sources.