Telescopes

1. Seeing refers to

a. the clarity of the atmosphere

b. how far a telescope can see

c. the faintest object observable through a telescope

d. the smearing of an image caused by atmospheric motions*

e. the smearing of an image caused by the variation of refraction with color.

2. In which spectral region is it possible for astronomers to observe through clouds?

a. visual

b. radio*

c. ultraviolet

d. x-ray

e. gamma-ray.

3. Stars twinkle because of motions

a. in their atmosphere

b. of gas in interstellar space

c. of gas in the solar system

d. of gas in the Earth's atmosphere*

e. of the observer.

4. Why might some stars appear double in blue light though they could not be resolved in red light?

a. The eye is more sensitive to blue light.

b. The wavelength of blue light is shorter, so smaller angles can be resolved.*

c. Photographic plates are more sensitive to blue light.

d. Photographic plates are more sensitive to red light.

e. None of the above.

5. Why can't we use ordinary photographic plates to record infrared images?

a. The wavelength of infrared light is too long to expose a normal photographic emulsion.

b. The frequency of infrared light is too big to expose a normal photographic emulsion.

c. The velocity of infrared light is too high to expose a normal photographic emulsion.

d. The energy in an infrared photon is too small to expose a normal photographic emulsion.*

e. None of the above.

6. No matter how big we make a telescope on Earth, its resolving power is limited because of

a. variable atmospheric refraction ("seeing").*

b. clouds.

c. limited abilities in making mirrors.

d. light pollution.

e. None of the above.

7. Why does it matter whether a telescope is in the northern or southern hemisphere?

a. Many countries in the southern hemisphere are politically unstable.

b. Some stars can be seen in one hemisphere, but not in the other.*

c. Mountains are higher in the northern hemisphere.

d. Travel expenses for astronomers must be kept low.

e. None of the above.

8. Why is it better for some purposes to use a medium-size telescope on a mountain instead of a telescope in space?

a. It is easier to get to a telescope on a mountain than to one in space.

b. It is much less expensive to use a telescope on Earth than in space; very large and state-of-the-art equipment can usually only be used on Earth.*

c. Telescopes on mountains are better than telescopes in space.

d. Telescopes in space cannot be pointed near the direction of the Sun.

e. None of the above.

9. Why can the Hubble Space Telescope observe fainter objects than we can now study from the ground?

a. Because electronic detectors have higher resolution than photographic plates.

b. Because the space telescope can be pointed more accurately.

c. Because the space telescope has a bigger mirror than telescopes on Earth.

d. Because the sky background is darker from space.*

e. None of the above.

10. What is the advantage of an equatorial telescope mount?
With an equatorial mount,

a. a telescope can track the stars with motion around only one axis. *

b. a telescope can track the stars with motion around only two axes.

c. a telescope must use a computer to track the stars.

d. a telescope does not have to move to track the stars.

e. None of the above.

11. What is the most important function of a telescope?

a. magnification

b. resolution

c. light collection*

d. none of the above

12. The greater the ___ the greater the resolution of a telescope. (Pick the one most correct choice.)

a. objective focal length

b. eyepiece focal length

c. objective diameter*

d. objective area

e. magnification

13. The function of a telescope that is NOT directly dependent on the size of the objective is

a. resolving power

b. magnification*

c. light-gathering power

d. none of the above

14. Which one of the following is a disadvantage of a refractor compared with a reflector of the same diameter?

a. the refractor has a lower light gathering power

b. the refractor will have a longer focal length

c. the location of the refractor's focus depends on wavelength*

d. all the above are disadvantages of refractors.

15. Astronomers wish to build larger and larger telescopes because larger telescopes

a. allow fainter objects to be seen*

b. allow more detail in the image to be seen or photographed

c. produce greater magnification of the image

d. allow more wavelengths to be studies

e. both a and b

16. If telescope A has a mirror twice the diameter of telescope B, its light gathering power will be ___ times that of B?

a. 2

b. 4*

c. 8

d. 16.

17. If telescope A has a light gathering power 4 times that of telescope B, how much farther into space can telescope A penetrate?

a. 2*

b. 4

c. 8

d. 16.

18. New telescopes are currently being built that overcome the limitations of the older large telescopes. Some of these new telescopes

a. use segmented mirrors.

b. use mirrors that are very thin.

c. use active optics to control the shape of the mirror.

d. all of the above.

e. none of the above

19. Which of the following is the primary reason astronomers desire to have telescopes above the Earth's atmosphere?

a. the magnification will be improved

b. observations may be made in the ultraviolet*

c. observations may be made in the radio

d. the resolving power will be better than theoretically allowed on the Earth's surface.

20. The essential difference between infrared telescopes 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. infrared telescopes are longer in order to accommodate the longer wavelengths observed

21. Why can radio astronomers observe during the day, while optical astronomers are (for the most part) limited to nighttime observing?

a. The atmosphere absorbs optical but not radio radiation from the Sun.

b. The atmosphere emits optical but not radio radiation from the Sun.

c. The atmosphere scatters optical but not radio radiation from the Sun.*

d. The atmosphere absorbs optical but not radio radiation from the stars.

e. None of the above.

22. Radio telescopes are large because of the small amount of radio energy from astronomical objects, and

a. because bigger is better

b. since no dome is needed, there is no reason not to make them large

c. because short wavelengths of radio waves are detected better with large telescopes

d. because larger telescopes have better resolving power.*

23. The technique of connecting multiple telescopes together to combine the images from each telescope is known as

a. abberation.

b. resolving power.

c. active optics.

d. adaptive optics.

e. interferometry. *

24. Astronomers have constructed radio interferometers mainly to

a. spend lots of money

b. increase resolving power*

c. increase light-gathering power

d. increase magnification

25. The Very Large Array is

a. A set of 27 radio telescopes in a large Y-pattern located in New Mexico used for synthetic aperture imaging.*

b. A set of radio telescopes in California and Massachusetts used for very long baseline interferometry.

c. A set of infrared telescopes on Mauna Kea, Hawaii used for mapping molecular clouds.

d. A set of ultraviolet telescopes located on orbiting spacecraft used to map the center of the galaxy.

e. None of these.

26. The Very Long Baseline Interferometer (VLBI)

a. is the highest resolution optical telescope ever built.

b. is located in Arecibo, Puerto Rico.

c. is a matched pair of 8 m telescopes, one of which is in Chile and the other in Hawaii..

d. is an air-borne infrared telescope

e. is a set of radio telescopes linked together electronically to provide very high resolution. *

27. X-ray astronomy must utilize spacecraft because x-rays are absorbed by

a. The ozone layer.

b. The stratosphere.

c. The mesosphere.

d. The ionosphere.*

e. None of these.