Lesson 6

Question 1

Which of the following statements about light focusing is not true?

Answer 1

The focal plane of a reflecting telescope is always located within a few inches of the primary mirror.

Question 2

Which of the following is a principal advantage of CCDs over photographic film?

Answer 2

CCDs capture a much higher percentage of the incoming photons than does film.

Question 3

What do we mean by the diffraction limit of a telescope?

Answer 3

It is the best angular resolution the telescope could achieve with perfect optical quality and in the absence of atmospheric distortion.

Question 4

What is the purpose of adaptive optics?

Answer 4

to eliminate the distorting effects of atmospheric turbulence for telescopes on the ground

Question 5

Which of the following is not an advantage of the Hubble Space Telescope over ground-based telescopes?

Answer 5

It is closer to the stars.

Question 6

Telescopes operating at this wavelength must be cooled to observe faint astronomical objects.

Answer 6

extreme infrared

Question 7

What does the technique of interferometry allow?

Answer 7

It allows two or more telescopes to obtain the angular resolution of a single telescope much larger than any of the individual telescopes.

Question 8

The largest effective telescope, created by radio interferometry, is the size of

Answer 8

Earth

Question 9

What is the angular resolution of the human eye?

Answer 9

about 1 arcminute, or 1/60 of a degree

Question 10

Which of the following statements best describes the difference between a refracting telescope and a reflecting telescope?

Answer 10

A refracting telescope uses a transparent glass lens to focus light while a reflecting telescope uses a mirror to focus light.

Question 11

Suppose you want to determine the chemical composition of a distant planet or star. Which of the following will be most useful to have?

Answer 11

High spectral resolution

Question 12

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?

Answer 12

The one that still looks sharp at large size has better (smaller) angular resolution than the one that looks fuzzy.

Question 13

How does the light-collecting area of an 8-meter telescope compare to that of a 2-meter telescope?

Answer 13

The 8-meter telescope has 16 times the light-collecting area of the 2-meter telescope

Question 14

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?

Answer 14

The thin air on mountaintops makes the glass in telescope mirrors less susceptible to warping

Question 15

The Chandra X-Ray Observatory must operate in space because

Answer 15

X rays do not penetrate Earth’s atmosphere.

Question 16

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.)

Answer 16

Observatory X can detect dimmer stars and Observatory Y reveals more detail in images.

Question 17

Which of the following is not a major reason why astronomers would like an observatory on the far side of the Moon?

Answer 17

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.