Chapter 5

Question 1

If a telescope has a resolving power of 0.1 sec of arc, what do two stars 1.5 seconds of arc apart look like through this telescope?

Answer 1

two separate blobs of light

Question 2

Most of Galileo’s telescopes had objective lenses which were only about 2 cm in diameter. Theoretically, should he have been able to resolve two stars 14 seconds of arc apart? (Hint: resolving power in seconds of arc = 0.113/diametr of objective (in meters)

Answer 2

Yes, because the objective is sufficiently large.

Question 3

Which is better, the resolving power of an 8-m telescope on Earth without adaptive optics or that of the 2.5-m Hubble Space Telescope?

Answer 3

Hubble Space Telescope

Question 4

A spy satellite orbiting 500 km above Earth is supposedly capable of counting individual people in a crowd. Roughly what minimum-diameter telescope must the satellite carry? (Hint: Use the small-angle formula. Assume that a human is about 0.5 m from shoulder to shoulder.)

Answer 4

56 cm

Question 5

The visible part of the electromagnetic spectrum can be divided into seven color bands: red, orange, yellow, green, blue, indigo, and violet (from long to short wavelength). A single photon of which of these colors has the greatest amount of energy?

Answer 5

violet

Question 6

The entire electromagnetic spectrum can be divided into seven bands: radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray (from longest to shortest wavelength). To which of these two bands is Earth’s atmosphere the most transparent?

Answer 6

visible and radio

Question 7

Astronomers are both hindered and assisted by chromatic aberration. In which device is chromatic aberration a big problem for astronomers?

Answer 7

the primary lenses of refracting telescopes

Question 8

Why have no large refracting telescopes been built since 1900?

Answer 8

All of these choices are correct.

Question 9

Which power of a telescope might be expressed as “0.5 seconds of arc”?

Answer 9

resolving power

Question 10

Which power of a telescope is the least important?

Answer 10

magnifying power

Question 11

Which theoretical power of an optical telescope is determined by the diameter of the primary mirror or lens?

Answer 11

light-gathering power and resolving power

Question 12

What advantage do the builders of large telescopes today have over the previous generation of telescope builders?

Answer 12

All of these choices are correct.

Question 13

In which device do astronomers take advantage of chromatic aberration?

Answer 13

the prism

Question 14

Which power of a large ground-based optical telescope is severely limited by Earth’s atmosphere on a cloudless night?

Answer 14

resolving power

Question 15

What do the newer light-sensitive electronic CCD chips do better than the older photographic plates coated with light-sensitive chemicals?

Answer 15

All of these choices are correct.

Question 16

What is a disadvantage of radio telescopes compared to optical telescopes?

Answer 16

All of these choices are correct.

Question 17

Radio telescopes are often connected together to do interferometry. What is the primary problem overcome by radio interferometry?

Answer 17

poor resolving power

Question 18

Which is not a type of electromagnetic wave?

Answer 18

sound

Question 19

Which is something that all electromagnetic waves have in common?

Answer 19

All of these choices are correct.

Question 20

Which type of telescope is more expensive?

Answer 20

for the same size objective, refractors

Question 21

Why do nocturnal animals usually have large pupils in their eyes?

Answer 21

To gather more light, so they can see better at night.

Question 22

Which is the reason that radio telescopes are often put in valleys?

Answer 22

interference

Question 23

Which reason to build a large radio telescope also applies to optical telescopes?

Answer 23

better resolution

Question 24

Which reason for building a large telescope applies only to radio telescopes?

Answer 24

long wavelength light

Question 25

Which could be a disadvantage of a thin or “floppy” telescope mirror?

Answer 25

It tends to sag under its own weight.

Question 26

You see a telescope advertised as 200 power.

What quality of a telescope is probably being advertised?

Answer 26

magnifying power

Question 27

You see a telescope advertised as 200 power.

What qualities of a telescope are important to you as a potential buyer?

Answer 27

All of the these choices are important.

Question 28

Not long ago, an astronomer said: “Some people think I should give up photographic plates.”

What device could replace photographic plates in astronomy?

Answer 28

CCD

Question 29

Which is true about a prism spectrograph?

Answer 29

It divides light into the individual components of its spectrum.

Question 30

When telescopes in different locations work together, it is called which of the following?

Answer 30

interferometery

Question 31

Why are telescopes in different locations working together especially desirable for radio telescopes?

Answer 31

because radio telescopes have such poor resolution

Question 32

If two radio telescopes work together, which of the following is the size of the effective telescope?

Answer 32

It is equal to the distance between the telescopes.

Question 33

Why do radio telescopes have such poor resolution?

Answer 33

because radio waves have such a long wavelength

Question 34

Which is better observed by an X-ray telescope than an infrared telescope?

Answer 34

hot gas trapped in galactic clusters