Chapter 6

Question 1

What is an astronomer’s most important tool?

Answer 1

A telescope

Question 2

What are the two primary types of optical telescopes?

Answer 2

1. Refracting

2. Reflecting

Question 3

What does a reflecting telescope use for collecting and focusing incoming light?

Answer 3

A primary mirror, a secondary mirror, and an eyepiece on the side of the telescope

Question 4

What does a refracting telescope use for collecting and focusing incoming light?

Answer 4

An objective lens & eyepiece

Question 5

What is the focal plane?

Answer 5

The plane, perpendicular to the optical axis of a lens or mirror, on which an image is formed

Question 6

What is the focal point?

Answer 6

The point at which light from a very distant object converges after being refracted or reflected

Question 7

What is the focal length?

Answer 7

The distance from the lens or mirror to its focal point

Question 8

What type of telescope does chromatic aberration occur in?

Answer 8

Refracting telescopes

Question 9

How can chromatic aberration be corrected?

Answer 9

You add in a second lens that is made from a different kind of glass

Question 10

What is chromatic aberration?

Answer 10

Its when the lens acts slightly like a prism. It bends different colored lights by different amounts

Question 11

What is the best resolution that a given telescope can achieve?

Answer 11

Diffraction limit

Question 12

What’s the advantage of launching a telescope above earth’s atmosphere?

Answer 12

They aren’t affected by astronomical seeing

Question 13

Which dimensions of the refracting telescope determine its magnification?

Answer 13

Focal lengths of the objective lens / focal length of the eyepiece

Question 14

Describe the advantages of reflecting telescopes over refracting telescopes

Answer 14

1. No chromatic aberration

2. The mirror can be supported by a bracket on it’s back

Question 15

What is spherical aberration?

Answer 15

Light from different parts of the mirror converge at different focal points due to the shape of the mirror

Question 16

What are the two ways that you can correct spherical aberration?

Answer 16

1. You can use a parabolic mirror instead of a spherical one

2. You can put a correcting lens in front of the mirror

Question 17

What criteria would you employ to evaluate a telescope when you want to buy one? Explain

Answer 17

1. Light-gathering power - Provides a brighter image

2. Resolving power - Provides sharp and crisp images

Question 18

Compare an optical reflecting telescope and a radio telescope. How are they different?

Answer 18

Since radio waves are much longer, radio telescopes have to be bigger. Also, optical telescopes work during the night while radio telescopes work during the day

Question 19

Compare an optical reflecting telescope and a radio telescope. What do they have in common?

Answer 19

They both use a curved reflecting surface to focus the incoming radiation

Question 20

What is the optical window and the radio window?

Answer 20

They are wavelength regions where our atmosphere is transparent

Question 21

Why isn’t there an X-ray window or an ultraviolet window?

Answer 21

Our atmosphere is not transparent to these wavelength ranges, so the waves aren’t able to reach the earth’s surface

Question 22

Why do we need Gamma-ray, X-ray, UV and Infrared telescopes? Explain.

Answer 22

So we can study extremely hot objects

Question 23

How do you find the magnification of a reflecting telescope?

Answer 23

Focal length of primary mirror / focal length of eyepiece

Question 24

Explain the different designs of reflecting telescopes

Answer 24

You have a primary mirror and a secondary mirror, so your head doesn’t block some of the light