ASTR 101-3, FALL 2010 1

LECTURE 17, OCTOBER 28, 2010

ASTR 101, SECTION 3INSTRUCTOR, JACK BRANDT

jcbrandt@unm.edu

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Question 1

Some regions of the Milky Way’s disk appear dark because

a) there are no stars there.b) stars in that direction are obscured by

interstellar gas.c) stars in that direction are obscured by

interstellar dust.d) numerous black holes capture all the

starlight behind them.

Question 1

Some regions of the Milky Way’s disk appear dark because

a) there are no stars there.b) stars in that direction are obscured by

interstellar gas.c) stars in that direction are obscured by

interstellar dust.d) numerous black holes capture all the

starlight behind them.

Dust grains are about the same size as visible light, and they can scatter or block the shorter wavelengths.

Question 2

When a star’svisible light passes through interstellar dust, the light we see

a) is dimmed and reddened.b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color.e) ionizes the dust and creates emission

lines.

Question 2

When a star’svisible light passes through interstellar dust, the light we see

a) is dimmed and reddened.b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color.e) ionizes the dust and creates emission

lines.

The same process results in wonderful sunsets, as dust in the air scatters the Sun’s blue light, leaving dimmer, redder

light.

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Question 4

Interstellar gas is composed primarily of

a) 90% hydrogen, 9% helium, and 1% heavier elements.

b) molecules including water and CO2.

c) 50% hydrogen, 50% helium.d) hydrogen, oxygen, and nitrogen.e) 99% hydrogen, and 1% heavier elements.

Question 4

Interstellar gas is composed primarily of

a) 90% hydrogen, 9% helium, and 1% heavier elements.

b) molecules including water and CO2.

c) 50% hydrogen, 50% helium.d) hydrogen, oxygen, and nitrogen.e) 99% hydrogen, and 1% heavier elements.

The composition of interstellar gas mirrors that of the Sun, stars,

and the jovian planets.

Question 6

21-centimeter radiation is important because

a) its radio waves pass unaffected through clouds of interstellar dust.

b) it arises from cool helium gas present throughout space.

c) it can be detected with optical telescopes.d) it is produced by protostars. e) it reveals the structure of new stars.

Question 6

21-centimeter radiation is important because

Cool atomic hydrogen gas produces 21-cm radio radiation as its electron

“flips” its direction of spin.

a) its radio waves pass unaffected through clouds of interstellar dust.

b) it arises from cool helium gas present throughout space.

c) it can be detected with optical telescopes.d) it is produced by protostars. e) it reveals the structure of new stars.

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Question 12

Stars in clusters & associations have about the same

a) age.b) temperature. c) mass.d) color.e) luminosity.

Question 12

Stars in clusters & associations have about the same

Most of the stars in a cluster form about the same time.

Stars in the Omega Centauri globular cluster are estimated to

be about 14 billion years old.

a) age.b) temperature. c) mass. d) color.e) luminosity.

Question 13

Objects more massive than our Sun form into stars

a) much slower, over billions of years.b) in about the same time.c) much faster, over tens of thousands of

years.d) not at all – they are unstable.

Question 13

Objects more massive than our Sun form into stars

a) much slower, over billions of years.b) in about the same time.c) much faster, over tens of thousands of

years.d) not at all – they are unstable.

More mass faster collapse

More mass faster start of fusion reactions

More mass a hotter, more luminous main sequence star