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Astronomy > THE Milky Way 2 > Flashcards

THE Milky Way 2 Flashcards

1
Q

what is the diffuse band of light across the sky

A

Milky Way

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2
Q

what is the “milky light” caused by?

A
  • due to stars

- Galileo, 1610

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3
Q

why does our galaxy have a very flattened (disk-like) shape?

A

to see the concentration of stars

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4
Q

why did Herschels think that sun was approx at center of MWG?

A

they counted roughly same number of stars in all directions

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5
Q

what did Kapteyn discover about motion of stars and how?

A

that they were due to orbit of stars about Galaxy center

-doppler shift

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6
Q

globular clusters

A

extremely compact star cluster

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7
Q

star cluster

A

stars bound together by gravity

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8
Q

what did Harlow Shapley do in order to get distances to globular clusters?

A

used RR Lyrae variable stars

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9
Q

RR Lyrae stars have predictable what….?

A

luminosities

-allows us to measure distances into space

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10
Q

what did the discovery that globular clusters were offset from Sun tell astronomers?

A

sun was at edge of Galaxy and galaxy was much larger than Kapteyn estimated

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11
Q

What did the Kapteyn and Shapley models neglect the effects of in terms of measuring distances to stars?

A

neglected the effects of dust that lies between stars (interstellar medium)

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12
Q

what color brightness does dust reduce more?

A

it reduces blue light brightness more than red light brightness

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13
Q

what is the effect of dust blocking blue light better than red light?

A

stars look redder than they would if there was no dust

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14
Q

what is a very reliable measure of temperature?

A

spectral type

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15
Q

what kind of wavelength makes us able to see past the dust?

A

infrared wavelengths

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16
Q

what is the temperature of dust?

A

cold, 10-20 Kelvin

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17
Q

at what wavelengths does thermal dust emission occur?

A

very long infrared or radio wavelengths

18
Q

interstellar medium contains more gas or dust?

A

GAS

19
Q

does gas produce visible light?

A

no

  • too far away from stars
  • too cold
20
Q

energy difference in atomic hydrogen atoms?

A

energy diff is small, so can be readily excited by collisions in cold interstellar medium

21
Q

how are molecules formed in the denser regions of the interstellar medium?

A

the atomic gas can undergo chemical reactions

22
Q

when were radio spectral lines produced by quantized rotation of molecules detected?

A

1960s and 1970s

23
Q

does it take little or lots of energy to set a molecule into rotation?

A

takes little energy

-this emission can be produced by very cold molecular gas

24
Q

where do stars form?

A

in the dense, molecular clouds

25
Q

how do individual stars and planetary systems form?

A

gas in molecular clouds fragments and collapses

26
Q

visible material in MWG by mass…

A

90% stars

10% gas/dust (interstellar medium)

27
Q

MWG structure

A

spiral galaxy with a central bar

28
Q

what is the spiral pattern a result of?

A

spiral density waves

29
Q

“the wave pattern moves thru that galactic disk, but what 3 things do not remain in the spiral arms?

A

stars, gas, and dust

30
Q

why do stars, gas, and dust bunch up?

A

due to the spiral density wave

31
Q

what do the spiral arms represent a mixture of?

A

crowding of stars and interstellar medium

32
Q

what is the spiral density wave?

A

moves around galaxy, compressing stars/gas/dust and rarifying

33
Q

what does gas compressed in the spiral density wave do?

A

initiates the gravitational collapse of the gas to form dense molecule clouds and eventually stars

34
Q

what do spiral arms represent?

A

waves of star formation in the gaseous disk

35
Q

what kind of stars delineate the arms well? (3 characteristics)

A

young, luminous, massive stars

36
Q

who discovered the two stellar populations and when?

A

Walter Baade, 1940s

Pop I and Pop II

37
Q

population I stars

A

young, disk stars

-abundant in elements heavier than H and He

38
Q

population II stars

A

old, bulge and halo stars

39
Q

what do the two stellar populations have differences in?

A

age, size, color, orbits, amounts of heavy elements

40
Q

Population I star orbits?

A

orbits confined to the disk of the Milky Way

41
Q

Population II star orbits?

A

often have elliptical orbits that extend into the halo

42
Q

recycling in the galaxy

A

MWG recycles material from gas to stars back to gas and the process repeats
-enriches MWG in fusion products (heavy elements)

Astronomy (14 decks)

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