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Astronomy > The Milky Way > Flashcards

The Milky Way Flashcards

1
Q

milky way

A

diffuse band of light that we see across the sky

-Galileo, 1610 w/ telescope

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2
Q

shape of Milky Way galaxy

A

-very flattened (disk-like) system to see the concentration of stars

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3
Q

where are we located in the Milky Way

A

sun is approx. in center

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4
Q

William and Caroline Herschel

A 
English astronomers (1780s) 
-counted stars, found we were in center since # of stars was same in each direction
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5
Q

size of Milky Way Disk

A

diameter of disk was about 10 times its thickness

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6
Q

Dutch astronomer Kapteyn

A
  • early 1900s

- noted that motion of stars were not random: due to orbit of stars about Galaxy center (Doppler shift)

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7
Q

Kapteyn 1922

A

used star counts and stellar motions to determine sun was in center

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8
Q

Kapteyn Model

A

15,000 pc, but most stars were within a few kpc of center

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9
Q

star cluster

A

stars bound together in groups by their gravity

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10
Q

globular cluster

A

extremely compact star cluster

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11
Q

Harlow Shapley

A
  • 1920s
  • used RR Lyrae variable stars (predictable luminosities) to find that glob clusters were distributed well offset from Sun
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12
Q

Shapley’s Model

A

shows that Sun was at the edge of the Galaxy and galaxy was much larger than thought

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13
Q

Discrepancy b/w Kapteyn and Shapley Models

A
  • both wrong!

- did not account for effects of dust that lies between stars

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14
Q

interstellar medium

A

dust lying b/w stars

-dust grains=effective in blocking visible star light…distorted view of Milky Way

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15
Q

interstellar dust

A

dust grains=small particles of matter

-can only see stars near the Sun (probs w/ Kapteyn/Shapley models)

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16
Q

dust’s effect on brightness

A

reduces brightness of background stars

-reduces blue light more than red light

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17
Q

Reddening

A

stars look redder than they should if there is no foreground dust

18
Q

reliable measure of temperature

A

spectral type

19
Q

thermal dust emission

A

dust=10-20 K

-emission occurs at very long infrared or radio wavelengths

20
Q

Gas in the Interstellar Medium

A

medium contains more gas than dust

-near hot star, can become hot enough to produce emission line spectrum (visible light emission)

21
Q

radio wave from cold interstellar gas

A

atomic hydrogen atoms in space emits radio spectral line emission at wavelength of 21 cm due to spin or electron and proton (1951)

22
Q

collisions in cold interstellar medium

A

energy difference is small=readily excited by collisions

23
Q

molecular clouds

A

in denser regions of interstellar medium, atomic gas undergoes chem reactions to form molecules

24
Q

how are radio spectral lines produced

A

By the quantized rotation of molecules (1960s/70s)

25
Q

why can radio spectral lines be produced by very cold molecular gas?

A

takes lil energy for collisions to set a molecule into rotation

26
Q

where do stars form?

A

dense, molecular clouds where gas in interstellar medium is molecular rather than atomic

27
Q

how do stars form?

A

gas in molecular clouds fragments and collapses to form individuals stars/planetary systems

28
Q

visible material in Milky Way (%)

A

90% stars

10% gas and dust

29
Q

Structure of Galaxy

A
  • spiral structure w/ central bar
  • spiral pattern is result of spiral density waves
  • wave pattern moves thru galactic disk, but stars/gas/dust do not remain in spiral arms
30
Q

spiral arms

A

stars, gas, and dust bunch up in spiral arms due to spiral density wave

31
Q

spiral density wave

A

moves around the galaxy alternatively compressing the stars, gas, and dust (spiral arm) and rarifying (inter-arm region)

32
Q

gas compressed in spiral density wave

A

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

33
Q

what do spiral arms represent?

A

waves of star formation in the gaseous disk

-young massive stars delineate the arms

34
Q

Walter Baade

A

discovered two stellar populations:

  1. Pop I=young disk stars
  2. Pop II=old, bulge and halo stars
35
Q

what are the differences b/w Population I and Population II?

A

differ in color, age, shape, orbits, amounts of heavy elements

36
Q

Population I

A

less than a few billion years old

  • still have big blue stars
  • more abundant than H and He
37
Q

Population II

A

over 10 billion years old, red stars

38
Q

Population I Orbits

A

confined to the disk of the Milky Way

39
Q

Population II Orbits

A

elliptical orbits that extend into the halo

40
Q

What does the Milky Way recycle?

A

its material from gas to stars to gas and this process repeats
-enriches Milky Way in fusion products

Astronomy (14 decks)

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