THE Milky Way 2

Question 1

what is the diffuse band of light across the sky

Answer 1

Milky Way

Question 2

what is the “milky light” caused by?

Answer 2

• due to stars

- Galileo, 1610

Question 3

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

Answer 3

to see the concentration of stars

Question 4

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

Answer 4

they counted roughly same number of stars in all directions

Question 5

what did Kapteyn discover about motion of stars and how?

Answer 5

that they were due to orbit of stars about Galaxy center

-doppler shift

Question 6

globular clusters

Answer 6

extremely compact star cluster

Question 7

star cluster

Answer 7

stars bound together by gravity

Question 8

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

Answer 8

used RR Lyrae variable stars

Question 9

RR Lyrae stars have predictable what….?

Answer 9

luminosities

-allows us to measure distances into space

Question 10

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

Answer 10

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

Question 11

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

Answer 11

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

Question 12

what color brightness does dust reduce more?

Answer 12

it reduces blue light brightness more than red light brightness

Question 13

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

Answer 13

stars look redder than they would if there was no dust

Question 14

what is a very reliable measure of temperature?

Answer 14

spectral type

Question 15

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

Answer 15

infrared wavelengths

Question 16

what is the temperature of dust?

Answer 16

cold, 10-20 Kelvin

Question 17

at what wavelengths does thermal dust emission occur?

Answer 17

very long infrared or radio wavelengths

Question 18

interstellar medium contains more gas or dust?

Answer 18

GAS

Question 19

does gas produce visible light?

Answer 19

no

• too far away from stars
• too cold

Question 20

energy difference in atomic hydrogen atoms?

Answer 20

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

Question 21

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

Answer 21

the atomic gas can undergo chemical reactions

Question 22

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

Answer 22

1960s and 1970s

Question 23

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

Answer 23

takes little energy

-this emission can be produced by very cold molecular gas

Question 24

where do stars form?

Answer 24

in the dense, molecular clouds

Question 25

how do individual stars and planetary systems form?

Answer 25

gas in molecular clouds fragments and collapses

Question 26

visible material in MWG by mass...

Answer 26

90% stars | 10% gas/dust (interstellar medium)

Question 27

MWG structure

Answer 27

spiral galaxy with a central bar

Question 28

what is the spiral pattern a result of?

Answer 28

spiral density waves

Question 29

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

Answer 29

stars, gas, and dust

Question 30

why do stars, gas, and dust bunch up?

Answer 30

due to the spiral density wave

Question 31

what do the spiral arms represent a mixture of?

Answer 31

crowding of stars and interstellar medium

Question 32

what is the spiral density wave?

Answer 32

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

Question 33

what does gas compressed in the spiral density wave do?

Answer 33

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

Question 34

what do spiral arms represent?

Answer 34

waves of star formation in the gaseous disk

Question 35

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

Answer 35

young, luminous, massive stars

Question 36

who discovered the two stellar populations and when?

Answer 36

Walter Baade, 1940s | Pop I and Pop II

Question 37

population I stars

Answer 37

young, disk stars | -abundant in elements heavier than H and He

Question 38

population II stars

Answer 38

old, bulge and halo stars

Question 39

what do the two stellar populations have differences in?

Answer 39

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

Question 40

Population I star orbits?

Answer 40

orbits confined to the disk of the Milky Way

Question 41

Population II star orbits?

Answer 41

often have elliptical orbits that extend into the halo

Question 42

recycling in the galaxy

Answer 42

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