ASTR 1346 TEST 3 QUESTIONS AND CORRECT DETAILED
ANSWERS (VERIFIED ANSWERS) ALREADY GRADED A+
What is a galaxy? Ans✓✓✓A huge collection of stellar and interstellar
matter---stars, gas, neutron stars, black holes etc--- isolated in space and
held together by its own gravity
What did the Shapley Curtis debate argue? Ans✓✓✓The scale of the
universe
What did Shapley believe? Ans✓✓✓Spiral nebulae are relatively small,
nearby objects scattered around our galaxy
What did Curtis believe? Ans✓✓✓Each of these spiral nebulae is a
separate rotating system of stars much like our own galaxy
How did Hershel measure the structure of the Milky Way Galaxy?
Ans✓✓✓Star Counting
Describe Hershel's result (picture). Ans✓✓✓Flattened Milky Way
Extends 6000 light years
We are in the center of the galaxy
What was wrong with Hershel's results? Ans✓✓✓Interstellar extinction.
There are gas and dust particles in interstellar space. Stars appear
dimmer and hence appear further away than they really are.
,Hershel saw only what percentage of our Galaxy? Ans✓✓✓5%
This view was distorted by variable amounts of dust
What did Shapley observe? Ans✓✓✓Measured globular cluster
distances from RR Lyrae stars.
2. Mapped th cluster distribution in space.
What were shapleys results? Ans✓✓✓We are not in the center. Milky
Way is a flattened disk (300,000 light years across)
What did Shapleys model correct for? Ans✓✓✓Effects of interstellar
absorption
What is used to map our galaxy? Ans✓✓✓21 CM radio
How does a 21 CM radio work? Ans✓✓✓Waves emitted by changes in
the relative spins of electrons and protons
What are characteristics of the galactic bulge? Ans✓✓✓Spherical
20,000 light years across
13,000 light years thick
,What kinds of stars mingle in the galactic bulge? Ans✓✓✓Old and
young stars
What is the color if the galactic bulge? Ans✓✓✓Yellow-white
Is there gas and dust in the galactic bulge? Ans✓✓✓Yes, more gas and
dust (indication of star formation, especially in the inner parts)
What is the shape of the galactic halo? Ans✓✓✓Spherical
What kind of stars are in the galactic halo? Ans✓✓✓Old metal-poor
stars---> population II stars. Globular clusters & RR Lyrae stars
Is there gas and dust in the galactic halo? Ans✓✓✓No
Where is the galactic halo located? Ans✓✓✓Region around the disk and
bulge
What are characteristics of the galactic disk in light years?
Ans✓✓✓100,000 light years across
2,000 light years thick
What is in the galactic disk? Ans✓✓✓Spiral arms and Dusty Giant
Molecular Clouds
, Is there gas and dust in the galactic disk? Ans✓✓✓Yes
What kinds of stars are in the galactic disk? Ans✓✓✓Young and old
metal rich stars---> population I stars
What is the color of the galactic disk? Ans✓✓✓Blue-whitish
What are the major arms of our galaxy? Ans✓✓✓Sagittarius, Perseus,
Norma, Scaton-Centauras
Where are we located in the galaxy? Ans✓✓✓Orion spur
What does the rotation curve of our galaxy show? Ans✓✓✓There is
dark matter
What is dark matter? Ans✓✓✓The undetected matter in the universe
that is under luminous and probably white different from ordinary matter
Why is it also called missing mass? Ans✓✓✓Starlight cannot trace it
How much percentage of our galaxy is composed of dark matter?
Ans✓✓✓90%
ANSWERS (VERIFIED ANSWERS) ALREADY GRADED A+
What is a galaxy? Ans✓✓✓A huge collection of stellar and interstellar
matter---stars, gas, neutron stars, black holes etc--- isolated in space and
held together by its own gravity
What did the Shapley Curtis debate argue? Ans✓✓✓The scale of the
universe
What did Shapley believe? Ans✓✓✓Spiral nebulae are relatively small,
nearby objects scattered around our galaxy
What did Curtis believe? Ans✓✓✓Each of these spiral nebulae is a
separate rotating system of stars much like our own galaxy
How did Hershel measure the structure of the Milky Way Galaxy?
Ans✓✓✓Star Counting
Describe Hershel's result (picture). Ans✓✓✓Flattened Milky Way
Extends 6000 light years
We are in the center of the galaxy
What was wrong with Hershel's results? Ans✓✓✓Interstellar extinction.
There are gas and dust particles in interstellar space. Stars appear
dimmer and hence appear further away than they really are.
,Hershel saw only what percentage of our Galaxy? Ans✓✓✓5%
This view was distorted by variable amounts of dust
What did Shapley observe? Ans✓✓✓Measured globular cluster
distances from RR Lyrae stars.
2. Mapped th cluster distribution in space.
What were shapleys results? Ans✓✓✓We are not in the center. Milky
Way is a flattened disk (300,000 light years across)
What did Shapleys model correct for? Ans✓✓✓Effects of interstellar
absorption
What is used to map our galaxy? Ans✓✓✓21 CM radio
How does a 21 CM radio work? Ans✓✓✓Waves emitted by changes in
the relative spins of electrons and protons
What are characteristics of the galactic bulge? Ans✓✓✓Spherical
20,000 light years across
13,000 light years thick
,What kinds of stars mingle in the galactic bulge? Ans✓✓✓Old and
young stars
What is the color if the galactic bulge? Ans✓✓✓Yellow-white
Is there gas and dust in the galactic bulge? Ans✓✓✓Yes, more gas and
dust (indication of star formation, especially in the inner parts)
What is the shape of the galactic halo? Ans✓✓✓Spherical
What kind of stars are in the galactic halo? Ans✓✓✓Old metal-poor
stars---> population II stars. Globular clusters & RR Lyrae stars
Is there gas and dust in the galactic halo? Ans✓✓✓No
Where is the galactic halo located? Ans✓✓✓Region around the disk and
bulge
What are characteristics of the galactic disk in light years?
Ans✓✓✓100,000 light years across
2,000 light years thick
What is in the galactic disk? Ans✓✓✓Spiral arms and Dusty Giant
Molecular Clouds
, Is there gas and dust in the galactic disk? Ans✓✓✓Yes
What kinds of stars are in the galactic disk? Ans✓✓✓Young and old
metal rich stars---> population I stars
What is the color of the galactic disk? Ans✓✓✓Blue-whitish
What are the major arms of our galaxy? Ans✓✓✓Sagittarius, Perseus,
Norma, Scaton-Centauras
Where are we located in the galaxy? Ans✓✓✓Orion spur
What does the rotation curve of our galaxy show? Ans✓✓✓There is
dark matter
What is dark matter? Ans✓✓✓The undetected matter in the universe
that is under luminous and probably white different from ordinary matter
Why is it also called missing mass? Ans✓✓✓Starlight cannot trace it
How much percentage of our galaxy is composed of dark matter?
Ans✓✓✓90%
