AST1002 EXAM 3 ACTUAL TEST QUESTIONS
AND SOLUTIONS GRADED A+ PREMIUM
RESOURCE
●● What type of galaxy is the Milky Way?
Know the different components.
Answer: Spiral.
Components: thin galactic disk of matter that fattens into a galactic
bulge at the center. Disk and bulge are embedded in a roughly spherical
ball of faint old stars known as the galactic halo. Halo: no gas or dust;
disk and bulge: gas and dust (interstellar matter common) Redder stars:
bulge and halo; disk: blue white tint; yellowish coloration of bulge.
Disk: bright blue stars. (p. 388)
●● Where are Young Stars located in the Galaxy?
Answer: Disk: ongoing star formation.
●● Where are the Old Stars?
Answer: Halo: old, no new stars forming there.
●● Where are New Stars forming?
Answer: Bulge: vigorous ongoing star formation, both very old and very
young stars.
,●● How are the Orbits of the Stars in different Regions of our Galaxy
different?
Answer: Stars in Galactic Disk: circular orbits.
Halo Stars move randomly around the center; high above galactic disk,
down through disk plane, out the other side and far below the disk.
Bulge Stars: intermediate orbits between those of disk and halo stars
(largely random, but with some rotation about center) p. 387.
●● How can we know the amount of Mass in our Galaxy?
Answer: Total mass (solar masses)=orbit size (AU)^3/orbit period
(years)^2. We can measure mass by studying the motions of gas clouds
and stars in the galactic disk.
●● What does the observed rotation curve (graph of rotation velocity vs.
distance) of our Galaxy tell us about the mass in the Galaxy?
Answer: The rotation curve for the Milky Way Galaxy plots rotation
speed against distance from the Galactic center. The dashed curve is the
rotation curve expected if the galaxy ended abruptly at a radius of 15
kpc, the limit of most of the known spiral structure. The fact that the red
curve doesnt follow the dashed line, but instead stays well above it,
**indicates that there must be additional unseen matter beyond that
radius. Using the curve, we can compute the total mass within about 15
kpc from the center=twice the amount of mass contained within the suns
orbit.** Dist of matter continues beyond 15 kpc.
, ●● What do we know about the amount of mass in our Galaxy beyond
the orbit of the Sun?
Less?
More?
What type?
Answer: There's more matter beyond the orbit of the sun, up to 50 kpc,
made of stars, star clusters, and spiral arms----dark matter???
●● What are the Spiral Arms?
Answer: pinwheel like structures originating close to the Galactic bulge
and extending outward throughout the galactic disk (where star
formation takes place). Spiral arms come from instabilities in gas in
galactic bulge, grav effects of nearby galaxies, etc---not sure.
●● What type of Stars do we find in Spirals?
What is the amount of dust and gas compared to other type of Galaxies?
Answer: O and B type stars, emission nebulae, recently formed open
clusters.
Spiral density waves: coiled waves of gas compression that move
through the galactic disk, squeezing out clouds of interstellar gas and
triggering star formation. Spiral arms have denser than normal clouds of
gas.
●● What are Irregulars?
AND SOLUTIONS GRADED A+ PREMIUM
RESOURCE
●● What type of galaxy is the Milky Way?
Know the different components.
Answer: Spiral.
Components: thin galactic disk of matter that fattens into a galactic
bulge at the center. Disk and bulge are embedded in a roughly spherical
ball of faint old stars known as the galactic halo. Halo: no gas or dust;
disk and bulge: gas and dust (interstellar matter common) Redder stars:
bulge and halo; disk: blue white tint; yellowish coloration of bulge.
Disk: bright blue stars. (p. 388)
●● Where are Young Stars located in the Galaxy?
Answer: Disk: ongoing star formation.
●● Where are the Old Stars?
Answer: Halo: old, no new stars forming there.
●● Where are New Stars forming?
Answer: Bulge: vigorous ongoing star formation, both very old and very
young stars.
,●● How are the Orbits of the Stars in different Regions of our Galaxy
different?
Answer: Stars in Galactic Disk: circular orbits.
Halo Stars move randomly around the center; high above galactic disk,
down through disk plane, out the other side and far below the disk.
Bulge Stars: intermediate orbits between those of disk and halo stars
(largely random, but with some rotation about center) p. 387.
●● How can we know the amount of Mass in our Galaxy?
Answer: Total mass (solar masses)=orbit size (AU)^3/orbit period
(years)^2. We can measure mass by studying the motions of gas clouds
and stars in the galactic disk.
●● What does the observed rotation curve (graph of rotation velocity vs.
distance) of our Galaxy tell us about the mass in the Galaxy?
Answer: The rotation curve for the Milky Way Galaxy plots rotation
speed against distance from the Galactic center. The dashed curve is the
rotation curve expected if the galaxy ended abruptly at a radius of 15
kpc, the limit of most of the known spiral structure. The fact that the red
curve doesnt follow the dashed line, but instead stays well above it,
**indicates that there must be additional unseen matter beyond that
radius. Using the curve, we can compute the total mass within about 15
kpc from the center=twice the amount of mass contained within the suns
orbit.** Dist of matter continues beyond 15 kpc.
, ●● What do we know about the amount of mass in our Galaxy beyond
the orbit of the Sun?
Less?
More?
What type?
Answer: There's more matter beyond the orbit of the sun, up to 50 kpc,
made of stars, star clusters, and spiral arms----dark matter???
●● What are the Spiral Arms?
Answer: pinwheel like structures originating close to the Galactic bulge
and extending outward throughout the galactic disk (where star
formation takes place). Spiral arms come from instabilities in gas in
galactic bulge, grav effects of nearby galaxies, etc---not sure.
●● What type of Stars do we find in Spirals?
What is the amount of dust and gas compared to other type of Galaxies?
Answer: O and B type stars, emission nebulae, recently formed open
clusters.
Spiral density waves: coiled waves of gas compression that move
through the galactic disk, squeezing out clouds of interstellar gas and
triggering star formation. Spiral arms have denser than normal clouds of
gas.
●● What are Irregulars?
