Structure
Part where arms are located
Age of stars in the disk
Young and old; but this is the only part with young star formation
found here
Galactic halo
formed from this
Spectral class of stars in the arms
O & B
Galactic Bulge
Population I stars are found here
galactic disk
Age of these stars
Old
Tiny galaxies that collide
dwarf galaxies
Matter that we cannot see but that accounts for about half the matter in the Milky Way
Dark Matter
Color of stars in the disk
blue
Color of these stars
Red
Makes the galaxy rotate
angular momentum
Area of the galaxy with lots of matter we cannot see
Dark halo
Part of the galaxy with the fewest stars so it is hard to see
Galactic Halo
direction that population I stars rotate
same direction
Randomly
Holds the galaxy together
gravity
Variable star with the longest period of pulses (1 - 100 days)
Cepheids
The sun is located here
in the edge of one of the spiral arms about 8 kpc from the center
Contain lots of ___ and dust
gas
shape
Spherical
Shape of our galaxy
Spiral (actually a barred spiral)
Variable stars with a period from .5 to 1 day
RR Lyrae