Unit 6 Flashcards
Galaxy
a large group of stars
Average galaxy size
100 billion stars, 100,000 light years in diameter
galacitic disk
center of galaxy and flat disk
globular cluster
stars orbiting the galactic center
interstellar dust
obscures our view of the galaxy
radio waves help us what
map out the galaxy
How fast is the Sun revolving around the center of the Galaxy?
500,000 mi/hr
What type of radiation can penetrate the dust clouds of our Galaxy, allowing us to see the spiral structure? (It is also known as 21 cm hydrogen radiation.)
radio
cepheid variable star
gets brighter and dimmer in a regular pattern
Henrietta Leavitt
figured out the pattern that relates to luminosity and cepheid variable stars, this allows us to find distance of stars
Distant indicator and millions of light years
cepheid variables 15-20 ly, red supergiants 50 ly, blue supergiants 80 ly, Novae 80 ly, globular clusters 130 ly, supernovae 8,000 ly, brightest galaxy in cluster 15,000 ly
What two properties of a Cepheid variable star do we need to know in order to calculate the approximate distance from Earth?
apparent magnitude
luminosity
What two properties of a Cepheid variable star do we need to know in order to calculate the approximate distance from Earth?
apparent magnitude
luminosity
types of galaxies
spiral, barred spiral, ellipticals, irregulars
spiral
Sa, Sb, Sc, (a is tightly wrapped) SBa, SBb, SBc (B means barred)
ellipticals
look like circles, E0-E7 (0 is more circular and 7 is more oval)
irregulars
any other type of galaxy
clusters
groups of galaxies
dark matter
matter we are unable to observe from Earth
quasars
100 times brighter than average galaxy, very far away
Who developed a classification system for galaxies?
Edwin Hubble
black hole
so strong gravity that light can’t escape
escape velocity
how fast something must go to escape an objects gravity (shrink something and it has a higher escape velocity)
event horizon
boundary of black hole
active galaxies
brightness between normal galaxy and quasar
galactic nuclei
bright starlike, called seyfert galaxies
capricornus
the goat, shaped like a big upside down triangle, no bright stars
libra
themis, shaped like a trapazoid, no bright star
scorpius
the scorpion, shaped like a curved hook, bright star Antares
sagittarius
the archer, shaped like someone with a bow, no bright star
Observing a significant wobble in a star’s orbit would suggest what possibility (if no binary star is visible)?
Its companion star became a black hole.
t/f Cepheid variables are useful for determining the distances to some galaxies.
true
t/f Earth is near the center of the Milky Way Galaxy.
false
Edwin Hubble’s discovery of a Cepheid variable in the Andromeda nebula led him to conclude that the nebula was what?
a distant galaxy
Who developed a classification system for galaxies?
Edwin Hubble
Henrietta Leavitt found that the brighter appearing Cepheids always had longer periods of light variation. This is an expression of what?
period-luminosity relation
If the Sun were to become a black hole, what would happen to Earth?
It would continue in the same orbit.
How long does it take the Sun to revolve around the center of the galaxy?
two hundred million years
Our sun is a member of which galaxy?
Milky Way
Which type of radiation helped us map the galaxy?
21 cm radio waves
What is the surface or boundary of a black hole called?
event horizon
The Local Group contains
twenty-four galaxies
t/f Quasars appear to be among the most distant objects known in the universe.
true
What is believed to be at the center of most galaxies?
black holes
t/f It would be impossible to orbit a black hole, because you would always be sucked in.
false
