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176 Cards in this Set

  • Front
  • Back
Why is our galaxy called the Milky Way?
Because when you look up at the night sky, it likes there is a flowing ribbon of milk, that is what it looked like to the ancient Greeks
Who proved in 1600s with his telescope, that the light of the Milky Way comes from a myriad individual stars
Galileo
What is the Greek word for milk?
galactos
T or F
Much of the Milky Way's visible light is hidden from our view?
True
How many stars does the Milky Way hold?
over 100 billion stars
What shape is used to describe the Milky Way?
Spiral galaxy
Why is the Milky Way considered a spiral galaxy?
Because of the spectacular spiral arms it has
What do the spiral arms of the Milky Way form?
A fairly flat disk
What does the flat disk of the Milky Way surround?
A bright central bulge
What surrounds the entire disk of the Milky Way?
A dimmer, rounder halo
Where do most of the Milky Way's bright stars reside?
Inside the disk
Where are most prominent stars in the halo found?
In about 200 globular cllusters of stars.
How large is the Milky Way?
100,000 lights in diameter
How large is the Milky Way's disk?
1,000 light years thick
Where is our Sun located in the Milky Way?
Inside the disk, about 28,000 from the galactic center; or
a little more than halfway from the center to the edge of the disk.
What word is used for the collective term for the clouds of interstellar gas and dust found in the Milky Way?
Interstellar medium
What obscures our view of the rest of the Milky Way when we try to observe it in visible light?
Interstellar medium
the interstellar gas and dust
Who proved that our solar system did not reside in the galactic center of the Milky Way?
Harlow Shapley
How did Shapely prove that our Solar System did not reside in the center of the Milky Way?
He demonstrated that the Milkyt Way's globular clusters are centered on a point tens of thousands of light-years from our Sun;
He concluded that this point, not our Sun, was the center of the galaxy.
When did Shapley prove that our solar system was not in the galactic center of the Milky Way?
1920's
T or F
The Milky Way is relatively a small galaxy.
False,
The Milky Way is relatively a LARGE galaxy.
T or F
The Milky Way's gravity influences smaller galaxies in its vicinity.
True
What other galaxy in our local group is similar in size to the Milky Way?
The Adromeda Galaxy
Name 2 galaxies that orbit the Milky Way at distances of 150,000 and 200,000 light years away?
1. Large Magellanic Cloud
2. Small Magellanic Cloud
Where are the Large Magellanic Cloud and the Small Magellanic Cloud visible to the naked eye?
In the Southern Hemisphere
Name the 2 galaxies that are closer than the Magellanic Clouds that are in the process of colliding with the Milky Way's disk?
1. Sagittarius Dwarf
2. Canis Major Dwarf
When was the Sagittarius Dwarf galaxy discovered?
1. 1994
When was the Canis major Dwarf galaxy discovered?
1. 2003
How much larger than the Magellanic Clouds and the Sagittarius and Canis Major Dwarfs galaxies (4total) is the Milky Way
hundreds of times larger than these 4 galaxies
How much larger are the Magellanic Clouds and the Sagittarius and Canis Major Dwarfs galaxies than typical globular clusters?
1,000 more larger than typical globular clusters
T or F
The Milky Way is not a solid structure.
True
How does each individual star travel in the Milky Way?
Each individual star follows its own orbital path around the center of the Milky Way.
How many orbital paths do stars in the Milky Way follow?
Two
Describe the 2 basic orbital paths that stars in the Milky Way follow?
1. circular paths that go in the same direction in nearly the same plane; and
2. soar high at randomly oriented orbits
In what location of the Milky Way do stars reside that follow a circular paths that go in the same direction?
disk
In what location of the Milky Way do stars that follow randomly oriented orbits reside?
Stars in the bulge and halo that soar high above and below the disk
T or F
If you were standing outside of the Milky Way for a few billion years, the disk would resemble a huge merry-go-round.
True
What cause the general orbit of a star around the galaxy?
the stars gravitational attraction toward the galactic center
What pulls a bobbing star that is too far above the disk?
It is pulled back into the disk by gravity
What causes the bobbing stars to "fly" through the disk?
the relatively low density of the interstellar gas
What gives the disk of the Milky Way its 1,000 light years of thickness?
The up and down motions of the of the disk stars
How long does it take for each star near our Sun to orbit ?
200 million years
How long is each up and down "bob" take for those stars?
tens of millions of years
T or F
Merry-go-round horses near the edge move much faster than those near the center.
True
T or F
In our galaxy's disk, the orbital velocities of stars near the edge and those near the center are about the same.
True
T or F
The velocities of stars near the galactic center behave much like the horses in a merry-go-round?
False.
T or F
Stars closer to the center complete each orbit in less time than stars farther out.
True
Describe the shapes of the orbital paths of individual bulge and halo stars:
Elliptical
T or F
Neighboring halo stars always circle the galactic center in the same direction.
False,
Neighboring halo stars can circle the galactic center in opposite directions.
T or F
The Milky Way's disk's gravity hardly alters the trajectories of halo stars
True
What causes the bulge and halo of the Milky Way to appear puffier than the rest of the disk?
The swooping orbits of the halo and bulge stars
Which stars have wider swooping orbits, halo and bulge, or disk stars?
Halo and Bulge stars
T or F
The Sun's orbital path is fairly typical of disk stars located near our 28,000 light year distance from the galactic center.
True
How fast does our Sun and its neighbors orbit the center of the Milky Way?
220 kilometers per second
What does 220 kilometers per second equal in terms of kilometers per hour?
800,000 kilometers per hour
How many years does it take our Sun to complete one orbit around the galactic center of the Milky Way?
230 million years
What animals were just emerging on the Earth the last time our Sun visited this side of the galaxy?
The dinosaurs were just emerging.
What is the formula for the orbital velocity law for an object on a circular orbit?
2
r X v/
M = / G
r
What is the mass of the Milky Galaxy within our Sun's orbit?
41
@ 2 X 10 kg
What is the mass of the galaxy within the Sun's orbit?
@ 100 billion kg or
11
10 kg
T or F
Why does the Sun's orbital motion allows us to calculate only the mass within the Sun's orbit , rather than the total mass of the galaxy?
True
What pulls the Suns orbit toward the galactic center?
Net gravitational forces from mass within the Sun's orbit
T or F
Most of spiral galaxies' mass is in their centers.
False.
Where does most of the mass reside in a spiral galaxy?
far from its center and is distributed throughout its halo
T or F
We can see most of the galaxy's matter.
False,
Because we see few stars and virtually no gas or dust in the halo, most of the galaxy's mass must not give off any light that we can detect.
What is the term used for the mass in a galaxy that we cannot see and that does not give off any light?
Dark matter
What action by the galaxy formed our solar system?
Galactic recycling
What gradually changes the chemical composition of the interstellar medium?
Galactic recycling
What elements existed when the Universe was formed?
1. Hydrogen
2. Helium
What is the term used by astronomers for all of the elements that are heavier than helium?
Heavy elements
What causes the existence of the heavier elements?
Fusion in stars
What percent of the galaxy's gaseous content by mass is made up of heavy elements?
2 %.
What percent of the galaxy's gaseous content by mass is made up of hydrogen?
70%
What percent of the galaxy's gaseous content by mass is mad up of helium?
28%.
What does the star-gas-star cycle stand for?
The action of galactic recycling process.
How are stars born?
When gravity causes the collapse of molecular clouds
How do stars die?
When they have exhausted their fuel for fusion.
T or F
All stars return much of their original mass to interstellar space in 2 basic ways.
True
Describe the 2 basic ways that all stars return much of their original mass to interstellar space:
1. stellar winds that blow throughout their lives
2. "death events" of planetary nebulae(low mass stars) or supernovae(high mass stars)
T or F
Low mass stars generally have strong stellar winds.
False
Low mass stars generally have weak stellar winds.
T or F
Low mass stars' winds become stronger and carry more material into space when they become red giants.
True
How much of the original mass is returned to the interstellar medium when a low-mass star ends it life with the ejection of a planetary nebula?
Almost half of its original mass is returned to the interstellar medium.
T or F
Low mass stars lose mass in the most dynamically and explosive ways.
False,
High mass stars lose mass much more dynamically and explosively
At the end of their lives what do supergiant and massive O and B stars explode into?
Suprenovae
What is the term for a gas in which atoms are missing some of their electrons?
Ion
What is the term used to describe the shape of the hot, ionized gas around the exploding supergiant or O or B star?
Bubble
T or F
Bubbles are easy to detect.
False.
Bubbles are not easy to detect
How are many bubbles observed?
Through radio emssion from the shell of gas that surround them
What is the term for the waves of pressure that move faster than the speed of light that are generated by supernovae?
Shock waves
What sweeps up surrounding gas as it travels, creating a wall of fast-moving gas on its leading edge?
Shock waves from supernovae
What is the term for the aftermath of a supernovae's shockwave, which compresses, heats, and ionizes all the interstellar gas it encounters?
Shock remnant
Eventually in what direction does the shocked gas radiate from most of its original energy?
Away from the original energy
What results when the top of a giant bubble breaks out of the disk, nothing remains to slow down it expansion except gravity?
A blowout
What is similar to a volcanic eruption on a galactic scale?
A blowout caused when a giant bubble breaks out of the disk.
What do supernovae emit that can cause genetic mutations in living organisms?
Cosmic rays
What are cosmic rays made up of?
1. electrons
2. protons
3. atomic nuclei

all zipping through interstellar space at close to the speed of light
How often do cosmic rays strike our bodies each second?
@ one cosmic ray strikes our bodies each second
At altitudes on Earth is the rate of bombardment of cosmic rays the highest?
The higher altitudes
In a bubble caused by a supernovae, what gas remains neutral rather than being ionized?
Hydrogen
What is the term for the gas in a bubble that remains neutral even though it is mixed with neutral atoms of helium and heavy elements in the usual proportions?
atomic hydrogen gas
T or F
Atomic hydrogen gas contains helium and heavy elements.
True
How do we map the distribution of atomic hydrogen gas in the Milky Way?
radio observations
How long is the radio wavelength of atomic hydrogen?
21 centimeter line
From direction(s) do we observe radio wavelengths indicating atomic hydrogen?
From all directions
What slowly draws blobs of atomic hydrogen together into tighter clumps, which radiate energy more efficiently as they grow denser?
Gravity
What process takes longer, star death, or star birth, or the cooling of the and contraction of the atomic hydrogen clouds?
Cooling and contraction of the atomic hydrogen clouds
What is the term used for the tiny, solid flecks of carbon and silicon minerals that resemble particles of smoke and form in the winds of red giant stars
Interstellar dust grains
What prevents us from seeing through the disk of the galaxy?
Interstellar dust grains
What percentage of the mass of atomic hydrogen clouds is made up of interstellar dust grains?
1 %
What is the term given to the coldest, densest collections of gas in the interstellar medium?
Molecular clouds
How are molecular clouds formed?
As the temperature drops further in the center of a cool cloud of atomic hydrogen
What is the term for congregating molecular clouds that hold up to a million solar masses of gas?
Giant Molecular Clouds
What is the estimated total mass of molecular clouds?
1. @ the same as the total mass of atomic hydrogen gas or
2. 5 billion solar masses
What is the average temperature of molecular gas?
@ few higher than absolute zero
What is the symbol for molecular hydrogen?
H
2
What gas do we use to study the composition of molecular clouds?
Carbon monoxide
Why do we use carbon monoxide to study molecular clouds?
it produces strong emission lines in the radio portion of the spectrum at the 10-30 K temperatures
Where in the Milky Way do molecular clouds tend to settle towards?
The central layers of the Milky Way's disk
What gives birth to a cluster of stars?
A large molecular cloud
What prevents much of the gas in a molecular cloud from turning into stars?
a.The radiation generated by a few stars formed in the newborn cluster, and
b.the ultraviolet photons from high-mass stars heat and ionize the gas, and
c.winds and radiation pressure push the ionized gas away
T or F
The star-gas-star cycle can go on forever.
False,
The star-gas-star cycle cannot go on forever
Why won't star formation go on forever?
1.Some of the galaxy's gas becomes permanently locked away in brown drawfs that never return material to space
2. stellar corpses are left behind in the form of white drawfs, neutron stars, and black holes
When is it estimated that star formation will cease?
50 billion years
What causes the erosion of molecular clouds causing them to glow?
Radiation
List the 7 ways that we can view the disk of the Milky Way:
1. 21cm radio emission of atomic hydrogen gas;
2. radio emission of carbon monoxide;
3. infrared emission from interstellar dust;
4. infrared emission from stars that penetrate clouds of gas and dust;
5. visible light emitted by stars that is scattered and absorbed by dust;
6. X-ray emission from hot gas bubbles and X-ray binaries
7. Gamma-ray emission from collisions of cosmic rays with atomic nuclei in interstellar clouds
T or F
New stars are spread evenly across the Milky Way.
False,
New stars are not spread evenly across the Milky Way.
T or F
Some regions of the Milky Way appear to be more fertile to forming new stars.
True
What is the most obvious clue in finding a region of active star formation?
A hot massive star
Why are hot massive stars signs for regions of star formation?
Because the live fast and die young, and therefore cannot move far from their birthmates
They signal the presences of star clusters
What in our galaxy signals the presence of star clusters?
Hot massive stars
What is the term for the colorful, wispy blobs of glowing gas found near hot stars?
Ionization nebulae
What are the 2 other names for ionization nebulae?
1. emission nebulae
2. H II regions (atomic hydrogen regions)
What causes ionization nebulae to glow?
electrons in their atoms are raised to high energy levels; or
ionized when they absorb ultraviolet photons from the hot stars;
they emit light as the electrons fall back to lower energy levels.
What nebula seen in our night sky is nearly unmatched in its spectacular beauty due to its glow?
Orion Nebula, in the sword of the constellation Orion
What causes the striking colors in ionization nebula?
Particular atomic transitions of electrons falling from one energy level to another
What color is the predominate color for ionization nebulae?
Red
Why are ionization nebula predominantly red?
all of the red photons generated when a hydrogen atom's electron falls from the energy level 3 to energy level 2
What photons are the most common emitted from ionization nebulae?
Ultraviolet
T or F
Ultraviolet photons can only be studied with ultraviolet telescopes.
True
What color is the starlight reflected from interstellar dust grains?
Blue and black
What is the name for nebulae that are bluer in color than the stars supplying the light because of the nature of light on the interstellar dust grains?
Reflection Nebulae
What makes up the black regions of a nebulae?
Dark, dusty gas clouds that block our view of the stars beyond them
T or F
The Spiral arms of the Milky Way is home to both molecular clouds and numerous clusters of young, bright blue stars surrounded by ionization nebulae.
True
Why do we know that the spiral arms of the Milky Way is fertile regions for star formation?
Presence of :
1. molecular clouds
2. numerous clusters of young, bright, blue stars surrounded by ionization nebulae
T or F
Stars near the center of a spiral galaxy complete their orbits faster (in less time) than stars far from the center.
True
What would eventually happen if the spiral arms of the galaxy moved along with the stars?
The spiral arms would tightly wind up around the center.
Why do we conclude that spiral arms of the galaxy are more like swirling ripples in a whirlpool rather than like fins of a giant pinwheel?
We don't generally see a arms tightly winding up.
What regions of the galaxy do we now recognize as the sites of star formation that propagate through the gaseous disk of a spiral galaxy
The spiral arms
What is believed to be responsible for the formation of the spiral arms?
Spiral density waves
What is the term for the gravitationally driven waves of enhanced density that move through a spiral galaxy and are responsible for maintaining its spiral arm?
Spiral density waves
What plays the role of a tractor in a spiral density wave?
Gravity
What plays the role of cars in a spiral density wave?
Stars and gas
What temporarily halt the escape of stars and gas clouds from completely escaping?
Spiral density wave
What is needed to generate a density wave within a galaxy's disk?
A gravitational tug from another galaxy
T or F
We don't observe any new stars in the halo of the Milky Way.
True
T or F
The spectra of halo stars show that they contain fewer elements than do disk stars.
True
What is the name given to the population of stars that contain both young stars and old stars, all of which have heavy-element proportions of about 2% , like our Sun?
Disk population
What population of stars have heavy-element proportions similar to our Sun?
Disk population
What population of stars consists of stars in the halo and bulge, both of which are roughly spherical in shape?
Spheroidal population
What population of stars are always old and therefor low in mass, with heavy-element proportions low?
Spheroidal population
What population of stars are considered Population I stars?
Disk population
What population of stars are considered Population II stars?
Spheroidal population
What population of stars have the rarest amounts of heavy elements?
Population II or Spheroidal Population
T or F
The halo of the Milky Way contains the cold, dense molecular clouds required for star formation.
False,
The halo of the Milky Way does NOT contain the cold, dense molecular clouds required for star formation.
What region of the Milky Way is the only place where molecular clouds are found?
Disk
T or F
The relative lack of heavy elements in halo stars indicates that they must have formed early in the galaxy's history.
True
Describe the most basic model explaining how the Milky Way formed?
Gravity from a giant cloud containing all the hydrogen and helium gas caused contraction and fragmentation to occur
What is the name for the basic model explaining how the Milky Way formed based on the gravity from a giant cloud?
Protogalactic cloud
Which stars formed first in the Protogalactic cloud model explaining the formation of the Milky Way?
Spheroidal population, the bulge and the halo
What is the term for the record that is written within the stars of the Milky Way?
Fossil record of the Milky Way
Beside the single protogalactic cloud theory, describe another theory involving protogalactic clouds?
The theory is that several protogalactic cloudes collided and combined to create the full protogalactic cloud that went on to become the Milky Way
Which is thought to be the more plausibe based on the ratio of heavy-elements in some stars?
The mulitple protogalactic clouds colliding theory
In what direction does the galactic center of the Milky Way reside?
Towards Sagittarius constellation
What is thought to be at the center of the Milky Way?
A large black hole
Why is it thought that a large black hole is at the center of the Milky Way?
Observations show that there are not nearly enough stars in this region to account for so much mass, even though stars there are much more crowded together than in our region of the galaxy.
How does the "black hole" thought to be at the center of the Milky Way behave differently from other black holes observed?
Matter appears to fall into it in big chunks instead of in the smooth, swirling flow of an accretion disk.