HW                                           Our Galaxy



1)  What is the diameter of the disk of the Milky Way?

A) 100 light years

B) 1,000,000 light years

C) 1,000 light years

D) 100,000 light years

E) 10,000 light years



2)  What kinds of objects lie in the halo of our galaxy?

A) gas and dust

B) O and B stars

C) open clusters

D) globular clusters

E) all of the above



3)  What makes up the interstellar medium?

A) K and M stars

B) open clusters

C) O and B stars

D) gas and dust

E) all of the above



4)  How can we see through the interstellar medium?

A) by using only the biggest telescopes

B) by observing only the brightest visible sources

C) by observing in high-energy wavelengths such as X rays and long wavelengths of light such as radio waves

D) by using telescopes above the earth's atmosphere

E) We cannot see through the interstellar medium.



5)  Approximately how far is the Sun from the center of the galaxy?

A) 28 light-years

B) 2,800 light-years

C) 28 million light-years

D) 28,000 light-years

E) 280 light-years



6)  All the iron on Earth originated from

A) nuclear fusion within the cores of high-mass stars.

B) the bombardment of comets in the late stages of planet formation.

C) white dwarfs.

D) the Big Bang, when the universe first began.

E) nuclear fusion within the cores of low-mass stars.



7)  Compared with our Sun, most stars in the halo are

A) young, red, and dim and have fewer heavy elements.

B) old, red, and dim and have fewer heavy elements.

C) old, red, and dim and have much more heavy element material.

D) young, blue, and bright and have much more heavy element material.

E) old, red, and bright and have fewer heavy elements.



8)  Compared with stars in the disk, orbits of stars in the halo

A) are elliptical, with random orientation.

B) are elliptical but orbiting in the same direction.

C) do not have to pass through the plane of the galaxy.

D) do not have to be around the galactic center.

E) are relatively uniform to each other.



9)  Approximately how long does it take the Sun to orbit the Milky Way Galaxy?

A) 23,000 years

B) 23 billion years

C) 2.3 million years

D) 230 million years

E) 230,000 years



10)  Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter?

A) The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.

B) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches are dark matter located in the halo.

C) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.

D) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter.



11)  Where does most star formation occur in the Milky Way today?

A) in the Galactic center

B) in the spiral arms

C) uniformly throughout the Galaxy

D) in the bulge

E) in the halo



12)  How do we learn about what is going on in the center of our own galaxy (the Milky Way)?

A) We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.

B) We must look at the centers of other galaxies and hope that ours is just like others.

C) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.

D) We cannot see the galactic center with visible or ultraviolet light, but radio and X rays from the center can be detected.



13)  What evidence supports the theory that there is a black hole at the center of our galaxy?

A) We can see gas falling into an accretion disk and central mass at the center of our galaxy.

B) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.

C) We observe a large, dark object that absorbs all light at the center of our galaxy.

D) We observe an extremely bright X-ray source at the center of our galaxy.

E) all of the above



14)  What is Sgr A *?

A) the brightest star in the constellation Sagittarius

B) a source that is bright in the visible wavelengths in the center of our galaxy

C) a source of bright X-ray emission coming from the entire constellation of Sagittarius

D) a source of bright radio emission in the center of our galaxy

E) the bulge at the center of our galaxy



15)  What do we call the bright, sphere-shaped region of stars that lie within a few thousand light-years of the center of the Milky Way Galaxy?

A) a globular cluster B)  the galaxy's bulge

C) the galaxy's halo D)  the galaxy's disk



16)  What are the Magellanic Clouds?

A) two small galaxies that probably orbit the Milky Way Galaxy

B) the clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy

C) two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere

D) star-forming clouds found in the constellation Orion



17)  What do we mean by the star-gas-star cycle?

A) It is the set of nuclear reactions by which heavy elements are produced in the cores of massive stars.

B) It is another name for what is sometimes called the galactic fountain, in which gas rises out of the disk and then falls back down.

C) It is the idea that stars in close binary systems can exchange gas with one another.

D) It is the continuous recycling of gas in the galactic disk between stars and the interstellar medium.



18)  Which of the following correctly describes dark matter?

A) It is a minor constituent of the gas in the interstellar medium.

B) It is matter that emits only infrared light, which our eyes cannot see.

C) It is another name for black holes, which emit no light.

D) It is matter that exerts a gravitational effect but does not emit any light we have been able to detect.



19)  Where does most star formation occur in the Milky Way Galaxy?

A) It occurs throughout the disk of the galaxy at a uniform rate.

B) It occurs in the galaxy's spiral arms.

C) It occurs around the central bulge.

D) It occurs within the halo.



20)  If we could see our own galaxy from 2 million light-years away, it would appear 

A) like a single, dim star.

B) to be a flattened disk with a central bulge and spiral arms.

C) to fill the sky with widely spaced stars.

D) as a faintly glowing band of light stretching all the way around the sky.





1)  D



2)  D



3)  D



4)  C



5)  D



6)  A



7)  B



8)  A



9)  D



10)  A



11)  B



12)  D



13)  B



14)  D



15)  B



16)  A



17)  D



18)  D



19)  B



20)  B