What is located in the nucleus of the Galaxy?

Which statement about the Milky Way Galaxy is correct?

What was the Shapley–Curtis debate all about? Was a winner declared at the end of the debate? Whose ideas turned out to be correct?

How did Edwin Hubble prove that M31 is not a nebula in our Milky Way Galaxy?

What observations led Harlow Shapley to conclude that we are not at the center of the Galaxy?

Explain why globular clusters spend more time in the galactic halo than in the plane of the disk, even though their eccentric orbits take them across the disk of the Galaxy.

How do hydrogen atoms generate 21-cm radiation? What do astronomers learn about our Galaxy from observations of that radiation?

Why do astronomers believe that vast quantities of dark matter surround our Galaxy?

Why are there no massive O and B stars in globular clusters?

What evidence indicates that a supermassive black hole is located at the center of our Galaxy?

What are the least massive galaxies in the universe?

Spiral density waves are directly responsible for which of the following?

Which of the following statements about the motion of galaxies is correct?

What is the common name for the sonic boom created by lightning?

In spiral galaxies, what spectral classes of stars are only found in spiral arms?

What is the Hubble classification scheme? Which category includes the biggest galaxies? Into which category do the smallest galaxies fall? Which type of galaxy is the most common?

In which Hubble types of galaxies are new stars most commonly forming? Describe the observational evidence that supports your answer.

What is the difference between a flocculent spiral galaxy and a grand-design spiral galaxy?

Briefly describe how the theory of self-propagating star formation accounts for the existence of spiral arms in some spiral galaxies.

Briefly describe how the spiral density wave theory accounts for the existence of spiral arms in some spiral galaxies.

How is it possible that galaxies in our Local Group still remain to be discovered? In what part of the sky are these galaxies located? What sorts of observations might reveal these galaxies?

Can any galaxies besides our own be seen with the naked eye? If so, name one.

What is the difference between a rich cluster and a poor cluster of galaxies? What is the difference between a regular cluster and an irregular cluster of galaxies?

Why do astronomers believe that considerable quantities of dark matter must exist in clusters of galaxies?

What is the Hubble law?

Some galaxies in the Local Group exhibit blueshifted spectral lines. Why are these blueshifts not violations of the Hubble law?

What is a standard candle? Why are standard candles important to astronomers trying to measure the Hubble constant?

What kinds of stars would you expect to find populating the space between galaxies in a cluster?

What is a double-radio source seen along one axis of a jet called?

What two things does the engine of a quasar contain?

Suppose you suspected a certain object in the sky to be a quasar. What sort of observations would you perform to confirm your hypothesis?

What is an active galaxy? List the different kinds of active galaxies. How do they differ from one another?

Why do astronomers believe that the energy-producing region of a quasar is very small?

How is synchrotron radiation produced?

What evidence indicates that quasars are extremely distant active galaxies?

What is a double-radio source?

What is a supermassive black hole? What observational evidence suggests that supermassive black holes are located at the centers of many galaxies?

Why do many astronomers believe that the engine at the center of a quasar is a supermassive black hole surrounded by an accretion disk?

How does the orientation of the jets that emanate from the center of a galaxy (relative to our line of sight) relate to the type of active galaxy that we observe?

Why do astronomers not detect 21-cm radiation from the hydrogen in giant molecular clouds?

Describe the rotation curve you would get if the Galaxy rotated like a rigid body.

Compare the apparent distribution of open clusters, which contain young stars, with the distribution of globular clusters in the Milky Way. Why are open clusters also referred to as galactic clusters?

In the 1960s, some astronomers suggested that quasars might be compact objects ejected at high speeds from the centers of nearby ordinary galaxies. Why do astronomers now believe that is not correct? (Hint: Consider the directions in which those objects would be ejected.)

When quasars were first discovered, many astronomers were optimistic that these extremely luminous objects could be used to probe distant regions of the universe. For example, it was hoped that quasars would provide high-redshift data from which the Hubble constant could be more accurately determined. Why have these hopes not been realized?

Discuss the advantages and disadvantages (for example, reliability, repeatability, etc.) of using the various standard candles to determine extragalactic distances.

Discuss whether the various Hubble types of galaxies actually represent some sort of evolutionary sequence.

Discuss the sorts of phenomena that can occur when galaxies collide. Do you think that such collisions can change the Hubble type of a galaxy? Explain your answers.

From what you know about stellar evolution, the interstellar medium, and spiral density wave theory, explain the appearance and structure of the spiral arms of grand-design spiral galaxies.

Does the Sun move in the Milky Way? If so, describe its motion.

About what fraction (or percent) of the matter in the Milky Way can astronomers see with current technology?

Where in the Galaxy is the solar system located?

Is the Milky Way in close contact with other galaxies? Explain.

What shape(s) do galaxies have?

With most galaxies in the universe moving away from us equally in all directions, are we at the center of the universe? Explain.

Are galaxies uniformly distributed throughout the universe? Explain your answer.

Is the Milky Way Galaxy moving through the universe? Justify your answer.

What is a quasar?

What does a quasar look like through an optical telescope?