Quiz 5

Question 1

William Herschel’s work of counting the number of stars in different directions led him to conclude that:

Answer 1

The stars of the galaxy are shaped in a disk.

Question 2

Cepheid Variable Stars are used to:

Answer 2

Measure great distances in space.

Question 3

Harlow Shapley’s work with globular clusters at the Mt. Wilson observatory just north of Pasadena lead to the understanding of:

Answer 3

The size of the galaxy.

Question 4

What is the approximate diameter of the galaxy?

Answer 4

75,000 light years.

Question 5

An important tool for galactic astronomers is to observe 21 cm radiation caused by the spin-flip transitions in neutral hydrogen. The radiation is useful because:

Answer 5

• It’s long wavelength can easily pass through gas and dust in the galaxy.
• It can be used to construct the rotation curve for the galaxy.
• It is emitted by the most common atom in the universe, hydrogen.

Question 6

The rotation curve of a galaxy shows that if you look at the speed of stars and gas that orbit the galaxy that their speed does not decrease as would be expected by Kepler’s second law. This leads to one of the fundamental problems of modern astronomy and currently is best explained by:

Answer 6

The existence of dark matter.

Question 7

The spiral structure of galaxies is now thought to be best explained by:

Answer 7

The density wave theory.

Question 8

The nucleus of our galaxy is now thought to be an energetic environment because of the presence of:

Answer 8

A supermassive black hole.

Question 9

What are the four main galaxy shapes?

Answer 9

• Spiral.
• Barred spiral.
• Elliptical.
• Irregular.

Question 10

The relationship between the distance a galaxy is from Earth and the speed it appears to be moving away from us is called:

Answer 10

Hubble’s Law.