Chapter 20
Basic Skills/Definitions Quiz
Part A
Based on the number of galaxies visible in the Hubble Deep Field (Figure 20.1 in your text), the number of galaxies in our observable universe is estimated to be somewhere around ______.
Hint A.1
Study Section 20.1

80 billion Infinity 50,000 80 million
Part B
Which of the following is NOT one of the three major categories of galaxies?
Hint B.1
Study Section 20.1

Elliptical galaxies. Spiral galaxies. Globular galaxies. Irregular galaxies.
Part C
Galaxies with disks but no evident spiral arms are called ______.
Hint C.1
Study Section 20.1

irregular galaxies barred spiral galaxies spheroidal components lenticular galaxies
Part D
Which of the following best describes the status of the Milky Way in our Local Group of galaxies?
Hint D.1
Study Section 20.1

It is one of about a dozen large spiral galaxies in the group. It is quite average among the galaxies in the group. It is one of the two largest galaxies in the group. It is by far the largest galaxy in the group.
Part E
A standard candle is ______.
Hint E.1
Study Section 20.3

another name for a main-sequence star. another name for a barred-spiral galaxy. a light source of known luminosity. a 7-cm wax candle.
Part F
What is main-sequence fitting?
Hint F.1
Study Section 20.2

It is the way we construct an H-R diagram by plotting the surface temperatures and luminosities of stars. A way of forcing stars to fit into a standard main sequence, even when they have some unusual characteristics. A method for determining the distance to a star cluster by assuming that its main sequence should line up with the main sequence on a standard H-R diagram. A method for determining the age of a star cluster.
Part G
What is a Cepheid variable?
Hint G.1
Study Section 20.2

It is a type of galaxy that varies in its light output. It is a main sequence star of spectral type B5. A bright source of variable X-ray emission, thought to harbor a supermassive black hole. A type of very luminous star that makes an excellent standard candle.
Part H
What two properties of a Cepheid variable are directly related to one another?
Hint H.1
Study Section 20.2

Its luminosity and its mass. Its mass and its distance. The period between its peaks of brightness and its luminosity. The period between its peaks of brightness and its distance.
Part I
What does Hubble's law tell us?
Hint I.1
Study Section 20.3

The more distant a galaxy, the faster it is moving away from us. The faster a spiral galaxy's rotation speed, the more luminous it is. For every force, there is an equal and opposite reaction force. The longer the period of a Cepheid variable, the greater its luminosity.
Part J
Given that white dwarf supernovae are such good standard candles, why don't we use them to measure the distance to ALL galaxies?
Hint J.1
Study Section 20.2

They are rare events, so we have observed them in only a tiny fraction of all galaxies. We would, but we don't have enough telescopes. We cannot see them beyond a distance of about 100 million light-years. They can occur only in spiral galaxies, not elliptical galaxies.
Part K
The Tully-Fisher relation allows us to estimate the luminosity of a spiral galaxy by measuring its ______.
Hint K.1
Study Section 20.2

period of variability in brightness. rotation rate. redshift. distance.
Part L
Overall, what is our most accurate technique for measuring the distance to a nearby star?
Hint L.1
Study Section 20.2

Hubble's law stellar parallax main-sequence fitting radar ranging
Part M
When we use an analogy that represents the expanding universe with the surface of an expanding balloon, what does the inside of the balloon represent?
Hint M.1
Study Section 20.3

Regions of the universe beyond the Milky Way Galaxy. The inside of the balloon does not represent any part of our universe. The entire universe. The center of the universe.
Part N
If we say that a galaxy has a lookback time of 1 billion years, we mean that ______.
Hint N.1
Study Section 20.3

It is 400 million years old. It is now 1 billion light-years away. It was 1 billion light-years away when the light left the galaxy. Its light traveled through space for 1 billion years to reach us.
Part O
Cosmological redshift is the result of ______.
Hint O.1
Study section 20.3

the high speeds at which galaxies move in clusters. Tully-Fisher relation. the expansion of the universe. supermassive black holes.
Part P
Although the entire universe may be much larger than our observable universe, we can see only within our observable universe. The "boundary" of our observable universe is called ______.
Hint P.1
Study Section 20.3

the Big Bang. the lookback time. the Tully-Fisher relation. the cosmological horizon.
Part Q
Current estimates place the age of the universe at about ______.
Hint Q.1
Study Section 20.3 (and chapter 1!)

14 thousand years. 14 billion years. 14 million years. 14 trillion years.
Part R
You observe the peak brightnesses of two supernovae. Supernova A is 4 times fainter than Supernova B. What can you say about their relative distances?
Hint R.1
Study Section 20.2, and review the luminosity-distance-brightness relationship.

Supernova A is 4 times farther than Supernova B. Supernova A is 2 times farther away than Supernova B. Supernova B is 4 times farther than Supernova A. We can't say anything about their relative distances because we do not have enough information. Supernova B is 2 times farther than Supernova A.
Part S
Which of the following systems is experiencing the cosmological expansion of space?
Hint S.1
Study Section 20.3

The Local Group The Milky Way. Space is expanding in ALL of these systems. Clusters of galaxies. The observable universe
Part T
The redshift of galaxy A is 0.10 and the redshift of galaxy B is 0.20. What can you say about their approximate relative distances?
Hint T.1
Study Section 20.3.

Galaxy A is twice as far as Galaxy B. Galaxy A is four times as far as Galaxy B. Not enough information to say - you need the Hubble constant to answer this question. Galaxy B is four times as far as Galaxy A. Galaxy B is twice as far as Galaxy A.