31 terms

NATS 1740 Assignment 19

PLAY
Which of these galaxies is most likely to be oldest?

1. a galaxy in the Local Group
2. a galaxy observed at a distance of 5 billion light-years
3. a galaxy observed at a distance of 10 billion light-years
1. a galaxy in the Local Group
Which of these galaxies would you most likely find at the center of a large cluster of galaxies?

1. a large spiral galaxy
2. a large elliptical galaxy
3. a small irregular galaxy
2. a large elliptical galaxy
About how many galaxies are there in a typical cluster of galaxies?

2. a few dozen
3. a few hundred
2. a few dozen
When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of

1. X rays.
2. slightly more energetic ultraviolet light.
3. visible light.
3. visible light.
Why do virtually all the galaxies in the universe appear to be moving away from our own?

1. Because we are located near where the Big Bang happened.
2. Because we are located near the center of the universe.
3. Observers in all galaxies observe a similar phenomenon because of the universe's expansion.
3. Observers in all galaxies observe a similar phenomenon because of the universe's expansion.
If you observed the redshifts of galaxies at a given distance to be twice as large as they are now, then you would determine a value for Hubble's constant that is

1. twice as large as its current value.
2. equal to its current value.
3. half its current value.
1. twice as large as its current value.
Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately

1. 100 billion.
2. 100 million.
3. 10 billion.
4. 1 trillion.
5. 1 billion.
1. 100 billion.
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest?

1. the one that is closest to us
2. the one that is farthest away
3. the one that is reddest in color
4. the one that appears smallest in size
5. the one that is bluest in color
2. the one that is farthest away
Which of the following types of galaxies are most spherical in shape?

1. irregulars
2. spirals
3. lenticulars
4. ellipticals
4. ellipticals
Which of the following types of galaxies are reddest in color?

1. spirals
2. lenticulars
3. ellipticals
4. irregulars
3. ellipticals
Which of the following statements about galaxies is true?

1. Small galaxies outnumber large galaxies and produce most of the light in the universe.
2. Most galaxies in the universe are about the same size as the Milky Way.
3. There is an approximately equal number of small and large galaxies in the universe and together they each contribute an equal amount of light.
4. Galaxies come in a wide variety of shapes and sizes but are all very blue in color.
5. Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.
5. Small galaxies outnumber large galaxies but large galaxies produce most of the light in the universe.
Which types of galaxies have a clearly defined spheroidal component?

1. irregulars only
2. lenticulars only
3. ellipticals only
4. spirals only
5. all but irregulars
5. all but irregulars
Which types of galaxies have a clearly defined disk component?

1. irregulars only
2. lenticulars only
3. ellipticals only
4. spirals only
5. spirals and lenticulars
5. spirals and lenticulars
Compared to spiral galaxies, elliptical galaxies are

1. always much smaller.
2. redder and rounder.
3. redder and flattened.
4. bluer and flattened.
5. bluer and rounder.
2. redder and rounder.
How does a lenticular galaxy differ from a normal spiral galaxy?

1. It is flatter in shape.
2. It has an elongated bulge resembling a bar more than a sphere.
3. It has no spiral arms.
4. It has no bulge.
5. It has no gas or dust.
3. It has no spiral arms.
The disk component of a spiral galaxy includes which of the following parts?

1. globular clusters
2. bulge
3. spiral arms
4. halo
5. all of the above
3. spiral arms
What is the major difference between an elliptical galaxy and a spiral galaxy?

1. Elliptical galaxies are not as big as spiral galaxies.
2. A spiral galaxy has a spherical halo.
3. An elliptical galaxy lacks a disk component.
4. There are no dwarf spiral galaxies, but there are dwarf ellipticals.
5. A spiral galaxy contains mostly younger stars.
3. An elliptical galaxy lacks a disk component.
Most large galaxies in the universe are

1. elliptical.
2. abnormal.
3. spiral or lenticular.
4. irregular.
3. spiral or lenticular.
Which of the following types of galaxies are most commonly found in large clusters?

1. ellipticals
2. irregulars
3. lenticulars
4. spirals
1. ellipticals
Which of the following is true about irregular galaxies?

1. They are composed solely of old stars.
2. They have reddish colors.
3. They generally have significant bulge populations.
4. They have well defined spiral arms.
5. They were more common when the universe was younger.
5. They were more common when the universe was younger.
How was Edwin Hubble able to use his discovery of a Cepheid in Andromeda to prove that the "spiral nebulae" were actually entire galaxies?

1. From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
2. He used main-sequence fitting to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
3. He measured the stellar parallax of the Cepheid in Andromeda, was able to determine the distance to it, and showed that it was far outside the Milky Way Galaxy.
4. Since a Cepheid is a type of luminous galaxy, when he found it in Andromeda he was able to prove that Andromeda was a separate galaxy from the Milky Way.
5. There are no Cepheids in the Milky Way, so his discovery proved that it had to be in another galaxy.
1. From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda and show that it was far outside the Milky Way Galaxy.
What two quantities did Edwin Hubble plot against each other to discover the expansion of the Universe?

1. luminosity and temperature
2. velocity and temperature
3. velocity and distance
4. luminosity and distance
5. age and distance
3. velocity and distance
What is Hubble's law?

1. The longer the time period between peaks in brightness, the greater the luminosity of the Cepheid variable star.
2. The faster a spiral galaxy's rotation speed, the more luminous it is.
3. The faster a spiral galaxy's rotation speed, the less luminous it is.
4. The recession velocity of a galaxy is inversely proportional to its distance from us.
5. The recession velocity of a galaxy is directly proportional to its distance from us.
5. The recession velocity of a galaxy is directly proportional to its distance from us.
Which of the following is a consequence of Hubble's Law?

1. the closer a galaxy is to us, the faster it moves away from us
2. more distant galaxies appear younger
3. the more distant a galaxy is from us, the faster it moves away from us
4. all galaxies are moving away from us equally fast
5. the Big Bang
3. the more distant a galaxy is from us, the faster it moves away from us
What is the primary practical difficulty that limits the use of Hubble's law for measuring distances?

1. The motion of Earth relative to the Milky Way is difficult to account for.
2. We do not know Hubble's constant very accurately yet.
3. Redshifts of galaxies are difficult to measure.
4. The recession velocities of distant galaxies are so great that they are hard to measure.
5. Hubble's law is only useful theoretically; it is difficult to use in practice.
2. We do not know Hubble's constant very accurately yet.
Based on current estimates of the value of Hubble's constant, how old is the universe?

1. between 20 and 40 billion years old
2. between 16 and 20 billion years old
3. between 8 and 12 billion years old
4. between 4 and 6 billion years old
5. between 12 and 16 billion years old
5. between 12 and 16 billion years old
Why can't we see past the cosmological horizon?

1. The cosmological horizon is infinitely far away, and we can't see to infinity.
2. Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
3. We do not have telescopes big enough.
4. The universe extends only to this horizon.
5. We do not have sensitive enough detectors.
2. Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
Following are a number of distinguishing characteristics of spiral and elliptical galaxies. Match each characteristic to the appropriate galaxy type.

- have a flattened disk of stars
- are rare in central regions of galaxy clusters
- are more reddish in color
- contain many bright, hot stars
- have significant, ongoing star formation
- contain primarily old, low-mass stars
- contain abundant clouds of cool gas and dust
Spiral galaxies
- contain abundant clouds of cool gas and dust
- are rare in central regions of galaxy clusters
- have significant, ongoing star formation
- contain many bright, hot stars
- have a flattened disk of stars

Elliptical galaxies
- are more reddish in color
- contain primarily old, low-mass stars
The following figures give the approximate distances of five galaxies from Earth. Rank the galaxies based on the speed with which each should be moving away from Earth due to the expansion of the universe, from fastest to slowest.

- 800 million ly
- 2 billion ly
- 70 million ly
- 230 million ly
- 5 billion ly
- 5 billion ly
- 2 billion ly
- 800 million ly
- 230 million ly
- 70 million ly
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on their distance from Earth, from farthest to closest.

- 18,730 km/s
- 5,264 km/s
- 130,000 km/s
- 45,000 km/s
- 1,577 km/s
- 130,000 km/s
- 45,000 km/s
- 18,730 km/s
- 5,264 km/s
- 1,577 km/s
The following figures give the approximate speeds at which five galaxies are moving away from Earth due to the expansion of the universe. Rank the galaxies based on the amount of redshift that would be observed in each galaxy's spectrum, from largest to smallest.

- 18,730 km/s
- 5,264 km/s
- 130,000 km/s
- 45,000 km/s
- 1,577 km/s
- 130,000 km/s
- 45,000 km/s
- 18,730 km/s
- 5,264 km/s
- 1,577 km/s