Question 1

Overall,what is our most accurate technique for measuring the distance to a nearby star?

Accepted Answer

Stellar parallax is the most accurate technique for measuring the distance to a nearby star as it relies on measuring the shift of a star's position relative to background stars as the Earth orbits the Sun. This phenomenon allows astronomers to calculate the distance of a star using basic trigonometry. Radar ranging is used for measuring distances to planets and other objects within our solar system, Hubble's law is used for measuring the distance to objects at very large scales, and white dwarf supernovae are used for measuring distances to more distant galaxies. However, for nearby stars, stellar parallax is the most accurate technique.

Question 2

Current estimates place the age of the universe at about

Accepted Answer

The current estimate places the age of the universe at about 14 billion years based on observations of cosmic microwave background radiation and other astronomical data. Choices A, B, and D are incorrect as they do not align with the current scientific consensus on the age of the universe.

Question 3

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?

Accepted Answer

The analogy only represents the surface of the balloon expanding, which is like the universe expanding. The inside of the balloon does not represent any specific part of our universe.

Question 4

The most basic difference between elliptical galaxies and spiral galaxies is that

Accepted Answer

Elliptical galaxies lack the prominent disk structure that characterizes spiral galaxies, which includes the spiral arms where active star formation occurs.

Question 5

You observe the peak brightnesses of two white dwarf supernovae.Supernova A is only 1/4 as bright as Supernova B.What can you say about their relative distances?

Accepted Answer

The brightness of a supernova decreases with the square of the distance. If Supernova A is 1/4 as bright as Supernova B, it is twice as far away, because (1/2)^2 = 1/4.

Question 6

Which of the following best describes the status of the Milky Way in our Local Group of galaxies?

Accepted Answer

The Milky Way is one of the two largest galaxies in the Local Group, the other being the Andromeda Galaxy (M31). These two galaxies are significantly larger and more massive than the other members of the Local Group, which consists of more than 54 galaxies, most of which are dwarf galaxies.

Question 7

What does Hubble's law tell us?

Accepted Answer

Hubble's law states that the more distant a galaxy is, the faster it is moving away from us. This is due to the expansion of the universe.

Question 8

If we say that a galaxy has a lookback time of 1 billion years,we mean that

Accepted Answer

Lookback time refers to the amount of time it took for light from an object to reach us. Therefore, if a galaxy has a lookback time of 1 billion years, it means that it took 1 billion years for its light to travel through space and reach us.

Question 9

The fact that the universe is expanding means that space itself is growing within

Accepted Answer

The expansion of the universe is observed by the fact that distant galaxies appear to be moving away from us, and this effect is observed uniformly throughout the observable universe. Therefore, the expansion of space is occurring within the entire observable universe, not just within a single galaxy (A), group of galaxies (D), or cluster of galaxies (B).

Question 10

Given that white dwarf supernovae are such good standard candles,why don't we use them to measure the distance to all galaxies?

Accepted Answer

White dwarf supernovae, while excellent standard candles due to their consistent luminosity, are rare events. This rarity means they have only been observed in a small fraction of galaxies, limiting their use for measuring distances to all galaxies.

Question 11

Galaxies with disks but no evident spiral arms are called

Accepted Answer

Galaxies with disks but no evident spiral arms are called lenticular galaxies. They are often referred to as intermediate between spiral and elliptical galaxies, with a smooth central bulge and a disk-like structure.

Question 12

In a photo like the Hubble Deep Field (Figure 20.1 in your textbook),we see galaxies in many different stages of their lives.In general,which galaxies are seen in the earliest (youngest)stages of their lives?

Accepted Answer

The galaxies that are farthest away are seen in their earliest stages of life because the light from these galaxies has taken the longest time to reach us. This means we are seeing them as they were in the distant past, closer to the beginning of the universe.

Question 13

Which of the following statements about types of galaxies is not true?

Accepted Answer

Elliptical galaxies are typically redder and less dusty than spiral galaxies, as they are made up of older stars with less ongoing star formation.

Question 14

A standard candle is

Accepted Answer

A standard candle is a light source of known luminosity. This can be used to calculate the distance to a celestial object by comparing its observed brightness to the expected brightness of the standard candle.

Question 15

Hubble's galaxy classification diagram (the "tuning fork")

Accepted Answer

Hubble's tuning fork diagram classifies galaxies based on their shapes (ellipticals, spirals, and barred spirals) without implying any evolutionary relationship between these different types.

Question 16

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

Accepted Answer

The boundary of our observable universe is called the cosmological horizon, beyond which we cannot observe because light has not had enough time to reach us since the Big Bang.

Question 17

What two observable properties of a Cepheid variable are directly related to one another?

Accepted Answer

The period between the peaks of brightness of a Cepheid variable and its luminosity are directly related to one another. This means that astronomers can use an observed period to estimate the star's luminosity, which in turn can be used to calculate its distance. This relationship is known as the period-luminosity relationship, and it has been used to measure distances to many galaxies beyond our own Milky Way. The other choices listed are not directly related to each other in the same way as the period-luminosity relationship.

Question 18

Cosmological redshift is the result of

Accepted Answer

Cosmological redshift is the result of the expansion of the universe. As the universe expands, the light from distant galaxies is stretched, resulting in a shift towards longer wavelengths, which appear as redshifts in spectral lines. This is different from the redshift caused by the motion of galaxies within clusters, known as Doppler redshift. The age or type of stars in galaxies and the presence of supermassive black holes do not have a direct impact on cosmological redshift.

Question 19

What is a Cepheid variable?

Accepted Answer

Cepheid variables are a type of very luminous star that pulsates in brightness with a period directly related to their luminosity. This makes them excellent standard candles for measuring distances in astronomy, particularly in other galaxies.

Question 20

Spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A.According to Hubble's law,what can you say about their approximate relative distances?

Accepted Answer

Hubble's law states that the recessional velocity of a galaxy is proportional to its distance from us. Since the spectral lines from Galaxy B are redshifted from their rest wavelengths twice as much as the spectral lines from Galaxy A, we can infer that Galaxy B is moving away from us faster than Galaxy A. Therefore, according to Hubble's law, Galaxy B is also farther away from us than Galaxy A. The redshift factor is proportional to the relative velocity and therefore, the redshift factor of Galaxy B is double that of Galaxy A, which implies that Galaxy B is twice as far away from us as Galaxy A. Hence, the correct answer is D.

Quiz 20: Galaxies and the Foundations of Modern Cosmology