Ch20

The graph of Hubble's law shows that galaxies with high speeds as measured from Earth are __________.

By looking at the graph of Hubble's law, what can we say about the galaxies that have the lowest speeds?

Suppose that galaxy B is twice as far from Earth as galaxy A. Hubble's law predicts that galaxy B will be moving away from Earth with approximately _____.

Imagine that when we looked out into the universe we found that the light from all galaxies was blueshifted (rather than redshifted) and that the light from the most distant galaxies was blueshifted by the greatest amount. Which statement best describes what we would conclude about the motions of galaxies in this case?

The age of the universe is related to the slope of the graph of Hubble's law, and current data put the age of the universe at about 14 billion years. Suppose that future observations showed that the slope of Hubble's law on the graph is actually steeper than that shown. In that case, the age of the universe would be _________ than 14 billion years because the universe is expanding ______ than current data suggest. (Each choice gives words to fill in the two blanks, separated by a slash.)

Which of the following best describes the status of the Milky Way in our local group of galaxies

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

A standard candle is _________.

What is main-sequence fitting?

What is a Cepheid variable?

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

What does Hubble's law tell us?

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?

Current estimates place the age of the universe at about ______.

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

Based on the number of galaxies visible in the Hubble eXtreme Deep Field (Figure 20.1 in your text), the estimated number of galaxies in our observable universe is about ______.