Consider the following hypothetical observations, some of which are real and some of which are fictional. Process of Science: Testing the Expanding UniverseĪ. What can you say about their relative distances? Supernova A is twice as far away as Supernova B.
Supernova A is only one-quarter as bright as Supernova B. a light source of known luminosity What is main-sequence fitting? 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 What is a Cepheid variable? A type of very luminous star that makes an excellent standard candle You observe the peak brightnesses of two white dwarf supernovae. 10,000 solar luminosities Overall, what is our most accurate technique for measuring the distance to a nearby star? Stellar Parallax A standard candle is _.
2000 solar luminosities Estimate the luminosity of the Cepheid with a period of 35 days. Which kind of object is the best standard candle for measuring distances to extremely distant galaxies? a white dwarf supernova Estimate the luminosity of the Cepheid with a period of 8 days. (Each choice gives words to fill in the two blanks, separated by a slash.) younger/more rapidly We determine the distance of a Cepheid by determining its luminosity from the period-luminosity relation and then applying the inverse square law for light. In that case, the age of the universe would be _ than 14 billion years because the universe is expanding _ than current data suggest. Suppose that future observations showed that the slope of Hubble's law on the graph is actually steeper than that shown. 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. Which statement best describes what we would conclude about the motions of galaxies in this case? All are moving toward Earth, with distant galaxies moving faster than nearby galaxies. twice the velocity of galaxy A 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. Hubble's law predicts that galaxy B will be moving away from Earth with approximately _. (This is the essence of Hubble's law: More distant galaxies are moving away from us faster) By looking at the graph of Hubble's law, what can we say about the galaxies that have the lowest speeds? They are moving away from Earth and are closer to Earth than galaxies with high speeds Suppose that galaxy B is twice as far from Earth as galaxy A. moving away from Earth and are farther from Earth than galaxies with lower speeds The graph of Hubble's law shows that galaxies with high speeds as measured from Earth are _. According to Hubble's law, approximately how far away is the galaxy? 1.4 billion light-years Based on what you have learned, which of the following best describes the meaning of Hubble's constant (H0 )? It describes the expansion rate of the universe, with higher values meaning more rapid expansion. measuring the distances to many distant galaxies with a standard candle technique Suppose that you measure a galaxy's redshift, and from the redshift you determine that its recession velocity is 30,000 (3×104) kilometers per second. But before we can use Hubble's law, we must first calibrate it by _. the distance of a galaxy and the speed at which it is moving away from us We can always determine the recession velocity of a galaxy (at least in principle) from its redshift.
If that method led us to underestimate the Earth-Sun distance by 10%, how would it affect other measurements in the distance chain? They would all be off by the same 10% Which technique is the most useful for measuring the distance to a galaxy located 10 million light-years away? Cepheids Hubble's law expresses a relationship between _.
Imagine that radar had never been invented and that we instead had to rely on a less reliable method of measuring distances in our solar system.
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