Review the events listed under “Work, Exchange, and Technology” on the thematic timeline on page 283. In what ways was the economy different in 1860 from what it had been in 1800? Which factors listed in the thematic timeline best explain the changes?

Select the correct answer. what was edwin hubble's contribution to the field of astronomy? a. he discovered variable stars. b. he proved that the heliocentric model accurately described our solar system. c. he found a relationship between the period luminosity and distance of stars. d. he proved that the universe is finite. e. he discovered that the universe was expanding.