Key Ideas and Terms

15-1 The darkness of the night sky tells us about the nature of the universe

15-2 Our observations show us that the universe is expanding

15-3 The expanding universe emerged from a cataclysmic event called the Big Bang

15-4 The microwave radiation that fills all space is compelling evidence of a hot Big Bang

15-5 The universe was a rapidly expanding, hot, opaque plasma during its first 300,000 years and has slowly cooled

15-6 The shape of the universe indicates its matter and energy content

15-7 Observations of distant supernovae indicate that we live in an accelerating universe