UNIT NINE: Matter and Motion in the Universe Chapter 26 The Solar System Chapter 27 Stars Chapter 28 Exploring the Universe Chapter Twenty-Eight: Exploring the Universe 28.1 Tools of Astronomers 28.2 Galaxies 28.3 Theories about the Universe Section 28.3 Learning Goals Explore theories about the origin of the universe. Discuss the evidence in support of the Big Bang theory. Describe planetary systems. 28.3 Doppler Shift In the 1800s, Christian Doppler discovered that when the source of a sound wave is moving, its frequency changes. The change in sound you hear is caused by a Doppler shift. Doppler shift is related to the net change between the source of the waves and the observer. 28.3 Doppler Shift Doppler shift also occurs with electromagnetic waves, such as visible light, X-rays, and microwaves. This phenomenon is an important tool used by astronomers to study the motion of objects in space. 28.3 The expanding universe The faster the source of light is moving away from the observer, the greater the redshift. The opposite (blueshift) happens when an object is moving toward the observer. 28.3 The expanding universe Edwin Hubble discovered that the farther away a galaxy was, the faster it was moving away from Earth. This concept came to be known as the expanding universe. 28.3 The Big Bang theory The theory that the universe was expanding implies the universe must have been smaller in the past than it is today. It implies that the universe must have had a beginning. Astronomers today believe the universe exploded outward from a single point. This idea is known as the Big Bang theory. 28.3 The Big Bang theory The Big Bang theory says the universe began as a huge explosion between 10 billion and 20 billion years ago. According to this theory, all matter and energy started in a space smaller than the nucleus of an atom. 28.3 Evidence for the Big Bang theory In the 1960s, Arno Penzias and Robert Wilson were trying to measure electromagnetic waves given off by the Milky Way. The “noise” these scientists found was the cosmic microwave background radiation predicted by the Big Bang theory. 28.3 Evidence for the Big Bang theory The proportion of hydrogen to helium is consistent with the physics of the Big Bang. If the universe were significantly older, there would be more heavy elements present compared with hydrogen and helium. 28.3 Planetary systems A star with orbiting planets is called a planetary system. Scientists now believe that planets are a natural by-product of the formation of stars. 28.3 How the solar system formed Scientists think that the solar system was formed out of the same nebula that created the Sun. 28.3 Binary stars A binary star is a system with two stars that are gravitationally tied and orbit each other. About half of the 60 nearest stars are in binary (or multiple) star systems. Optional* Investigation 28C The Time Machine Key Question: How long does it take for starlight to reach Earth? Searching the Cosmos Astrophysicist Dr. Hakeem Oluseyi (Oh-lu-SHAY-ee) is fascinated by stars. A physics and space science professor at the Florida Institute of Technology, he has invented several new instruments to give astronomers a closer look at the cosmos.