Section 3 Galaxies Bellringer Concerning a spiral galaxy

Section 3 Galaxies Bellringer Concerning a spiral galaxy: • Describe the evidence that indicates that the galaxy is rotating. • What other objects have you seen look similar to a spiral galaxy? Do they rotate? Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 3 Galaxies Types of Galaxies • Spiral Galaxies have a bulge at the center and spiral arms. • The Milky Way Astronomers think that our solar system is in a spiral galaxy. • Elliptical Galaxies About one-third of all galaxies are simply massive blobs of stars. These are called elliptical galaxies. • Irregular Galaxies Irregular galaxies are galaxies that don’t fit into any other class. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 3 Galaxies Contents of Galaxies • Gas Clouds Galaxies have nebulas (or nebulae), which are large clouds of gas and dust. • Star Clusters A globular cluster is a group of stars that looks like a ball. Open clusters are groups of closely grouped stars that are usually located along the spiral disk of a galaxy. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 3 Galaxies Origin of the Galaxies • Time Travel Looking at distant galaxies reveals what early galaxies looked like. • Quasars are starlike sources of light that are extremely far away. Some scientists think that quasars may be the core of young galaxies that are in the process of forming. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 4 Formation of the Universal Expansion • Galaxy Movement To understand how the universe formed, scientists study the movement of galaxies. • A Raisin-Bread Model The universe, like the rising raisin bread dough, is expanding. Think of the raisins in the dough as galaxies. As the universe expands, the galaxies move farther apart. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Formation of the Universe The Big Bang Theory Section 4 • A Tremendous Explosion The theory that the universe began with a tremendous explosion is called the big bang theory. The big bang theory is illustrated on the next slide. • Cosmic Background Radiation In 1964, two scientists using a huge antenna accidentally found radiation coming from all directions in space. One explanation for this radiation is that it is cosmic background radiation left over from the big bang. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 4 The Big Bang Theory Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 4 Formation of the Universe Structure of the Universe • Universe is Systematic The universe contains a variety of objects. But these objects in the universe are not simply scattered through the universe in a random pattern. The universe has a structure that is loosely repeated over and over again. • A Cosmic Repetition Every object in the universe is part of a larger system. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 4 Formation of the Universe How Old Is the Universe? • Age of the Universe One way scientists can calculate the age of the universe is to measure the distance from Earth to various galaxies. predict its rate of expansion. Another way to estimate the age of the universe is to calculate the ages of old, nearby stars. A Forever Expanding Universe • Cosmic Death Stars will age and die, and the universe will probably become cold and dark after many billions of years. End of Slide Copyright © by Holt, Rinehart and Winston. All rights reserved.