Download Star Power - Net Texts

Star Power
Dana Desonie, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2014 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: December 7, 2014
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Star Power
1
Star Power
• Describe nuclear fusion.
• Explain how nuclear fusion causes stars to shine.
Did you know that the night sky is so bright?
Starlight can be surprisingly bright in the night sky. Of course, daytime is all about starlight. The star is our Sun,
and it shines so brightly because it is so close to us. Even the Moon is bright because of light from the Sun. Some
stars produce much more energy than the Sun. They’re just farther away, so the light is not as obvious. How do stars
generate so much energy?
Nuclear Fusion
Stars shine because of nuclear fusion. Fusion reactions in the Sun’s core keep our nearest star burning. Stars are
made mostly of hydrogen and helium. Both are very light gases, but a star contains so much hydrogen and helium
that its total mass is enormous. The pressure at the center of a star is great enough to heat the gases. This causes
nuclear fusion reactions.
1
www.ck12.org
A nuclear fusion reaction is so named because the nuclei (center) of atoms fuse (join) together in the process. In
stars like our Sun, hydrogen atoms join together to create a helium atom. Nuclear fusion reactions need a lot of
energy to get started. Once they begin, they produce even more energy. ( Figure 1.1).
FIGURE 1.1
A thermonuclear bomb is an uncontrolled fusion reaction in which enormous amounts of energy are released.
Particle Accelerators
Scientists have built machines called particle accelerators. These amazing tools smash particles that are smaller
than atoms into each other head-on. This creates new particles. Scientists use particle accelerators to learn about
nuclear fusion in stars. They can also learn about how atoms came together in the first few minutes of the Universe.
Two well-known accelerators are SLAC, in California, and CERN, in Switzerland ( Figure 1.2).
FIGURE 1.2
The SLAC National Accelerator Lab in California can propel particles a straight 2 mi (3.2 km).
Vocabulary
• nuclear fusion: When nuclei of two or more atoms fuse together, giving off tremendous amounts of energy.
• particle accelerator: Technologically advanced device that propels particles; this simulates conditions in the
first minutes of the Universe or in stars.
2
www.ck12.org
Chapter 1. Star Power
Summary
• In a nuclear fusion reaction, nuclei combine to form a larger nucleus.
• The energy from fusion reactions keeps the star shining.
• Particle accelerators simulate nuclear fusion in stars.
Explore More
Use the resource below to answer the questions that follow.
• What Is Fusion? at http://www.youtube.com/watch?v=bg3Q98bolK8 (1:59)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/118822
1.
2.
3.
4.
5.
6.
What happens during nuclear fusion?
What allows the positively charged hydrogen nuclei to collide, instead of repelling each other?
What is produced by the collision?
What kind of fusion powers the Sun?
What characteristics of stars make them good nuclear fusion reactors?
What did nuclear fusion contribute to the Universe billions of years ago?
Review
1. How do stars get their power?
2. Why can this happen in stars and not elsewhere?
3. What do scientists learn from particle accelerators?
References
1. Courtesy of the US Department of Energy. A thermonuclear bomb is an uncontrolled fusion reaction in which
enormous amounts of energy are released. Public Domain
2. Courtesy of Peter Kaminski/US Geological Survey. Particle accelerators are used to learn about nuclear fusion
in stars and about conditions in the first few minutes of the universe. Public Domain
3