Seeds/Backman, THE SOLAR SYSTEM 10e, Instructor’s Manual
CHAPTER 1
HERE AND NOW
As you study astronomy, you will learn about yourself. You are a planet-walker, and this chapter will give
you a preview of what that means. The planet you live on whirls around a star that moves through a Universe
filled with other stars and galaxies which are all results of billions of years of history and evolution. You owe
it to yourself to know where you are in the Universe and also to know when you are in its history because
those are important steps toward knowing what you are. In this chapter, you will consider three important
questions about astronomy:
► Where is Earth in the Universe?
► How does human history fit into the history of the Universe?
► Why study astronomy?
1-1 WHERE ARE WE?
You surveyed the Universe by taking a cosmic zoom in which each field of view was 100 times
wider than the previous field of view.
Astronomers use the metric system because it simplifies calculations and scientific notation for
very large or very small numbers.
You live on a planet, Earth, which orbits our star, the Sun, once a year. As Earth rotates once a
day, you see the Sun rise and set.
The Solar System includes the Sun at the center, all of the major planets that orbit around it—
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune—plus the moons of the planets
and other objects such as asteroids, comets, and dwarf planets like Pluto, bound to the Sun by its
gravity.
The astronomical unit (AU) is the average distance from Earth to the Sun. The light-year (ly) is
the distance light can travel in one year.
Astronomers have found thousands of planets orbiting stars other than our Sun, even though such
distant and small bodies are very difficult to detect.
The Milky Way, the hazy band of light that encircles the sky, is the Milky Way Galaxy seen from
inside. Galaxies contain many billions of stars. The Milky Way Galaxy is about 80,000 ly in
diameter and contains over 100 billion stars, including our Sun.
Our galaxy is just one of billions of galaxies that fill the Universe in great clusters, clouds,
filaments, and walls—the largest structures in the Universe.
1-2 WHEN IS NOW?
Astronomers have evidence that the Universe began about 14 billion years ago in an event called
the Big Bang that filled the Universe with hot gas.
1- 1
, Seeds/Backman, THE SOLAR SYSTEM 10e, Instructor’s Manual
The hot gas cooled, the first galaxies began to form, and stars began to shine about 400 million
years after the Big Bang.
The Sun and planets of our Solar System formed about 4 .6 billion years ago.
Life began in Earth’s oceans soon after Earth formed but did not emerge onto land until 400 million
years ago, less than 1/30 of the age of the Universe. Dinosaurs evolved relatively soon after that and
went extinct just 65 million years ago.
Humanlike creatures developed on Earth only about 4 million years ago, less than 1/3000 of the age
of the Universe, and human civilizations developed just 10,000 years ago.
1-3 WHY STUDY ASTRONOMY?
Although astronomy seems to be about stars and planets, it describes the Universe in which you
live, so it is really about you. Astronomy helps you answer the question, “What are we?”
As you study astronomy, you should ask, “How do we know?” and that will help you understand
how science gives us a way to understand nature.
In its simplest outline, science follows the scientific method, in which scientists test hypotheses
against evidence from experiments and observations. This method is a powerful way to learn about
nature.
CHAPTER OUTLINE
1-1 Where Are We?
1-2 When Is Now?
1-3 Why Study Astronomy?
How Do We Know? 1-1: The Scientific Method
What Are We? Participants
KEY TERMS
astronomical unit (AU) planet
dwarf planet scientific method
field of view scientific notation
galaxy Solar System
light-year (ly) star
Milky Way Galaxy
RESOURCES AND TIPS
1. Ask students to watch this cosmic zoom sequence, which is similar to the one in the chapter and a
second version of a famous earlier film.
Powers of Ten™ (1977) by Charles and Ray Eames: http://www.youtube.com/watch?v=0fKBhvDjuy0
Which power of ten is most surprising to them and why?
1- 2
CHAPTER 1
HERE AND NOW
As you study astronomy, you will learn about yourself. You are a planet-walker, and this chapter will give
you a preview of what that means. The planet you live on whirls around a star that moves through a Universe
filled with other stars and galaxies which are all results of billions of years of history and evolution. You owe
it to yourself to know where you are in the Universe and also to know when you are in its history because
those are important steps toward knowing what you are. In this chapter, you will consider three important
questions about astronomy:
► Where is Earth in the Universe?
► How does human history fit into the history of the Universe?
► Why study astronomy?
1-1 WHERE ARE WE?
You surveyed the Universe by taking a cosmic zoom in which each field of view was 100 times
wider than the previous field of view.
Astronomers use the metric system because it simplifies calculations and scientific notation for
very large or very small numbers.
You live on a planet, Earth, which orbits our star, the Sun, once a year. As Earth rotates once a
day, you see the Sun rise and set.
The Solar System includes the Sun at the center, all of the major planets that orbit around it—
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune—plus the moons of the planets
and other objects such as asteroids, comets, and dwarf planets like Pluto, bound to the Sun by its
gravity.
The astronomical unit (AU) is the average distance from Earth to the Sun. The light-year (ly) is
the distance light can travel in one year.
Astronomers have found thousands of planets orbiting stars other than our Sun, even though such
distant and small bodies are very difficult to detect.
The Milky Way, the hazy band of light that encircles the sky, is the Milky Way Galaxy seen from
inside. Galaxies contain many billions of stars. The Milky Way Galaxy is about 80,000 ly in
diameter and contains over 100 billion stars, including our Sun.
Our galaxy is just one of billions of galaxies that fill the Universe in great clusters, clouds,
filaments, and walls—the largest structures in the Universe.
1-2 WHEN IS NOW?
Astronomers have evidence that the Universe began about 14 billion years ago in an event called
the Big Bang that filled the Universe with hot gas.
1- 1
, Seeds/Backman, THE SOLAR SYSTEM 10e, Instructor’s Manual
The hot gas cooled, the first galaxies began to form, and stars began to shine about 400 million
years after the Big Bang.
The Sun and planets of our Solar System formed about 4 .6 billion years ago.
Life began in Earth’s oceans soon after Earth formed but did not emerge onto land until 400 million
years ago, less than 1/30 of the age of the Universe. Dinosaurs evolved relatively soon after that and
went extinct just 65 million years ago.
Humanlike creatures developed on Earth only about 4 million years ago, less than 1/3000 of the age
of the Universe, and human civilizations developed just 10,000 years ago.
1-3 WHY STUDY ASTRONOMY?
Although astronomy seems to be about stars and planets, it describes the Universe in which you
live, so it is really about you. Astronomy helps you answer the question, “What are we?”
As you study astronomy, you should ask, “How do we know?” and that will help you understand
how science gives us a way to understand nature.
In its simplest outline, science follows the scientific method, in which scientists test hypotheses
against evidence from experiments and observations. This method is a powerful way to learn about
nature.
CHAPTER OUTLINE
1-1 Where Are We?
1-2 When Is Now?
1-3 Why Study Astronomy?
How Do We Know? 1-1: The Scientific Method
What Are We? Participants
KEY TERMS
astronomical unit (AU) planet
dwarf planet scientific method
field of view scientific notation
galaxy Solar System
light-year (ly) star
Milky Way Galaxy
RESOURCES AND TIPS
1. Ask students to watch this cosmic zoom sequence, which is similar to the one in the chapter and a
second version of a famous earlier film.
Powers of Ten™ (1977) by Charles and Ray Eames: http://www.youtube.com/watch?v=0fKBhvDjuy0
Which power of ten is most surprising to them and why?
1- 2
