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Chapter 1
Learning Objectives
1 Our Modern View of the Universe
What is our place in the universe?
How did we come to be?
How can we know what the universe was like in the past?
Can we see the entire universe?
2 The Scale of the Universe
How big is Earth compared to our solar system?
How far away are the stars?
How big are the Milky Way Galaxy and the universe?
3 Spaceship Earth
How is Earth moving in our solar system?
How is our solar system moving in the Milky Way Galaxy?
How do the galaxies move within the universe?
Are we ever sitting still?
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Chapter 1 Our Modern View of the Universe
Basic Astronomical Objects
Planet/Dwarf Planet
Orbits a star
Is large enough for its gravity to make it round
Planets have cleared most other objects from their orbital
paths, while dwarf planets have not
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Chapter 1 Our Modern View of the Universe
Basic Astronomical Objects
Star
A large, glowing ball of gas that
generates heat and light through
nuclear fusion in its core.
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Chapter 1 Our Modern View of the Universe
Basic Astronomical Objects
Moon (or Satellite)
An object that orbits a
planet. The term
satellite is also used
more generally to refer
to any object orbiting
another object.
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Chapter 1 Our Modern View of the Universe
Basic Astronomical Objects
Asteroid
A relatively small and rocky
object that orbits a star.
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Chapter 1 Our Modern View of the Universe
Basic Astronomical Objects
Comet
A relatively small and ice-rich
object that orbits a star.
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Chapter 1 Our Modern View of the Universe
Collections of Astronomical Objects
Solar (or Star) System
The Sun (or any other
star) and all of the
material that orbits it.
The Solar System formed
about 4 1 billion years ago.
2
Figure 1.6a
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Chapter 1 Our Modern View of the Universe
Collections of Astronomical Objects
Galaxy
A great island of stars in
space, containing from a
few hundred million (108 )
to a trillion (1012 ) or more
stars, all held together by
gravity and orbiting a
common center. We live
in the Milky Way Galaxy,
which formed about 13
billion years ago.
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Chapter 1 Our Modern View of the Universe
Collections of Astronomical Objects
Cluster (or Group) of Galaxies Supercluster
A collection of galaxies bound A gigantic region of space where
together by gravity. many individual galaxies and
clusters of galaxies are packed
more closely together than
elsewhere in the universe.
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Chapter 1 Our Modern View of the Universe
Collections of Astronomical Objects
Universe Observable Universe
The sum total of all matter and The portion of the entire universe
energy—that is, all galaxies and that can be seen from Earth, at
everything between them. The least in principle. The observable
universe formed about 14 billion universe is probably only a tiny
years ago. portion of the entire universe.
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Figure 1.1
Chapter 1 Our Modern View of the Universe
Our Cosmic Origins
Figure 1.2a
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Chapter 1 Our Modern View of the Universe
Our Cosmic Origins
Figure 1.2b
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Chapter 1 Our Modern View of the Universe
Our Cosmic Origins
Figure 1.2c
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Chapter 1 Our Modern View of the Universe
Our Cosmic Origins
Figure 1.2d
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Chapter 1 Our Modern View of the Universe
Looking Into the Past
Figure 1.3
Light Travel Time to Earth
Moon 1 second
Sun 8 minutes
Sirius 8 years
Andromeda Galaxy 2.5 million years
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Chapter 1 Our Modern View of the Universe
Why Can’t We See the Entire Universe?
Figure 1.4
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Chapter 1 Our Modern View of the Universe
TPS
Which of the following is correctly ordered from LARGEST to
SMALLEST?
a) Solar System, Galaxy, Star, Planet, Asteroid
b) Galaxy, Star, Solar System, Planet, Asteroid
c) Galaxy, Solar System, Star, Planet, Asteroid
d) Galaxy, Solar System, Star, Asteroid, Planet
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Chapter 1 The Scale of the Universe
Learning Objectives
1 Our Modern View of the Universe
What is our place in the universe?
How did we come to be?
How can we know what the universe was like in the past?
Can we see the entire universe?
2 The Scale of the Universe
How big is Earth compared to our solar system?
How far away are the stars?
How big are the Milky Way Galaxy and the universe?
3 Spaceship Earth
How is Earth moving in our solar system?
How is our solar system moving in the Milky Way Galaxy?
How do the galaxies move within the universe?
Are we ever sitting still?
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Chapter 1 The Scale of the Universe
Astronomical Distance Units
Astronomical Unit (AU)
The average distance between the Earth and the Sun, which is
about 150 million kilometers (1.5 × 1011 m).
Light-year
The distance light can travel in one year, which is about 10 trillion
kilometers (1016 m).
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Chapter 1 The Scale of the Universe
The Closest Star to the Sun
Figure 1.8
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Chapter 1 The Scale of the Universe
Size of the Galaxy and Universe
Milky Way Galaxy
100,000 light-years
across
100 billion (1011 )
stars
Observable Universe
Everything within 14
billion light-years
from Earth
100 billion (1011 )
galaxies
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Chapter 1 The Scale of the Universe
Video
Powers of Ten
Charles and Ray Eames
1977
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Chapter 1 The Scale of the Universe
TPS
About how many stars are there in the Observable Universe?
a) A Thousand
b) A Million (the number of letters in a 600 page paperback book)
c) Ten Billion (somewhat more than the number of people on
Earth)
d) 1022 (the number of dry grains of sand on Earth)
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Chapter 1 Spaceship Earth
Learning Objectives
1 Our Modern View of the Universe
What is our place in the universe?
How did we come to be?
How can we know what the universe was like in the past?
Can we see the entire universe?
2 The Scale of the Universe
How big is Earth compared to our solar system?
How far away are the stars?
How big are the Milky Way Galaxy and the universe?
3 Spaceship Earth
How is Earth moving in our solar system?
How is our solar system moving in the Milky Way Galaxy?
How do the galaxies move within the universe?
Are we ever sitting still?
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Chapter 1 Spaceship Earth
Rotation and Orbit
Rotation
Orbit (or Revolution)
Figure 1.12
Figure 1.11
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Chapter 1 Spaceship Earth
The Solar System is Moving
Figure 1.13
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Chapter 1 Spaceship Earth
Dark Matter
Figure 1.14
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Chapter 1 Spaceship Earth
The Milky Way Galaxy is Moving
Within the Local Group
Moving towards the
Andromeda Galaxy
The Large and Small
Magellanic Clouds orbit the
Milky Way
The Universe is Expanding
All galaxies outside of the
local group are moving away
from us
The more distant the galaxy,
the faster it appears to be
moving
Figure 1.15
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Chapter 1 Spaceship Earth
Motion Summary
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