Download Some space objects are visible to the human eye.

KEY CONCEPT
Some space objects are
visible to the human eye.
Sunshine State
STANDARDS
SC.C.2.3.7: The student
knows that gravity is a
universal force that
every mass exerts on
every other mass.
SC.E.1.3.3: The student
understands that our
Sun is one of many
stars in our galaxy.
SC.H.2.3.1: The student
recognizes that patterns exist within and
across systems.
BEFORE, you learned
NOW, you will learn
• Earth is one of nine planets
that orbit the Sun
• The Moon orbits Earth
• Earth turns on its axis every
24 hours
• How the universe is arranged
• How stars form patterns in
the sky
• How the motions of bodies in
space appear from Earth
EXPLORE Distance
How far is the Moon from Earth?
PROCEDURE
1
FCAT VOCABULARY
solar system p. 674
galaxy p. 674
universe p. 674
constellation p. 676
VOCABULARY
orbit p. 674
Tie one end of the string around the
middle of the tennis ball. The tennis ball
will represent Earth.
2 Wrap the string 9.5 times around the tennis
MATERIALS
• tennis ball
• aluminum foil
(5 cm strip)
• string (250 cm)
• felt marker
ball, and make a mark on the string at that
point. Wrap the aluminum foil into a ball
around the mark. The foil ball will
represent the Moon.
3 Stretch out the string to put the
model Moon and Earth at the right
distance compared to their sizes.
WHAT DO YOU THINK?
• How does the scale model compare with your previous
idea of the distance between Earth and the Moon?
• How many Earths do you estimate would fit between
Earth and the Moon?
We see patterns in the universe.
MAIN IDEA WEB
Record details about
patterns in space.
For most of history, people had very limited knowledge of space. They
saw planets and stars as points of light in the night sky. However, they
did not know how far those bodies were from Earth or from each
other. Early observers made guesses about planets and stars on the
basis of their appearance and the ways they seemed to move in the sky.
Different peoples around the world connected the patterns they saw in
the sky with stories about imaginary beings.
Chapter 19: Exploring Space 673
We still have much to learn about the universe. Within the last few
hundred years, however, new tools and scientific theories have greatly
increased our knowledge. In this chapter you will learn about the
arrangement of planets and stars. You will also learn about the ways
in which astronomers explore and study space.
Arrangement of the Universe
If you look up at the sky on a clear night, you will see only a tiny
fraction of the planets and stars that exist. The number of objects in
the universe and the distances between them are greater than most
people can imagine. Yet these objects are not spread around randomly.
Gravity causes objects in space to be grouped together in different ways.
The images on page 675 show some basic structures in the universe. Like a camera lens zooming out, the images provide views of
space at different levels of size.
1
Our planet’s diameter is about 13,000 kilometers (8000 mi).
This is almost four times the diameter of the Moon, which orbits
Earth. An orbit is the path of an object in space as it moves
around another object because of gravity.
2
Earth and eight other major planets orbit the Sun.
The Sun, the planets, and various smaller bodies make up the
solar system. The Sun is about 100 times greater in diameter
than Earth. You could fit more than 4000 bodies the size of the
Sun between the Sun and the solar system’s outermost planet at its
average distance from the Sun. The Sun is one of countless stars in
space. Astronomers have detected planets orbiting some of these
other stars.
3
Our solar system and the stars you can see with
your bare eyes are part of a galaxy called the Milky Way. A galaxy
is a group of millions or billions of stars held together by their own
gravity. If the solar system were the size of a penny, the Milky Way
would stretch from Chicago to Dallas. Most stars in the Milky Way
are so far away that our galaxy appears to us as a hazy band of light.
4
The Universe
reading tip
The word orbit can be
a noun or a verb.
Earth
Solar System
The Milky Way
The universe is everything—space and all the matter and energy in it. The Milky Way is just one of many billions of
galaxies in the universe. These galaxies extend in all directions.
Astronomers study space at each of these different levels. Some
focus on planets in the solar system. Other astronomers study distant
galaxies. To learn how the universe formed, astronomers even study
the smallest particles that make up all matter.
check your reading
674 Unit 6: Space Science
What is the relationship between the solar system and the
Milky Way?
Structures in the Universe
Gravity causes objects to be grouped
together in space.
2
1
Earth
We live on Earth, a planet that
orbits the Sun.
Solar System
The solar system contains the Sun, nine
major planets, and many smaller objects.
3
Milky Way
The Sun and billions of other stars are grouped
together in a galaxy called the Milky Way.
4
Universe
Billions of galaxies are spread throughout
the universe.
How are these structures different from one
another? How are they similar?
Chapter 19: Exploring Space 675
Cygnus (the Swan)
Constellation Patterns
The stars of a constellation are often far
apart from one another, but they appear
grouped together when viewed from Earth.
Albireo
Deneb
Sadr
Gienah
Cygni
1500 light-years
Delta
Cygni
1000 light-years
500 light-years
1 light-year = 9.5 trillion kilometers
Which two stars in Cygnus are farthest apart from each other
in space?
Constellations
If you want to find a particular place in the United States, it helps to
know the name of the state it is in. Astronomers use a similar system
to describe the locations of objects in the sky. They have divided the
sky into 88 areas named for the constellations.
VISUALIZATION
CLASSZONE.COM
View images of the
night sky taken
throughout the year.
A constellation is a group of stars that form a pattern in the sky.
In the constellation Cygnus, for example, a group of bright stars form
the shape of a flying swan. Any other objects in that area of the sky,
such as galaxies, are said to be located in Cygnus, even if they are not
parts of the swan pattern. The ancient Greeks named many of the
constellations for animals and imaginary beings.
Unlike the planets in the solar system, the stars in a constellation
are usually not really close to each other. They seem to be grouped
together when viewed from Earth. But as the illustration above shows,
you would not see the same pattern in the stars if you viewed them
from another angle.
check your reading
676 Unit 6: Space Science
What relationship exists among the stars in a constellation?
The sky seems to turn as
Earth rotates.
You cannot see all of the constellations at once,
because Earth blocks half of space from your
view. However, you can see a parade of
constellations each night as Earth rotates. As
some constellations slowly come into view over
the eastern horizon, others pass high in the sky
above you, and still others set at the western
horizon. Throughout the ages, many peoples have
observed these changes and used them to help
in navigation and measuring time.
If you extended the North Pole into space, it
would point almost exactly to a star called Polaris,
or the North Star. If you were standing at the North Pole, Polaris
would be directly over your head. As Earth rotates through the night,
the stars close to Polaris seem to move in circles around it. Although
not the brightest star in the sky, Polaris is fairly bright and easy to
find. You can use Polaris to figure out direction and location.
check your reading
The stars in this image
were photographed over
several hours to show
how they move across the
night sky.
What causes constellations to change positions during the night?
Constellation Positions
Position
How does time of day affect the positions
of constellations?
SKILL FOCUS
Analyzing
PROCEDURE
1
Cut out both diagrams on the Constellation Wheel Sheet and assemble
them as shown.
2 Rotate the wheel so that the current month is aligned with 9 P.M.
Observe the positions of the constellations.
3 Align the current month with other times to determine how the
positions of the constellations change during the night.
MATERIALS
• Constellation
Wheel Sheet
• scissors
• brass fastener
TIME
20 minutes
WHAT DO YOU THINK?
• How do the positions of the constellations change
during the night?
• In which direction does the northern sky seem to turn?
CHALLENGE Earth’s rotation makes the sky seem to
turn. What does the model tell you about the direction of
Earth’s rotation?
Chapter 19: Exploring Space 677
The movements of planets and other nearby
objects are visible from Earth.
A jet plane travels at a greater speed and altitude than a bird. Yet if a
bird and a plane flew overhead at the same time, you might think that
the bird was faster. You would have this impression because the farther
away a moving object is from you, the less it seems to move.
Stars are always moving, but they are so far away
that you cannot see their movements. Observers have
seen the same constellation patterns for thousands
of years. Only over a much longer period does the
motion of stars gradually change constellation patterns.
The Motion of Mars
Sept. 20th
Oct. 4th
Mars
Mars
By contrast, the Moon moves across the star
background a distance equal to its width every hour
as it orbits Earth. The Moon is our closest neighbor.
The planets are farther away, but you can see their
gradual movements among the constellations over
a period of weeks or months.
These illustrations show how Mars changes
positions in the constellation Gemini over a
period of two weeks.
Planet comes from a Greek word that means
“wanderer.” Ancient Greek astronomers used this
term because they noticed that planets move among
the constellations. It is easiest to see the movements of Venus and
Mars, the two planets closest to Earth. They change their positions
in the sky from night to night.
The apparent movement of the sky led early astronomers to
believe that Earth was at the center of the universe. Later astronomers
discovered that Earth and the other planets orbit the Sun. The timeline on pages 736–739 introduces some of the astronomers who
helped discover how planets really move in the solar system.
KEY CONCEPTS
CRITICAL THINKING
1. What are the basic structures
in which objects are grouped
together in space?
4. Compare and Contrast
How is the grouping of stars
in a constellation different
from the grouping of planets
in the solar system?
2. What is a constellation?
3. How does Earth’s rotation
affect our view of stars?
678 Unit 6: Space Science
5. Apply The planet Jupiter is
farther than Mars from Earth.
Which planet seems to move
faster when viewed from
Earth? Explain.
CHALLENGE
6. Predict Suppose that you
are standing at the North Pole
on a dark night. If you keep
turning clockwise at the same
speed as Earth’s rotation, how
would your movement affect
your view of the stars?