KEY CONCEPT
Telescopes allow us to
study space from Earth.
Sunshine State
STANDARDS
SC.B.1.3.3: The student
knows the various
forms in which energy
comes to Earth from
the Sun.
SC.H.1.3.2: The student
knows that the study
of the events that led
scientists to discoveries
can provide information about the inquiry
process and its effects.
SC.H.1.3.5: The student
knows that a change in
one or more variables
may alter the outcome
of an investigation.
BEFORE, you learned
NOW, you will learn
• Objects in the universe
are grouped together in
different ways
• The motions of planets
and other nearby objects
are visible from Earth
• About light and other forms
of radiation
• How astronomers gather
information about space
EXPLORE Distortion of Light
How can light become distorted?
PROCEDURE
1
Place a white sheet of paper behind a glass
filled with plain water. Shine a flashlight
through the glass, and observe the spot of
light on the paper.
2 Pour a spoonful of salt into the water.
FCAT VOCABULARY
electromagnetic radiation
p. 679
wavelength p. 680
VOCABULARY
spectrum p. 680
telescope p. 681
Stir the water, and observe the spot of light.
MATERIALS
• flashlight
• glass filled with
water
• sheet of white
paper
• spoon
• salt
WHAT DO YOU THINK?
• How did the spot of light change after
you mixed the salt into the water?
• How could Earth’s atmosphere cause
similar changes in light from space?
Light and other forms of radiation carry
information about space.
VOCABULARY
Add a magnet word diagram for electromagnetic
radiation to your notebook.
When you look at an object, your eyes are gathering light from that
object. Visible light is a form of electromagnetic radiation (ih-LEHKtroh-mag-NEHT-ihk), which is energy that travels across distances
as certain types of waves. There are other forms of electromagnetic
radiation that you cannot see directly, such as radio waves and x-rays.
Scientists have developed instruments to detect these other forms.
Electromagnetic radiation travels in all directions throughout space.
Almost everything we know about the universe has come from our
study of radiation. Astronomers can often learn about the size, distance,
and movement of an object by studying its radiation. Radiation can
also reveal what an object is made of and how it has changed.
Chapter 19: Exploring Space 679
The Electromagnetic Spectrum
The different forms of electromagnetic
radiation vary in their wavelengths.
visible light
wavelength
radio waves
microwaves
infrared
ultraviolet
x-rays
gamma rays
Radio Waves
Visible Light
X-Rays
This image of a galaxy shows
where radio waves are emitted.
Visible light is the only form of
radiation our eyes can detect.
This image shows where the
same galaxy emits x-rays.
reading tip
A prism is a transparent
object that is used to
separate the wavelengths
of light.
If you shine a flashlight through a prism, the beam of white light
will separate into a range of colors called a spectrum (SPEHK-truhm).
The colors that make up visible light are red, orange, yellow, green,
blue, indigo, and violet. These are the colors in a rainbow, which
appears when light spreads out as it passes through raindrops.
In a spectrum, the colors of visible light appear in the order of
their wavelengths. Wavelength is the distance between one wave peak
and the next wave peak. Red light has the longest wavelength. Violet
light has the shortest.
FLORIDA
Content Preview
reminder
Electromagnetic waves are
different from mechanical
waves like ocean waves,
but both carry energy. You
will learn more about waves
in grade 8.
680 Unit 6: Space Science
As you can see in the illustration above, visible light is just a tiny
part of a larger spectrum called the electromagnetic spectrum. The
electromagnetic spectrum includes all the forms of electromagnetic
radiation. Notice that the wavelength of infrared radiation is longer
than the wavelength of visible light but not as long as the wavelength
of microwaves or radio waves. The wavelength of ultraviolet radiation
is shorter than the wavelength of visible light but not as short as the
wavelength of x-rays or gamma rays.
Check Your Reading
How is visible light different from other forms of
electromagnetic radiation?
Astronomers use telescopes to collect
information about space.
A telescope is a device that gathers electromagnetic radiation. If you
have ever looked through a telescope, it was probably one that gathers
visible light. Such telescopes provide images that are much clearer than
what is seen with the naked eye. Images from other types of telescopes
show radiation that your eyes cannot detect. Each form of radiation
provides different information about objects in space.
Astronomers usually record images from telescopes electronically,
which allows them to use computers to analyze images. Different
colors or shades in an image reveal patterns of radiation. For example,
in the right-hand image on page 680, the colors yellow and red indicate where the galaxy is emitting large amounts of x-rays.
Most types of telescopes gather radiation with a glass lens or a
reflecting surface, such as a mirror. Larger lenses and reflecting
surfaces produce brighter and more detailed images. You can magnify
an image from a telescope to any size. However, enlarging an image
will not bring out any more details of an object. If the image is fuzzy
at a small size, it will remain fuzzy no matter how much it is enlarged.
Visible-Light, Infrared, and Ultraviolet Telescopes
There are two types of visible-light telescopes: reflecting telescopes
and refracting telescopes. Reflecting telescopes can also be built to
gather infrared or ultraviolet radiation.
This type of telescope has a curved mirror
that gathers light. The image comes into focus in front of the
mirror. Many reflecting telescopes have a second mirror that
reflects the image to recording equipment or to a lens called
an eyepiece.
• Reflecting Telescope
• Refracting Telescope
This type of telescope
has an objective lens,
or curved piece of glass,
at one end of a long
tube. The lens gathers
light and focuses it to
form an image near the
other end of the tube.
An eyepiece magnifies
this image.
Reflecting Telescope
Refracting Telescope
eyepiece
objective lens
main mirror
eyepiece
secondary
mirror
Chapter 19: Exploring Space 681
Radio Telescope
Most powerful visible-light telescopes are built on mountaintops
in rural areas. Rural areas offer a much better view of the night sky
than cities do, because the many electric lights in cities make dim
space objects hard to see. By locating telescopes on mountaintops,
astronomers reduce problems caused by Earth’s atmosphere. The
atmosphere interferes with light coming in from space. In fact,
movements of the air are what make stars appear to twinkle. At high
altitudes there is less air above the ground to interfere with light.
Radio Telescopes
Radio telescopes show where radio waves are being emitted by objects
in space. A radio telescope has a curved metal surface, called a dish,
that gathers radio waves and focuses them onto an antenna. The dish
works in the same way as the main
mirror of a reflecting telescope.
Some radio telescopes have dishes
made of metal mesh rather than
solid metal.
Because radio waves are so long,
a single radio telescope must be
very large to produce useful images.
To improve the quality of images,
astronomers often aim a group of
radio telescopes at the same object.
Signals from the telescopes are combined and then converted into an
image. Groups of radio telescopes,
like the Very Large Array in New
Mexico, can show more detail than
even the largest single dish.
Signals from these radio
telescopes in New Mexico
can be combined to
produce clearer images.
Unlike visible-light telescopes, radio telescopes are not affected by
clouds or bad weather. They even work well in daylight. In addition,
radio telescopes can be located at low altitudes because most radio
waves pass freely through Earth’s atmosphere.
check your reading
RESOURCE CENTER
CLASSZONE.COM
Find out more about
telescopes.
682 Unit 6: Space Science
What is the function of the dish in a radio telescope?
Telescopes in Space
Many exciting images have come from the Hubble Space Telescope
and other telescopes in space. The Hubble telescope is a reflecting
telescope. It was placed in orbit around Earth in 1990. Astronomers
operate it from the ground, although astronauts have visited it to
make repairs and improvements. The telescope sends images and
measurements back to Earth electronically.
The Hubble Space
Telescope produced this
image of a part of a
galaxy where new stars
are appearing.
Because the Hubble telescope is located in space, Earth’s atmosphere
does not interfere with light from objects the telescope is aimed at.
This lack of interference allows it to obtain clearer images than
ground-based telescopes with much larger mirrors. In addition to
collecting visible light, the Hubble telescope produces images of
ultraviolet and infrared radiation.
The Hubble Space Telescope is part of a group of telescopes that
orbit Earth. The telescopes allow astronomers to gain information
from the full range of electromagnetic radiation. The Compton
Gamma-Ray Observatory was sent into orbit in 1991. The Chandra
X-Ray Observatory was launched eight years later. These telescopes
were placed in space because Earth’s atmosphere blocks most x-rays
and gamma rays.
Check Your Reading
Why does the Hubble telescope produce clearer images than
a telescope of the same size on Earth?
KEY CONCEPTS
CRITICAL THINKING
1. How are visible light, radio
waves, and other forms of
electromagnetic radiation
different from each other?
4. Compare and Contrast
What are the similarities
and differences between
refracting telescopes and
reflecting telescopes?
2. What function do mirrors serve
in reflecting telescopes?
3. Why are some telescopes
placed on mountains or in
orbit around Earth?
CHALLENGE
6. Analyze Why might
astronomers use different types
of telescopes to obtain images
of the same object in space?
5. Analyze Why would it be
difficult to build radio telescopes if they did not work
well at low altitudes?
Chapter 19: Exploring Space 683