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ARIZONA ON LOCATION
Casa Grande Ruins National Monument
More than 2000 years ago, the Hohokam Native American tribe established a great
culture in the Sonoran Desert of southern Arizona. This area did not have much
water, but the Hohokam were able to grow crops there. They built large irrigation
canals that brought water to the desert. They were the first people in the Southwest
to farm the barren land.
The Hohokam were skillful in other ways. Beginning in the 1200s, they constructed
large adobe buildings. The largest of these buildings, Casa Grande ("big house"),
was four stories high. Other Hohokam structures show that they enjoyed sports.
They built many oval-shaped ball courts that were partly underground.
The walls of Casa Grande are more than 1 m (3 feet) thick at the base.
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The Hohokam Vanished
The first Europeans arrived in the area in the 1600s. By then, the Hohokam had
disappeared. All that remained were the ruins of their villages, canals and some
objects that they had used. What happened to the Hohokam? No one knows.
Perhaps they joined other tribes that lived in the Southwest.
The Hohokam and Astronomy
Casa Grande contains many untold secrets. For example, it has a series of mysterious
holes in its walls. In the early 1900s, a park employee suspected that the holes were
used for astronomical investigation. But he couldn't prove it. Then, in the 1960s, an
archaeologist was hired to study the holes. He concluded that 14 of them were used
to make observations of the sun and the moon. Studies in the 1970s provided more
evidence on the subject. One archaeologist discovered that two holes on the east
wall aligned with the sun on the first days of spring and fall. He also discovered that
a hole on the west wall aligned with the setting sun at the summer solstice, on June
21 or 22.
Archaeologists have found many objects around Casa Grande.
Think and Do
1. SCIENCE AND TECHNOLOGY The Hohokam used technology to build canals
for watering their crops. They also developed a system for observing the
movements of the sun and the moon. Which of these accomplishments do you think
was more important? Write a paragraph explaining why you think so.
2. SCIENTIFIC THINKING Research information about other Native American
cultures that had a knowledge of astronomy. Make a table that compares the
Hohokam with another tribe. What conclusions can you draw?
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Meteor Crater
Have you ever seen a "shooting star"? The brilliant yet brief trail of light is really not a
star. It's really a meteor, a flash caused by a chunk of rock or metal from outer
space. Such objects travel toward Earth at tremendous speeds. Usually they burn up
as they speed through the atmosphere. But sometimes the objects survive the
journey and crash onto Earth's surface. A meteor that does reach the surface is
called a meteorite.
About 50,000 years ago, a giant object streaked toward Earth. The meteorite crashed
into Earth near what is now Winslow, Arizona, with explosive force. It gouged out a
huge bowl-shaped area, or crater. Meteor Crater, as it is called, is a real spectacle.
Every year, thousands of visitors come to Arizona to view it. It's about 175 m (570
ft) deep and more than a kilometer (nearly a mile) wide. Visitors can view the crater
from a 5-km (3-mi) trail that goes around it. Meteor Crater is the best-preserved
crater in the world.
Solving the Meteorite Mystery
Scientists have long studied Meteor Crater and the meteorite that formed it. They believe
the meteorite weighed 63,000
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tons and broke apart on impact. The largest remaining piece weighs about 640 kg (1400
lb). It is on display in the Meteor Crater Museum, near the impact site. Many other,
smaller fragments are under the crater and near it. In addition, particles the size of
sand grains are scattered over a large area. Those are called spheroids.
What exactly happened to the original giant object that crashed into Earth? Did much of
it vaporize as it raced through the atmosphere? Until recently, scientists thought that
this was a good explanation. They believed the spheroids and other particles formed
when resistance from Earth's atmosphere blasted them away from the huge chunk.
The vaporized particles then condensed and scattered over a wide area near the
crater.
In 1999, however, scientists developed another explanation. Using a computer model,
they determined that little if any of the object vaporized as it sped toward Earth.
Instead, much of it melted as it crashed into Earth and exploded. The force of the
explosion scattered the melted material over a wide area. Some of the melted
material then cooled in the form of spheroids.
Small — meteorites hit Earth every day.
The largest fragment of meteorite is called the Canyon Diablo Meteor.
Think and Do
1. SCIENCE AND TECHNOLOGY Use the Internet to find out more about the
computer model that scientists used to develop their recent explanation. What did
the model tell them about the speed of the giant object when it crashed into Earth?
2. SCIENTIFIC THINKING Meteors the size of the Canyon Diablo Meteor reach
Earth about once every 6000 years. Write a paragraph explaining why scientists
should learn as much as they can about such objects. How could knowing about the
objects help people in the future?
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The Challenger Space Center
The Challenger Space Center in Peoria, Arizona, is a great place to learn about space
exploration. The center, which opened in 2000, has a wide variety of activities,
programs, and exhibits for students as well as the general public.
At the space center, you can see a display honoring the seven crew members of the space
shuttle Columbia who lost their lives on a mission in 2003. You can also see an
Atlantis space shuttle model standing 3 m (10 ft) high and an exhibit tracing the
history of the U.S. space program.
The Challenger Science Center is named for the crew of the Challenger.
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Want to Be an Astronaut?
Have you ever wondered what it's like to be an astronaut? You can find out at the
Challenger Space Center if you participate in the To Be an Astronaut program.
Students in this program learn how and what astronauts eat on their missions, and
they discover many other things about living, working, and communicating in orbit
around Earth.
Want to Discover an Asteroid?
Visitors to the Challenger Space Center can also take part in a special astronomy
program. This program is dedicated to finding real asteroids and comets. Students
and their teachers use Asteroid Discovery Stations to download images of space.
Students then study the images and file reports with the Minor Planet Research
Center in Massachusetts about their observations and discoveries. One observer
recently discovered an asteroid that was the closest ever known to pass Earth!
Students who make discoveries receive official recognition.
Think and Do
1. SCIENCE AND TECHNOLOGY Technology helps scientists discover and study
objects in space. Make a list of some of the modern tools for exploring space. Write
a paragraph explaining why you think one of those tools is the most important.
2. SCIENTIFIC THINKING Imagine that you discover a new asteroid while you are
studying images at the Challenger Space Center. Describe why it is important to
report your discovery and to have scientists track the path of the asteroid.
Space campers experiment with different ways to explore space.
Visitors can build working models of moon rovers.
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ARIZONA PROJECTS AND INVESTIGATIONS
Materials
 current newspaper
 ruler
 construction paper
Procedure
1. Look in the newspaper for information about the phases of the moon. You might find
the information near the weather forecast.
2. Use the ruler and the construction paper to make a calendar with seven columns.
Write the names of the days at the tops of the columns, and below, write the dates
for the current month. To show all the moon's phases, you may need to make a
calendar for the next month, too.
3. Draw a new moon, a first quarter, a full moon, a third quarter, and another new moon
on your calendar. Use the newspaper information to draw those symbols next to the
correct dates.
4. How will the moon change from one phase to the next? Draw your predictions in the
spaces between your symbols.
Draw Conclusions
1. How long is the lunar cycle, from one new moon to the next?
2. What pattern do you see in the moon's phases? Do you think this pattern is always the
same? Explain.
3. How does your calendar show changes in the phases over time?
Extend the Activity
Draw the moon phases as you see them from your home during one cycle. Compare
these drawings to your calendar. How accurate were your predictions?
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Distance Between Planets
Materials
 sheet of tissue paper
 scissors
 roll of toilet paper
 masking tape
 marker
Procedure
1. Copy the data below into a notebook.
2. Cut out a circle from the tissue paper. This circle will represent the sun. Place the
circle on the floor.
3. An AU (astronomical unit) is Earth's average distance from the sun. In your model,
one sheet of toilet paper will equal 10 cm. It will also equal 1 AU.
4. Make a table with two columns. Put the distance in centimeters for each planet in one
column. Divide each number by 10 to find the AU. Put that data in the second
column.
5. Tape the first sheet of the toilet paper roll to the edge of the paper sun. Then unroll
the toilet paper in a straight line.
6. With your marker, write the names of the planets on the paper, at the correct
distances (in AUs) from the sun.
Planet Data
Mercury = 4 cm, Venus = 7 cm, Earth = 10 cm, Mars = 20 cm, Jupiter = 50 cm, Saturn =
100 cm, Uranus = 190 cm, Neptune = 300 cm, Pluto = 390 cm
Draw Conclusions
1. In your model, how far away from the sun is Mercury? How far away from the sun is
Pluto?
2. Why do scientists use AUs to measure distances in the solar system?
Extend the Activity
Use a calculator to make a model of planet diameters. Use 1 cm to represent Earth's
diameter. Then divide the other planets' diameters by Earth's diameter. Make a scale
drawing.