How to make a geocentric model tha shows Ptolemy’s view of the universe is learning objective of this project. Ptolemy made astronomical observations from Alexandria, Egypt, during the years 127–141 and probably spent most of his life there.
Science.aksiografi.com – Astronomy is the study of celestial bodies, which are natural things in the sky, such as stars, suns, moons, and planets. Observations of the sky probably date from prehistoric times, so astronomy is one of the oldest sciences. One ancient idea about the universe was that Earth rested on the back of a giant turtle. The motion of the turtle seemed to explain why Earth shook at times during what we now know to be earthquakes.
Cosmology is the branch of astronomy that deals with the study of the universe as a whole, including distant past and its future. Some ancient astronomers viewed the universe as being relatively small and basically made up of a flat Earth surrounded by a domelike shell with the Sun, Moon, and stars on it. As time passed, people’s views of the size of the universe increased. Today it is considered infinite (without limits).
Early views of the universe put Earth at the center. This is called a geocentric (Earthcentered) model. The Greek philosopher Aristotle (384–322 B.C.) supported the geocentric view, and his ideas about the universe were considered true by most people for almost 2,000 years. Another influential, Roman astronomer was Ptolemy (A.D. 100–170). Little is known of Ptolemy’s life, but he made astronomical observations from Alexandria, Egypt, during the years 127–141 and probably spent most of his life there. Ptolemy agreed with Aristotle’s geocentric view of the universe, and proposed a model of a motionless Earth with the known celestial bodies orbiting (moving in a curved path about another body) in the order of Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn.
Learning Objectives
To make a model that shows Ptolemy’s view of the universe.
Materials
yardstick (meterstick)
22-by-28-inch (55-by-70-cm) piece of poster board
pencil
26-inch (65-cm) piece of string
marker
Procedure
1. Lay the yardstick (meterstick) across the middle of the poster board, parallel with the long sides.
2. Using the pencil and the measuring stick, make nine small dots on the poster board 3 inches (7.5 cm) apart. The first dot will be 3 inches (25 cm) from the left edge of the poster board; the last dot will be 1 inch (2.5 cm) from the edge of the poster board.
3. Tie a loop in one end of the string.
4. Place the pencil point through the loop and position the point on the second dot from the left side of the paper. With your other hand, pull the string outward over the first dot. Hold the string on the first dot with your thumb as you move the pencil like a compass across the poster board to draw a circle.
5. Repeat step 4 for each of the remaining dots, drawing as much of a circle as will fit on the board for each dot.
6. Using the marker, draw circles at each dot and add labels to represent the planets as shown. Draw stars in the rightmost band to represent the space beyond Saturn.
Results
You have made a geocentric model that shows how Ptolemy thought the universe was organized.
Why?
Ptolemy believed that in relation to their starry background, the Sun and the Moon moved in a straight line in their paths across the sky, while other celestial bodies seemed to wander. Thus, these wandering celestial bodies were called planets (celestial bodies that orbit a sun) from the Greek word for “wanderers.” Today’s model of the universe is not geocentric. But the solar system is heliocentric, with nine planets orbiting the Sun.
Try New Approaches
The Milky Way Galaxy is a giant spiral of several billion stars, one of which is our Sun. Its true shape, size, and nature were discovered by astronomers only in the twentieth century. If it were possible to view our galaxy from above, it would look like a spinning pinwheel; from the side it would look flat and disklike, much like a CD with a swollen center. Our solar system lies within one of the spiral arms and is speeding around the center of the galaxy at about 563,000 miles (900,800 km) per hour. It takes about 200 million years for the solar system to make one complete revolution.
All the stars you see from Earth are part of the Milky Way Galaxy. When you look toward either edge of the galaxy as shown by the arrows in the figure, you are looking through the greatest number of stars. Most of these stars appear as a faint, irregular ribbon of light that spans the sky. This is ribbon called the Milky Way because early observers thought it looked like spilled milk.
The Milky Way is visible on most nights that are clear and moonless. If you look for the Milky Way on different nights during the year, you will discover that it changes position in the sky. This shows how Earth moves and our view of the galaxy changes.
References
Filkin, David. Stephen Hawking’s Universe. New York: Basic Books, 1997. A brief history of the universe and other astronomy topics.
Moeschl, Richard. Exploring the Sky. Chicago: Chicago Review Press, 1993. Projects and information about the universe and other astronomy topics for beginning astronomers.
VanCleave, Janice. Janice VanCleave’s Constellations for Every Kid. New York: Wiley, 1997. Fun, simple astronomy experiments, including information about the Milky Way and other star groups.
