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Module 4:

How the Students See It

What are the most difficult

astronomy concepts?

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From a study of 9th - 12th graders from 9 high schools in the Boston area:1

1. Why does the Moon have phases?

62% - something to do with shadows of the Earth or Sun.

36% - correctly understood that phases result because the Moon moves around the Earth.

2. Why do we experience summer and winter?

43% - something to do with the tilt of the earth.

“Earth is closer to the sun in summer than it is in winter.”

3. How long does it take the Earth to go around the Sun?

52% - one year

30% - knew it takes about a month for the Moon to go around the Earth

10% - knew the moon turns on its axis once a month.

This module is about

    1. assessing students’ knowledge and reasoning abilities;

    2. selecting concepts at the appropriate level for students to learn; and

    3. using techniques most likely to result in lasting conceptual change.

People construct their own meanings based on

    • what they already believe (prior knowledge) and

    • new learning experiences

Letting students discuss what they believe at the outset

  • helps you understand students’ starting points, and

  • alerts the students that theirs is not the only point of view

People’s reasoning abilities develop at different rates, 2,3

so select objectives and learning experiences accordingly.

A. Do Students Have Theories?

If you ask your students about the shape of the Earth,

most would say it is “round.”

But what do they mean by “round Earth?” 4, 5, 6, 7, 8

Recall from Module 1, Communication:

Instructor says: “A Wave.”

Student 1 imagines: “A Wave.”

Student 2 imagines: “A Wave.”

Interviews showed what some elementary and middle school students thought:

...The Earth is a

“circular island people can sail around”

(similar to models of the earth suggested by natural philosophers, thousands of years ago).

...The round earth is a “planet in the sky, where astronauts go.”

Thales’ idea of the world in 500 B.C.

“The earth is like a cork

bobbing in the sea.”

...The Earth is shaped like a ball but it's puzzling why people did not fall off the bottom of the ball.

People live just on top of the ball, or on the flat part in the middle.

Do children’s ideas deserve to be called “theories?”

Students have “mental models” about the Earth’s shape:

First graders' mental model of the Earth is a flat disk or rectangle.

Older children try to make models consistent with what teachers explain with an Earth globe.

The result can be a dual Earth model—the flat one we live on, and the ball-shaped planet Earth in the sky.

About half of fifth graders expressed more “scientific” mental models, that the Earth is shaped like a ball, with people living all around it.

Students’ Theories About Gravity

A study by Bar, Sneider, and Martimbeau has shown that

many 6th graders believe there is no gravity in space

“because there is no air there”

• and likewise there is no gravity on the Moon.

The study found that 6th graders can learn that gravity acts through space, beyond Earth’s atmosphere.


Predict the path that a ball would follow

when it rolls off a table,

then watch the actual trajectory.

Followed by a thought experiment:

Newton's Cannon.

The data from the study:

“Does gravity act in space where there is no air?” (N=48)

On vacation in Antarctica,

Mr. & Mrs. Smith experience

odd gravitational effects

The Earth, Moon, and Stars

from Great Explorations in Math and Science (GEMS - http://www.lhsgems.org/)

What Are Your Ideas About the Earth?


Why is the Earth flat in picture A and round in picture B?

(Circle the letter in front of the best answer.)

A. They are different Earths.

B. The Earth is round like a ball, but people live on the flat part in the middle.

C. The Earth is round like a ball, but it has flat spots on it.

D. The Earth is round like a ball, but looks flat because we only see a small part of the ball.

E. The Earth is round like a dinner plate so it seems round when you’re over it and flat when you’re on it.


Pretend that the Earth is glass and you can look through it. Which way would you look, in a straight line, to see people in far-off countries like China or India?


This drawing shows some enlarged people dropping rocks at various places around the Earth. Show what happens to each rock by drawing a line that demonstrates the complete path of the rock, from the person’s hand to where it finally stops.


Pretend that a tunnel was dug all the way through the Earth, from pole to pole. Imagine that a person holds a rock above the opening at the North Pole. Draw a line from the person’s hand showing the entire path of the rock.

Modified and adapted from the February issue of Learning 86,

copyright 1986, Springhouse Corporation.

Download activity as PDF


The Astronomer’s Answers

and some teaching ideas

Question 1:

This reasoning skill typically develops during the early elementary years, but understanding such a relationship is much easier if illustrated with a physical object, such as a large weather balloon.

Question 2:

Most people try to imagine which direction they would fly in a plane to get to China or India, and answer “eastward” or “westward.” You might use a globe and ruler to show what happens if you look due east or west—the ruler (representing the way you would look) points off into space.

Question 3:

Think about the people who live all around the ball-shaped Earth. The only way to explain why they don't fall off is to imagine that “down” is toward the center of the Earth.

Turn an Earth globe so that the South Pole is “up” and ask the students to imagine being there.

People on the South Pole must think that people in the Northern Hemisphere live upside-down!

Question 4:

This one stumps many adults!

Aristotle: everything goes to its “natural resting place” in the center of the universe, the center of the Earth. If Aristotle had filled out the questionnaire, he would have drawn a line to the center and stopped there.

Isaac Newton: Every particle within the Earth pulls on every particle within the rock.

Levels of Understanding About the Earth’s Shape and Gravity

SHAPE LEVEL 1—The Earth is flat.

SHAPE LEVEL 2—The Earth is shaped like a ball, but people live on the flat parts of it (or inside the ball).

SHAPE LEVEL 3—The Earth is shaped like a ball, but people live just on top of the ball.

SHAPE LEVEL 4—The Earth is shaped like a ball, and people live all around the ball.

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