## Key Idea: The earth’s spherical shape causes differences in the intensity of sunlight and thus the amount of energy from sunlight to be greater at some places than at other places. Sunlight is most intense at the single point where the sun is directly overhead (90° angle to the earth’s surface).

Students are expected to know that:

1. Because the sun is so far away from the earth, all sunlight that reaches the earth from the sun is in a straight line. And because the earth is spherical in shape, sunlight hits different parts of the earth at different angles.
2. Because the sun is so far away from the earth, the different distances that sunlight travels to reach different places on the surface of the earth cause no appreciable difference in the intensity of sunlight reaching those places.
3. Because the earth is spherical in shape, at any given time there is only one place on earth’s surface (the sub-solar point) where light from the sun strikes at a 90° angle and the intensity of sunlight is greater than at any other place. From the perspective of a person at that place, the sun appears to be directly overhead.
4. Because the earth is spherical in shape, the angle at which sunlight strikes any given place decreases the farther a place is from where the sun is directly overhead. Therefore, from the perspective of a person on earth, the farther the person is from where the sun is directly overhead, the smaller the angle at which sunlight strikes the earth and the lower the intensity of sunlight at that place. For example, for a person at a place that is on the boundary between the sunlit half of the earth and the half of the earth that sunlight cannot reach, the light striking the surface at that place is parallel to the surface (a 0° angle) and the sunlight is the least intense compared to the rest of the sunlit area of the earth.

Note: Because the earth is a sphere but from the perspective at any given place it appears to be flat, in the clarification the angle at which the sunlight strikes the tangent to a place on the surface of the earth will be referred to as the angle at which sunlight strikes a place on the surface of the earth. When referring to the angle that sunlight strikes the surface of the earth, we will always refer to the smaller of two supplementary angles, the one that is less than 90°.

Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
6–8
9–12
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Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

9–12

CLM062

Sunlight is more intense at some places on the surface of the earth because sunlight travels a shorter distance to get to those places (AAAS, Project 2061).

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CLM061

Sunlight is always more intense at the equator than at any other place on earth (AAAS Project 2061, n.d.).

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CLM060

Sunlight reaches the earth at different angles at different places because sunlight does not travel in parallel lines (AAAS Project 2061).

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CLM059

Sunlight reaches the earth at different angles at different places because sunlight does not travel in straight lines (AAAS Project 2061).

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CLM058

Sunlight reaches the earth at different angles at different places because the earth's axis is tilted (AAAS Project 2061).

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CLM057

Sunlight can strike more than one place on the surface of the earth at a 90° angle at the same time (AAAS Project 2061, n.d.).

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CLM056

Sunlight does not strike any point on the surface of the earth at a 90° angle (AAAS Project 2061, n.d.).

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CLM055

The sun is higher in the sky the farther a place is from where the sun is directly overhead (AAAS Project 2061).

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CLM054

How close a place is to where the sun is directly overhead is not related to the intensity of sunlight at that place (AAAS Project 2061).

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Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.