## 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:*

- 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.
- 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.
- 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.
- 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°.

Item ID Number |
Knowledge Being Assessed | Grades 6–8 |
Grades 9–12 |
Select This Item for My Item Bank |
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45% |
44% | |||

42% |
47% | |||

41% |
46% | |||

39% |
41% | |||

32% |
36% | |||

28% |
32% | |||

Sunlight strikes the earth at a 90° angle at only one place at any given time. | 29% |
27% | ||

27% |
30% | |||

27% |
25% | |||

25% |
27% | |||

24% |
26% | |||

Sunlight strikes only one point on the sunlit side of the earth at a 90° angle at any given time. | 21% |
27% | ||

22% |
24% | |||

The sun is directly overhead at only one place on earth at a single moment. | 21% |
22% |

Misconception |
Student Misconception |
Grades 6–8 |
Grades 9–12 |
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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.