Key Idea: Changes in the orientation of earth’s axis of rotation with respect to the sun over the course of a year causes the intensity of energy from the sun to be highest in the northern hemisphere when the north pole is tilted toward the sun and highest in the southern hemisphere when the south pole is tilted toward the sun.

Students are expected to know that:

Late June:

  1. On the same day each year in late June, the north pole is tilted 23.5° toward the sun, and the south pole is tilted 23.5° away from the sun. On that date, the sun is directly overhead at the northern border of the tropical region, i.e., the sub-solar point is at 23.5° north latitude, and the sun reaches a maximum angle of 90° along all places that are 23.5° north of the equator. As the earth turns on its axis, every place on the northern border of the tropical region is directly under the sun at some point during that day.
  2. The farther a place is from the northern border of the tropical region in late June, the smaller the maximum angle at which sunlight strikes that place during a day, the lower the intensity of the sunlight at that place over a day, and the less energy that is transferred from the sun to that place over a day.
  3. Because any place at a particular latitude in the northern hemisphere is closer to the northern border of the tropical region than a place at that same latitude in the southern hemisphere (i.e., at an equal distance from the equator), sunlight strikes the place in the northern hemisphere at a larger angle, and therefore transfers more energy to it from the sun than to a place at the same latitude in the southern hemisphere.

Late March and late September:

  1. On the same day each year in late March and late September, the north and south pole are not tilted toward or away from the sun, and the sun passes directly over the equator (i.e., the sub-solar point is at the equator). As the earth turns on its axis, every place on the equator is directly under the sun at some point during that day.
  2. In late March and late September, the maximum angle that sunlight hits the earth at the equator is 90°. Because the earth is a sphere and sunlight travels from the sun to the earth in a straight line, the maximum angle at which sunlight strikes a place on the surface of the earth is smaller the farther a place is from the equator. The smaller the maximum angle at which sunlight strikes a place during a day the lower the intensity of the sunlight at that place over a day, which means that less energy is being transferred from the sun to that place over a day. Therefore, the farther a place is from the equator, the less energy is transferred from the sun to that place over the course of a day in late March and late September.
  3. Because any place in the northern hemisphere has sunlight strike it at the same angle as a place in the southern hemisphere that is the equal distance from the equator, sunlight transfers the same amount of energy to both places.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

CLM073

In the middle of July, the place that receives the greatest intensity of sunlight is the equator (AAAS project 2061, n.d.).

32%

35%

CLM070

The sun is directly overhead at the equator in late June (AAAS project 2061, n.d.).

32%

33%

CLM072

The northern and southern hemispheres never receive the same amount of sunlight (AAAS project 2061, n.d.).

24%

23%

CLM071

The total amount of sunlight reaching the northern and southern hemispheres is the same every day of the year (AAAS project 2061, n.d.).

18%

15%

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.