Atmospheric Energy: Unequal Heating by the Earth's Surface

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Author: Janice VanCleave

The temperature of the Earth's atmosphere comes from the Sun's radiant energy warming the Earth's surface. The weather, climate, and seasons of a given area of the Earth depend on the temperature, which measures the energy of the atmosphere.

In this project, you will show how the directness of sunlight affects the heating of the Earth's atmosphere at the equator. You will demonstrate the effect of the Earth's shape on the unequal heating of the atmosphere. You will discover how the tilt of the Earth's axis affects the amount of sunlight that reaches different regions of the Earth's surface and thus causes different seasons. You will also see how the Earth's rotation affects atmospheric temperature.

Getting Started

Purpose: To determine why the atmosphere is warmest near the equator.


  • Masking tape
  • Ruler
  • Flashlight
  • Graph paper


Atmospheric Energy: Unequal Heating by the Earth's Surface

  1. Tape the ruler along the side of the flashlight so that a 6-inch (15-cm) section of the ruler extends past the lamp end of the flashlight.
  2. Lay the graph paper on a table.
  3. Hold the flashlight perpendicular to the paper so that the free end of the ruler is on the edge of the paper and the flashlight is over the paper.
  4. Darken the room and turn on the flashlight.
  5. Observe the number of squares covered on the paper by the inner bright circle of light (see Figure 24.1).
  6. Tilt the ruler down so the back end of the flashlight is about 6 inches (15 cm) above the table.
  7. Again observe the number of squares covered by the light.


The number of squares covered by the light depends on the size of the graph paper and the size of the flashlight. But more squares are illuminated when the light is held at an angle than when it is held perpendicular to the paper. The light covers about 4 squares when the flashlight is perpendicular to the paper and about 3 times that number of squares when the flashlight is held at an angle.


Roughly the same amount of light from the flashlight struck the paper each time, but when it was more direct—perpendicular—the light was more concentrated (gathered together in one place) and therefore covered fewer squares. When the light was less direct—at an angle—the light was spread across more squares. The Earth's surface and its atmosphere are heated by radiant energy from the Sun. Radiant energy is energy that can travel through matter or space in the form of waves, which include gamma rays, X rays, ultraviolet rays, infrared rays, radio waves, and visible light. Like the perpendicular flashlight beam, the Sun's radiant energy is more concentrated near the equator and less so nearer the North and South Poles. The surface of the Earth in the equatorial region is therefore heated more by direct sunlight than are the polar regions.

The heated Earth circulates the heat back to the overlying air in the lowest part of the atmosphere called the troposphere. The troposphere is the region of the atmosphere where there are changes in weather (condition of the atmosphere in a specific place at a particular time such as pressure, temperature, humidity, winds, precipitation, and clouds). The average of weather conditions over time produces the climate of a given region. The equatorial region receives more direct sunlight throughout the year, so it has the warmest climate. The increase in the angle of sunlight as one approaches the Poles explains the lower temperature and hence the colder climate of the polar regions.

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