Energy that is received on the roof of a house is more than enough to supply the heating needs of the home. The energy reaching the earth from the sun ranges from 600 to 2000 BTUs per square foot per day (averaged over a year). It is a function of the latitude of the place. The amount of solar radiation reaching the earth is called the insolation. This is a short from for incident solar radiation per day.
The earth revolves around the sun with its axis tilted toward the plane of rotation.
- In June, the North Pole is tilted toward the sun and the solar rays are incident perpendicularly. Therefore, the sun appears to be at a higher angle.
- In December, the North Pole is tilted away from the sun and therefore days are shorter and the solar rays are incident more obliquely, with lower energy flux (winter).
The sun also changes in position and angle from the earth during various times of the year.
Instructions: Press play to observe the movement of the sun as a function of the seasons.
Click here to open a text description of the movement of the Sun with the seasons.
Movement of the Sun with the Seasons
From June through December, the Sun's highest point in a given day moves lower and lower towards the horizon.