|
Earth System
Figure 2.10 Plane of the Ecliptic
The plane of the
ecliptic (also known as the "Earth-Sun plane") is a
plane that cuts through the center of the Earth and the Sun in which the
Earth revolves around the Sun. The Earth's axis of rotation (called the "axial tilt") is tilted 23 1/2 degrees
from being perpendicular to the plane of the ecliptic. The axis remains pointing in
the same direction as the Earth revolves around the Sun, pointing toward the star
Polaris. As a result, the Earth's axis of rotation remains parallel to its
previous position as it orbits the sun, a property called
"parallelism".
Figure 2.11 Orientation of Earth to
Sun
Courtesy NASA (Source)
The constant tilt and parallelism causes changes in the
angle that a beam of light makes with respect to a point on Earth during
the year, called the "sun angle". The most intense incoming solar radiation occurs where the sun's
rays strike the Earth at the highest angle.
During the summer months the Earth is inclined toward the Sun
yielding high sun angles. During the winter, the Earth is oriented away from
the Sun creating low sun angles.
 Figure 2.12
Effect of axial tilt on
incoming
solar radiation
Figure 2.24 shows the orientation of Earth with respect to the Sun during the northern hemisphere summer and its affect on sun angle. The dashed lines are the Tropic of Cancer (23.5oN) and Tropic of Capricorn 23.5oS). The northern hemisphere is tilted into the sun yielding a higher angle (A) and warmer temperatures than in the southern hemisphere were low angle sun angles are striking (B).
Previous | Continue
|
