Three other factors also influence seasonality:
- Axial tilt: Earth’s axis tilts 23.5 degrees
from the plane of the ecliptic, or the imaginary plane line that joins the centers of the Sun and Earth. Because of this tilt, one hemisphere is inclined towards the Sun, while the other is tilted away from it. The hemisphere tilted towards the Sun receives its direct, vertical rays, resulting in longer days than nights due to more intense insolation, or exposure to sunlight. In the hemisphere where the axis is tilted away, the reverse is true. Therefore, axial tilt determines the duration and intensity of insolation on Earth in the two hemispheres.
Axial parallelism: Earth’s axis points towards the same point, Polaris (the polestar) in the northern sky, all year round. The constant direction of the axial tilt allows both the Northern and Southern Hemispheres to face toward the Sun at different times of the year.Earth’s sphericity: Earth’s shape also affects the receipt of insolation. Areas along the equator receive the greatest amount of insolation, but insolation decreases toward the poles because the surface curves away.
The figure in the activity shows the Northern Hemisphere tilted towards the Sun, with the Sun’s rays (yellow arrows) directly striking the Tropic of Cancer. Note that the circle of illumination at different latitudes, which indicates the length of day and night at those latitudes. If the circle of illumination cuts a latitude in such a way that the lighted portion is greater than the dark portion, days are longer than nights. When the darkened portion is greater, the reverse is true.
Given these conditions, identify the effects of the three factors discussed above.
Drag the labels to their appropriate targets, placing the descriptions of insolation in the pink targets and all other descriptions in the blue targets.