Part A - Earth's key movements
The revolution of Earth on its orbit around the Sun, shown in Figure 1, takes about 365.25 days, measured as the time taken by the Sun to complete two crossings of the equator. This is known as the tropical, or solar, year-the length of year that remains relatively fixed. Earth's revolution determines the length of the tropical year and, therefore, of the seasons making up that year.
Rotation, also shown in Figure 1, takes 24 hours to complete. Since only half of Earth faces the Sun at any given time, the other half is in shadow. As a result, Earth's rotation ensures that all parts of its surface undergo alternating periods of light and darkness during this 24-hour timespan.
The circle of illumination demarcates the lighted and dark halves of Earth. It bisects the equator, resulting in equal days and nights of 12 hours each at that latitude (equator) throughout the year. The length of days at all other latitudes change throughout the year.
Figure 1. Earth's revolution and rotation
Which aspects of seasonality are caused by either revolution or rotation?
Select the three that apply.
Select the three that apply.
Shortening of the yearperpetual daylight at equatordaily pattern of days and nightsduration of the seasonslength of a tropical year