Mada za sehemu hiiThe Solar SystemMada 2
- The solar system
- The earth
The earth is one of the planets which make up the solar system. In studying the solar system, we have seen that the planets are in a special arrangement. The earth is the third in the arrangement of the planets from the sun. The earth has several characteristics. It is the only planet where all living things are found. Also, three quarters of the earth is covered by water. It also has oxygen and carbon dioxide which are important to living things. Moreover, the earth receives light from the sun.
The earth has two movements. The first movement is known as rotation. This movement involves the spinning of the earth on its axis (refer to Figure ). The second movement is known as revolution. This movement involves the earth revolving around the sun. These two movements occur at the same time. The earth rotates from West to East. It completes one rotation on its axis in 24 hours or 1 day. The earth revolves around the sun for 365 ¼ or 366 days, which are equal to one year.
When the earth rotates on its axis, we get day and night, the rising and falling of tides, as well as change in the direction of winds and ocean currents. Also, we get differences in time between one longitude and another. The earth takes four minutes to rotate from one degree of longitude to another; therefore, it uses 60 minutes, which is equal to one hour, to rotate 15 degrees of longitude. Thus, the difference in time between each 15 degrees of longitude is one hour.
These involve a steady rise and fall of the levels of ocean water. In some coastal areas, there are times when water moves away from the shore and times when water moves closer to the shore. Such movements are called low and high tides. When water moves away from the shore, it is known as a low tide and when it returns to the shore, it is known as a high tide.
The rise and fall of oceanic tides occurs because of the changes caused by gravitational force between the earth and the moon. This force causes the rise and fall of the level of water in an ocean, and thus produce the tides. The part of the earth which is facing the moon at that moment is the one that is mostly affected by the force of attraction; water piles up and causes a high tide. The moon's attraction causes water to be drawn from the side which is not facing the moon at that moment and causes a low tide. The moon causes two high tides and two low tides in 24 hours or in one day.
When sea water makes high and low tides, it can have the following results:
- Soil erosion on sea shores, especially when there are large waves;
- Low and high tides bring certain sea products onto the shore. The products include corals, shells of sea snails, shallow shells and small cowry shells. These sea products are used by people for decoration and other purposes.
Sea products on the shore
Examples of sea shells
When the earth is revolving around the sun, we get four seasons of the year: summer, winter, autumn and spring. Also, we get differences in length between night and day for a certain period of the year. For example, the sun sets very late in the period from November to January but sets early in the period from June to July. In its revolution, the earth is closest to the sun on 3rd January each year. This period is known as Perihelion. On 6th July each year, the earth is farthest from the sun. This period is called Aphelion (Figure 4). Also, when the earth is revolving around the sun, we get different dimensions of the overhead sun in different periods of the year. Moreover, when the earth is revolving around the sun, it causes solar and lunar eclipses.
The earth revolving around the sun
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