|Intelligent Systems And Their Societies||Walter Fritz|
The majority of persons would agree that the sun and its planets form a system. There is a flow of energy from the sun to its environment. A very small portion of this energy reaches the planets. (Less than one part in a million.) The rest goes to interstellar matter and the stars. Also there is a very small movement of matter, the solar wind, which in part falls on the planets. These are very small effects, but there is also a very strong effect of the sun on its planets. Without the sun the movement of the planets would be in a straight line. Due to the sun the movement is an ellipse around the sun.
The system sun/earth and the system earth/moon
People say that the planet earth and the moon form a system and that seems reasonable. The earth has a tremendous effect on the movement of the moon; and the moon has a small effect on the movement of the earth, but a great effect on the movement of the waters of the earth: the tides. But is the moon not part of the solar system? Obviously it is. But the earth has a greater effect on the moon than the sun. Therefore, we also talk about an earth and moon system. Also the earth is more affected by the sun than by the moon. Therefore, we talk about a sun and earth system.
To help rectify this overlap, we can also say that the solar system has a subsystem, namely the earth and moon system.
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