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Material in the Solar System

Discussion Questions

The solar system consists of the Sun, with 9 planets around it. The planets in order from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto as shown above. This diagram is from The planets. The information on solar system is provided by NASA, which also provides the Solar System Simulator that alows you to see all planets from any planet of the solar system.

The Solar System

It was, and still is, natural for one to consider oneself the center of everything. Thus, people have always considered Earth the center of universe, with the Sun revolving around it. At the dawn of civilization, when the society was controlled by a few powerful figures, those spoke of the Earth not being the center would be executed, because spreading information different from the authorities directly threatened their power to control people. Thus, only scholar with courage would speak out for the truth. About 250 BC, Aristarchus of Samos placed the sun at the center of the solar system, but his call was mostly ignored.

After having spent a life time observing the movements of stars and planets, Copernicus (1473 - 1543) realized that the earth revolved around the sun, a fact contradicting his Church's view. He carefully recorded his observation, plotted his diagrams, made his conclusion, and arranged the publication of his book not long before his death. His prudent work convinced many astronomers, including Galileo (1564 - 1642), to examine the solar system closely. Due to the Copernican revolution, the study of astronomy flourished. The results are summarized in a table form as below.

Mass Equatorial radius Mean density No. of satellites Distance from Sun Surface temperature /K
Sun 332,945. 109.2 1.4 - - 4,700-5,000
Mercury 0.056 0.382 5.5 0 0.4 900
Venus 0.815 0.949 5.25 0 0.7 725
Earth* 1. 1. 5.52 1 1. 290
Mars 0.107 0.533 3.94 2 1.6 230
Minor planets Many (about 1,600) asteroids in the region between mars and Saturn, mostly concentrated at 2.8 AU from the sun, and their diameters range from 800 to a few km.
Jupiter 317.88 11.20 1.33 12 + 5.2 150?
Saturn 95.17 9.38 0.72 10 + 9.5 95?
Uranus 14.60 4.23 1.10 5 + 19.2 90?
Neptune 17.25 3.95 1.57 2 + 30.1 80?
Pluto 0.095 0.5 ? 0 (40?) 60?
Masses, equatorial radii, and distances from the Sun are compared with those of the Earth. Thus, these values of the Earth are given as unity. The mean distance between the Sun and Earth is usually called an Astronomical Unit (AU), which is 149,597,870.7 km (one hundred fifty million kilometers), 4.3 light minutes, or 499.0 light seconds.

Recent observation showed that Jupiter, Saturn, Uranus, and Neptune all have rings, and they all have more satellites than indicated here, but we don't have the exact numbers.

Some interesting features about the planets in our solar system are given below:

The Planets

The term planet was derived from Greek, meaning wanderer. There are three theories concerning the formation of the planets in the solar system, and none accounts for all facts. Since we know of no other solar system, the answer as to how planets form remains to be debated. Here are some current thoughts.

Confidence Building Questions

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