IN THIS CHAPTER
The Solar System
The Solar System
The Earth is a planet or secondary circling the Sun or primary at a mean distance of about 93 million miles. The mean Earth-Sun distance is taken as one astronomical unit (AU). The plane of the Earth’s orbit around the Sun in the course of one year is called the plane of the ecliptic or zodiac. The ecliptic is the circle on the Celestial Sphere (at an infinite distance) at the intersection of the Celestial Sphere and the plane of the Earth’s orbit. The Earth’s axis of rotation is not perpendicular to the plane of the ecliptic, but is inclined about 23.5-degrees to the perpendicular. The North Pole of the Earth does not point in the direction of the ecliptic north pole.
There are at least nine planets, including the Earth, revolving around the Sun. The closest to the Sun is Mercury (at a mean distance of about .4 AU) and the most distant is Pluto (at a mean distance of 39.4 AU). The planes of the orbits for all the planets are quite close to the plane of the ecliptic, except that of Pluto, which is inclined some 17-degrees.
Six of the nine planets have satellites. In addition, there are thousands of small bodies revolving around the Sun between the orbits of Mars and Jupiter, the asteroids or minor planets. The system, including the Sun, its planets and asteroids, is referred to as the solar system. In addition to these main members of the solar system, there is a significant amount of gas, dust and small solids (including meteors and comets), which may be collectively referred to as inter-planetary matter.
The main purpose of this section is to provide reference information useful in connection with sections. The following pages contain tables of pertinent information concerning the planets, their satellites, the asteroids, comets and meteors. There are many good texts available describing the nature of our solar system in great detail and it is assumed that the reader either has some familiarity with our system or can obtain this at the local library. Here we are interested in the significant points and directions in space rather than an examination of the many different qualities of the members of our solar system.
