The Earth in Space The Solar System
Earth’s solar system comprises the Sun and its planets, as well as all the natural satellites, asteroids, meteors, and comets that are captive around it. The solar system formed from an interstellar cloud of dust and gas, or nebula, about 4.6 billion years ago. Gravity drew most of the dust and gas together to make the Sun, a medium-size star with an estimated life span of ten billion years. During the Sun’s first 100 million years, the remaining rock and ice smashed together into increasingly larger chunks, until the planets, moons, asteroids, and comets reached their present state.
The Sun. The center of Earth’s solar system, the Sun is but one ordinary star among some 100 billion stars in an ordinary cluster of stars called the Milky Way galaxy. (There are at least ten billion galaxies in the universe, each with billions of stars). The Sun’s surface gravity is thirty four times that of Earth. The conversion of hydrogen into helium in the Sun’s interior, a process known as nuclear fusion, is the source of the Sun’s energy. Earth Revolution. The earth moves about the Sun in a slightly elliptical orbit called a revolution. It takes one year for the earth to make one revolution at an average orbital velocity of about (29.6 kilometers per second). (365.25 average solar days)
Earth’s Moon
Our Moon, however, is more than a quarter the diameter of the Earth, which makes ours the only planet (but pluto) in the solar system with a sizeable moon in comparison to itself, and that makes a difference to us. Without the Moon’s steadying influence, the Earth would wobble like a dying top, with goodness knows what consequences for climate and weather. The Moon’s steady gravitational influence keeps the Earth spinning at the right speed and angle to provide the sort of stability necessary for the long and successful development of life. This won’t go on forever. The Moon is slipping from our grasp at a rate of about 1.5 inches a year. In another two billion years it will have receded so far that it won’t keep us steady and we will have to come up with some other solution, but in the meantime you should think of it as much more than just a pleasant feature in the night sky.
The Sun and the Earth
Of all the astronomical phenomena that one can consider, few are more important to the survival of life on Earth than the relationship between Earth and the Sun. Almost all forms of life, including human, depend on the light and energy that the earth receives directly from the Sun. The various ecosystems on Earth are highly dependent on the angles at which the Sun’s rays strike Earth’s spherical surface. These angles, which vary greatly with latitude and time of year, determine many commonly observed phenomena, such as the height of the Sun above the horizon, the changing lengths of day and night throughout the year, and the rhythm of the seasons. Daily and seasonal changes have profound effects on the many climatic regions and life cycles found on earth.
The Seasons
Earth’s Interior
Earth’s Internal Structure
Plate Tectonics
Volcanoes
Earth’s Surface
Internal Geological Processes
External Processes
Earth’s Climates
The Atmosphere
Global Climates
