Motions of the Earth
The earth is continuously moving. It has three motions; 1) spins, 2)travels around the sun, and 3)moves through the Milky Way. We use the spinning and traveling to measure our days and years. The earth spins around it's axis. This spin makes it seem that the sun is moving from east to west. One day is the time it takes for the earth to spin once. It takes 23 hours, 56 minutes, and 4.091 seconds for the earth to do this. This length of time is called a sidereal day.
Next is the traveling. The earth travels around the sun in 365 days, 6 hours, 9 minutes and 9.54 seconds. This is called a sidereal year. The earth travels 595 million miles around the sun at a speed of 66,600 miles per hour. The path the earth takes to move around the sun is called an orbit.
The Milky Way spins as well. It revolves around the center of the Galaxy at 155 miles per second! The earth only has one moon. Its diameter is 2,160 miles.
The earth has a North and South Pole. Halfway between these poles is the equator. The earth is not perfectly spherical. It is slightly flatter at the poles. Characteristics:
The earth's atmosphere consists of 78% Nitrogen, 21% Oxygen, and 1% argon and other gases. It also contains water vapor and dust particles. Clouds float in the troposphere, the lowest part of the atmosphere. The air gets thinner as it gets further from the earth.
The earth's crust is about 5 miles thick under the oceans and about 25 miles thick under the continents. Temperatures can reach up to 1600 degrees Fahrenheit. This crust is made of three types of rock; 1) igneous, 2) sedimentary, and 3) metamorphic. Igneous rocks are formed when melted rock such as lava cools and hardens. Sedimentary rock develops from material such as plants or animals. Metamorphic rocks formed deep in the crust by heating of other rocks. The crust consists of oceanic and continental crust.
Beneath the crust is a sphere of hot rock and metal. It is divided in to the mantle, outer core, and the inner core. The mantle is a layer of rock under the crust. It is about 1,800 miles deep and made of silicon, oxygen, aluminum, iron and magnesium. The temperature ranges from 1,600 degrees Fahrenheit to about 8,000 degrees. The outer core is under the mantle. It is about 1,400 miles thick and consists of melted iron, oxygen and sulfur. The temperature range is 8,000 degrees to 11,000 degrees. The inner core is the center of the earth. It is believed that this is consisted of solid iron mixed with other elements such as oxygen and sulfur. The temperature can range up to 13,000 degrees Fahrenheit.
Another interesting feature of earth and other planets is that there is a force called gravity. This is the force that causes objects to fall if dropped. The earth and the planets travel around the sun because gravity pulls them towards it. On earth, gravity is stronger at the poles and at sea level.
We always hear about magnetic poles, but what are they really? The earth spins around an imaginary line that connects the north and the south poles. Near these poles are the magnetic poles. These poles acts just as a bar magnet. The north magnetic pole is on Ellef Ringnes Island in N. Canada. The south magnetic pole is off the coast of Wilkes Land, a part of Antarctica. It is believed that magnetism comes from the "circulation of molten rock in the earth's outer core." Magnetic force is present in the magnetosphere, a region shaped like a teardrop. This magnetosphere acts on electrons and protons that move throughout space and shields the earth from them.
Now go on to Mars.....
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