Earth

The Earth is the planet on which humans live. It is mostly covered by water with many mountains and plains. The atmosphere contains oxygen that humans can breath. The Earth day is 24 hrs. and it takes 365 days to revolve around the sun. The Earth has only one natural satellite called the moon.

The Earth is made up of layers. One can compare the outer layer of the Earth to the thin layer of a peach. The outer layer of the Earth is known as the crust. The crust is a very thin layer of hard rock from 50-70 kilometers thick. Beneath the crust is the mantle. The mantle is the thickest layer of the Earth. It is made up of very hot rock. The mantle is about 3,000 kilometers thick. The innermost layer of the Earth is the core. The outer core is solid and seems to be made of iron and nickel. The outer core is solid and seems to be iron.

On July 20, 1969, Neil Armstrong and Eldwin Aldrin left the first foorprints on the moon. The surface of the moon is rugged with mountains and craters due in part to the absence of eroding forces. Scientists believe the craters were formed when objects traveling in space hit and dented the moon's surface. The seas of the moon are large flat plains called maria. Maria is the latin word for sea. Early astronomers believed the smooth areas on the surface of the sun to be seas but actually there is on water on the moon. Maria are dry lava beds that were formed by volcanic action on the moon millions of years ago.

Phases refer to the different shapes the moon appears from the earth. During it's monthly cycle the moon goes from New Moon (all in shadow) through first quarter( half illuminated) to Full ( illuminated as a round circle) to last quarter (again half illuminated) then back to new moon. Waxing refers to the moon when it is getting larger or more illuminated from New to Full. Wanning refers to the moon when it is getting smaller or less illuminated from Full to New. Crescent is when the moon is slightly illuminated either before first quarter or after last quarter. Gibbous is when the moon is mostly illuminated either just before or after Full Moon. The moon has no light of its own reflecting the light of the sun. The moon revolves around the earth in a counterclockwise direction. The shape of the moon is always the same, but we see different portions of its lighted surface as it makes its trip around the earth. It takes 29 and a half days for the moon to pass through all its phases.

The Earth moves at a speed of 30 km per hour. It travels in a circular motion around the sun. This path is called its orbit. Each complete orbit or revolution around the sun, takes 365 days. The Earth has a second type of motion. It spins, or rotates, like a top about an imaginary line that runs from the North Pole to the South Pole. This imaginary line is called the earth's axis. Each complete rotation on the earth takes 24 hours. This motion gives us night and day.

Due to the Earth revolving around the sun tilted on its axis, most of the earth experiences different seasons. The tilt of the earth causes different parts of the earth to get varying amounts of sunlight as it orbits the sun. During the sumer months, the North Pole is tilted toward the sun. The Northern Hemisphere receives more of the sun's direct rays causing the days to become warmer and the number of daylight hours to increase. Six months later the North Pole is tilted towards the sun. Then the days become colder and the number of daylight hours decreases. The Earth is a very fascinating planet continually changing. The earth is able to support life. Scientists are constantly exploring to find other planets that might contain life.

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