Earth: Third planet from the Sun

Average distance from the Sun: 1 AU (150 million km)
Orbital period (Length of Year): 365.26 Earth days
Rotational period (Length of Day): 23.93 Earth hours
Orbital inclination: 0 deg
Average orbital speed around the Sun: 29.79 km/s
Diameter: 12,756 km
Axial inclination: 23.4 deg
Mass: 5.98 x 10^24 kg (1 Earth mass
Relative surface gravity (Earth = 1): 1
Average temperature: 8 deg C (46 deg F)
Atmosphere: nitrogen, oxygen, argon
Albedo: 0.39
Number of moons: 1 (the Moon, sometimes called Luna)

When seen from space, the Earth appears as a blue ball, partially covered with swirls of white clouds. A bluish envelope of gas surrounds the Earth - our atmosphere. At a closer range, you can see land, oceans, mountains, and cloud patterns. The surface is not smooth, but covered with mountains, plains, and valleys. There are two polar caps - white areas of frozen water at the North and South Poles. Two-thirds of the Earth's surface is covered with water, while the other one-third is land . In time, you could detect seasonal changes on Earth's surface. The first evidence of life you would see would probably be the proliferation of artificial outdoor lighting on the night side of the planet. The Earth is the only planet known to have life.

A planet actually has two types of days: a sidereal day, which is its rotation with respect to the stars and a solar day, which is its rotation with respect to the Sun. For most planets, like Earth, which rotate very rapidly compared to their orbit speed , the two types of days are almost the same. For example, Earth's sidereal day is only four minutes shorter than its solar day (which is what our clocks use.)

Much of what we know about the interior of the Earth is from studies of earthquakes and man-made underground explosions. The Earth appears to be divided into several shells. At the center there is a very dense metallic core about 2,580 kilometers (1,600 miles) in diameter. This inner core is surrounded by an outer core of molten iron, nickel and cobalt (over 2,100 kilometers or 1,300 miles thick), and then a crystalline mantle (2,900 kilometers or 1,800 miles thick). It is primarily granite under the continents and basalt under the oceans. On the surface, hydrogen and oxygen form the water in the oceans.

Bound by gravity to the Earth, practically all of the atmosphere lies within one hundred miles of the Earth's surface. It is 78% nitrogen, 21% oxygen, and has small amounts of carbon dioxide and other gases, and unfortunately, an increasing quantity of man-made pollutants which can damage other parts of the atmosphere. For instance, some of these pollutants reduce the amount of ozone in the upper atmosphere. Ozone is vital because it protects us from harmful ultraviolet and x-ray radiation from the Sun.

The other planets in the solar system do not seem to have abundant free oxygen. We believe that a billion years of plant life on the Earth explains why we do. The Earth also has a magnetic field which traps charged particles such as protons and electron s which make up the solar wind.

Information Source:  http://www.moreheadplanetarium.org/index.cfm