Of course, since this Hitchhiker's Guide to the Solar System is written by "earthlings," this is our favorite planet of all. We have plenty of water and the sun warms our days without being too hot.

About 93 million miles away, the Earth is the third planet from the Sun. Among the inner or rocky planets Earth is the largest and the only one to have water on its surface. It is the fifth largest in the solar system and the only one to have known life residing on it. This includes animal and plant life, as well as intelligent beings. Animals, plants, and intelligent beings require three things to live: water, air, and tolerable temperatures. Earth offers all three of these things.

Water is stored in its oceans (known as the hydrosphere) that cover over 71% (or almost 140 million square miles) of its surface and that are the principal habitat of life on the planet. Human beings live on the other 29% of Earth's surface (known as the lithosphere) which covers about 57 million square miles.

The process of evaporation and its atmospheric qualities provide for a water cycle. Earth's water cycle is actually quite easy to understand. Water from the different bodies around the Earth is evaporated into the atmosphere. Under certain conditions, clouds form and then through rain the water is redistributed to the Earth's surface.

The Earth's atmosphere is gaseous and in such a delicate balance that animals, plants, and humans can live on it. Earth's atmosphere consists of 21% oxygen, 78% nitrogen, and .9% argon. The other tenth percent consists of many different forms of gaseous properties, which absorb radiation from the Sun. If these gases were to increase in their levels, the Earth's inhabitants would be poisoned. Like the water cycle, sustenance of life has its cycle. Plants require carbon dioxide in their photosynthesis process and provide more oxygen for the humans.

The water on Earth's surface as well as the water vapor in its atmosphere keeps the Earth's temperature moderate enough to sustain animal, plant, and human life. If the Earth was closer to the Sun, it would be too hot. If it were further away from the Sun, then it would be too cold to sustain life.

The balance of life on Earth between its animals, plants and humans creates a food chain to nourish humans. Animals and plants from both the ocean and the land are the primary nourishment for the Earthlings, but of late they have learned to create food and drink from chemicals.

Earth rotates on its axis about the same speed as Mars and makes one complete rotation in 23 hours and 56 minutes. It takes 365 days and 6 hours to complete its revolution around the Sun. Other planets' days and years are measured against Earth's in this Guide. Earth has one moon.

Even the Earth's rotation supports life. Since it spins like a top, half of the Earth faces the Sun and has light, which we Earthlings call "day." The other half of the Earth faces away from the sun and has darkness, which we call "night." Some light is shed from the Earth's one moon which revolves around the Earth about every thirty days. During the night, human beings sleep and rejuvenate and recreate themselves. During the day, they have been sentenced to toil for their food and their shelter against the elements.

The Earth is so perfectly designed that even as it travels around the Sun, it tilts to one side so that one of the poles is facing the Sun and the other pole is facing away from the Sun. The side that is facing away from the Sun is experiencing a season called winter when crops are dormant. The portion of Earth that is moving toward the Sun is experiencing a season called spring when crops are planted. The side that is facing the Sun is experiencing a season called summer when crops grow. The portion of Earth that is moving away from the Sun is experiencing a season called autumn when crops are harvested.

The stars in Earth's sky are also effected by the rotation and revolution of the Earth. Depending upon your position on Earth, you will see different constellations in the summer and in the winter. Check out Winter Constellations for further information.

The Earth is primarily made of different layers of rock. The innermost core is made of hot iron. That core is surrounded by hot, liquid iron and nickel. Then there is a thick layer of hot rock which is referred to as the mantle. There is a thin, hard shell on the very top surface called the crust. As a result of tectonic plates, the Earth's crust splits and opens itself for volcanic action. There are many active and inactive volcanoes on Earth.

The Earth's atmosphere causes most meteorites to dissolve or break apart before hitting its surface. Therefore, there are very few craters on its surface.

The Earth's rapid spin and its metallic core cause a magnetic field that surrounds it. When charged particles from the Sun fall towards Earth, they are trapped by this magnetic field before reaching the Earth's surface. These charged particles react with the gases in the atmosphere and begin to glow, which creates aurorae in the Arctic Circle and the Antarctic Circle.

Java enabled browsers can visit NASA's Color Me Site and learn more about the Earth's surface.

We welcome you to visit our planet and enjoy its beautiful sunrises and sunsets and see intelligent life in paradise.

Check out other interesting sites about the Earth:

More links to the Hitchhiker's Guide to the Solar System: