Basic Data

• Mean Distance from Sun: 149.6 million km.
• Equatorial Radius: 6378 km.
• Mass: 5.97 x 10²⁴ kg.
• Surface Gravity: 9.8 m/s²
• Length of Year: 365.3 days
• Length of Day: 23h 56m
• Surface Air Pressure: 101.3 kPa

Wikipedia - Earth

About Earth

Our home world rightly deserves an entire page all its own—or more. Everything associated with human history since the beginning of mankind has taken place on what is often called this "small blue planet". Actually, Earth is the largest planet in the solar system that has a solid surface; only the four gas giants are larger. Similarly, terrestrial gravity is higher than on any other solid body in the solar system.

Temperatures vary widely; diurnally, seasonally, and from equator to poles. During Antarctic winter it can get down to -89° C, and some desert summer highs have reached as high as 57° C. Precipitation plays an important part in the hydrological cycle, evaporating water from the seas that cover 3/4 of the planet and returning the moisture to the land surface.

Earth has a relatively strong dipolar magnetic field, probably generated by currents in its molten core. This magnetic field is important, because it helps deflect a lot of the charged particles that would otherwise bombard the planet. Additionally, a layer of ozone in the upper atmosphere reduces the amount of ultraviolet radiation reaching the surface. This lack, and the subsequent high amount of UV bombardment, is one of the arguments against life on Mars. As with so many other phenomena on the planet, the ozone layer undergoes periodic fluctuations.

Unlike most other solid bodies in our solar system, Earth has very few clear meteor craters. Given the effects of weathering and erosion, this is not surprising. And although most modern scientists ridicule the notion, there are still a number who accept the idea that Earth's history has not been one of constant uniformitarianism. Catastrophic events—meaning sudden, major events that are not part of normal, everyday processes—actually do a better job of explaining a number of features of the planet, and could also be effective in erasing past cratering to a large degree.

Of all the planets in our solar system, Earth is the one that is "out of place". It possesses physical characteristics that are very difficult to account for naturally, such as the presence of oxygen in its atmosphere (oxygen is a reactive gas that would quickly combine with other elements and vanish, on a cosmic timescale). The presence of life is the greatest anomaly. The commonly accepted theory is that life arose as a result of natural processes over geologic time scales. However, a critical examination of the evidence reveals enormous flaws—including certain assumptions that violate basic laws of nature—which most scientists choose to ignore. The alternative, of course is the theory of intelligent design. I personally find it fascinating to note that recent models of planetary formation predict an Earth surrounded by a dense atmosphere of mostly water vapor, carbon dioxide and nitrogen—such a world would be dark and covered in liquid water, which is amazingly similar to the way Genesis describes the world at the time of Creation. Coincidence?

Earth's Moon

Earth has a single large satellite—the Moon—which is nearly a quarter of the diameter of Earth itself and orbits the planet in around one month (the word "month" comes from "moon-th"). The Moon has been visited by numerous space probes, and is the only other body in the solar system—indeed, the universe—that has actually been visited by humans. In July of 1969 the Apollo 11 lunar module landed on the surface of the Moon, carrying two astronauts, Neil Armstrong and Buzz Aldrin.

The Moon is essentially without atmosphere, and is covered in craters and maria, also commonly called "seas". These are immense solidified lava flows that essentially erased craters within their boundaries by filling them in. They are found almost exclusively on the side facing Earth.

Observation from Space

Earth and Moon seen from Mars orbit
by Mars Global Surveyor

Earth has been observed and studied by so many satellites that "space trash" is starting to become a hazard. However, some of the more interesting observations are those made by spacecraft not orbiting Earth. At least one view of Earth as an "evening star" in the Martian skies has been returned from surface probes. The Cassini probe orbiting Saturn has taken our picture. Several probes returning to use Earth for a gravitational assist to take them on to further targets have imaged our planet. But probably the most famous of all extraterrestrial shots of our world are those taken from the Moon.

Today, most satellites launched into Earth orbit serve purposes other than science. Communication and military satellites are among the most common. And the satellites that do look at Earth are usually there for the purpose of tracking weather or looking for minerals or other resources. Additionally, there is now a continuous manned presence in Earth orbit: the International Space Station.

And, of course, there are orbiting observatories such as the Hubble Space Telescope that are used to study the universe from a vantage point above the interference of the atmosphere. Without such hindrances as clouds and "seeing" (the blurring of an image due to turbulence in the atmosphere) telescopes can work twenty-four hours a day. The only inconvenience is servicing; entire Space Shuttle missions have been dedicated to repairs and upgrading on the Hubble Telescope.