- EQUATORIAL RADIUS: 6378.140 km
- POLAR RADIUS: 6356.752 km
- MASS: 1.000 (Earth=1)
- DENSITY: 5.52 (g/cm^3)
- GRAVITY: 1.000 (Earth=1)
- ORBIT PERIOD: 365.26 (Earth days)
- ROTATION PERIOD: 1.00 (Earth days)
- SEMIMAJOR AXIS OF ORBIT: 1.000 au
- ECCENTRICITY OF ORBIT: 0.017
Early philosophy had the Earth as the center of the universe. Although Aristarchus of Samos, in the 3rd Century B.C., figured out how to measure the distances to and sizes of the Sun and the Moon, and concluded that the Earth orbited the Sun, this view didn't attract followers until Nicolaus Copernicus, a Polish astronomer, published "On the Revolutions of the Celestial Spheres" in 1543.
The Earth, itself, is composed primarily of iron, oxygen, silicon, magnesium, nickel, sulfur, and titanium. 71 Percent of its surface is covered with water. Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water.
Earth has only one natural satellite, the Moon at a distance of 384,000km, with a radius of 1738KM and a mass of 7.32e22kg. However, there are thousands of small artificial satellites which have been placed in orbit around the Earth. Also, asteroids 3753 Cruithne and 2002 AA29 have complicated orbital relationships with the Earth; they're not really moons, the term "companion" is being used.