A planet as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.
The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people’s lives, although such a causation is rejected by the scientific community.
Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.
Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. As of February 2009, there are 342 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets
In 2009 the world celebrates the International Year of Astronomy to commemorate the 400th anniversary of Galileo’s use of a telescope to study the night sky. 2009 is also the anniversary of many other important dates in the history of science, such as the publishing of Kepler’s Astronomia Nova, Huygens’ Systema Saturnium, and the first moon landing. You can follow IYA2009 now on Twitter
Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Terra.
The planet’s natural resources are being consumed faster than they can be replaced, according to the WWF.
If current trends continue two planets would be needed by 2050 to meet humanity’s demands.