Sunday, 11 December 2011

The following are videos about solar system


Discovery and exploration of the Solar System
For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People believed the Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system. His 17th-century successors, Galileo Galilei, Johannes Kepler and Isaac Newton, developed an understanding of physics that led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed the Earth. Additionally, the invention of the telescope led to the discovery of further planets and moons. In more recent times, improvements in the telescope and the use of unmanned spacecraft have enabled the investigation of geological phenomena such as mountains and craters, and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.

The following is Solar System showing the plane of the ecliptic of the Earth's orbit around the Sun in 3D view showing Mercury, Venus, Earth, Mars and Jupiter making one full revolution. Saturn and Uranus also appear in their own respective orbits around the Sun.
http://upload.wikimedia.org/wikipedia/commons/0/08/Solarsystem3DJupiter.gif
The following is Solar System showing plane of the Earth's orbit around the Sun in 3D view with only Mercury, Venus, Earth and Mars.
http://upload.wikimedia.org/wikipedia/commons/0/0d/Ecliptic_plane_3d_view.gif

Sunday, 27 November 2011

Comets


Comets are small Solar System bodies,typically only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.
Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are believed to originate in the Kuiper belt, while long-period comets, such as Hale–Bopp, are believed to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent. Some comets with hyperbolic orbits may originate outside the Solar System, but
determining their precise orbits is difficult. Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.