CASE 408 - Stars and planets

Our Solar System could be called our neighborhood in our home Galaxy, the Milky Way. Our solar system has 8 planets; in order of increasing average distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The International Astronomy Union has an official definition for a planet. It states, "A 'planet' is defined as a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit." Pluto is a dwarf planet. Stars are balls of mostly hydrogen and helium gas that shine extremely brightly but are lightyears away from us except our sun, which is a star which eventually in around 8 billion years will explode and then spend a futher 2 billion years cooling and burning out. A star is so massive that its core is extremely dense and hot. At the high core temperatures of a star, atoms move so fast that they sometimes stick to other atoms when they collide with them, forming more massive atoms and releasing a great amount of energy. This process is known as nuclear fusion.



There are (as of June 11, 2012) 102 known multiplanetary systems (i.e. stars with at least two confirmed planets), beyond our Solar System. The star table below contains information about the coordinates, spectral and physical properties, and number of confirmed planets.



http://en.wikipedia.org/wiki/List_of_multiplanetary_systems