Solar   System

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Planets and dwarf planets of the Solar System. Sizes are to scale, but relative distances from the Sun are not.

              

          This article is about the Sun and its planetary system. For other systems, see planetary system and star system. For a list of physical and orbital statistics for the Solar System's largest bodies, see List of gravitationally rounded objects of the Solar System

     The Solar System^[a] consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass (well over 99%) is in the Sun. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets^[e] whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".

 

 

Solar System showing plane of the Earth's orbit around the Sun in 3D view with only Mercury, Venus, Earth and Mars



                 The Solar System is also home to a number of regions populated by smaller  objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc; linked populations of trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these populations, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets.^[e] In addition to thousands of small bodies^[e] in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.
              Six of the planets and three of the dwarf planets are orbited by natural satellites,^[b] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.

              The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.
The Solar System is located in the Milky Way galaxy, which contains about 200 billion stars.

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

Discovery and exploration

               Main article: 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,^[1] Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system.^[2] 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.


                                                                  Structure

The orbits of the bodies in the Solar System to scale (clockwise from top left

               
                  The principal component of the Solar System is the Sun, a main-sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally.^[3] The Sun's four largest orbiting bodies, the gas giants, account for 99 percent of the remaining mass, with Jupiter and Saturn together comprising more than 90 percent.^[c]        Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are frequently at significantly greater angles to it.^[4][5] All the planets and most other objects orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above the Sun's north pole).^[6] There are exceptions, such as Halley's Comet.
                  
                   The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of rocky asteroids, and four gas giants surrounded by the outer Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giant planets.^[7] Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.^[8]
                           
                 



 

Taiwan presidential challenger admits defeat

            

     Taiwan presidential challenger    

                    admits defeat

credit :  http://www.bbc.co.uk/news/world-asia-16557209 

Mr Ma has sought to bolster economic ties with China

                      Taiwan opposition candidate Tsai Ing-wen has admitted defeat in the island's presidential election.

              

            Ms Tsai congratulated incumbent President Ma Ying-jeou on his victory and resigned as chairwoman of the Democratic Progressive Party (DPP).

            Mr Ma had campaigned on his record of improving economic ties with neighbouring China.

            China does not recognise Taiwan, regarding the island as a breakaway province. It wants unification.

              "We accept the Taiwan people's decision and congratulate President Ma," Ms Tsai told party workers.

"We want to give our deepest apology to our supporters for our defeat."

Ma Ying-jeou, who is seeking a second term as president, at a flag-raising ceremony for the anniversary of the founding of the Republic of China

             Ms Tsai's DPP favours formal independence from China, although Beijing has repeatedly threatened retaliation if Taiwan makes such a move.

          In her campaign, she stressed economic issues and downplayed the pro-independence stance.     With about 90% of votes counted, Taiwan's Central Election Commission said Mr Ma had won 51% against 46.3% for Ms Tsai.

          A third contender, James Soong, once a senior figure in Mr Ma's party, the Kuomintang (KMT), had 2.7%.

"This is not my personal victory, the victory belongs to all Taiwanese," Mr Ma told jubilant supporters in central Taipei.

"They told us that we are on the right track."

Cross-strait relations

Taiwan has been suffering its worst economic downturn in decades and unemployment has been rising.

However, most voters still view relations with China as the most important issue.

          During Mr Ma's presidency regular direct flights and shipping links have been established with China and a landmark trade deal has been signed that cuts tariffs on hundreds of Taiwanese exports to the mainland.

Mr Ma, 61, said a vote for him was a vote for peace.

But some voters fear that Mr Ma's policies will pave the way for unification.

Ms Tsai and Mr Ma both cast their votes early in the capital.

"I'm very happy, I urge everyone to come out early and vote. This weather should help the voting rate," Mr Ma told reporters at his polling station in a Taipei church as the light rain eased.

Beijing has 1,500 missiles aimed at the island to deter any attempt to declare independence.

The United States, which is a key ally of Taiwan, will also be watching the outcome of the vote closely.

Under the Taiwan relations act passed by the US Congress in 1979, the US is obliged to come to the defence of the island if it is attacked by any other party.

While Washington has not openly endorsed Mr Ma, observers say it is an open secret that the US prefers his approach to China.