Contents |


|
||||||||
The Solar System is the astronomical name for the Sun and other objects such as the planets which are bound to it by gravity.
The main component of the Solar System is the Sun, which contains 98.6 percent of the system's mass and whose gravity holds everything else in orbit. All the main objects in the Solar System formed at the same time, as part of the same process (see Age of the Earth). [[File:|390px|thumb|center|Planets and dwarf planets of the Solar System. Compared with each other, the sizes are correct, but the distance is not.]]
Contents |
The formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud.[1]
Most of the collapsing mass collected in the centre, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.
This widely accepted model, known as the nebular hypothesis, was first developed in the 18th century by Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace. Its subsequent development has interwoven a variety of scientific disciplines including astronomy, physics, geology, and planetary science. Since the dawn of the 'space age' in the 1950s and the discovery of extrasolar planets in the 1990s, the models have been adjusted to account for new observations.
The Solar System has evolved considerably since its initial formation. Many moons have formed from circling discs of gas and dust around their parent planets, while other moons are believed to have formed independently and later been captured by their planets. Still others, as the Earth's Moon, may be the result of giant collisions.
Collisions between bodies have occurred continually, and have been important to the evolution of the Solar System. The positions of the planets often shifted, and planets have switched places.[2][3] This planetary migration is thought to have been responsible for much of the Solar System's early evolution.
The Earth's orbit around the Sun is nearly a perfect circle, but when mapped it is found that the Earth moves around the Sun in a very slightly oval shaped, or elliptical orbit. The other planets in the Solar System also circle the Sun in slightly elliptical orbits. Mercury has a more elliptical orbit than the others, and some of the smaller objects orbit the Sun in very eccentric orbits.
For thousands of years, most people did not believe that the Solar System was real. They thought that the Earth stayed still at the center of the universe. Although the Greek philosopher Aristarchus of Samos suggested that there was a special order in the sky,[4] Nicolaus Copernicus was the first to develop a mathematical system. In the 17th-century, Galileo Galilei, Johannes Kepler and Isaac Newton began helping people understand physics more clearly. This made people slowly accept the idea that Earth moves around the Sun and that the planets have the same physical laws that control Earth. More recently, telescopes and spacecrafts have led to discoveries of mountains and craters, and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.
In their order from the Sun, and labelled with the numbers like the picture on the right:
The planets are the biggest objects that go around Sun. It took people many years of looking carefully through telescopes to find the farthest away ones. No one expects to find new planets, but more small objects are found every year. Most of the planets have moons that orbit around them. There are at least 173 of these moons in the solar system.
Pluto had been called a planet since it was discovered in 1930, but in 2006 astronomers meeting at the International Astronomical Union decided for the first time on the definition of a planet, and Pluto did not fit. Instead they defined a new category of dwarf planet, into which Pluto did fit along with some other objects.
Astronomers think they will find more dwarf planets soon.
There are a few main parts of the Solar System. Here they are in order from the Sun, with the planets numbered, and the dwarf planets marked with the letters a - e.
Sometimes people use alternative names for similar regions defined above. These are less formal, and less well defined.
Sometimes the Outer solar system is taken to mean and the Gas Giant Planets, the Kuiper Belt, and the Scattered Disk. But with more recent discoveries of objects in the Kuiper Belt, and the Scattered Disk, and with more dwarf planet discoveries, the Outer solar system is now usually defined as above.
The Oort cloud is separate from the Tran-Neptune region, and much farther out.
The plane of the ecliptic is defined by the Earth's orbit around the Sun. All of the planets orbit the Sun roughly around this plane. The farther away from this plane a planet orbits, the more inclined is its orbit. If you could look at the solar system "edge on" then all the planets would be roughly in a horizontal plane around a centre line of the Sun, but not around the Sun's equator.
The Solar System
| |||||||
|---|---|---|---|---|---|---|---|
| Sun • Heliosphere | Planets ☾ = moon(s) ∅ = rings | Mercury | Venus | Earth ☾ | Mars ☾ | ||
| Jupiter ☾ ∅ | Saturn ☾ ∅ | Uranus ☾ ∅ | Neptune ☾ ∅ | ||||
| Dwarf planets | Ceres | Pluto ☾ | Haumea ☾ | Makemake | |||
| Eris ☾ | |||||||
| Small Solar System bodies | Asteroids (minor planets) | Groups and families: Vulcanoids · Near-Earth asteroids · Asteroid belt Jupiter Trojans · Centaurs · Neptune Trojans · Asteroid moons · Meteoroids · Pallas · Juno · Vesta · Hygiea · | |||||
| See also the list of asteroids, and the meaning and pronunciation of asteroid names. | |||||||
| Trans- Neptunians | Kuiper belt – Plutinos: Orcus · Ixion – Cubewanos: 556372002 UX · Varuna · 15760 1992 QB · 556362002 TX · Quaoar · Huya · 555652002 AW | ||||||
| Scattered disc: 845222002 TC · 2004 XR190 · Sedna | |||||||
| Comets | Lists of periodic and non-periodic comets · Damocloids · Hills cloud · Oort cloud | ||||||
| See also Geology of solar terrestrial planets, astronomical objects, the solar system's list of objects, sorted by radius or mass, and the Solar System Portal | |||||||
bjn:Tata Suryakrc:Кюн система
frr:Sansüsteem
rue:Сонячна сістема
Here are sentences from other pages on Sun, which are similar to those in the above article.
|
|