What is the Solar System ?The Solar System consists of the Sun and those celestial objects bound to it bygravity. These objects are the eight planets and their 166 known moons, four dwarfplanets and billions of small bodies, including asteroids, icy Kuiper belt objects,comets, meteoroids, and interplanetary dust.Broadly, the charted regions of the Solar System are the Sun, four terrestrial innerplanets, the asteroid belt, four gas giant outer planets, the Kuiper belt, the scattereddisc, and ultimately perhaps the hypothetical Oort cloud.A flow of charged particles from the Sun (the solar wind) permeates the SolarSystem. This creates a bubble in the interstellar medium known as the heliosphere,which terminates at the heliopause, near the scattered disc.In order of their distances from the Sun, the eight planets are:MercuryVenusEarthMarsJupiterSaturnUranusNeptune
The Sun (Latin: Sol) is the star at the centre of the Solar System. The Earthand other matter (including other planets, asteroids, meteoroids, comets,and dust) orbit the Sun, which by itself accounts for about 99.8% of theSolar Systems mass. Energy from the Sun, in the form of sunlight andheat, supports almost all life on Earth via photosynthesis, and drives theEarths climate and weather.
Mercury is the innermost and smallest planet in the solar system, orbiting the Sunonce every 88 days. Mercury is bright when viewed from Earth, ranging from −2.0 to5.5 in apparent magnitude, but is not easily seen as its greatest angular separationfrom the Sun (greatest elongation) is only 28.3°: It can only be seen in morning andevening twilight. Comparatively little is known about it; the first of two spacecraft toapproach Mercury was Mariner 10 from 1974 to 1975, which mapped only about 45%of the planet’s surface. The second was the MESSENGER spacecraft, which mappedanother 30% of the planet during its flyby of January 14, 2008. MESSENGER will maketwo more passes by Mercury, followed by orbital insertion in 2011, and will surveyand map the entire planet.
Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earthdays. The planet is named after Venus, the Roman goddess of love. It is thebrightest natural object in the night sky, except for the Moon, reaching anapparent magnitude of −4.6. Because Venus is an inferior planet from Earth, itnever appears to venture far from the Sun: its elongation reaches a maximumof 47.8°. Venus reaches its maximum brightness shortly before sunrise orshortly after sunset, for which reason it is often called the Morning Star or theEvening Star.
Earth is the third planet from the Sun. Earth is the largest of the terrestrialplanets in the Solar System in diameter, mass and density. It is also referred to asthe Earth, Planet Earth, the World, and Terra.Home to millions of species, including humans, Earth is the only place in theuniverse where life is known to exist. Scientific evidence indicates that the planetformed 4.54 billion years ago, and life appeared on its surface within a billionyears. Since then, Earths biosphere has significantly altered the atmosphere andother abiotic conditions on the planet, enabling the proliferation of aerobicorganisms as well as the formation of the ozone layer which, together withEarths magnetic field, blocks harmful radiation, permitting life on land.
Mars pronounced is the fourth planet from the Sun in the Solar System. The planet is namedafter Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddishappearance.Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both ofthe impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of Earth. Itis the site of Olympus Mons, the highest known mountain in the Solar System, and of VallesMarineris, the largest canyon. Furthermore, in June 2008 three articles published in Naturepresented evidence of an enormous impact crater in Mars northern hemisphere, 10,600 kmlong by 8,500 km wide, or roughly four times larger than the largest impact crater yetdiscovered, the South Pole Aitken basin. In addition to its geographical features, Mars’ rotationalperiod and seasonal cycles are likewise similar to those of Earth.
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is twoand a half times as massive as all of the other planets in our Solar System combined. Jupiter isclassified as a gas giant, along with Saturn, Uranus and Neptune. Together, these four planetsare sometimes referred to as the Jovian planets, where Jovian is the adjectival form of Jupiter.The planet was known by astronomers of ancient times and was associated with themythology and religious beliefs of many cultures. The Romans named the planet after theRoman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of−2.8, making it the third brightest object in the night sky after the Moon and Venus.
Saturn is the sixth planet from the Sun and the second largest planet in the SolarSystem, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gasgiant. Together, these four planets are sometimes referred to as the Jovian planets, whereJovian is the adjectival form of Jupiter.Saturn is named after the Roman god Saturnus, equated to the Greek Kronos and theBabylonian Ninurta. Saturns symbol represents the gods sickle.The planet Saturn is composed of hydrogen, with small proportions of helium and traceelements. The interior consists of a small core of rock and ice, surrounded by a thick layerof metallic hydrogen and a gaseous outer layer. The outer atmosphere is generally bland inappearance, although long-lived features can appear. Wind speeds on Saturn can reach1,800 km/h, significantly faster than those on Jupiter. Saturn has a planetary magnetic fieldintermediate in strength between that of Earth and the more powerful field around Jupiter.
Uranus or is the seventh planet from the Sun and the third-largest and fourth-most massiveplanet in the solar system. It is named after the ancient Greek deity of the sky (Uranus), thefather of Kronos (Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the nakedeye like the five classical planets, it was never recognized as a planet by ancient observersdue to its dimness and slow orbit. Sir William Herschel announced its discovery on March13, 1781, expanding the known boundaries of the solar system for the first time in modernhistory. This was also the first discovery of a planet made using a telescope.
Neptune is the eighth and farthest planet from the Sun in the Solar System. It is the fourthlargest planet by diameter, and the third largest by mass. Neptune is 17 times the mass ofEarth and is slightly more massive than its near-twin Uranus, which is 15 Earth masses andless dense. The planet is named after the Roman god of the sea.Discovered on September 23, 1846, Neptune was the first planet found by mathematicalprediction rather than regular observation. Unexpected changes in the orbit of Uranus ledastronomers to deduce the gravitational perturbation of an unknown planet. Neptune wasfound within a degree of the predicted position. The moon Triton was found shortlythereafter, but none of the planets other 12 moons were discovered before the 20thcentury. Neptune has been visited by only one spacecraft, Voyager 2, which flew by theplanet on August 25, 1989.
A star is a massive, luminous ball of plasma. The nearest star to Earth is the Sun, which is thesource of most of the energy on Earth. Other stars are visible in the night sky, when they arenot outshone by the Sun. For most of its life, a star shines because thermonuclear fusion in itscore releases energy that traverses the stars interior and then radiates into outer space.Almost all elements heavier than hydrogen and helium were created by fusion processes instars. Astronomers can determine the mass, age, chemical composition and many otherproperties of a star by observing its spectrum, luminosity and motion through space. Othercharacteristics of a star are determined by its evolutionary history, including the diameter,rotation, movement and temperature. A plot of the temperature of many stars against theirluminosities, known as a Hertz sprung-Russell diagram allows the age and evolutionary stateof a star to be determined. The star which is closest to the Earth is the Sun.
A meteorite is a natural object originating in outer space that survives an impact with theEarths surface. While in space it is called a meteoroid. When it enters theatmosphere, impact pressure causes the body to heat up and emit light, thus forming afireball, also known as a meteor or shooting star. The term bolide refers to either anextraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-likemeteor regardless of whether it ultimately impacts the surface.More generally, a meteorite on the surface of any celestial body is a natural object that hascome from elsewhere in space. Meteorites have been found on the Moon and Mars.
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