Solar System – the planetary system, which includes the central star – the Sun – and the natural space objects orbiting the Sun.
Most of the mass of objects related to the Sun by gravity, contained in eight relatively solitary planets have nearly circular orbits and located within a nearly flat disc – the plane of the ecliptic. Four smaller inner planets: Mercury, Venus, Earth and Mars (also called the terrestrial planets), composed mainly of silicates and metals. The four outer planets: Jupiter, Saturn, Uranus and Neptune, also called gas giants, are composed largely of hydrogen and helium, and much more massive than the terrestrial planets.
Six of the eight planets and three dwarf planets are surrounded by natural satellites. Each of the outer planets is surrounded by a ring of dust and other particles.
In our solar system, there are two areas filled with small bodies. The asteroid belt located between Mars and Jupiter, is similar in composition to the terrestrial planets, because it consists of silicates and metals. Large objects of the asteroid belt is Ceres, Pallas and Vesta. Beyond the orbit of Neptune, are trans-Neptunian objects consisting of frozen water, ammonia and methane, the largest of which are Pluto, Sedna, Haumea, Makemake and Eris. In our solar system, there are other populations of small bodies such as planetary kvazisputniki the Trojans, near-Earth asteroids, centaurs, damokloidy and moving in comets, meteoroids, and cosmic dust.
The solar wind (a stream of plasma from the sun) creates a bubble in the interstellar medium, called the heliosphere, which extends to the edge of the scattered disc. The hypothetical Oort cloud, serves as a source of long-period comets, may extend to a distance of about a thousand times on the heliosphere.
The solar system is part of the Milky Way galaxy
The central object of the Solar System is the Sun – main sequence star of spectral type G2V, yellow dwarf. In the vast majority of the sun concentrated the entire mass of the system (about 99.866%), it retains its gravity planets and other bodies belonging to the solar system . The four largest facility – gas giants – represent 99% of the remaining mass (with the bulk of it falls on Jupiter and Saturn – about 90%).
Most large objects that orbit the sun, moving almost in the same plane, called the ecliptic plane. At the same time, comets and Kuiper belt objects often have a large inclination angles to this plane.
All the planets and most other objects orbit the Sun in the same direction as the sun’s rotation (counter-clockwise when viewed from the north pole of the Sun). There are exceptions, such as Halley’s Comet. The largest angular velocity has Mercury – he manages to make a complete revolution around the sun in only 88 Earth days. And for the most distant planet – Neptune – orbital period is 165 Earth years.
Most of the planet rotates on its axis in the same direction as the orbit around the Sun. The exceptions are Venus and Uranus, and Uranus rotates almost “lying on its side” (axial tilt of about 90 °). To demonstrate the rotation of a special device – tellurium.
Many models of the solar system conditionally show the planet orbits at regular intervals, but in fact, with few exceptions, the farther a planet or the Sun Belt, the greater the distance between its orbit and the orbit of the previous object. For example, Venus is approximately 0.33 a. is farther from the Sun than Mercury, while Saturn is 4.3 a. is on Jupiter, Neptune and 10.5. is beyond Uranus. There have been attempts to deduce the correlation between the orbital distances (for example, the Titius – Bode), but none of the theories has become common.
Objects orbit around the Sun are described by the laws of Kepler. According to them, each object is drawn in an ellipse, at one focus of which is the sun. We are closer to the Sun, objects (with smaller semi-major axis) is greater than the angular velocity of rotation, so the shorter the period (year). The elliptical orbit of the object distance from the sun varies during his year. The closest point to the Sun is called the perihelion of the orbit of the object, the most remote – aphelion. Each object is moving fastest in its perihelion and slowest at aphelion. The orbits of the planets are close to the circle, but many comets, asteroids and Kuiper belt objects have highly elliptical orbits.
Most planets have their own subordinate systems. Many satellites are surrounded by some of the companions of the size exceeds Mercury. Most of the larger satellites are in synchronous rotation, with one side always facing the planet. The four largest planets – gas giants also have rings, thin bands of tiny particles that circulate at very close orbits almost in unison.
Sometimes, the solar system is divided into regions. The interior of the solar system has four terrestrial planets and the asteroid belt. The external part starts outside of the asteroid belt and includes four gas giants. After the discovery of the Kuiper belt the most remote part of the solar system, consider a region consisting of the objects located on Neptune .
All objects in the solar system except the Sun itself, formally divided into three categories: planets, dwarf planets and small bodies of the solar system. Planet – any body in orbit around the sun, which turned massive enough to acquire a spherical shape, but not enough to start a massive thermonuclear fusion, and managed to clear the neighborhood of its orbit from planetesimals. Under this definition, the Solar System has eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto does not fit this definition, because it does not cleared its orbit of surrounding Kuiper belt objects. Dwarf planet – a celestial body, which becomes an orbit around the Sun that is massive enough to under its own gravity to maintain near-spherical shape, but the space is not cleared its orbit of planetesimals and is not a satellite of a planet. By this definition, in the solar system, there are five recognized dwarf planets: Ceres, Pluto, Haumea, Makemake and Eris. In the future, other objects can be classified as dwarf planets, such as Sedna, Quaoar and Orcus. Dwarf planets whose orbits are in the region trans-Neptunian objects, called Plutoid. Rest of the objects orbiting the Sun – small bodies of the solar system .
The terms gas, ice and stone used to describe the various classes of substances found throughout the solar system. Stone used to describe compounds with high condensing temperatures or melting, which remained in the protoplanetary nebula in the solid state for almost all conditions . Stone connections typically include silicates and metals such as iron and nickel. They predominate in the inner solar system, forming the majority of the terrestrial planets and asteroids. Gaza – materials with extremely low melting points and high vapor pressure such as molecular hydrogen, helium and neon, which were always in the nebula, the gaseous state. They are dominant in the middle of the solar system, accounting for most of Jupiter and Saturn. Ices of substances such as water, methane, ammonia, hydrogen sulfide and carbon dioxide have melting points up to a few hundred kelvins, while their thermodynamic phase depends on the ambient pressure and temperature . They may occur as ices, liquids, or gases in various regions of the solar system, in the nebula they were in the solid or gaseous phase . Most satellites of giant planets contain icy substance, and they make up most of Uranus and Neptune (the so-called “ice giants”) and the numerous small objects located beyond the orbit of Neptune. Gases and ice together are classified as volatile substances.
Most of our Solar System is still unknown.
According to estimates, the gravitational field of the sun dominates the gravitational forces of surrounding stars at a distance of about two light years (125 000 a. AU). In comparison, the lower estimates of the radius of the Oort cloud do not put it on a 50 000. is, Despite the discovery of such objects as Sedna, the region between the Kuiper belt and Oort cloud with a radius of tens of thousands as well. is, and the more self Oort cloud, and what might be behind him, still virtually unexplored. Also continue to study the region between Mercury and the Sun .
According to the generally accepted hypothesis, the formation of the solar system began about 4.6 billion years ago with the gravitational collapse of a small part of a giant interstellar gas and dust clouds. This initial cloud was probably the size of a few light years and is the father of a number of stars .
In the process of gravitational collapse dust cloud size decreases, and the law of conservation of angular momentum, growing speed of the cloud. Center, where most of the gathered masses, became more and more heated than the surrounding disc . The rotation speed of the cloud compression parallel and perpendicular to the axis of rotation varied, leading to a flattening of the cloud and the formation of a characteristic of a protoplanetary disk with a diameter of about 200 a. is, and a hot, dense protostar at the center . It is believed that at this point the evolution of the Sun was the star T Tauri. Study of T Tauri stars show that they are often accompanied by protoplanetary disks with masses 0.001-0.1 solar masses, with the overwhelming percentage of the mass of the nebula, which is concentrated in the star itself . The planets formed by accretion from this disk.
For 50 million years the pressure and density of hydrogen in the center of the protostar became large enough to start a fusion reaction . Temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved, with the thermal energy, the opposing force of gravitational contraction. At this stage, the Sun became a full-fledged main sequence star .
The solar system as known today, will last until the sun begins to develop outside the main sequence Hertzsprung – Russell. As the Sun burns hydrogen fuel reserves, the energy released, which supports the core, has a tendency to run out, causing the sun to shrink. This increases the pressure in his bowels, and heats the core, thus speeding up the burning of fuel. As a result, the sun gets brighter by about ten percent every 1.1 billion years.
After about 5.4 billion years from now, the hydrogen in the Sun’s core is completely converted into helium, which will complete the main sequence phase. At this time, the outer layers of the Sun will expand about 260 times – the sun will be a red giant. Due to the extremely increase the surface area, it will be much cooler than when on the main sequence (2600 K) .
In the end, as a result of thermal instabilities The outer layers of the Sun will be thrown into space, forming a planetary nebula in the center of which will be only a small core of the star – a white dwarf, an unusually dense object in half the original mass of the Sun, only the size of the Earth . This nebula return of the material that formed the Sun, in the interstellar medium.
The fact that the observed motion of heavenly bodies man was forced to the surface of a rotating on its axis and orbiting the Earth for centuries hindered the realization structure of the solar system. The apparent motion of the sun and planets were seen as their true motion around a stationary Earth.
The naked eye from Earth can be observed the following objects in the solar system: the Sun, Mercury, Venus (both just before sunrise or just after sunset), Mars, Jupiter and Saturn, as well as the moon. Through binoculars or a small telescope can observe four largest satellites of Jupiter (the so-called. Galilean satellites), Uranus, Neptune, and Titan (the largest moon of Saturn). The naked eye can see as many comets as they approach the Sun. At high magnification you can see the spots on the sun, the phases of Venus, the rings of Saturn and the Cassini gap between them .
Geocentric and heliocentric
Has long been the dominant geocentric model, according to which the universe rests in the center of a stationary earth and around it for quite complex laws moving heavenly bodies. The most complete, the system was developed ancient mathematician and astronomer Claudius Ptolemy, and allows very high accuracy to describe the observed motions of celestial bodies.
The most important breakthrough in understanding the true structure of the solar system occurred in the XVI century, when the great Polish astronomer Nicolaus Copernicus developed the heliocentric system of the world. It was based on the following statements:
in the center of the world is the sun, not the earth;
spherical Earth rotates on its axis, and this rotation explains the apparent daily motion of heavenly bodies;
Earth, like all the other planets revolving around the sun in a circle, and this rotation explain the apparent motion of the sun among the stars;
All movement is a combination of uniform circular motion;
seemingly direct and backward movements of the planets do not belong to them, but the world.
The sun stopped in the heliocentric system considered a planet, like the moon, the satellites of the Earth. Were soon discovered four satellites of Jupiter, so that the exceptional position of the Earth in the solar system was abolished. The theoretical description of the motion of the planets became possible after the discovery of Kepler’s laws in the early XVII century, and the wording of the laws of gravity quantitative description of the motion of the planets, their satellites and small bodies were put on a sound basis.
In 1672 Giovanni Cassini and Jean Richer determined the distance to Mars, so the astronomical unit was expressed in units of the distance of the earth.
The history of professional study of the solar system began in 1610, when Galileo Galilei discovered in his telescope four largest satellites of Jupiter. This discovery was a proof of the correctness of the heliocentric system. In 1655, Christian Huygens discovered Titan – the largest moon of Saturn . Until the end of XVII century Cassini were discovered four of Saturn .
XVIII century was an important event in astronomy – the first time through a telescope was opened previously known planet Uranus . Soon John Herschel, the discoverer of a new planet had been discovered two satellites of Uranus and Saturn 2 .
XIX century began with the new astronomical discoveries – was discovered first star-like object – the asteroid Ceres, in 2006, transferred to the status of dwarf planet. And in 1846, opened the eighth planet – Neptune. Neptune was discovered “on the tip of the pen”, that is, first predicted theoretically, and then detected with a telescope, and independently of each other in England and in France .
In 1930, Clyde Tombaugh (USA) discovered Pluto, the ninth planet called the Solar System. However, in 2006, Pluto has lost status as a planet and “became” dwarf planet .
In the second half of the XX century it was discovered a number of large and very small satellites of Jupiter, Saturn, Uranus, Neptune, Pluto . The most significant role in this series of scientific discoveries played the mission “Voyager” – U.S. AMS.
At the turn of the XX-XXI centuries, opened a number of small bodies in the solar system, including dwarf planets, plutino and some satellites and satellites of giant planets.
The solar system is part of the Milky Way – a spiral galaxy with a diameter of about 30 thousand parsecs (or 100 thousand light-years), consisting of about 200 billion stars . The solar system is located near the plane of symmetry of the galactic disk (20-25 parsecs above, that is north of it), at a distance of about 8000 parsecs (27,000 light years) from the galactic center (almost equidistant from the center of the galaxy and its Territory), on the outskirts of the Orion arm – one of the galactic arms Milky Way.
The sun revolves around the galactic center on a nearly circular orbit at about 254 km / s (updated in 2009), and makes a complete revolution in about 230 million years . This period of time is called a galactic year . Solar Apex (the direction of the path of the Sun through the interstellar medium), is located in the constellation of Hercules in the direction of the current position of the bright star Vega .
In addition to the circular motion of the orbit, the solar system performs vertical oscillations about the galactic plane, crossing it every 30-35 million years, and then they find themselves in the north, in the southern galactic hemisphere .
Location of the solar system in the galaxy is probably a factor in the evolution of life on Earth. Its orbit is almost circular, and the rate is approximately equal to the speed of the spiral arms, which means it passes through them is extremely rare. This gives the Earth long periods of interstellar stability for the development of life, as the spiral arms have a significant concentration of potentially dangerous supernovae . The solar system is also far away from the crowded neighborhoods of the stars of the galactic center. Near the center, the gravitational effects of nearby stars could perturb the Oort cloud objects and send many comets into the inner solar system, causing a collision with catastrophic consequences for life on Earth. The intense radiation of the galactic center could also affect the development of highly organized life . Some scholars hypothesize that it is possible, even in the current situation the solar system, recent supernovae adversely affected the life in the past 35 000 years, throwing out of the stellar cores to the Sun in the form of particles of radioactive dust and large comet-like objects .
The immediate galactic neighborhood of the solar system known as the Local Interstellar Cloud. It is more dense area of rarefied gas or local bubble – the cavity in the interstellar medium length of about 300 mph. years, has the shape of an hourglass. Bubble filled high-temperature plasma, implying that the bubble formed by the explosion of several recent supernovae .
Relatively few stars within ten St. years (95 trillion km) from the Sun. The closest is the triple star system Alpha Centauri, at a distance of about 4.3 mph. years. Alpha Centauri A and B – a close binary system similar characteristics solar-type stars, while the small red dwarf Alpha Centauri C (also known as Proxima Centauri) orbits the pair at 0.2 mph. years. The next nearest star is a red dwarf star Barnard (5.9 mph. Years), Wolf 359 (7.8 mph. Years) and Lalande 21185 (8.3 mph. Years). The largest star within ten light years – Sirius, the brightest star of the main sequence with a mass of about two solar masses, and a companion, a white dwarf called Sirius B. Sirius is located at a distance of 8.6 mph. years. The remaining systems within ten light years – a dual system of red dwarfs Leith 726-8 (8.7 mph. Years) and a single red dwarf Ross 154 (9.7 mph. Years) . The nearest similar single solar-type stars – Tau Ceti, is located 11.9 mph. years. Has about 80 percent of the Sun’s mass, but only 60 percent of its brightness. The closest known extrasolar planet is closest to us is the Alpha Centauri star system, located at a distance of 4.3 mph. years. Only confirmed planet in the system – the Alpha Centauri B b, with a mass of about 1.1 Earth masses and an orbital period of only 3.2 days