Stars are celestial bodies that emit light. There is a pseudo star and a real star. Pseudo star is a star that does not produce its own light, but reflects light received from another star. The real star is a star that produces its own light. In general designation of outer space is the object that produces its own light (real star).
According to the science of astronomy, star definition is:
"All massive objects (with mass between 0.08 to 200 solar masses) which was and never carry energy generation through nuclear fusion reactions. "
Therefore, white dwarfs and neutron stars that have not emit light or energy is still considered as a star. The closest star to Earth is the Sun at a distance of about 149,680,000 kilometers, followed by Proxima Centauri in the constellation Centaurus is about four light-years away.
History Observations.
The stars have been part of every culture. The stars used in religious practices, in navigation, and grow crops. Gregorian calendar, which is used almost in all parts of the world, is the calendar of the Sun, based on the position of the Earth relative to the nearest star, the Sun.
Early astronomers Tycho Brahe successfully recognize as 'rising stars' in the sky (later called novae) show that the sky is not eternal. In 1584 Giordano Bruno suggested that the stars are actually other Sun-sun, and may only have planets like Earth in its orbit, an idea that had been proposed earlier by the ancient Greek philosophers such as Democritus and Epicurus. In the following century, the idea that the Sun is a star that is far reaching a consensus among astronomers. To explain why these stars do not provide the gravitational pull on the Solar System, Isaac Newton suggested that the stars were equally distributed across the sky, an idea derived from the theologian Richard Bentley.
Italian astronomer Geminiano Montanari record any changes in the luminosity of the star Algol 1667 Edmond Halley published the first measurements of the proper motion of a pair of "fixed" near, showed that they changed the position of measurements taken since Ptolemaeus and Hipparchus. Direct measurement of the distance of 61 Cygni conducted in 1838 by Friedrich Bessel using the parallax technique.
William Herschel was the first astronomer who tried to determine the distribution of stars in the sky. During the enumeration 1780an he did around 600 different sky regions. He then concluded that the number of stars steadily increased to a sky, the center of the Milky Way galaxy. His son John Herschel repeated the same work in the southern hemisphere sky and found the same results. In addition, William Herschel also discovered that some of the couple is not the stars that happened to be in the direction of the line of sight, but they are physically pair up to form a double star system.
Naming.
The concept of constellations has been known since the time of Babylon. Ancient sky watchers imagined a particular pattern formed by the arrangement of a prominent, and relating it to a specific aspect of their nature or mythology. Twelve of this arrangement lies in the ecliptic line and the basis for astrology.
Many of the individual stars that stand out given the name of its own, particularly with Arabic or Latin names.
As some certain constellations and the sun, some stars also have their own mythology. For the ancient Greeks, some "stars", known as planets (Greek: πλανήτης [planētēs], wanderer), representing various important deities they are the source of the name for the planet Mercury, Venus, Mars, Jupiter and Saturn. Uranus and Neptune also are the gods of Greece and Rome, but has not been known in ancient times as the dim light. The name given by astronomers both next.
Approximately in 1600, the name is used to name the constellations of stars in the sky region. German astronomer Johann Bayer created a series of star maps that use Greek letters as the name for the stars in each constellation. After that numbering system based on the star right ascension was invented by John Flamsteed and added to the star catalog in his book "Historia coelestis Britannica". This numbering system will be known as
Flamsteed Flamsteed naming or numbering.
The only internationally recognized authority in naming celestial bodies is the International Astronomical Union (International Astronomical Union, IAU). There are a number of private companies sell names of stars, which the British Library is an unregulated commercial enterprise. However, the IAU has severed ties with this commercial practice, and these names are not recognized and are not used by the IAU. One of the naming company is the International Star Registry so (ISR), which in the 1980s was accused of deceptive practices because it makes as if the names they give official. ISR practice that has been stopped is informally labeled as fraud and cheating and Consumer Affairs Department of the City of New York published a warning to the ISR as deceptive trade practices.
Radiation.
The energy generated by nuclear fusion of stars radiating into space in the form of electromagnetic radiation and particle radiation. Radiation emitted particles manifested in the form of stellar wind, the stream of free protons, alpha particles are electrically charged, and beta particles from the star's outer layers. There is also a fixed stream of neutrinos emanating from the star's core, although the neutrinos are almost massless.
Stars shine very bright due to the production of energy at the core, which combines two or more atomic nuclei and atomic nuclei to form a single heavier elements and releasing photons of gamma rays in the process. Once this energy reaches the star's outer layer, this energy transformed into other forms of electromagnetic energy that is lower frequency, such as visible light.
The star, which is determined by the frequency of the light seems to be the most powerful, depending on the temperature of the star's outer layers, including its photosphere. Besides visible light, stars also emit other forms of electromagnetic radiation that are invisible. Actually, the electromagnetic radiation of the whole electromagnetic spectrum includes, from the longest wavelengths of radio waves, to infrared, visible light, ultraviolet, X-rays to gamma rays and the shorter wavelengths. If the views of the total energy emitted by a star, not all components of the electromagnetic radiation has a significant amount, but all of these frequencies gives us insight into the physical star.
By using the spectra of stars, astronomers can determine the surface temperature, surface gravity, metalisitas, and the speed of rotation of a star. If the distance of a star is known, for example by measuring paralaksnya, then luminositasnya can be calculated. The mass, radius, surface gravity, and rotation period can be estimated on the basis of the model. (The mass of the stars in a binary system can be calculated by measuring the distance and speed of its orbit. Effects of gravitational micro-lenses are used to measure the mass of a single star).
By using these parameters, astronomers can also estimate the age of a star. The sun is the closest star to Earth.
Almost anything involving a star initially influenced by the mass, including essential characteristics such as luminosity and size, as well as the evolution, the age and condition of the end.
Diameter.
Stars are very diverse in size. In each panel in the figure above, the rightmost object appears as the leftmost object on the next panel. Earth is located in the right-most solar panels located on the first and second from the right in the third panel. Due to their remoteness from the Earth, all stars except the sun looks just like the shining points in the night sky when viewed with the naked eye, and flickering caused by the effects of the Earth's atmosphere. The sun is also a star, but it is pretty close to the earth so it looks like a disc in the sky and be able to illuminate the earth. Besides the sun, stars with the biggest size is R Doradus appears, that it was only 0.057 arcseconds.
Disc mostly angular diameter of the star is too small to be observed with optical telescopes existing earth, so interferometer telescopes are needed to produce the image of a star. Another technique for measuring the angular diameter of stars is through occultation. By precisely measuring the drop in the light of a star during the occultation of the month (or the increase in the light of the star when the star reappears), the star's angular diameter can be computed.
The size of a very diverse, ranging from neutron stars, which just a diameter between 20 and 40 km, until the supergiant star like Betelgeuse in the constellation Orion, whose diameter is about 650 times the diameter of the sun or about 900 million miles. However, Betelgeuse has a much lower density than the sun.
Kinematics.
Pleiades, an open cluster in the constellation Taurus. These stars are moving together in space.
The motion of a star relative to the Sun can provide important information about the origin and age of the star, even on the structure and evolution of the surrounding galaxy. Component of the motion of a star consist of the radial velocity toward or away from the sun, and the so-called shift-sectional motion.
Radial velocity of a star is measured by the doppler shift of the spectrum lines and is expressed in units of kilometers per second. Proper motion of a star is determined through careful astronomical measurements in milliseconds of arc per year. By determining the parallax of a star, the proper motion can then be converted into units of velocity. Stars with high proper motion velocity likely is close to the sun, making it suitable for paralaksnya measured.
When the speed of the second movement known star space velocity relative to the Sun or the Milky Way can be calculated. Among the stars around us, it is known that stars a younger population I usually have a lower rate than population II stars are older. Population II stars have elliptical orbits are inclined to the plane of the Milky Way galaxy. Comparison of the kinematics of the stars around the sun also causes the discovery of a set of the most likely location is a collection of the same origin in giant molecular clouds.
Chemical composition.
When formed, the stars in the Milky Way's mass is made up of about 71% hydrogen and 27% helium, and the remaining elements are slightly heavier. Typically the portion of heavy elements determined by measuring the amount of charge contained iron in stellar atmospheres, because iron is a common element and spectral absorption lines are relatively easy to calculate. Because the molecular clouds where stars form continuously enriched with elements heavier, measuring the chemical composition of a star can be used to determine its age. The portion of elements heavier can also be used as an indication whether a star has a planetary system or not.
Star with the lowest iron content ever measured is the dwarf star HE1327-2326, with an iron content of only 1 / 200,000 of the iron content of the sun. In contrast, metal-rich star μLeonis, which contains almost twice the sun belongs, are star-planet 14 Herculis, which contains nearly three times as belonging to the sun. There is also a peculiar chemical composition of stars, which shows the remarkable abundance of certain elements in their spectrum; especially chromium and rare earth metals.
Mass stars.
One of the most massive stars known is Eta Carinae. With masses up to 100-150 times the mass of the sun, this star also has a life span of only a few million years. Research on Arches cluster shows that the upper limit of the mass of stars in the current era of the universe is 150 times the mass of the sun. The reason for this limit is not known for certain, but partly due to the Eddington luminosity, ie the maximum amount of luminosity that can pass through the atmosphere of without having to eject gas into space. However, a star named R136a1 in RMC136a star clusters, measured to have a mass 265 times the mass of the sun, making the limit is questionable.
A study showed that the stars in the star cluster R136 having mass greater than 150 times the mass of the sun formed by the collision and merging of massive stars from several adjacent binary systems; so that the stars are able to cross the line 150 times the mass of the sun.
Nebula NGC 1999 brightly illuminated by V380 Orionis with (center), a variable star with a mass about 3.5 times the mass of the sun. Part black sky is a big hole of empty space and not a dark nebula as previously thought.
The first stars formed after the Big Bang are likely to be larger than they are now, reaching up to 300 times the mass of the sun, even more, due to the absence of elements heavier than lithium in the womb. However, generation of population III stars are massive long-extinct and only theoretically.
With a mass only 93 times the mass of Jupiter, AB Doradus C, a friend of AB Doradus A, is the smallest known star is still doing nuclear fusion in its core. For stars with metalisitas similar to the sun, the theoretical minimum mass the star can have, but still be able to perform nuclear fusion in its core, is estimated to about 75 times the mass of Jupiter. However, if a star metalisitas very low, the minimum mass is about 8.3% of the solar mass, or about 87 times the mass of Jupiter, based on the latest research on the most dim stars. Smaller stars again called brown dwarf, which occupies a gray area that has not been clearly terdefenisi between stars and gas giants.
Large surface gravity of a star is determined by the diameter and mass. Giant stars have a surface gravity that is much lower than main sequence stars, while the opposite for compact stars such as white dwarfs. Surface gravity affect the appearance of a star spectrum, with higher gravity causing widening of the absorption lines.
Magnetic field.
The magnetic field of a star is generated in the interior of stars where convective circulation occurs. This movement of conductive plasma functions like a dynamo, generating magnetic fields that cover the entire star. The strong magnetic field of a star depends on the mass and the content of the star, and the amount of magnetic surface activity depends on the speed of rotation of the star. This surface activity produces star spots, which is the surface area of the star with a strong magnetic field but the temperature is much lower than other surface regions. Corona arch is a curved magnetic field and reaches up into the corona from active regions star. Star bursts are bursts of high-energy particles are emitted due to the same magnetic activity. Young stars that spin rapidly tend to have high levels of surface activity due to the influence of the magnetic field. This magnetic field can also affect the stellar wind, which acts like a brake and gently slow the rate of rotation of a star along with aging. Therefore, the stars are older like the sun, has a rotation rate and a lower surface activity. The level of surface activity with a slow rotation rate tends to be a cycle, and sometimes none at all for a certain period of time.
During the Maunder minimum, for example, the sun showed virtually no sunspots activity for 70 years.
Rotation.
The rate of rotation of the star can be determined through spectroscopy, or can be measured more accurately by observing the rate of rotation of the star spots. Young stars can have a high rotation rate, to above 100 km / s measured at its equator. B-class star Achernar, for example, has a rotation speed of about 225 km / s or more at the equator, causing its equatorial regions protruding out so that this star has equatorial diameter that is more than 1.5 times the distance between the poles. The rate of rotation is just below the critical rotation rate of 300 km / s that will cause a shattered star. Instead, the sun rotates only once during 25-35 days, with the equatorial rotation rate 1.99 km / s. Wind magnetic field and slow the rate of rotation of the stars on the main sequence is significantly along with the development of a star in the main sequence.
Degenerate star is a star that has shrunk into a compact mass and resulted in a high rate of rotation. However, the rotation rate is still lower than that predicted by the law of conservation of angular momentum. Most of the star's angular momentum disappeared as a result of mass loss by stellar wind. Even so, the rate of rotation of the pulsar can be very high. Star Nebula Crab pulsar at the center, for example, rotates 30 times a second. The rotation rate of the pulsar will gradually slow due to the emission of radiation.
Temperature.
The surface temperature of a main sequence star is determined by the rate of energy in its core income is generally estimated from the color index of the star. Usually the temperature is expressed by the effective temperature, which is the temperature when a star is considered as an ideal black body that radiates energy with the same luminosity in the entire surface. So the effective temperature is only a picture, because the temperature in a star higher if getting close to the point. The temperature in the core region of a star reaches up to a few million degrees celsius. The temperature of a star determines the rate of ionization of various elements in it, also specify the nature of the absorption line spectrum. Surface temperature, absolute magnitude and absorption properties of Spectrograph used as the basis for classifying stars.
Massive stars in the main sequence can be up to 50,000 ° C temperature. Being smaller stars, like the sun, has a surface temperature of several thousand degrees Celsius. Red giants have relatively low surface temperatures of about 3,300 ° C, but this star has a high luminosity due to extensive outer surface.
Age.
Most were between the ages of 1-10 billion years. Some stars may even approach the 13.8 billion years old-the observed age of the universe. Oldest stars found to date, HE 1523-0901, was estimated to be 13.2 billion years old.
The higher the mass of a star, the shorter its age anyway. This is mainly due to the high mass star will have a high pressure also on the point which causes it to burn hydrogen more rapidly. The stars are the most massive stars last an average of only a few million years, while stars with a minimum mass (red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years.
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DatePublished: August 24, 2014 at 17:12
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