“star”的概念、定义、翻译、参考文献-科学参考

star

Physics

A self-luminous celestial body, such as the sun, that generates nuclear energy within its core. Stars are not distributed uniformly throughout the universe, but are collected together in galaxies. The age and lifetime of a star are related to its mass (see stellar evolution; Hertzsprung–Russell diagram).

Astronomy

A luminous ball of gas that, at some stage of its life, produces energy by the nuclear fusion of hydrogen to form helium. The term thus not only includes stars such as the Sun, which is currently burning hydrogen, but also protostars, not yet hot enough for such burning to have begun, and various evolved objects such as giant and supergiant stars, which are burning other nuclear fuels, or white dwarfs and neutron stars, which consist of spent nuclear fuel.
The maximum mass of a star is about 120 solar masses, above which it would be blown apart by its own radiation. The minimum mass is 0.08 solar masses; below this, objects never become hot enough at their cores for hydrogen burning to begin, and instead become brown dwarfs. Star luminosities range from about half a million times the Sun’s luminosity for the hottest to under one-thousandth of the Sun’s for the faintest dwarfs. Although the most prominent stars visible to the naked eye are more luminous than the Sun, most stars are actually fainter than the Sun and hence insignificant to the naked eye.
Stars shine as a result of the conversion of mass into energy through nuclear reactions, of which those involving hydrogen are the most important. For every kilogram of hydrogen thus burnt, about 7 grams of mass is converted to energy. According to the famous equation E = mc², the 7 grams provides an energy of 6.3 × 10¹⁴ joules. Nuclear reactions not only provide the stars' heat and light, they also produce elements heavier than hydrogen and helium. These heavy elements have been distributed throughout the Universe either by supernova explosions or via planetary nebulae and stellar winds.
Stars are classified in a number of ways. One way is by their evolutionary stage: into pre-main-sequence, main-sequence, giant, supergiant, white-dwarf, or neutron stars. Another classification is in terms of their spectra, which indicate their surface temperature (see morgan–keenan classification). Another way is into Populations I, II, and III, which represent stars with progressively lower abundances of heavy elements, indicating progressively greater age. See also stellar evolution; Tables 4 and 5, Appendix.

Space Exploration

A luminous globe of gas, mainly hydrogen and helium, which produces its own heat and light by nuclear reactions. Although stars shine for a very long time—many billions of years—they change in appearance at different stages in their lives (they are said to have a ‘life cycle’). Stars seen at night belong to our galaxy, the Milky Way. The Sun is the nearest star to Earth; other stars in the Milky Way are large distances away.
The smallest mass possible for a star is about 8% that of the Sun (80 times that of Jupiter), otherwise nuclear reactions do not occur. Objects with less than this critical mass shine only dimly, and are termed brown dwarfs.

origin
Stars are born when nebulae (giant clouds of dust and gas) contract under the influence of gravity. These clouds consist mainly of hydrogen and helium, with traces of other elements and dust grains. The temperature and pressure in its core rises as the star grows smaller and denser.
At first, the temperature of the star scarcely rises, as dust grains radiate away much of the heat, but as it grows denser less of the heat generated can escape, and it gradually warms up. At about 10 million °C the temperature is hot enough for a nuclear reaction to begin, and hydrogen nuclei fuse to form helium nuclei; vast amounts of energy are released, contraction stops, and the star begins to shine.

main-sequence stars
Stars at this stage are called main-sequence stars. When all the hydrogen at the core of a main-sequence star has been converted into helium, the star swells to become a red giant, about 100 times its previous size and with a cooler, redder surface.

white dwarfs
What happens next depends on the mass of the star. If this is less than 1.2 that of the Sun, the star's outer layers drift off into space to form a planetary nebula, and its core collapses in on itself to form a small and very dense body called a white dwarf. Eventually the white dwarf fades away, leaving a non-luminous dark body.

supernovae
If the mass is greater than about eight times that of the Sun, the star does not end as a white dwarf but passes through its life cycle quickly, becoming a red supergiant. The star eventually explodes into a brilliant supernova. Part of the core remaining after the explosion may collapse to form a small superdense star, consisting almost entirely of neutrons and therefore called a neutron star. Neutron stars, also called pulsars, spin very quickly, giving off pulses of radio waves.

black holes
If the collapsing core of the supernova has a mass more than three times that of the Sun it does not form a neutron star; instead it forms a black hole, a region so dense that its gravity not only draws in all nearby matter but also all radiation, including its own light, as the velocity of escape from its surface exceeds that of light.

单词	star
释义	star Physics A self-luminous celestial body, such as the sun, that generates nuclear energy within its core. Stars are not distributed uniformly throughout the universe, but are collected together in galaxies. The age and lifetime of a star are related to its mass (see stellar evolution; Hertzsprung–Russell diagram). Astronomy A luminous ball of gas that, at some stage of its life, produces energy by the nuclear fusion of hydrogen to form helium. The term thus not only includes stars such as the Sun, which is currently burning hydrogen, but also protostars, not yet hot enough for such burning to have begun, and various evolved objects such as giant and supergiant stars, which are burning other nuclear fuels, or white dwarfs and neutron stars, which consist of spent nuclear fuel. The maximum mass of a star is about 120 solar masses, above which it would be blown apart by its own radiation. The minimum mass is 0.08 solar masses; below this, objects never become hot enough at their cores for hydrogen burning to begin, and instead become brown dwarfs. Star luminosities range from about half a million times the Sun’s luminosity for the hottest to under one-thousandth of the Sun’s for the faintest dwarfs. Although the most prominent stars visible to the naked eye are more luminous than the Sun, most stars are actually fainter than the Sun and hence insignificant to the naked eye. Stars shine as a result of the conversion of mass into energy through nuclear reactions, of which those involving hydrogen are the most important. For every kilogram of hydrogen thus burnt, about 7 grams of mass is converted to energy. According to the famous equation E = mc², the 7 grams provides an energy of 6.3 × 10¹⁴ joules. Nuclear reactions not only provide the stars' heat and light, they also produce elements heavier than hydrogen and helium. These heavy elements have been distributed throughout the Universe either by supernova explosions or via planetary nebulae and stellar winds. Stars are classified in a number of ways. One way is by their evolutionary stage: into pre-main-sequence, main-sequence, giant, supergiant, white-dwarf, or neutron stars. Another classification is in terms of their spectra, which indicate their surface temperature (see morgan–keenan classification). Another way is into Populations I, II, and III, which represent stars with progressively lower abundances of heavy elements, indicating progressively greater age. See also stellar evolution; Tables 4 and 5, Appendix. Space Exploration A luminous globe of gas, mainly hydrogen and helium, which produces its own heat and light by nuclear reactions. Although stars shine for a very long time—many billions of years—they change in appearance at different stages in their lives (they are said to have a ‘life cycle’). Stars seen at night belong to our galaxy, the Milky Way. The Sun is the nearest star to Earth; other stars in the Milky Way are large distances away. The smallest mass possible for a star is about 8% that of the Sun (80 times that of Jupiter), otherwise nuclear reactions do not occur. Objects with less than this critical mass shine only dimly, and are termed brown dwarfs. origin Stars are born when nebulae (giant clouds of dust and gas) contract under the influence of gravity. These clouds consist mainly of hydrogen and helium, with traces of other elements and dust grains. The temperature and pressure in its core rises as the star grows smaller and denser. At first, the temperature of the star scarcely rises, as dust grains radiate away much of the heat, but as it grows denser less of the heat generated can escape, and it gradually warms up. At about 10 million °C the temperature is hot enough for a nuclear reaction to begin, and hydrogen nuclei fuse to form helium nuclei; vast amounts of energy are released, contraction stops, and the star begins to shine. main-sequence stars Stars at this stage are called main-sequence stars. When all the hydrogen at the core of a main-sequence star has been converted into helium, the star swells to become a red giant, about 100 times its previous size and with a cooler, redder surface. white dwarfs What happens next depends on the mass of the star. If this is less than 1.2 that of the Sun, the star's outer layers drift off into space to form a planetary nebula, and its core collapses in on itself to form a small and very dense body called a white dwarf. Eventually the white dwarf fades away, leaving a non-luminous dark body. supernovae If the mass is greater than about eight times that of the Sun, the star does not end as a white dwarf but passes through its life cycle quickly, becoming a red supergiant. The star eventually explodes into a brilliant supernova. Part of the core remaining after the explosion may collapse to form a small superdense star, consisting almost entirely of neutrons and therefore called a neutron star. Neutron stars, also called pulsars, spin very quickly, giving off pulses of radio waves. black holes If the collapsing core of the supernova has a mass more than three times that of the Sun it does not form a neutron star; instead it forms a black hole, a region so dense that its gravity not only draws in all nearby matter but also all radiation, including its own light, as the velocity of escape from its surface exceeds that of light.
随便看	voters’ paradox voting voting logic voting share voucher voxel Voyager VPE VPN VPSV VR VRM Chancellor of the Exchequer chance nodes chancery chance variable Chandler period Chandler, Seth Carlo Chandler wobble Chandragupta Maurya (325–297) Chandrasekhar limit Chandrasekhar, Subrahmanyan Chandrasekhar, Subrahmanyan (1910–95) Chandrasekhar–Schönberg limit Chandra X-Ray Observatory

main-sequence starsStars at this stage are called main-sequence stars. When all the hydrogen at the core of a main-sequence star has been converted into helium, the star swells to become a red giant, about 100 times its previous size and with a cooler, redder surface.

main-sequence stars
Stars at this stage are called main-sequence stars. When all the hydrogen at the core of a main-sequence star has been converted into helium, the star swells to become a red giant, about 100 times its previous size and with a cooler, redder surface.