Big Bang:
The Big Bang is a cosmological model of the universe that has become well supported by several independent observations. After Edwin Hubble discovered that galactic distances were generally proportional to their redshifts in 1929, this observation was taken to indicate that the universe is expanding. If the universe is seen to be expanding today, then it must have been smaller, denser, and hotter in the past. This idea has been considered in detail all the way back to extreme densities and temperatures, and the resulting conclusions have been found to conform very closely to what is observed.
Big Crunch:
Is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity. If there is enough matter in the Universe eventually gravitaional forces will stop its expansion. When this happens gravity will cause the universe to reverse its direction and begin to collapse under its own weight. This phase of the Universe's life is known as the Big Crunch.
Black Holes:
They are places where ordinary gravity has become so extreme that it overwhelms all other forces in the Universe. Once inside, nothing can escape a black hole's gravity — not even light.
Blueshift:
Refers to a shortening of a transmitted signal's wavelength, and/or an increase in its frequency. The name comes from the fact that the shorter-wavelength end of the optical spectrum is the blue (or violet) end, hence, when visible light is compacted in wavelength, it is "shifted towards the blue", or "blue-shifted". Some possible causes of blue shift in astronomy are: 1. Movement of the source towards us, as seen in: a) the edge of a rotating galaxy moving towards us; b) In blazars which propel relativistic jets towards us. 2. Gravitational effects.
Cosmic Microwave Background Radiation:
In cosmology, the cosmic microwave background radiation is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. It has a thermal black body spectrum at a temperature of 2.725 kelvin. Thus the spectrum peaks in the microwave range at a frequency of 160.2 GHz, corresponding to a wavelength of 1.9 mm. Most cosmologists consider this radiation to be the best evidence for the Big Bang model of the universe.
Cosmological Constant:
In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary. However, the discovery of cosmic acceleration in the 1990s has renewed interest in a cosmological constant.
Cosmological Principle:
Is a principle invoked in cosmology that, when applied, severely restricts the large variety of possible cosmological theories. It follows from the observation of the Universe on a large scale, and states that:
On large spatial scales, the Universe is homogeneous and isotropic.
Or simply put, the universe is the same everywhere on a large scale.
This principle means that averaged over large enough distances, one part of the Universe looks approximately like any other part.
Lookback Time:
Is a phenomenon that, owing to the finite velocity of light, the more distant an object being observed, the older is the information received from it. A galaxy one billion light-years away, for instance, is seen as it looked one billion years ago. Light travels at the finite speed of 300,000 kilometers per second. The Sun is so distant that light takes 8.3 minutes to travel from it to Earth. Hence, the Sun has a lookback time of 8.3 minutes; we see it as it was 8.3 minutes ago. The Andromeda Galaxy has a lookback time of 2 million years; we see it as it was 2 million years ago
Neutron Star:
A neutron star is formed from the collapsed remnant of a massive star; i.e. a Type II, Type Ib or Type Ic supernova. Models predict that neutron stars consist mostly of neutrons, hence the name. Such stars are very hot, as supported by the Pauli exclusion principle indicating repulsion between neutrons. A neutron star is one of the few possible conclusions of stellar evolution.
Quasars:
Are the brightest and most distant objects in the known universe. In the early 1960's, quasars were referred to as radio stars because they were discovered to be a strong source of radio waves. The quasars themselves can burn up to the energy of a trillion suns and recent evidence shows that this may all happen because of black holes. What we know about quasars is that they have great energy, but are not immense in size
Redshift:
In physics and astronomy, redshift occurs when the electromagnetic radiation, usually visible light, that is emitted from or reflected off an object is shifted towards the (less energetic) red end of the electromagnetic spectrum. More generally, redshift is defined as an increase in the wavelength of electromagnetic radiation received by a detector compared with the wavelength emitted by the source. An object that is receding from us at very high velocities has its spectral lines red-shifted.
Relativity:
General relativity is a theory of gravitation developed by Einstein in the years 1907–1915 that generalizes Isaac Newton´s original theory of gravity. The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. In this theory gravity is supposed to be a distortion of space and time itself.
http://en.wikipedia.org/
http://hubblesite.org/explore_astronomy/black_holes/home.html ,
http://www.seasky.org/cosmic/sky7a09.html ,
http://www.site.uottawa.ca:4321/astronomy/index.html#lookbacktime ,
http://www.rdrop.com/users/green/school/quasars.htm , http://wise.ssl.berkeley.edu/glossary/lookback_time.html
The Big Bang is a cosmological model of the universe that has become well supported by several independent observations. After Edwin Hubble discovered that galactic distances were generally proportional to their redshifts in 1929, this observation was taken to indicate that the universe is expanding. If the universe is seen to be expanding today, then it must have been smaller, denser, and hotter in the past. This idea has been considered in detail all the way back to extreme densities and temperatures, and the resulting conclusions have been found to conform very closely to what is observed.
Big Crunch:
Is one possible scenario for the ultimate fate of the universe, in which the metric expansion of space eventually reverses and the universe recollapses, ultimately ending as a black hole singularity. If there is enough matter in the Universe eventually gravitaional forces will stop its expansion. When this happens gravity will cause the universe to reverse its direction and begin to collapse under its own weight. This phase of the Universe's life is known as the Big Crunch.
Black Holes:
They are places where ordinary gravity has become so extreme that it overwhelms all other forces in the Universe. Once inside, nothing can escape a black hole's gravity — not even light.
Blueshift:
Refers to a shortening of a transmitted signal's wavelength, and/or an increase in its frequency. The name comes from the fact that the shorter-wavelength end of the optical spectrum is the blue (or violet) end, hence, when visible light is compacted in wavelength, it is "shifted towards the blue", or "blue-shifted". Some possible causes of blue shift in astronomy are: 1. Movement of the source towards us, as seen in: a) the edge of a rotating galaxy moving towards us; b) In blazars which propel relativistic jets towards us. 2. Gravitational effects.
Cosmic Microwave Background Radiation:
In cosmology, the cosmic microwave background radiation is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. It has a thermal black body spectrum at a temperature of 2.725 kelvin. Thus the spectrum peaks in the microwave range at a frequency of 160.2 GHz, corresponding to a wavelength of 1.9 mm. Most cosmologists consider this radiation to be the best evidence for the Big Bang model of the universe.
Cosmological Constant:
In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary. However, the discovery of cosmic acceleration in the 1990s has renewed interest in a cosmological constant.
Cosmological Principle:
Is a principle invoked in cosmology that, when applied, severely restricts the large variety of possible cosmological theories. It follows from the observation of the Universe on a large scale, and states that:
On large spatial scales, the Universe is homogeneous and isotropic.
Or simply put, the universe is the same everywhere on a large scale.
This principle means that averaged over large enough distances, one part of the Universe looks approximately like any other part.
Lookback Time:
Is a phenomenon that, owing to the finite velocity of light, the more distant an object being observed, the older is the information received from it. A galaxy one billion light-years away, for instance, is seen as it looked one billion years ago. Light travels at the finite speed of 300,000 kilometers per second. The Sun is so distant that light takes 8.3 minutes to travel from it to Earth. Hence, the Sun has a lookback time of 8.3 minutes; we see it as it was 8.3 minutes ago. The Andromeda Galaxy has a lookback time of 2 million years; we see it as it was 2 million years ago
Neutron Star:
A neutron star is formed from the collapsed remnant of a massive star; i.e. a Type II, Type Ib or Type Ic supernova. Models predict that neutron stars consist mostly of neutrons, hence the name. Such stars are very hot, as supported by the Pauli exclusion principle indicating repulsion between neutrons. A neutron star is one of the few possible conclusions of stellar evolution.
Quasars:
Are the brightest and most distant objects in the known universe. In the early 1960's, quasars were referred to as radio stars because they were discovered to be a strong source of radio waves. The quasars themselves can burn up to the energy of a trillion suns and recent evidence shows that this may all happen because of black holes. What we know about quasars is that they have great energy, but are not immense in size
Redshift:
In physics and astronomy, redshift occurs when the electromagnetic radiation, usually visible light, that is emitted from or reflected off an object is shifted towards the (less energetic) red end of the electromagnetic spectrum. More generally, redshift is defined as an increase in the wavelength of electromagnetic radiation received by a detector compared with the wavelength emitted by the source. An object that is receding from us at very high velocities has its spectral lines red-shifted.
Relativity:
General relativity is a theory of gravitation developed by Einstein in the years 1907–1915 that generalizes Isaac Newton´s original theory of gravity. The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. In this theory gravity is supposed to be a distortion of space and time itself.
http://en.wikipedia.org/
http://hubblesite.org/explore_astronomy/black_holes/home.html ,
http://www.seasky.org/cosmic/sky7a09.html ,
http://www.site.uottawa.ca:4321/astronomy/index.html#lookbacktime ,
http://www.rdrop.com/users/green/school/quasars.htm , http://wise.ssl.berkeley.edu/glossary/lookback_time.html
No comments:
Post a Comment