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Observational Cosmology
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. Early observations The science of physical cosmology as it is practiced today had its subject material defined in the years following the Shapley-Curtis debate when it was determined that the universe had a larger scale than the Milky Way galaxy. This was precipitated by observations that established the size and the dynamics of the cosmos that could be explained by Albert Einstein's General Theory of Relativity. In its infancy, cosmology was a speculative science based on a very limited number of observations and characterized by a dispute between steady state theorists and promoters of Big Bang cosmology. It was not until the 1990s and beyond that the astronomical observations would be able to eliminate competing theories and drive the science to the "Golden Age of Cosmology" which was heralded by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. According to this theory, space and time emerged together ago, and the universe has been expanding ever since the Big Bang. While the spatial size of the entire universe is unknown, it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's wor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Henrietta Swan Leavitt
Henrietta Swan Leavitt (; July 4, 1868 – December 12, 1921) was an American astronomer. A graduate of Radcliffe College, she worked at the Harvard College Observatory as a "computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first " standard candle" with which to measure the distance to faraway galaxies. Before Leavitt discovered the period-luminosity relationship for Cepheid variables, the only techniques available to astronomers for measuring the distance to a star were based on parallax and triangulation. Such techniques can only be used for measuring distances up to hundreds of light years. Leavitt's work allowed astronomers to measure distances up to about 20 million light years. As a result of this, it is now known that our own galaxy, the Milky Way, has a diam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hubble's Law
Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away from Earth. The velocity of the galaxies has been determined by their redshift, a shift of the light they emit toward the red end of the visible spectrum. Hubble's law is considered the first observational basis for the expansion of the universe, and today it serves as one of the pieces of evidence most often cited in support of the Big Bang model. The motion of astronomical objects due solely to this expansion is known as the Hubble flow. It is described by the equation , with ''H''0 the constant of proportionality—the Hubble constant—between the "proper distance" ''D'' to a galaxy, which can change over time, unlike the comoving distance, and its speed of separation ''v'', i.e. the derivative of proper distance with respect to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
General Relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the ' is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations. Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Georges Lemaître
Georges Henri Joseph Édouard Lemaître ( ; ; 17 July 1894 – 20 June 1966) was a Belgian Catholic priest, theoretical physicist, mathematician, astronomer, and professor of physics at the Catholic University of Louvain. He was the first to theorize that the recession of nearby galaxies can be explained by an expanding universe, which was observationally confirmed soon afterwards by Edwin Hubble. He first derived "Hubble's law", now called the Hubble–Lemaître law by the IAU, and published the first estimation of the Hubble constant in 1927, two years before Hubble's article. Lemaître also proposed the "Big Bang theory" of the origin of the universe, calling it the "hypothesis of the primeval atom", and later calling it "the beginning of the world". Early life After a classical education at a Jesuit secondary school, the Collège du Sacré-Coeur, in Charleroi, in Belgium, Lemaître began studying civil engineering at the Catholic University of Louvain at the age of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. In astronomy and cosmology, the three main causes of electromagnetic redshift are # The radiation travels between objects which are moving apart (" relativistic" redshift, an example of the relativistic Doppler effect) #The radiation travels towards an object in a weaker gravitational potential, i.e. towards an object in less strongly curved (flatter) spacetime ( gravitational redshift) #The radiation travels through expanding space ( cosmological redshift). The observation that all sufficiently distant light sources show redshift corresponding to their distance from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vesto Slipher
Vesto Melvin Slipher (; November 11, 1875 – November 8, 1969) was an American astronomer who performed the first measurements of radial velocities for galaxies. He was the first to discover that distant galaxies are redshifted, thus providing the first empirical basis for the expansion of the universe. He was also the first to relate these redshifts to velocity. Biography Slipher was born in Mulberry, Indiana, and completed his doctorate at Indiana University in 1909. He spent his entire career at Lowell Observatory in Flagstaff, Arizona, where he was promoted to assistant director in 1915, acting director in 1916, and finally director from 1926 until his retirement in 1952. His great grandfather helped established a Lutheran church. His brother Earl C. Slipher was also an astronomer and a director at the Lowell Observatory. Slipher used spectroscopy to investigate the rotation periods of planets and the composition of planetary atmospheres. In 1912, he was the first ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Immanuel Kant
Immanuel Kant (, , ; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. Born in Königsberg, Kant's comprehensive and systematic works in epistemology, metaphysics, ethics, and aesthetics have made him one of the most influential figures in modern Western philosophy. In his doctrine of transcendental idealism, Kant argued that space and time are mere "forms of intuition" which structure all experience, and therefore that, while " things-in-themselves" exist and contribute to experience, they are nonetheless distinct from the objects of experience. From this it follows that the objects of experience are mere "appearances", and that the nature of things as they are in themselves is unknowable to us. In an attempt to counter the skepticism he found in the writings of philosopher David Hume, he wrote the '' Critique of Pure Reason'' (1781/1787), one of his most well-known works. In it, he developed his theory of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galaxy
A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a hundred million stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies. Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular. Many are thought to have supermassive black holes at their centers. The Milky Way's central black hole, known as Sagittarius A*, has a mass four million times greater than the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sky, night, but their immense distances from Earth make them appear as fixed stars, fixed points of light. The most prominent stars have been categorised into constellations and asterism (astronomy), asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated to stars. Only about 4,000 of these stars are visible to the naked eye, all within the Milky Way galaxy. A star's life star formation, begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Its stellar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mount Wilson Observatory
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observatory contains two historically important telescopes: the Hooker telescope, which was the largest aperture telescope in the world from its completion in 1917 to 1949, and the 60-inch telescope which was the largest operational telescope in the world when it was completed in 1908. It also contains the Snow solar telescope completed in 1905, the 60 foot (18 m) solar tower completed in 1908, the 150 foot (46 m) solar tower completed in 1912, and the CHARA array, built by Georgia State University, which became fully operational in 2004 and was the largest optical interferometer in the world at its completion. Due to the inversion layer that traps warm air and smog over Los Angeles, Mount Wilson has steadier air than any other location in Nor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hooker Telescope
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observatory contains two historically important telescopes: the Hooker telescope, which was the largest aperture telescope in the world from its completion in 1917 to 1949, and the 60-inch telescope which was the largest operational telescope in the world when it was completed in 1908. It also contains the Snow solar telescope completed in 1905, the 60 foot (18 m) solar tower completed in 1908, the 150 foot (46 m) solar tower completed in 1912, and the CHARA array, built by Georgia State University, which became fully operational in 2004 and was the largest optical interferometer in the world at its completion. Due to the inversion layer that traps warm air and smog over Los Angeles, Mount Wilson has steadier air than any other location in Nor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
