Galaxy

http://en.wikipedia.org/wiki/Galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, aninterstellar medium of gas, dust, and an important but poorly understood component tentatively dubbeddark matter.^[1][2] The name is from the Greek word galaxias [γαλαξίας], literally meaning "milky", a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (10⁷) stars,^[3] up to giants with a hundred trillion (10¹⁴) stars,^[4] all orbiting the galaxy's center of mass. Galaxies may contain many star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy,^[5] which has an ellipse-shaped light profile.Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as irregular galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called astarburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.^[6]

There are probably more than 170 billion (1.7 × 10¹¹) galaxies in the observable universe.^[7][8] Most galaxies are 1,000 to 100,000^[9] parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs).^[10] Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atomper cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.^[11]

Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests thatsupermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus.^[12]

Famous Astrologers

Stephen Hawking


http://en.wikipedia.org/wiki/Stephen_Hawking

Stephen William Hawking, CH, CBE, FRS, FRSA (born 8 January 1942)^[1] is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity. He is an Honorary Fellow of the Royal Society of Arts,^[2] a lifetime member of the Pontifical Academy of Sciences,^[3] and in 2009 was awarded the Presidential Medal of Freedom, the highest civilian award in the United States.^[4]

Hawking was the Lucasian Professor of Mathematics at the University of Cambridge for 30 years, taking up the post in 1979 and retiring on 1 October 2009.^[5][6] He is now Director of Research at the Centre for Theoretical Cosmology in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. He is also a Fellow of Gonville and Caius College, Cambridge and a Distinguished Research Chair at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario.^[7] He is known for his contributions to the fields of cosmology and quantum gravity, especially in the context of black holes. He has also achieved success with works of popular science in which he discusses his own theories and cosmology in general; these include the runaway best seller A Brief History of Time, which stayed on the British Sunday Times best-sellers list for a record-breaking 237 weeks.^[8][9]

Hawking's key scientific works to date have included providing, with Roger Penrose, theorems regardinggravitational singularities in the framework of general relativity, and the theoretical prediction that black holesshould emit radiation, which is today known as Hawking radiation (or sometimes as Bekenstein–Hawking radiation).^[10]

Hawking has a motor neurone disease that is related to amyotrophic lateral sclerosis, a condition that has progressed over the years and has left him almost completely paralysed.

Roger Penrose

http://en.wikipedia.org/wiki/Roger_Penrose

Sir Roger Penrose OM FRS (born 8 August 1931) is an English mathematical physicist and Emeritus Rouse Ball Professor of Mathematics at the Mathematical Institute, University of Oxford and Emeritus Fellow ofWadham College. He has received a number of prizes and awards, including the 1988 Wolf Prize for physics which he shared with Stephen Hawking for their contribution to our understanding of the universe.^[1] He is renowned for his work in mathematical physics, in particular his contributions to general relativity andcosmology. He is also a recreational mathematician and philosopher.


Albert Einstein


http://en.wikipedia.org/wiki/Albert_Einstein

Albert Einstein ( /ˈælbərt ˈaɪnstaɪn/; German: [ˈalbɐt ˈaɪnʃtaɪn] ( listen); 14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution inphysics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history.^[2][3] He received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect".^[4] The latter was pivotal in establishing quantum theory within physics.

Near the beginning of his career, Einstein thought that Newtonian mechanics was no longer enough to reconcile the laws of classical mechanics with the laws of the electromagnetic field. This led to the development of his special theory of relativity. He realized, however, that the principle of relativity could also be extended to gravitational fields, and with his subsequent theory of gravitation in 1916, he published a paper on the general theory of relativity. He continued to deal with problems of statistical mechanics and quantum theory, which led to his explanations of particle theory and the motion of molecules. He also investigated the thermal properties of light which laid the foundation of the photon theory of light. In 1917, Einstein applied the general theory of relativity to model the structure of the universe as a whole.^[5]

He was visiting the United States when Adolf Hitler came to power in 1933, and did not go back to Germany, where he had been a professor at the Berlin Academy of Sciences. He settled in the U.S., becoming a citizen in 1940. On the eve of World War II, he helped alert President Franklin D. Roosevelt that Germany might be developing an atomic weapon, and recommended that the U.S. begin similar research; this eventually led to what would become the Manhattan Project. Einstein was in support of defending the Allied forces, but largely denounced using the new discovery of nuclear fission as a weapon. Later, together with Bertrand Russell, Einstein signed the Russell–Einstein Manifesto, which highlighted the danger of nuclear weapons. Einstein was affiliated with the Institute for Advanced Study in Princeton, New Jersey, until his death in 1955.

Einstein published more than 300 scientific papers along with over 150 non-scientific works.^[5][6] His great intelligence and originality have made the word "Einstein" synonymous with genius.^[7]