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Edwin Powell Hubble

(1889—1953) American astronomer

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Abell cluster

Abell cluster  

A cluster of galaxies listed in the Abell Catalogue. To appear in the catalogue, a cluster must satisfy selection criteria which include containing more than 50 galaxies and having a dense ...
acceleration of the Universe

acceleration of the Universe  

The expansion rate of the Universe, measured by the Hubble parameter, would normally be expected to be slowing down, as the gravitational force between objects opposes the expansion. That is ...
age of the Universe

age of the Universe  

A time determined by the reciprocal of the value of the Hubble constant to be about 13.7 billion years. The calculation of the Hubble constant, and hence the age of the universe, depends on which ...
Albert Einstein

Albert Einstein  

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(1879–1955)German-born physicist, a thinker of astounding insight, author of the special and general theories of relativity, and winner of the 1921 Nobel Prize for Physics for his work on the ...
Alexander Friedmann

Alexander Friedmann  

(1888–1925)Alexander Friedmann (sometimes translated as ‘Friedman’; Fig. 1) was a Russian mathematician, born in St Petersburg in June 1888. He was educated and spent most of his life in ...
Allan Rex Sandage

Allan Rex Sandage  

(1926–2010)American astronomer. In 1950 he became an assistant to E. P. Hubble, whose work on measuring the distances of galaxies and refining the value of the Hubble constant he continued, finding a ...
Cepheid variable

Cepheid variable  

One of an important group of yellow giant or supergiant pulsating variables, named after the prototype, Delta Cephei. This general term is commonly applied to more than one stellar type, in ...
cluster of galaxies

cluster of galaxies  

An aggregation of galaxies, which may or may not be bound together by gravity. For example, our Galaxy, the Milky Way, is a member of the Local Group, a rather small cluster of which the only other ...
Coma cluster

Coma cluster  

A large, regular cluster of more than 3000 galaxies, about 280 million l.y. away in Coma Berenices; also known as Abell 1656. It covers more than 4° of sky and has a true diameter of at least 20 ...
cosmological constant

cosmological constant  

(Λ) A mathematical term introduced by A. Einstein into the equations of general relativity to obtain a solution corresponding to a static universe. This term describes a kind of pressure or (if it ...
cosmological perturbation theory

cosmological perturbation theory  

Cosmological perturbation theory is the study of the development of irregularities in the distribution of matter in the Universe as it evolves. The term ‘perturbation theory’ indicates that the ...
cosmological tests

cosmological tests  

The purpose of cosmological tests is to derive constraints on the cosmological parameters from observations such as counts and angular sizes of distant objects such as galaxies and quasars. Since ...
cosmology

cosmology  

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Religion
[Th]The world view and belief system of a community based upon their understanding of order in the universe.
curvature perturbation

curvature perturbation  

The curvature perturbation tells us how the curvature of the Universe is affected by the distribution of material within it. The Universe possesses density perturbations, being variations in the ...
deceleration parameter

deceleration parameter  

(q)A figure that describes the slowing-down of the expansion of the Universe. In a Friedmann universe, the deceleration parameter is simply half the density parameter, Ω. A value of q greater than ...
degeneracy

degeneracy  

A state of matter attained when atomic particles are packed together as tightly as is physically possible, at densities of several thousand tonnes per cubic metre. Particles which are very close ...
density parameter

density parameter  

The ratio of the actual mean density of matter in the Universe to the critical density required for the Universe to collapse. In the absence of a cosmological constant, a universe with Ω less than 1 ...
density perturbations

density perturbations  

One of the most fundamental properties of the Universe is the density of material at different locations. Since this varies from point to point, the density is said to have ...
distance

distance  

A scalar measurement of the extent of a body's motion, irrespective of the direction in which it has travelled. Thus, when a body moves from one location to another, the distance through which it ...
Einstein–de Sitter universe

Einstein–de Sitter universe  

A type of universe in which the mean density of matter is precisely matched to the critical density. Such a model will not actually collapse, but will expand for ever with a continually decreasing ...

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