Library: Physics by Credo Reference: Astrophysics

Theoretical Astronomy

Astronomy: Topic Page
Branch of science that studies the motions and natures of celestial bodies, such as planets, stars, and galaxies; more generally, the study of matter and energy in the universe at large.
Big bang theory: Topic Page
In astronomy, the explosive event that marked the origin of the universe as we know it. At the time of the Big Bang, the entire universe was squeezed into a hot, superdense state. The Big Bang explosion threw this compact material outwards, producing the expanding universe seen today.
Black hole: Topic Page
A region in space, believed to be formed when a large star has collapsed in on itself at the end of its life, with such a strong gravitational pull that not even light waves can escape from it.
Cosmic microwave background
From Astronomy Encyclopedia
Remnant radiation from the creation of the Universe. Early cosmologists predicted theoretically that the Universe originally began as a singularity that expanded into a small, hot ‘soup’ of radiation and elementary particles.
Cosmic rays: Topic Page
Radiation which consists of streams of high-energy particles from outer space, travelling at about the speed of light, most of which are thought to originate from supernovas.
Dark matter: Topic Page
Matter not visible but making up a large proportion of the mass of the universe, and sufficient to change its expansion into contraction.
Expanding universe
From Atlas of the Universe
Before we can make any attempt to trace the history of the universe, we must look carefully at the situation we find today. As we have seen, each group of galaxies is receding from each other group, so that the entire universe is expanding.
Galaxy Formation and Evolution
From Collins Dictionary of Astronomy
Galaxies must have condensed out of the gases expanding from the Big Bang, beginning at a time when the average density of the Universe was roughly the same as the current mean density of a galaxy.
Gamma-ray astronomy: Topic Page
The branch of astronomy that deals with the origin and nature of emissions from extraterrestrial sources in the gamma-ray range of electromagnetic radiation rather than in the visible range.
Gravitational waves
From Collins Dictionary of Astronomy
Extremely weak wavelike disturbances that were predicted by Einstein's general theory of relativity. They represent the radiation associated with the gravitational force, and are produced when massive bodies are accelerated or otherwise disturbed.
Stellar evolution: Topic Page
Life history of a star, beginning with its condensation out of the interstellar gas (see interstellar matter) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable configuration.
Superstring Theory
From The Hutchinson unabridged encyclopedia with atlas and weather guide
In physics and cosmology, a mathematical theory developed in the 1980s to explain the properties of elementary particles and the forces between them (in particular, gravity and the nuclear forces) in a way that combines relativity and quantum theory.

Terms & Concepts

Cosmic inflation
From Collins Dictionary of Astronomy
A short period of very rapid expansion of the Universe postulated to occur very soon after the big bang. The hypothesis of inflation in the early Universe solves a number of cosmological problems.
Extrasolar planets
From Astronomy Encyclopedia
Planet not associated with our Solar System. The existence of other worlds, especially inhabited ones, has been the subject of debate since ancient times. In the 20th century, stars with irregular proper motions were suspected of having planetary companions; BARNARD'S STAR was a famous candidate.
Gravity: Topic Page
Force of attraction that arises between objects by virtue of their masses. The larger the mass of an object the more strongly it attracts other objects.
Hertzsprung-Russell diagram: Topic Page
A graph in which the spectral types of stars are plotted against their absolute magnitudes. Stars fall into different groupings in different parts of the graph.
Interferometer: Topic Page
In physics, a device that splits a beam of light into two parts, the parts being recombined after travelling different paths to form an interference pattern of light and dark bands.
Oort's formulae
From Collins Dictionary of Astronomy
Two mathematical expressions derived by Jan Oort that describe the effects of differential galactic rotation on the radial velocities (vr) and tangential velocities (vt) of stars at an average distance r from the Sun.
Red shift: Topic Page
Or redshift, in astronomy, the systematic displacement of individual lines in the spectrum of a celestial object toward the red, or longer wavelength, end of the visible spectrum.
Schwarzschild radius
From Astronomy Encyclopedia
Radius that a body must exceed if light from its surface is to reach an outside observer. If an object collapses below this radius, its escape velocity rises to above the speed of light and the object becomes a black hole.
Ultraviolet astronomy: Topic Page
The study of radiation from celestial sources in the wavelength range 91.2 to 320 nanometres, 12 to 91.2 nanometres being the extreme ultraviolet range.