A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Albert Einstein the German-American physicist who developed the Special and General Theories of Relativity. Awarded the Nobel prize for physics in 1921. Active Galactic Nuclei (AGN) a core region in certain galaxies that, like a powerful engine, spews large amounts of energy from its center. Albert Michelson the Prussian-American who developed the interferometer, and the first to apply interferometry to astronomy. Awarded the Nobel prize for physics in 1907 Big Bang a theory in which the expansion of the Universe is presumed to have begun with a primeval explosion. Binary Systems two objects in space, such as black holes, stars, or neutron stars, that orbit each other Black Hole an object whose gravity is so strong that not even light can escape from it. Cosmic Background Radiation radiation of the cosmos left over from the Big Bang. Cosmological Constant a term Einstein added to his equations of the general theory of relativity, to account for an apparently non-expanding Universe, but later rejected when Hubble's observations seemed to indicate it was not needed. Can be interpreted as a special form of Dark Energy. Dark Energy the residual energy in empty space that is causing the expansion of the Universe to accelerate. Einstein's Cosmological Constant was a special form of dark energy. Doppler Effect An observer receives sound and light from bodies moving away from her with lower frequency and longer wavelength than emitted (see Redshift) and from bodies moving toward her with higher frequency and shorter wavelength. The shift in frequency increases as the speed of the body increases. Electromagnetic Spectrum the full range of frequencies, from radio waves to gamma rays, that characterizes light. Frequency the number of back-and-forth cycles per second, in a wave or wave-like process. Expressed this way, the frequency is said to be given in units of Hertz (Hz), named after the scientist who first produced and observed radio waves in the lab. Galaxy a component of our Universe made up of gas and a large number (usually more than a million) of stars held together by gravity. General Theory of Relativity Einstein's theory that matter, space, and time are linked. The gravity of any mass, such as our Sun, deforms or warps the space-time around it and this in turn will alter the path taken by any objects (or light) that pass close by. Gravitational Waves "ripples in the curvature of space-time" produced by disturbances caused by the movement of massive objects in space. Inflation Theory theory of extremely rapid expansion in the early Universe, stating that what is now the observable Universe was inflated from an atomic size to its cosmological size in a fraction of a second. This process makes the Universe very smooth and flat, as observed. Interstellar Dust dust among stars. Interferometry the use of interference phenomena of light waves to measure distances and angles between objects. Leptons a family of particles that have spin a very small number and that experience no strong forces. Light the common term for electromagnetic radiation, usually referring to that portion visible to the human eye. However, other bands of the electromagnetic spectrum are also often referred to as different forms of light. Milky Way the spiral shaped galaxy in which we live, made up of ten billion stars including our Sun. We see the Milky Way as a bright band of stars across the sky because our Sun lies in one of the spiral arms. Neutron Star the imploded core of a massive star remaining after a supernova explosion. Contains about the mass of the Sun in less than a trillionth of the Sun's volume. Pulsar a rotating neutron star which generates regular pulses of radiation. Quarks elementary particles that supposedly come in pairs. Quasar an enormously bright object at the edge of our Universe that emits massive amounts of energy. In an optical telescope, they appear point-like, similar to stars, from which they derive their name. Their high luminosity is created from matter falling into a supermassive black hole in the centers of distant galaxies. Radiation some type of electromagnetic wave: radio, microwave, light (infrared, visible or ultraviolet), x-rays or gamma rays are all types of radiation. Redshift a shift toward longer wavelengths of the radiation caused by the emitting object moving away from the observer. When this occurs we see the light from the object become more red. See also Doppler effect. Resonant-mass Detectors a type of gravitational wave detector that uses large (1-2 ton) aluminum cylinders. Passing gravitational waves will stretch the bar and deposit mechanical energy. If the gravitational wave is near the resonant frequency of the aluminum cylinder, the cylinder will "ring." Solar System the region within which the Sun, and all the planets and other bodies that travel around it, move. Space the expanse in which the Solar System, stars, and galaxies exist. Space-Time part of Einstein's Theory of General Relativity, that space and time are linked. Star a large ball of gas held together by gravity that creates and emits its own radiation from a nuclear fusion process. Stellar star-like. Supernova the death explosion of a massive star, resulting in a sharp increase in brightness followed by a gradual fading. At peak light output, supernova explosions can outshine a galaxy containing a billion stars. The outer layers of the exploding star are blasted out in a radioactive cloud. This expanding cloud, visible long afterthe initial explosion fades from view, forms a supernova remnant. Wavelength the distance between adjacent peaks in a series of periodic waves. Also see electromagnetic spectrum. White Dwarf a small, hot, faint star, essentially the leftover and exposed core of a red giant star that has puffed off its outer layers to form a planetary nebula. It is the last stage of evolution for stars like our Sun.