Physics Reference Libraries

Page 6 of about 84 Articles
2005-05-26 12:07:27

Beryllium is the chemical element in the periodic table that has the symbol Be and atomic number 4. A toxic bivalent element, beryllium is a steel grey, strong, light-weight yet brittle, alkaline earth metal, that is primarily used as a hardening agent in alloys (most notably, beryllium copper). Notable characteristics Beryllium has one of the highest melting points of the light metals....

2005-05-25 11:04:31

Uranium is a chemical element in the periodic table that has the symbol U and atomic number 92. A heavy, silvery-white, toxic, metallic, and naturally-radioactive element, uranium belongs to the actinide series and its isotope 235U is used as the fuel for nuclear reactors and nuclear weapons. Uranium is commonly found in very small amounts in rocks, soil, water, plants, and animals (including...

Autumnal Equinox
2004-10-19 04:45:44

Autumnal Equinox -- In astronomy, is the equinox at the beginning of autumn in the northern hemisphere: the moment when the sun appears to cross the celestial equator, heading southward. The equinox occurs around September 22-24, varying slightly each year according to the 400 year cycle of leap years in the Gregorian Calendar. In the southern hemisphere, the equinox occurs at the same...

2004-10-19 04:45:44

Sky -- Although almost everyone have seen it, sky is hard to be defined precisely. Generally, sky is the space seen when one looks upward from the surface of a planet. Some people define sky as the denser gaseous zone of a planet's atmosphere. Clouds, rainbows and weather all occur amongst a planet's sky. In astronomy, the sky is divided into many regions, called constellations. The...

Ring Current
2004-10-19 04:45:44

Ring Current -- A ring current is an electric current carried by charged particles trapped in a planet's magnetosphere. It is caused by the longitudinal drift of energetic (10-200 keV) particles. Earth's Ring Current Earth's ring current is responsible for geomagnetic storms. The ring current system consists of a band, at a distance of 3-5 RE(1), which lies in the equatorial plane and...

Abbot Charles Greeley
2009-03-03 21:08:51

Charles Greeley Abbot (May 31, 1872 "“ December 17, 1973) was an American astrophysicist and astronomer born in Wilton, New Hampshire. He graduated from Phillips Academy in 1891 and MIT in 1894, with a degree in chemical physics. In 1895 Abbot was hired by Samuel Pierpont Langley as an assistant at the Smithsonian Astrophysical Observatory (SAO) despite his lack of experience in...

2004-10-19 04:45:44

Cosmology -- area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe. Modern Cosmological Theories Present models of the universe hold two fundamental premises: the cosmological principle and the dominant role of gravitation. Derived by Hubble, the cosmological principle holds that if a large enough sample of galaxies is...

Parabolic Mirror
2004-10-19 04:45:43

Parabolic Mirror -- A parabolic reflector or parabolic dish is a reflective device formed in the shape of a paraboloid of revolution. Parabolic reflectors can either collect or distribute energy such as light, sound, or radio waves. The parabolic reflector functions due to the geometric properties of the paraboloid shape: if the angle of incidence to the inner surface of the collector...

2004-10-19 04:45:43

Interferometry -- Interferometry is the applied science of combining two or more input points of a data type, such as optical, and combine these data to form a greater picture based on the combination of the two sources. This technique is the basis for proposed radio telescope arrays, which spread out upon a wide area of hundreds of miles, can together produce a picture with resolution...

Gamma-Ray Astronomy
2004-10-19 04:45:43

Gamma-Ray Astronomy -- Gamma-ray astronomy is the astronomical study of gamma rays. Long before experiments could detect gamma rays emitted by cosmic sources, scientists had known that the universe should be producing these photons. Work by Feenberg and Primakoff in 1948, Hayakawa and Hutchinson in 1952, and, especially, Morrison in 1958 had led scientists to believe that a number of...

Word of the Day
  • One of a pair of round metal cymbals attached to the fingers and struck together for rhythm and percussion in belly dancing.
The word 'zill' comes from a Turkish word meaning "cymbals".