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Ion thruster
An ion thruster (or ion drive), one of several types of spacecraft propulsion, uses beams of ions - electrically charged atoms or molecules - for propulsion. The precise method for accelerating the ... > more -
Nicolaus Copernicus
Nicolaus Copernicus (February 19, 1473 - May 24, 1543) was the astronomer who formulated the first modern heliocentric theory of the solar system. His epochal text, De revolutionibus orbium ... > more -
Doppler effect
The Doppler effect, named after Christian Andreas Doppler, is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. The ... > more -
Lunar space elevator
A lunar space elevator (also called a moonstalk) is a proposed cable running from the surface of the Moon into space. It is similar in concept to the better known Earth space elevator idea (a cable ... > more -
Light-year
A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in a vacuum in one year. While there is no authoritative decision on which year is ... > more -
Quantum number
A quantum number describes the energies of electrons in atoms. Each quantum number specifies the value of a conserved quantity in the dynamics of the quantum system. Since any quantum system can have ... > more -
Holographic principle
The holographic principle is a property of quantum gravity theories which resolves the black hole information paradox within string theory. First proposed by Gerard 't Hooft, it was given a precise ... > more
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