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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 -
Radio telescope
A radio telescope is a form of radio receiver used in astronomy. In contrast to an "ordinary" telescope, which receives visible light, a radio telescope "sees" radio waves emitted by radio sources, ... > more -
Planetary nebula
A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. They are in fact unrelated to planets; the ... > more -
Dark matter
In astrophysics and cosmology, dark matter is hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can ... > 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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