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[[Image:lighterstill.jpg]] [[Image:The-light-from-abell.jpg‎|right|frame]].  

[[Image:lighterstill.jpg]] [[Image:The-light-from-abell.jpg‎|right|frame]].  

'''Light''', or '''visible light''', is [http://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic radiation] of a [[wave]]length that is visible to the [[human]] [http://en.wikipedia.org/wiki/Eye eye] (about 400–700 nanometre.  In a [[scientific]] [[context]], the [[word]] ''light'' is sometimes used to refer to the entire electromagnetic [[spectrum]].[http://www.lightsources.org/cms/?pid=1000166] (What Is a Light Source?) Light is composed of an elementary [[particle]] called a [http://www.wikipedia.org/wiki//Photon photon].

'''Light''', or '''visible light''', is [https://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic radiation] of a [[wave]]length that is visible to the [[human]] [https://en.wikipedia.org/wiki/Eye eye] (about 400–700 nanometre.  In a [[scientific]] [[context]], the [[word]] ''light'' is sometimes used to refer to the entire electromagnetic [[spectrum]].[https://www.lightsources.org/cms/?pid=1000166] (What Is a Light Source?) Light is composed of an elementary [[particle]] called a [https://www.wikipedia.org/wiki//Photon photon].

Three primary properties of light are:

Three primary properties of light are:

* [[Intensity]], or brightness;

* [[Intensity]], or brightness;

* [[Frequency]] or wavelength and;

* [[Frequency]] or wavelength and;

* [http://en.wikipedia.org/wiki/Polarization_(waves) Polarization] or direction of [[wave]] oscillation.

* [https://en.wikipedia.org/wiki/Polarization_(waves) Polarization] or direction of [[wave]] oscillation.

Light can exhibit properties of both [[wave]]s and [[particles]].  This property is referred to as [http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality wave-particle duality].  The study of light, known as [[optics]], is an important [[research]] area in modern [[physics]].

Light can exhibit properties of both [[wave]]s and [[particles]].  This property is referred to as [https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality wave-particle duality].  The study of light, known as [[optics]], is an important [[research]] area in modern [[physics]].

<center>For lessons on the [[topic]] of '''''Light''''', follow [https://nordan.daynal.org/wiki/index.php?title=Category:Light this link].</center>

<center>For lessons on the [[topic]] of '''''Light''''', follow [https://nordan.daynal.org/wiki/index.php?title=Category:Light this link].</center>

==Speed of light==  

==Speed of light==  

The ''speed of light'' in a [http://en.wikipedia.org/wiki/Free_space vacuum] is exactly 299,792,458 Metres per second|m/s (about 186,282.397 miles per second). The speed of light depends upon the [[medium]] in which it is [[traveling]], and the [[speed]] will be lower in a [[transparent]] medium. Although commonly called the "velocity of light", technically the word ''[[velocity]]'' is a [[vector]] [[quantity]], having both [[magnitude]] and direction.  ''Speed'' refers only to the [[magnitude]] of the velocity vector.  This fixed definition of the speed of light is a result of the modern attempt, in [[physics]], to define the basic [[unit]] of length in terms of the speed of light, rather than defining the speed of light in terms of a length.  

The ''speed of light'' in a [https://en.wikipedia.org/wiki/Free_space vacuum] is exactly 299,792,458 Metres per second|m/s (about 186,282.397 miles per second). The speed of light depends upon the [[medium]] in which it is [[traveling]], and the [[speed]] will be lower in a [[transparent]] medium. Although commonly called the "velocity of light", technically the word ''[[velocity]]'' is a [[vector]] [[quantity]], having both [[magnitude]] and direction.  ''Speed'' refers only to the [[magnitude]] of the velocity vector.  This fixed definition of the speed of light is a result of the modern attempt, in [[physics]], to define the basic [[unit]] of length in terms of the speed of light, rather than defining the speed of light in terms of a length.  

[[Different]] physicists have attempted to [[measure]] the speed of light throughout [[history]]. [http://www.wikipedia.org/wiki/Galileo Galileo] attempted to [[measure]] the speed of light in the seventeenth century.  A good early [[experiment]] to measure the speed of light was conducted by [http://www.wikipedia.org/wiki/Ole_Rømer Ole Rømer], a Danish physicist, in 1676. Using a telescope, Ole observed the motions of [http://www.wikipedia.org/wiki/Jupiter Jupiter] and one of its [[satellites]].  Noting discrepancies in the apparent period of Io's orbit, Rømer calculated that light takes about 18 minutes to traverse the [[diameter]] of [[Earth]]'s [[orbit]]. Unfortunately, this was not a [[value]] that was known at that time.  If Ole had known the diameter of the earth's orbit, he would have calculated a speed of 227,000,000 m/s.

[[Different]] physicists have attempted to [[measure]] the speed of light throughout [[history]]. [https://www.wikipedia.org/wiki/Galileo Galileo] attempted to [[measure]] the speed of light in the seventeenth century.  A good early [[experiment]] to measure the speed of light was conducted by [https://www.wikipedia.org/wiki/Ole_Rømer Ole Rømer], a Danish physicist, in 1676. Using a telescope, Ole observed the motions of [https://www.wikipedia.org/wiki/Jupiter Jupiter] and one of its [[satellites]].  Noting discrepancies in the apparent period of Io's orbit, Rømer calculated that light takes about 18 minutes to traverse the [[diameter]] of [[Earth]]'s [[orbit]]. Unfortunately, this was not a [[value]] that was known at that time.  If Ole had known the diameter of the earth's orbit, he would have calculated a speed of 227,000,000 m/s.

Another, more accurate, [[measurement]] of the speed of light was [[performed]] in Europe by [http://www.wikipedia.org/wiki/Hippolyte_Fizeau Hippolyte Fizeau] in 1849. Fizeau directed a beam of light at a [[mirror]] several kilometers away.  A rotating cog wheel was placed in the path of the light beam as it [[traveled]] from the [[source]], to the [[mirror]] and then returned to its [[origin]].  Fizeau found that at a certain rate of rotation, the beam would pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to calculate the speed of light as 313,000,000 m/s.

Another, more accurate, [[measurement]] of the speed of light was [[performed]] in Europe by [https://www.wikipedia.org/wiki/Hippolyte_Fizeau Hippolyte Fizeau] in 1849. Fizeau directed a beam of light at a [[mirror]] several kilometers away.  A rotating cog wheel was placed in the path of the light beam as it [[traveled]] from the [[source]], to the [[mirror]] and then returned to its [[origin]].  Fizeau found that at a certain rate of rotation, the beam would pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to calculate the speed of light as 313,000,000 m/s.

[http://www.wikipedia.org/wiki/Léon_Foucault Léon_Foucault] used an [[experiment]] which used rotating [[mirrors]] to obtain a [[value]] of 298,000,000 m/s in 1862.  [http://www.wikpedia.org/wiki/Albert_Abraham_Michelson Albert A. Michelson] conducted [[experiments]] on the speed of light from 1877 until his death in 1931.  He refined Foucault's [[methods]] in 1926 using improved rotating [[mirror]]s to [[measure]] the [[time]] it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California.  The precise measurements yielded a speed of 299,796,000 m/s.[http://en.wikipedia.org/wiki/Light]

[https://www.wikipedia.org/wiki/Léon_Foucault Léon_Foucault] used an [[experiment]] which used rotating [[mirrors]] to obtain a [[value]] of 298,000,000 m/s in 1862.  [https://www.wikpedia.org/wiki/Albert_Abraham_Michelson Albert A. Michelson] conducted [[experiments]] on the speed of light from 1877 until his death in 1931.  He refined Foucault's [[methods]] in 1926 using improved rotating [[mirror]]s to [[measure]] the [[time]] it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California.  The precise measurements yielded a speed of 299,796,000 m/s.[https://en.wikipedia.org/wiki/Light]

==Spirituality==

==Spirituality==