SPEED OF LIGHT

 MEASURING THE
 SPEED OF LIGHT
 OLE RØMER (1644–1710)

 

 






"For the distance of
about 3,000 leagues,
which is nearly equal
to the diameter of the
Earth, light needs not
one second of time"
   
 THE SPEED OF LIGHT IS=

299 792 458 m / s

 《   The speed of 

        light can be 

        calculated from the 

        time differences 

        and distances in the 

         solar system    

                                     》

    

            The speed of light in vacuum, commonly denoted c, is a universal physical constantimportant in many areas of physics. Its exact value is 299,792,458 metres per second(approximately 300,000 km/s (186,000 mi/s)^{[Note 3]}). It is exact because by international agreement a metre is defined to be the length of the path travelled by light in vacuum during a time interval of 1/299792458 second.^{[Note 4][3]} According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universecan travel. Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum 

Sunlight takes about 8 minutes 17 seconds to travel the average distance from the surface of the Sun to the Earth.
Exact values
metres per second	299792458
Planck length per Planck time (i.e., Planck units)	1
Approximate values (to three significant digits)
kilometres per hour	1080000000
miles per second	186000
miles per hour[1]	671000000
astronomical units per day	173[Note 1]
parsecs per year	0.307[Note 2]
Approximate light signal travel times
Distance	Time
one foot	1.0 ns
one metre	3.3 ns
from geostationary orbit to Earth	119 ms
the length of Earth's equator	134 ms
from Moon to Earth	1.3 s
from Sun to Earth (1 AU)	8.3 min
one light year	1.0 year
one parsec	3.26 years
from nearest star to Sun (1.3 pc)	4.2 years
from the nearest galaxy (the Canis Major Dwarf Galaxy) to Earth	25000 years
across the Milky Way	100000 years
from the Andromeda Galaxy to Earth	2.5 million years
from Earth to the edge of the observable universe	46.5 billion years