The Speed of Light – Facts & Figures

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The Speed of Light – Facts & Figures




Speed of light
The distance from the Sun to the Earth is shown as 150 million kilometers, an approximate average. Sizes to scale.

Sunlight takes about 8 minutes 17 seconds to travel the average distance from the surface of the Sun to theEarth.
Exact values
metres per second 299792458
Planck length per Planck time
(i.e., Planck units)
Approximate values
kilometres per second 300,000
kilometres per hour 1,080 million
miles per second 186,000
miles per hour 671 million
astronomical units per day 173
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
from nearest star to Sun (1.3 pc) 4.2 years
from the nearest galaxy (the Canis Major Dwarf Galaxy) to Earth 25,000 years
across the Milky Way 100,000 years
from the Andromeda Galaxy (the nearest spiral galaxy) to Earth 2.5 million years


The speed of light in vacuum, commonly denoted c

, is a universalphysical constant important in many areas of physics. Its value is exactly299,792,458 metres per second because the length of the metre is defined from this constant and the international standard for time.[1] This is, to three significant figures, 186,000 miles per second, or about 671 millionmiles per hour. According to special relativity, c is the maximum speed at which all matter and information in the universe can travel. It is the speed at which all massless particles and changes of the associated fields (includingelectromagnetic radiation such as light and gravitational waves) travel in vacuum. Such particles and waves travel at c regardless of the motion of the source or the inertial frame of reference of the observer. In the theory of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.[2]


The Speed of Light – Facts & Figures

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