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Speed of light: The concept put into perspective with three animated videos

Han Solo and Chewbacca on bord Faucon Millenium. Credits : davnes007, YouTube screenshot.

Three new animated videos give viewers an better understanding of speed of light.  Sometimes the speed of light can seem very fast or very slow however this depend on the  distances which separate the two points. 

The speed of light is the fastest speed ever recorded.  This speed, initially formed by all the energy available at the time of the Big Bang, hasn’t been surpassed since it was created. In a vacuum the speed of light equals 299,792 kilometers per second, or about 1,079 billion kilometers per hour. On paper, the speed at which these photons travel in space can make you feel dizzy. But as the distances between objects widen, the “light” seems to become much “slower”.

However the speed of light doesn’t reduce it’s speed.  This apparent decrease is in fact due to the immensity of the Universe. As this concept is difficult to understand, James O’Donoghue from NASA’s Goddard Space Flight Center has published three animated videos to help viewers better understand the speed of light.

Around Earth

Our planet has a circumference of 40, 075 km.  If Earth did not have an atmosphere (which slows down light a little), a photon placed above the surface could go around the equator nearly 7.5 times per second. But Earth does have an atmosphere. As shown in the example below, the speed of light is slowed down slightly although it still seems very fast.

vitesse lumière
Credits : James O’Donoghue/NASA

Between the Earth and the Moon

A second animated video helps us to understand the time it takes for light to reach the Moon. On average the distance that separates our planet from our satellite is around 384, 400 km.  At this distance, reflected photons from the moon, take about 1.255 seconds to reach Earth. (When you look at the moon it is like you are looking 1.255 seconds back into the past.)

vitesse lumière
Credits : James O’Donoghue/NASA

Light between Earth and Mars

Given the distance that separates Earth from Mars, light takes about 3 minutes 2 seconds to move between the two (when they are at the closest point). On average, Mars is about 158 million kilometers from Earth. A round-trip would then take on average 28 minutes and 12 seconds.

vitesse lumière
Credits : James O’Donoghue/NASA

During missions to the Moon and Mars for example, this data must therefore be taken into account. With so much “lag” time between Earth and other areas in space, NASA officials can not communicate directly with rovers. As a result, each command, each maneuver must be thought  out and anticipated in advance before they are programmed.


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