Speed of Light
at 186,000 miles a second.(299,792,458 m)
6 trillion miles a year (10 trillion km)
travel faster than the speed of light in a vacuum.
travels at a speed of 186,000 miles a second or 700 million
miles an hour. For scale, the distance from the Earth to the
Moon is about 239,000 miles. This seems pretty fast and indeed
theory says that nothing can travel faster than the speed of
our every day lives light seems to travel from one place to
another instantaneously. When we flip on the light in a room
there is no delay between when we first see the bulb start glowing
and when light illuminates the far corners of the chamber. Our
nervous systems are much too slow to notice the rays of light
that appear from the bulb and move like a wave washing over
we deal with the immense distances of space, though, even light
seems slow. When astronauts were on the Moon it took over a
second for the radio waves (which travel at the speed of light)
carrying their voices to reach us. Light coming from the sun
takes eight and one half minutes to hit Earth. (This means that
if the sun were suddenly to go dark, it would take over eight
minutes for us to notice) Light from the nearest stars, other
than the sun, takes four and a half years to get here. From
the farthest stars in distant galaxies it can take billions
of years for the light to arrive..
distance light can travel in a year is called a "light year."
The light year is one of the basic measures of distance for
designing probes for trips to other planets in our solar system
it is important for the planners to keep the communications
time lag, caused by the speed of light, in mind. For example,
a probe designed to land on Mars must be smart enough to handle
problems in the flight on its own without instructions from
Earth. If a course change is needed during landing the probe
would have to do it automatically. The delay caused by the probe
requesting instructions from Earth and getting commands back
might be nearly an hour, plenty of time for the probe to crash.
delay caused by the speed of light can sometimes be noticed
here on Earth during telephone calls. Long distance calls that
have been routed over one or more space satellites may cause
a half second or so delay between the speaker and the listener.
speed of light has several properties which may seem counter-intuitive
to us, but are true:
travels faster than the speed of light.
matter how fast you are moving the speed of light seems to be
the same speed as if you were not moving at all.
an object or person is accelerated toward the speed of light
time slows down for it/him.
last property leads to the "twins" effect: Twin brothers live
on Earth. One brother takes a trip to a distant star traveling
at a high percentage of the speed of light. When the twin returns
he will be younger than his brother because for him time slowed
down during the trip.
effect, called "time dilation," helps explain why the speed
of light is the same no matter how fast you are going. As a
traveler accelerates time slows down for him. This, in turn,
affects his measurements.
Lee Krystek, 1996-2013