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Astronomical Unit
The mean distance from the Earth to the Sun,
and often abbreviated to A.U. I think using this measure
gives the best idea of how far the closest objects are.
Light year
You're not going to believe this, but one
light year is the distance that light travels in one year!
That's through the vacuum of space. You can see how for
this is from the table above: a distance equal to over 9
trillion kilometres.
Parsec
The distance that light travels in 3.2616
years. Why!? I hear you cry. The word Parsec comes from
a mixture of Parallax and Second.
Does that clear it up? This is all to do with measuring
the distances to stars using their shifted position as the
Earth orbits the Sun. (Full explanation link follows soon).
Big
Numbers
The number 1000 can be written in mathematics
speak as 10³, or 10^3 which we shall use due to internet limitations. This means 10 to the power of 3 or 10 multiplied
by 10 multiplied by 10 (10x10x10). We can use larger powers
for millions, billions etc. Here's my guide:
| 10^2 |
100 |
Hundred |
| 10^3 |
1,000 |
Thousand |
| 10^6 |
1,000,000 |
Million |
| 10^9 |
1,000,000,000 |
Billion |
| 10^12 |
1,000,000,000,000 |
Trillion |
| 10^15 |
1,000,000,000,000,000 |
Quadrillion |
| 10^18 |
1,000,000,000,000,000,000 |
Quintillion |
A little more about
Light
Light travels at almost 300,000 kilometres per second (186,282
miles per second). Even at this tremendous speed light can
take a long time to get from one place to another. Starting
close to us, light takes 1˝ seconds to get from the Moon to
your eye. A little further away is the Sun, and light starting
its journey from there takes 8˝ minutes to reach the Earth.
So, we’re not actually seeing the Sun as it is right now,
but how it WAS 8˝ minutes ago: we’re looking into the past!
Much further away is the closest star, Proxima Centauri. Light
from this small red star takes over 4 years to get to Earth,
and the further we go the longer it takes light to reach us.
Some of the furthest objects are over 10,000 million light
years away! We’re looking back in time close to when the Universe
itself was formed.
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Light travels
at a constant speed in whatever it is zooming through. If
that is water then light-speed is two-thirds that of space.
The speed of
light is EXACTLY 299,792.458 kilometres per second.
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