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Light seconds, light years, light centuries: How to measure extreme distances - Yuan-Sen Ting
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Light is the fastest thing we know.
It's so fast that we measure enormous distances
by how long it takes for light to travel them.
In one year, light travels about 6 trillion miles,
a distance we call one light year.
To give you an idea of just how far this is,
the Moon, which took the Apollo astronauts four days to reach,
is only one light-second from Earth.
Meanwhile, the nearest star beyond our own Sun is Proxima Centauri,
4.24 light years away.
Our Milky Way is on the order of 100,000 light years across.
The nearest galaxy to our own, Andromeda,
is about 2.5 million light years away
Space is mind-blowingly vast.
But wait, how do we know how far away stars and galaxies are?
After all, when we look at the sky, we have a flat, two-dimensional view.
If you point you finger to one star, you can't tell how far the star is,
so how do astrophysicists figure that out?
For objects that are very close by,
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