Light-year

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• one light second is the distance that light travels in one second – 1,864 million miles!
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• one light-year is the distance that light travels in one year – 5.92 trillion miles! – nearly 6 trillion miles! – that’s a 6 with 12 zeros behind it.
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• “light-years” are one of the standard distance measurements in astronomy.
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• it takes nearly eight and half minutes for light from our Sun to reach Earth.
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•  if the sun was to suddenly disappear it would take eight minutes for us to see it disappear – the reason is that light takes eight minutes to travel from the sun to us.
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• also, the Moon is nearly one light second away, so were are looking at as it was one second ago.
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• light-travel takes 4.22 years to reach Earth from the nearest star – Proxima Centauri, this means more than 25 trillion miles!
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• viewed from earth, Proxima Centauri looks like it was 4.22 years ago because its light takes 4.22 years to Earth.
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• astronomers use parsecs to measure distances – originally from parallax shift measurements (see Distances page); a light year is 0.3066 parsecs.

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BSL Version

Did you know?
With powerful telescope astronomers can see galaxies two billion light years away.