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So can someone please help me with this? Can someone make the answer as simple as possible? So my question is if we see a star exploding like 100 light-years away, that means that star exploded 100 years in the past?

Chiral Anomaly
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Davi Sales
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2 Answers2

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It means the star exploded 100 years ago in our reference frame . You need to bear in mind that the elapsed time from an event some distance away depends upon the frame of reference in which the time is measured.

Marco Ocram
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As said in the comments, you are absolutely right.

Since light travels with a finite speed $c=299792458\,\text{km/s}$, everything you see has happened in the past. As $v=s/t$, if you see something at a distance $s$, you actually see it as it was $t=s/c$ ago.

For everyday situations, this delay is unperceivable and it's only really relevant on astronomical scales. If you have the distance to something given in x lightyears/days etc., you can just remove the "light" to know that the image of the object you see is what the object looked like x years/days etc. ago.

jng224
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