How Old is the Light from the Stars that we see in the Night Sky?

-- | January 29, 2016

Question: One of the questions that always has remained unanswered to me is the following. When we see the stars on naked eyes or by telescopes, those are obviously many light years away from us, but do we see them live or is it the light from several years back? — Sami

Answer: In fact, the answer is in that remarkably convenient distance unit that you referred to above: “light year”. A light year is the distance that light can travel in one year. So, if a star is one light year away, the light that it emits takes one year to get to us. For that same star that is one light year away, if it suddenly started to glow brighter one day, we would actually see that brightening until one year later.

Jeff Mangum

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