space
Astronomers often describe cosmic distances using a unit whose name sounds like it measures time.
A light-year measuring the distance light travels in one year is correct — it equals roughly 9.5 trillion kilometers, the distance a beam of light covers moving through the vacuum of space over 365 days. Astronomers use it because the numbers involved in measuring space in kilometers or miles would otherwise be almost impossibly large.
A light-year is not a measure of time, so it can't describe how long a star takes to orbit or how old a star is — those would need different units entirely, like years for age or orbital period, not a distance unit.
Because light takes time to travel, looking through a telescope is like looking into the past — a galaxy a billion light-years away is seen exactly as it looked a billion years ago, not as it looks right now.
space
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