Light Year Converter
A light year is the distance light travels in one year, which makes it a handy yardstick for distances between stars. This page turns a number of light years into ordinary miles or kilometres.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
One light year is about 9.46 trillion kilometres, based on the speed of light and a Julian year of 365.25 days. The distance here is the number of light years multiplied by that fixed length.
A light year measures distance, not time, even though its name suggests otherwise.
Worked example
A distance of 4.2 light years is about 24,690,226,567,371 mi.
Questions
Is a light year a unit of time?
No. It is a unit of distance, although its name comes from the time light takes to cross it.
Why use light years instead of miles?
Star distances are so large that miles would give long strings of digits. Light years keep the numbers easy to read.
Does this allow for the expansion of the universe?
No. It is a plain unit conversion, and it does not model how distant galaxies are moving.
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