Light Year
The light year is a unit of distance that comes from the knowledge that light (or electromagnetic radiation in general) takes a finite length of time to travel through space. It is defined as the distance that light travels in a year through a vacuum.
| The speed of light in a vacuum | = 299,792,458 metres/second |
| The number of seconds in a year | =60 × 60 × 24 × 365.25 |
| 1 light year or ly | = 60 × 60 × 24 × 365.25 × 299,792,458 |
| = 9.46 × 1015 m | |
| = 9.46 × 1012 km | |
| = 63,240 AU | |
| = 0.306 pc |
Remember that a light year is not a measure of time!
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