Light-Year
Light-Year (LY): A unit of measurement that uses the speed of light, rather than standard lengths, to define the great distances in Space.
Light travels at 186,000 miles per second, or 5,865,696,000,000 miles per year. Rather than define the star Sirius as being 50,444,985,600,000 miles away, we note it as being 8.6 light-years distant.
Using light-years gives us an idea of the vast distances between objects in Space, without having to use such huge numbers. Just imagine trying to note the distances of nebulae and galaxies in conventional measurements. At hundreds, thousands, millions, and even billions of light-years, miles and kilometers would require unreasonably large numbers.
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