Science 10 with CSS teacher

In space, light-years are often used as the main unit of measurement. The light-year is NOT a measurement of time; it's the distance that a beam of light travels in one year. The speed of light is 300 000 kilometres per second. In one year, light travels 9.46 trillion kilometres! Instead of saying 9 460 800 000 000 kilometres, astronomers say 1 light-year.

You can see that 1 light-year is a huge distance. But, in the scope of the universe, 1 light-year is quite small. For example, the Milky Way galaxy has a diameter of about 100 000 light-years. Try writing that number out—that's a lot of zeroes!