Question

What is a light-year?

Answer 1

A light-year is the distance that light travels in a year.

The speed of light is approximately 300,000,000 m/s or `3 \times 10^8` m/s. A more accurate number is 299 792 458 m/s.

We can take the speed of light and figure out how much light travels in one year, assuming 365 days in a year:

`3 \times 10^8 m//s \times 60 s//min \times 60 min//hr \times 24 hrs//day \times 365 days//year \approx 9.46 \times 10^15 m`

Some may prefer this formatting to see the cancellations:
`(3xx 10^8 m)/s xx (60 s)/(min) xx (60 min)/(hr) xx (24 hrs)/(day) xx (365 days)/(year) \approx 9.46 \times 10^15 m`