Daniel Zajdel, age 9., of Pittsburgh, Pa., for his question:

How long is a light year?

We can give the length of a light year in time, or we can give its length in miles. In time, a light year is 365 days long  which is equal to an ordinary calendar year. This part is simple, because our minds can understand the length of a year. But a light year is also very long in miles.

It is the number of miles a beam of light travels in an ordinary calendar year. And light travels about 186,000 miles every second. In one year it travels almost 6 trillion miles. If you want to write the distance length of a light year in figures, it is 6 followed by 12 zeros.