Louis Gentz, age 11, of East Peoria, Illinois, for his question:

How many miles long is a light year?

The light year is a convenient unit for measuring sky distance. A million ordinary miles is a mere hop between heavenly bodies. Our sun's star neighbors are around 27 trillion miles away ‑ but right on our doorstep as far as space distances are concerned.

Light travels at about 186,000 miles a second. The light year is the distance this speedy traveler covers in one year. It is about six million million, or six trillion, miles. Our nearest star neighbors are more than four light years away. In miles we would have to write this distance as 27 followed by 12 zeros.

Some of the stars we see are hundreds of light years away. Imagine trying to write these immense distances in mere miles. Instead, an astronomer can write one light year for six followed by 12 zeros in miles or 100 light years for six followed by 14 zeros in miles.