I got this for my 5 year old, to increase his interest in the outer space and our solar system. It was a very good first space encyclopedia. The first half has a lot of stuff about radio waves, space equipment, astronauts, rocket ships and space shuttles. The second half covers the solar system, planets, stars and the universe.
It was very easy for my son to read each section and look at the pictures.
Recommended ages - 5 to 10