If you have a reluctant reader who laughs through all of the Dr. Seuss books, here is a wonderful series for you. The energy of the Cat travels through the pages as you set out on your adventure into space. There's a visit to each planet and a few interesting facts are shared. There's a quick look at five constellations you may be able to find in your night sky and a pneumonic to remember the planets in order. The reading is easy and entertaining and informative. That's a combination a lot of young reluctant readers are comfortable with. Pluto is still a planet in this book so you'll have to do a bit of explaining on that one.
There's No Place Like Space! All About Our Solar System (Cat in the Hat Learning Library)