My kids adore this PBS show, and it's really well done.  I also love it because it comes on at 6:00pm, just around the time I need to start getting dinner going.  - Guilt-free TV when you need it most!  View Show Schedule

In a nutshell, the characters travel the galaxies to learn new and exciting things about science and space exploration. The series, targeted to pre-kindergarteners through third-graders, delivers both astronomy-based science education (orbits, eclipses, moon phases, asteroids, comets, gravity), as well as character-building lessons.

My 5 year old has learned a ton of great concepts from gravity & the properties of air, to nebulas and how stars are formed. It's fun, upbeat and really packs an educational punch.  I highly recommend.