My 3rd grade homeschool group, started our Space Unit with a read aloud of the Dr. Seuss book, There's No Place Like Space.
Our lessons will include stars & the Sun, gravity, telescopes, planets & seasons. This book touched on each one and was fun to read.
I looked for flashcards on the Solar System online and found several free versions however most had a dark background that weren't great for printing or the facts were too advanced.
I made these flashcards for the 8 planets, Moon and Sun for students to use in class to quiz each other. There are interesting facts on the back and illustrations on the front.
*These would be easy to adapt as a research project by copying them single sided and having students fill-in facts.