Ask groups of students each to create their own board game based on the solar system. The grading should be based on creativity and playability of the game as well as accuracy of solar system facts. Good games to give students as examples are Candyland or Trivial Pursuit, but they can of course choose a different game to base theirs on. On the day when games are due, each group can switch with each other to see how successful their game is when played by another team of students.
This game can be played by the whole class at one time. Split the classroom into two groups. As the game show host, prepare game cards ahead of time with questions and answers. Make some game cards worth a certain amount of points and other game cards worth more points. Ask the questions to the class. Team members will raise their hands if they know the answer. The team to get the most amount of points at the end will win a prize. Something like extra credit points or upping a letter grade on the next test can be a very valuable prize to win.
Split the class into groups. Ask each group to pick a planet they'd like to focus on. Each group will need to write a short script based on their planet. The script can be partly made up but will need to present enough accurate facts about the planet to show that they researched the planet. One example of fiction that can be in their script is the presence of aliens. This project should be graded based on creativity, accurate facts and overall entertainment value.
Post a big piece of black velvet on the wall. Make printouts of each planet as well as the sun and them cut out. Place hook-and-loop tape on the back of each planet and sun. Place each student's name in a hat, randomly pick a student, and give him one of the planets. Ask students to try to place the planets in the correct order until the solar system is all in place. This is a good project to do at the beginning of the lesson, perhaps even before they start studying the solar system.