This project was used for an enrichment Astronomy class, and took people anywhere from 3-6 days to complete. After everything Astronomy-related was taught, this is a great extension activity that allows students to both apply their previous knowledge and create new concepts related to Astronomy.
This includes a broad range of topics, and can be adjusted based on what you have taught. The kids really loved this activity and got very creative with it! I would suggest a high focus on keeping things creative yet realistic. For younger ages, a model slide/paragraph would be a good idea as well. Rubric included.