I really love planning my own. The solar system post got me thinking. We have never concentrated on just space. My son loves the idea but kind of threw a wrench in there. He wants to do time and space. Maybe having him read a book on the true stories of time travel was a mistake. I am pretty sure there is no curriculum for time and space. If anyone knows of any good resources let me know. Now comes the fun part of researching our new study.
I would probably rewatch the Cosmos episode that showed the timeline of the universe broken down like a calendar month. It would think it has some good resources listed on it. Episodes 6-12 are still free on hulu and all of them are on huluplus if you have it.
There's some great projects that involve building a rotating solar system, and guidelines to show how time works....like how we rotate around the sun once = one day, we rotate 365 times = 1 year etc. etc. etc.
I'm not sure about your sons age or grade level but here are a few things we did when my twins were into space and time: We followed the NASA program via online sources, kept up with the rover program etc... we studied the history of astronomers and each of them did a very detailed biography (research skills and how to write a bibliography) on the astronomer of their choice, we read the Time Machine by HG Wells along with a detailed novel unit (various writing and extension activities to cover grammar etc...) and then because of the Mars Rover program we branched off into robotics, built robots using spare parts around the house and then again with the fancy Lego Mindstorm kit, read iRobot, by Asimov and did a novel unit again. There's a ton of math opportunities to tie in with space and time, Kahn Academy helps make them understandable. This is one of my favorite aspects of homeschooling, being able to completely construct a curriculum around an interest area that my kids have discovered. Hope you have a great time with this one!!!