When I asked my 4th graders what they thought would be cool to learn about in Spanish several of them said, "Space!" So that's what we did. We learned about the solar system...certainly a first for me.
Many of the words are cognates so it did make for a nice beginning of the year unit to ease them into the language. Plus it related to their interests.
I've included 2 different versions of this picture vocabulary sheet--the pictures used for the planets are different. Make sure you check out the solar system assessment in my store; the kids LOVED it!