Introduction to MasteringAstronomy practice homework

I've received a few comments from students that missed points on Assignment 1 because they didn't know how to enter in their responses. Checking my gradebook, I discovered that the vast majority of these students had not done the "Introduction to MasteringAstronomy" practice homework that taught you how to do this in MasteringAstronomy. I've decided to re-open that practice homework so people can do it if they skipped it. Please, please, PLEASE go back and finish this if you haven't already. Even though it is not worth any points itself, you will likely miss points in the future on regular assignments if you haven't completed it.