MindTap Astronomy for Seeds/Backman's Foundations of Astronomy, 13th Edition This product requires a Course Key from your Instructor to fully activate. Please consult your Professor or class syllabus for the specific Course Key. ISBN: 9781305866164 Access to this product is valid for 180 days of usage. After this period, this product can be viewed under the "view expired" link in your CengageBrain account.