So I bought Chris Hadfield's Book ..

.. and destroyed it lol ... So that I could peel out his signature photo, seal the two pages with tape, and better share it here. Its now my goal to find someone who can calculate how much of the horizon is visible, based upon his elevation, which I believe is between 100 and 120,000 feet, whilst he 'allegedly' shuttled to the ISS (as he depicts in Chapter 2 of the book). Any mathematicians out there that can help -- how much horizon is revealed in this photograph?