I've read up to chapter ten, Strider, in The Fellowship of the Ring, on a quest to re-read LOTR. I haven't read the trilogy and The Hobbit since I was a kid, so I haven't gotten to any parts featuring Sauron yet.

But I would like to know: How big is the eye of Sauron? I'd prefer a LOTR canon-based answer; however, for purposes of this question, I'd definitely also consider a serious answer based on the eye of Sauron as he appears in the LOTR movies.