I just read an older, but interesting article here:
http://ibookcreatives.com/2012/01/27...-self-publish/
I've been using the ibooks Author app for about a week, and it does make it very easy to put together and publish an e-book.
I'm currently using it to make pseudo-apps for work, allowing our people to use their ipads as an interactive brochure when they go out to do measure and quotes. It is pretty neat, and would be an easy way to get your book of astro-photos published.
Yes, you need a mac to run the authoring software, but you can pick up a 2nd hand mac laptop for $300-$400 to run it, and that is a pretty cheap entry into the world of self-publishing.
The article is worth a read.
