According to the book the fictional Agnes is standing on the left side of this famous photo:
The title comes from something T.E. Lawrence wrote in The Seven Pillars of Wisdom, which is quoted in Dreamers of the Day:
Those who dream by night in the dusty recesses of their minds wake in the day to find that all was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes, and make it possible.
You can find discussion questions about the book on the Random House web site, which also has an interview with Mary Doria Russell. And below is a KPFA radio interview with the author about Dreamers of the Day:
Cover to Cover with Richard Wolinsky - April 10, 2008 at 3:00pm
How did you like the book? If you've also read A Thread of Grace by the same author, how does it compare?