Books take about a year to be published. They will not include the latest studies and research. Textbooks and encyclopedias are good for basic information. Further editions of books demonstrate that a source has been updated to reflect new information and may be a standard source in the field. Are there newer editions available?
A Brief History of Time by 
On the revolutions of the heavenly spheres by 
The achievement of Galileo by Dialogue concerning the two chief world systems, Ptolemaic & Copernican by 
Galileo's daughter : a historical memoir of science, faith, and love by 
Tycho & Kepler : the unlikely partnership that forever changed our understanding of the heavens by 
The Georgian star : how William and Caroline Herschel revolutionized our understanding of the cosmos by Cosmos by 
On the shoulders of giants : the great works of physics and astronomy by 
Newton's gift : how Sir Isaac Newton unlocked the system of the world by 
