Astronomy Picture of the Day . ... Credit: United States Naval Observatory Explanation: In the nineteenth century , dropping a time ball from a prominent location was a practical way of communicating the time to the surrounding country side and ships at sea . Initiating a fledgling time service for the United States , the U.S. Naval Observatory dropped a time ball at precisely noon every day begining in 1845. ... Publications with keywords: time - millennium - U.S. Naval Observatory . ...