 set clocks for noon based on Sun Time,  or the time the sun was directly overhead (high noon). If Sun Time  was being observed, noon in New York was five minutes ahead of  Philadelphia noon. Only until the nations railroads adopted  Standard Time and established the nations four time zones at  exactly 12 noon on Sunday, November 18, 1883 did we have regulated  time that coincides with the timekeeping system we employ today.