section_path: Definitions/Apparent and mean solar day/Civil day
section_name: Civil day
paragraph_text: Civil day
  
  For civil purposes, a common clock time is typically defined for an entire region based on the local mean solar time at a central meridian. Such time zones began to be adopted about the middle of the 19th century when railroads with regularly occurring schedules came into use, with most major countries having adopted them by 1929. As of 2015, throughout the world, 40 such zones are now in use: the central zone, from which all others are defined as offsets, is known as UTC±00, which uses Coordinated Universal Time (UTC).
  
  The most common convention starts the civil day at midnight: this is near the time of the lower culmination of the Sun on the central meridian of the time zone. Such a day may be called a calendar day.
  
  A day is commonly divided into 24 hours, with each hour being made up of 60 minutes, and each minute composed of 60 seconds.