Day - Civil Day

Civil Day

For civil purposes a common clock time has been defined for an entire region based on the mean local solar time at some central meridian. Such time zones began to be adopted about the middle of the 19th century when railroads with regular schedules came into use, with most major countries having adopted them by 1929. For the whole world, 40 such time zones are now in use. The main one is "world time" or Coordinated Universal Time (UTC).

The present common convention has the civil day starting at midnight, which is near the time of the lower culmination of the mean Sun on the central meridian of the time zone. A day is commonly divided into 24 hours of 60 minutes of 60 seconds each.