Double click to edit
Coordinated Universal Time (UTC) Zulu Time
Coordinated Universal Time (U T C) is the basis for civil time today. This 24-hour time standard is kept using highly precise
atomic clocks combined with the Earth’s rotation.
1. Add time zone to local time to obtain UTC (Zulu Time).
2. Subtract time zone number from UTC (Zulu Time) to obtain local time.
The World’s first atomic clock, at the ammonia absorption cell atomic clock at the National Bureau of Standards (now the National Technology) first operated in August 1 9 4 8. Dr. Harold Lyons, inventor is at the right, Dr. Edward U. Condon, Director of the NBS, is at the Left. The ammonia absorption cell is the coil of wave guide surrounding the clock face.
The standard practice is to establish a time zone for each 15° of longitude. This makes a difference of exactly 1 hour between each zone. In the United States, there are four time zones. The time zones are Eastern (75°), Central (90°), Mountain (105°), and Pacific (120°). The dividing lines are somewhat irregular because communities near the boundaries often find it more convenient to use time designations of neighboring communities or trade centers.
Meridians of longitude are drawn from the North Pole to the South
Pole and are a t right angles to the Equator. The “Prime
Meridian” which passes through Greenwich, England, is used as
the zero line from which measurements are made in degrees east
(E) and west (W) to 180°. The 48 conterminous states of the
United States are between 67° and 125° W longitude.
Time Zones, the meridians are also useful for designating time
zones. A day is defined as the time required for the Earth to make
one complete rotation of 360°. Since the day is divided into 24
hours, the Earth revolves at the rate of 15° an hour. Noon is the
time when the sun is directly above a meridian; to the west of that
meridian is morning, to the east is afternoon.