Coordinated Universal Time (UTC)

Coordinated Universal Time (UTC) is also called International Time, Universal Time (UT), Zulu Time or Greenwich Mean Time (GMT). GMT was established by international conference in 1884. It’s based on the local time in Greenwich England where noon is set to the sun's peak.

Twenty Four Hour time counts hours:minutes past midnight (00:00) to the end of the day (24:00). Twenty four hundred hours (24:00) is also 00:00 hours the next day.

LOCAL TIME
The earth is divided into 24 time zones. Each time zone is 1 hour long, or 15° wide in longitude. An area's local time is based on time zone hours ahead of (+ east), or behind (- west) Greenwich England.

Daylight savings time (DST) is used in the summer months in some regions. DST is 1 hour ahead of standard (real) time. There is no consistency between regions as to when DST takes affect, or reverts back to standard (real) time. DST was never practical and will eventually be phased out.

Hours behind (-), or ahead of, UT

• Mean Solar Time -- a measurement of the Earth's rotation with respect to the fictitious mean sun.

• Atomic Clock -- Measures seconds based on the frequency of the cesium 133 atom (Cs) oscillation.
• Second -- Based based on the duration of 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the Cesium 133 atom (Cs).
• Mean Solar Time -- a measurement of the Earth's rotation with respect to the fictitious mean sun.

• UT -- Universal Time is widely used and based on the average of multiple atomic clocks, UT0, UT1, UT2, and UTC.
• UT0 -- Mean Solar Time on the Greenwich meridian obtained from direct astronomical observation. The time 00 hours being at Greenwich mean midnight.
• UT1 -- UT0 corrected for polar motion (widely used).
• UT2 -- UT1 corrected for seasonal variation in the Earth's rotation (a smoothed scale that does not reflect the real periodic variations in the Earth's angular position).
• UTC -- Civil atomic time scale on or about the Greenwich meridian kept within 0.9 seconds of UT1.

Virtually the entire world formats time as Hours:Minutes:Seconds. The date format Year-Month-Day has become widely accepted as a standard in many countries.

International Standard ISO 8601,
United States ANSI X3.30 and NIST FIPS 4-1,
Canadian standard CSA Z234.5,
European standard EN 28601,
British standard BS EN 28601.

The United States and many other countries use the Christian Gregorian calendar to mark years. This calendar has become a standard in such worldwide industries as aviation, and international commerce and trade -- however, other calendars do exist.

       CALENDAR    YEAR

         Jewish    5760-5761
        Chinese    4698 (Year of the Dragon)
      Old Roman    2753
       Buddhist    2544
      Christian    2000
         Coptic    1716
        Islamic    1420-1421