UT 0 is determined directly from astronomical observations.  It is

non uniform due to the irregular rotation of the earth on its axis and to

polar motion.

3.

Universal Time 1 (UT 1)

UT 1 is UT 0 corrected for polar motion and is   therefore  more uniform

than UT 0.  UT 1 is the same as Greenwich Mean Time.

4.

Universal Time 2 (UT 2)

UT 2 is UT 1 corrected for mean seasonal variations and is therefore more

uniform than UT 1.

TIME BASE ON ROTATION OF

TIME BASE:  REVOLUTION OF

ATOMIC TIME

EARTH ON ITS AXIS

EARTH AROUND THE SUN

TIME BASED ON TRANSITIONS IN THE ATOM

(EPHEMERIS TIME)

USES THE FREQUENCY OF THE CESIUM

BEAM ATOM CLOCK.

TIME BASE ON LONG TERM

ATOMIC SECOND DEFINED AS 9.192.

OBSERVATIONS OF THE

631,770 CYCLES OF THE CESIUM

ANNUAL REVOLUTION OF THE

VARIOUS FORMS OF SOLAR

RESONANCE.

EARTH AROUND THE SUN.

AND SIDEREAL TIME

AGREES CLOSELY WITH EPHEMERIS

SECOND.

IT IS THE UNIFORM MEASURE

ATOMIC SECOND IS THE UNIT OF TIME IN THE

OF TIME DEFINED BY THE

INTERNATIONAL SYSTEM OF UNITS (SI).

LAW OF DYNAMICS.

INTERNATIONAL ATOMIC TIME (TAI)

ATOMIC TIME REFERENCE DERIVED

NOTE:  

OMEGA

FROM AVERAGING THE ATOMIC TIME

TRANSITION

STANDARDS OF SEVERAL COUNTRIES.

CYCLE IS

MAINTAINED BY

ATOMIC CLOCK

COORDINATED UNIVERSAL TIME (UTC)

ATOMIC TIME MAINTAINED BY THE ROYAL

OBSERVATORY AND THE U.S. NAVAL

OBSERVATORY AND ADJUSTED IN STEPS

(LEAP SECONDS) SO THAT IT IS

SYNCHRONIZED WITH UT1 TO WITHIN

0.9 SECONDS.

UNIVERSAL TIME (UT)

UTO

UT1

UT2

MEAN SOLAR TIME ON THE

DETERMINED DIRECTLY

UT1 IS UTO CORRECTED FOR

UT2 IS UT1 CORRECTED FOR MEAN

GREENWICH MERIDIAN.

FROM ASTRONOMICAL

POLAR MOTION HENCE MORE

SEASONAL VARIATIONS.  HENCE IS

USED IN THE APPLICATION

OBSERVATION.  IT IS NON 

UNIFORM THAN UTO.

MORE UNIFORM THAN UT1.

OF ASTRONOMY TO

UNIFORM DUE TO

UT1 IS THE SAME AS GMT.

NAVIGATION.

IRREGULAR ROTATION OF

EARTH, AND TO POLAR

MOTION.

Figure 11 2.  The Interrelationship of the Different Methods of

Measuring and Defining Time

11.4.3.2  Atomic Time/UTC Time

Atomic time is based on quantified energy transitions within the atom.  The atomic

second is defined as 9192631770 cycles of the cesium resonance and is the unit of

time used in International Systems of Units (SI).  Atomic time is obtained practically by

use of  cesium beam clocks.  However, no practical clock can be considered perfect at

11 8