Evolution of Time Scales

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Abstract:

Time scales have continued to evolve to meet the developing needs of users in modern times. Fifty years ago time based on astronomical observations of the Earths rotation was sufficient to meet the needs for time, both civil and technical. During that 50-year interval, however, not only have these scales been expanded, but the advent of practical atomic clocks has led to the development of time scales based on atomic frequency transitions. In addition, the development of modern space techniques and the improvement in observational accuracy by orders of magnitude have led to the improvement of the theoretical concepts of time and the resulting relativistic definitions of time scales. The following sections provide a brief description of the chronological development of time scales since the middle of the 20th century Mean Solar Time, Universal Time UT, Ephemeris Time ET, Atomic Time, Coordinated Universal Time UTC, Dynamical Time Scales, and the Future of Time Scales.

Author(s):
Mccarthy, Dennis D.
Author Organization(s):
NAVAL OBSERVATORY WASHINGTON DC
Descriptive Note:
Conference paper
Supplementary Note:
Pub. in the Proceedings of the "Journees 2005 Systemes de Reference Spatio-Temporels," Earth Dynamics and Reference Systems: Five Years after the Adoption of the IAU 2000 Resolutions, p247-252, Dec 2006. Presented at the Journees Systemes de Reference Spatio-Temporels conference held in Warsaw, Poland, on 19-21 Sep 2005.
Pagination:
0007

Security Markings

DOCUMENT & CONTEXTUAL SUMMARY

Distribution:
Approved For Public Release
Distribution Statement:
Approved For Public Release; Distribution Is Unlimited.

RECORD

Collection: TR
Identifying Numbers
Monitor Series:
NOBS
 Subject Terms
Joint Capability Areas:
JCA_1.2_Force Preparation; JCA_1_Force Support; JCA_6_Net Centric; JCA_6.4.1_Secure Information Exchange; JCA_1.2.6_Concepts; JCA_1.2.3_Educating; JCA_6.1_Information Transport; JCA_6.4_Information Assurance; JCA_8_Building Partnerships
Communities of Interest:
No COI(s) Identified
Descriptor(s):
*MEASUREMENT, *TIME, *HISTORY, *EVOLUTION(DEVELOPMENT), ANGLES, USER NEEDS, EARTH(PLANET), ATOMIC CLOCKS, ROTATION, ASTRONOMY, SYMPOSIA, OBSERVATION, ACCURACY
Field(s)/Group(s):
Astronomy, Test Facilities, Equipment and Methods
Keyword(s):
*TIME SCALES, EARTH ROTATION ANGLE, MEAN SOLAR TIME, UNIVERSAL TIME, EPHEMERIS TIME, ATOMIC TIME, UTC(COORDINATED UNIVERSAL TIME), DYNAMICAL TIME SCALES, CHRONOLOGIES
Report Date:
2006 Dec 01
Creation Date:
2007 Jun 13