scholarly journals ‘The Metrication of Navigation’

1968 ◽  
Vol 21 (2) ◽  
pp. 236-237
Author(s):  
D. H. Sadler
Keyword(s):  
Universal Time ◽  
Time System ◽  
Precise Position ◽  
The Earth ◽  
Time Signals ◽  
Time Argument ◽  
Orbital Periods ◽  
Rotation Of The Earth ◽  
Mean Time ◽  
Nautical Almanac

In his note (Journal 21, 81) on this subject, Ronald Turner says ‘No longer will orbital periods of the rotation of the Earth on its axis be measures of time’. This is not so, either in general or in the particular, case of navigation.Universal Time (U.T.), which is the generally accepted name for Greenwich Mean Time (G.M.T.), continues to be essential for all purposes (in astronomy, geodesy, surveying and navigation) for which are required astronomical observations related to the precise position of the observer on the Earth's surface. The Nautical Almanac must continue to tabulate the positions of the Sun, Moon, planets and stars with G.M.T. as the time-argument; and observations should be timed in a time-system related to U.T., such as the broadcast time-signals of Coordinated Universal Time (U.T.C:).

About the Future of UTC

2014 ◽  
Vol 511-512 ◽  
pp. 209-212
Author(s):  
Shao Wu Dong
Keyword(s):  
International Organizations ◽  
Time Scale ◽  
International System ◽  
Universal Time ◽  
Current Form ◽  
Reference Time ◽  
The Earth ◽  
Time Signals ◽  
Scale Interval ◽  
Rotation Of The Earth

The Coordinated Universal Time (UTC) is the international reference time-scale, and provides the basis for broadcast time signals and for time-keeping in the large majority of countries. In its current form, UTC is computed as the average of a large number of atomic clocks and its scale interval is based on the second in the International System units (SI), but it is adjusted by the occasional insertion of one second (called as leap second), to maintain close alignment with Universal Time 1 (UT1), a time-scale determined by the rotation of the Earth. The UTC system with leap seconds is not a continuous time scale, in resent years, several countries and international organizations have started a discussion on the need to abolish the application of leap second in UTC, however, some countries oppose it. Issues on leap second worldwide are presented in this paper.

scholarly journals A non-rotating origin on the instantaneous equator

1988 ◽  
Vol 128 ◽  
pp. 33-38 ◽  
Author(s):  
N. Capitaine ◽  
B. Guinot
Keyword(s):  
Specific Rotation ◽  
Universal Time ◽  
Reference Systems ◽  
The Earth ◽  
Adopted Model ◽  
Fixed Reference ◽  
Rotation Of The Earth ◽  
Definition Of ◽  
Clear Description ◽  
Angle Of Rotation

In order to give an exact and clear description of the angle of rotation of the Earth, we propose to use, as the reference point in space, a “non-rotating origin” (Guinot 1979) such that its hour angle, reckoned from the origin of the longitudes (or “non-rotating origin” in the Earth), represents strictly the specific rotation of the Earth. The position of this origin on the instantaneous equator depends only on the trajectory of the pole of rotation. We show that the estimation of the deduced angle of rotation is not critically affected by the precision with which this trajectory is known. We give therefore the formulae to obtain the non-rotating origin, at any date t, from a chosen fixed reference, and we propose a definition of the Universal Time which will remain valid, even if the adopted model for the precession and the nutation is revised. We show that the use of the non-rotating origin also simplifies the transformation of coordinates between the terrestrial and celestial reference systems.

A re-interpretation of the definition of UT1

1988 ◽  
Vol 128 ◽  
pp. 39-40
Author(s):  
A. T. Sinclair
Keyword(s):  
Time Scale ◽  
Universal Time ◽  
Sidereal Time ◽  
Broad Definition ◽  
The Earth ◽  
Average Person ◽  
Rotation Of The Earth ◽  
Definition Of ◽  
Sidereal Rotation

SummaryUniversal time is a commonplace quantity, and yet it has no generally accepted definition. The expression for sidereal time is often quoted as a definition, but this does not convey much meaning to the average person. Also sidereal time is measured from the equinox of date, and so involves the precession formulae of the stellar reference frame, and hence may not be ideal for other modern techniques of observation. Guinot (1979) has proposed a broad definition of UT1:“UT1 is an angle which is proportional to the sidereal rotation of the Earth, the coefficient of proportionality being chosen so that UT1, in the long term, remains in phase with the alternation of day and night. In some applications, UT1 can be considered as a non-uniform time scale”.

Time Determination and Time Keeping

1948 ◽  
Vol 1 (2) ◽  
pp. 109-117
Author(s):  
Harold Spencer Jones
Keyword(s):  
Frequency Control ◽  
Rate Of Change ◽  
Time Interval ◽  
The Earth ◽  
Convenient Means ◽  
Time Signals ◽  
Time Determination ◽  
The Mean ◽  
Rotation Of The Earth ◽  
Definite Manner

The rotation of the Earth provides the ultimate standard of time. As the fundamental unit of time we can use either the mean solar day or the sidereal day; these two units are related in a definite manner, so that when one is determined, the other can be inferred. The purpose of any timepiece is to subdivide the day into shorter intervals, and so give the time at any instant. No timepiece will give exact time; the error of the timepiece at some definite instant and the rate of change of that error, or, briefly, the rate, must be determined in order to extrapolate for the correct time at some subsequent instant. The accuracy of the extrapolation will depend upon the uniformity of the rate of the timepiece. Radio time signals sent out from an observatory, which is responsible for the determination and distribution of time, provide the most convenient means for deriving the error and rate of a timepiece. For normal navigational purposes an accuracy of about 0·05 seconds is adequate. But for the purpose of frequency control a very much higher precision is needed—but a precision in time interval rather than in absolute time. Some of the radio-aids to navigation depend upon the accuracy in standardization of frequency, so that high accuracy in time interval has become, indirectly, a navigational requirement.

Time Data and Navigation

1972 ◽  
Vol 25 (1) ◽  
pp. 13-31 ◽  
Author(s):  
Humphry M. Smith
Keyword(s):  
Universal Time ◽  
Time Data ◽  
Fundamental Properties ◽  
Time Signals ◽  
Rotation Of The Earth ◽  
Time Standard ◽  
Relationship Of ◽  
Time Systems ◽  
The Relationship ◽  
Ultimate Control

In 1972 an atomic time standard based on the fundamental properties of the caesium atom is being substituted for Greenwich Universal Time, based on the rotation of the Earth on its axis, as the ultimate control for international time signals. Greenwich Time and longitude are inseparable, so that any necessary correction to the time signals he receives will be of vital importance to the navigator.This paper was presented at a meeting of the Institute in London on 27 January 1970 with the Hydrographer of the Navy, Rear-Admiral G. S. Ritchie, C.B., D.S.C., in the Chair. Mr. Humphry Smith, head of the Time Department at the Royal Greenwich Observatory and Chairman of the Directing Board of the Bureau International de l'Heure, reviews the relationship of uniform time systems to the precise astronomical observations that determine the irregularities of the Earth's rotation. He outlines the current proposals for time signals, their correction to Universal Time and the implications for the navigator.

scholarly journals Division I: Fundamental Astronomy

2005 ◽  
Vol 1 (T26A) ◽  
pp. 1-1
Author(s):  
Toshio Fukushima ◽  
Jan Vondrak ◽  
Nicole Capitaine ◽  
Veronique Dehant ◽  
George Krasinsky ◽  
...  
Keyword(s):  
Celestial Mechanics ◽  
Future Development ◽  
Universal Time ◽  
Division I ◽  
The Earth ◽  
Dynamical Astronomy ◽  
Fundamental Astronomy ◽  
Working Groups ◽  
Rotation Of The Earth ◽  
Definition Of

IAU Division I includes Commission 4 (Ephemerides), Commission 7 (Celestial Mechanics and Dynamical Astronomy), Commission 8 (Astrometry), Commission 19 (Rotation of the Earth) and Commission 31 (Time). The Division has in addition five Working Groups on, respectively, Future Development of Ground-Based Astrometry, Nomenclature for Fundamental Astrometry, Definition of Coordinated Universal Time, and Precession and the Ecliptic.

The Terrestrial Coordinate System and International Earth-rotation Services

1985 ◽  
Vol 38 (02) ◽  
pp. 216-217
Author(s):  
G. A. Wilkins
Keyword(s):  
Coordinate System ◽  
Earth Rotation ◽  
Reference System ◽  
New Techniques ◽  
Crustal Movements ◽  
Earth Observations ◽  
The Earth ◽  
External Reference ◽  
External Objects ◽  
Rotation Of The Earth

New techniques of measurement make it possible in 1984 to determine positions on the surface of the Earth to a much higher precision than was possible in 1884. If we look beyond the requirements of navigation we can see useful applications of global geodetic positioning to centimetric accuracy for such purposes as the control of mapping and the study of crustal movements. These new techniques depend upon observations of external objects, such as satellites or quasars rather than stars, and they require that the positions of these objects and the orientation of the surface of the Earth are both known with respect to an appropriate external reference system that is ‘fixed’ in space. We need networks of observing stations and analysis centres that monitor the motions of the external objects and the rotation of the Earth. Observations of stars by a transit circle are no longer adequate for this purpose.

Sensing the rotation of the Earth

1992 ◽  
Vol 30 (2) ◽  
pp. 111-111
Author(s):  
H. Richard Crane
Keyword(s):  
The Earth ◽  
Rotation Of The Earth
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