The determination of universal time and ephemeris time

Atmospheric refraction, with its non-predictable variations, is one of the dominant sources of error in the precise determination of the apparent position of a star. It appears that this will be the dominant error source for the new generation of instrumentation now being installed for the determination of stellar catalog and Universal Time (i.e., the USNO 65-cm PZT). The effects of anomalous refraction measurements of stellar position propagate to the various quantities derived from this data. This includes the compilation of stellar catalogs, the determination of Universal Time, and variations in the latitude.

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Individual Star Catalogues of the Unified Time Service of Kharkov Scientific and Research Institute and Kharkov University Astronomical Observatory

Symposium - International Astronomical Union ◽

10.1017/s0074180900087301 ◽

1990 ◽

Vol 141 ◽

pp. 456-456

Author(s):

S. P. Izmailov ◽

N. G. Litkevich ◽

V. D. Simonenko ◽

V. I. Turenko

Keyword(s):

Seasonal Variation ◽

Universal Time ◽

Astronomical Observatory ◽

Time Service ◽

Common Time ◽

Individual Star ◽

New System ◽

Astronomical Constants ◽

New Time

The Time Service Catalogue (TSC), which is obligatory for use in all USSR Time Services, was created for the epoch 1958 in the 1970s. Research done in the succeeding years detected a seasonal variation of TSC errors. Thus, a new Time Service Catalogue (TSC2) was required, in order to remove the seasonal errors as well as to satisfy the increasing demands for accuracy in the determination of universal time. During 1986-88 the data of Kharkov Common Time Service for 1980-1987 were reanalyzed using the new system of astronomical constants and two new catalogues were produced.

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Precision Estimates of Universal Time from Radio-Interferometric Observations

Symposium - International Astronomical Union ◽

10.1017/s0074180900036275 ◽

1979 ◽

Vol 82 ◽

pp. 225-230

Author(s):

H. G. Walter

Keyword(s):

Very Long Baseline Interferometry ◽

High Accuracy ◽

Universal Time ◽

Considerable Improvement ◽

Radio Sources ◽

Long Baseline ◽

The Earth ◽

Order Of Magnitude ◽

Fringe Frequency

Considerable improvement in the determination of the motion of the Earth is possible by the potentially high accuracy inherent in very-long-baseline interferometry. Precisions of UT1 are estimated from time delay and fringe frequency measurements of extragalactic radio sources with positional uncertainties at the level. Case studies resulted in standard deviations about one order of magnitude smaller than those obtained by classical astrometric methods. The dependence of estimates on baseline orientations and source declinations is discussed.

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Classical Methods for the Determination of Universal Time and Polar Motion

International Astronomical Union Colloquium ◽

10.1017/s0252921100051101 ◽

1975 ◽

Vol 26 ◽

pp. 303-308

Author(s):

N. P. J. O’Hora ◽

B. D. Yallop

Keyword(s):

Polar Motion ◽

Universal Time ◽

Historical Survey

AbstractA brief historical survey of important improvements in the classical methods for the determination of universal time and of polar motion over the last 25 years is outlined. Some of the errors that affect the results and estimates of the ultimate accuracy that may be achieved by these methods are discussed. Attention is drawn to the value of the observations in the field of astrometry and to the desirability of the continuation of the classical methods for use in this field.

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Galactic orbits of stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900105340 ◽

1966 ◽

Vol 25 ◽

pp. 93-97

Author(s):

Richard Woolley

Keyword(s):

Globular Cluster ◽

Potential Field ◽

High Velocity ◽

Velocity Vector ◽

Variable Stars ◽

The Sun ◽

Proper Motions ◽

Rr Lyrae ◽

The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

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Distance to SN 1987A and the LMC

Symposium - International Astronomical Union ◽

10.1017/s0074180900118959 ◽

1999 ◽

Vol 190 ◽

pp. 549-554

Author(s):

Nino Panagia

Keyword(s):

Angular Size ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Light Curves ◽

Distance Modulus ◽

Absolute Size ◽

Sn 1987A

Using the new reductions of the IUE light curves by Sonneborn et al. (1997) and an extensive set of HST images of SN 1987A we have repeated and improved Panagia et al. (1991) analysis to obtain a better determination of the distance to the supernova. In this way we have derived an absolute size of the ringRabs= (6.23 ± 0.08) x 1017cm and an angular sizeR″ = 808 ± 17 mas, which give a distance to the supernovad(SN1987A) = 51.4 ± 1.2 kpc and a distance modulusm–M(SN1987A) = 18.55 ± 0.05. Allowing for a displacement of SN 1987A position relative to the LMC center, the distance to the barycenter of the Large Magellanic Cloud is also estimated to bed(LMC) = 52.0±1.3 kpc, which corresponds to a distance modulus ofm–M(LMC) = 18.58±0.05.

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International determination of the total motion of the pole

Symposium - International Astronomical Union ◽

10.1017/s0074180900177824 ◽

1961 ◽

Vol 13 ◽

pp. 29-41

Author(s):

Wm. Markowitz

Keyword(s):

Secular Motion ◽

The Future

A symposium on the future of the International Latitude Service (I. L. S.) is to be held in Helsinki in July 1960. My report for the symposium consists of two parts. Part I, denoded (Mk I) was published [1] earlier in 1960 under the title “Latitude and Longitude, and the Secular Motion of the Pole”. Part II is the present paper, denoded (Mk II).

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Time and Latitude in South Africa

International Astronomical Union Colloquium ◽

10.1017/s0252921100026816 ◽

1972 ◽

Vol 1 ◽

pp. 27-38

Author(s):

J. Hers

Keyword(s):

South Africa ◽

Cape Town ◽

Astronomical Observations ◽

Royal Observatory ◽

The Republic ◽

Astronomical Determination ◽

Limited Accuracy ◽

Better Than

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.

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