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The basic relations used in computing a physical ephemeris of Mars are given. The constants in these relations used at various times during the past 100 years are reviewed. A summary of a revised ephemeris computed at the American Ephemeris Office is given in Table V, based on the following constants: zero point of longitude ω0 = 344°.41 on JD 2418322.0 (adopted in 1909), sidereal rotation rate R = 350°.891962 (adopted in 1960), celestial coordinates of North Pole for 1905.0: α0 = 316°.55, δ0 = +52°.85 (new corrected value). Table VI gives the elements for the reduction of areographic coordinates based on earlier ephemerides to the revised ephemeris system for the period 1877 to 1965.

A combined analytical-numerical procedure for determining precise mean orbital elements is presented and applied to the orbits of GEOS-1 and GEOS-2. The precision of the mean semi-major axes of these orbits is a few tens of centimeters when optical flash data is used to determine two-day orbital arcs. Four-day Minitrack orbits give mean semi-major axes of a few meters precision. The mean orientation parameters are obtained to a precision of about 0.1 sec (about 3m) or better from the optical orbits. This precision is adequate for determinations of tidal parameters, particularly in the case of GEOS-2, where the tidal perturbation of the inclination is 10 sec.

This paper, in addition to describing precise time determination, also notes the many advantages and the limitations of universal time and reports a new unit to be designated ephemeris time.

The differential equations of rotational motion of the moon are solved by numerical integration methods. Euler's dynamical equations transformed to a convenient form are treated by techniques analogous to ordinary orbit determination procedures. The proposed method is fully consistent with the ephemeris of the moon and can utilize a variety of observational material for the solution of the selected parameters. Examples are given of comparison between the proposed method and Eckhardt's 1970 model of the physical librations of the moon. The merits of the new method are discussed in the light of conventional data sources like earth-based or satellite-based photography as well as newly available data types like laser ranging to retroreflectors on the moon.

Differential very-long-baseline interferometric observations of signals from Apollo Lunar Surface Experiment Package telemetry transmitters will yield the relative projected positions of the transmitters with uncertainty of only 1-3 m, set mainly by uncertainty of the lunar ephemeris. Noise and systematic instrumental errors which in the past affected similar observations have been reduced to the equivalent of a few centimeters on the lunar surface by the development of a new type of differential receiver. Continued observations should yield a determination of the motion of the moon about its center of mass with uncertainty less than 1 sec of selenocentric arc. Improvements (by other means) in our knowledge of the moon's orbital motion would allow a further order-of-magnitude refinement in the libration and relative position results obtainable by differential VLBI.

Approximation formulae describing the long-term changes in the rotation of the Earth are evaluated. The time scale reduction from Universal to Ephemeris Time can be accomplished by a 12th degree polynomial with a mean error of less than one second for the entire time span 1800–1988. The maximum residuals of least squares fits of the 19th and 20th century data, respectively, can be limited to this accuracy by even simpler expressions. [Russian Text Ignored.]

Photoelectric, photographic, and visual observations of second and third contacts of the total solar eclipses of 12 November, 1966 and 7 March, 1970 are analyzed. The observations indicate a difference in the reference system of Newcomb's Tables of the Sun as compared to the reference system of the Improved Lunar Ephemeris (J = 2) of 0s.911 ± 0s.034 m.e. The correction is to be applied in the sense of reducing the value of ΔT as tabulated in the American Ephemeris when interpolating the position of the Moon.

Lunar corner reflector landing proposal for laser beam precision measurements including Moon orbit, size, ephemeris time and libration

We consider only: Sidereal time ST, reckoned from 0h at upper transit of the First of Aries (sidereal noon). GST and LST correspond to Greenwich ST and local ST. Universal time UT, reckoned from 0h at lower transit of the mean sun (solar midnight) for the Greenwich meridian. Standard time, as used in civil life, differs from UT by a whole number of hours, according to the country. For simplification we shall neglect the small difference between ephemeris time and universal time. The conversion exercises must be carefully prepared, since the arrangement of the Astronomical Ephemeris has been repeatedly modified in recent years. The tables are so skilfully arranged, that time conversion becomes very easy.

The present paper deals with the problem of determining various solar eclipse variables as observed from a sounding rocket for various rocket trajectories. By applying the methods described to a set of trajectories, a set of boundary conditions, launch azimuth, quadrant elevation, and launch time may be selected to optimize any aspect of eclipse observation within the constraints imposed by rocket performance.

The problem of connecting the independent reference frames formed by the planetary ephemeris and the radio source catalog is one of growing importance to spacecraft navigation. Using quasar-relative VLBI delay data collected by the Deep Space Network, and Soviet coherent data from the Venus flyby of the Soviet Vega 1 and 2 spacecraft, a self-consistent estimate of the frame tie offset has been found, along with its uncertainty.

The visual observation of star occultations by the Moon involves the determination of the time of immersion and emersion and requires very few auxiliary devices. Not only is the impressive experience of the motion of our Moon a rich reward in itself, but every observer has here the opportunity of participating in a program that is of great importance for positional astronomy. The combination of many observations leads to an accurate knowledge of the position of the Moon, and thus to the determination of Ephemeris Time, that is, an improved Sidereal Time, in which the small irregular fluctuations in the Earth’s rotation, which serves as a clock, can be eliminated by a comparison with the motion of the Moon. For a detailed discussion of this time problem we refer particularly to special publications.1

A decrease in the solar radius is determined using the technique of Dunham and Dunham (1973), in which timed observations are made just inside the path edges. When the method is applied to the solar eclipses of 1715, 1976, and 1979, the solar radius for 1715 is 0.34 + or - 0.2 arc second larger than the recent values, with no significant change between 1976 and 1979. The duration of totality is examined as a function of distance from the edges of the path. Corrections to the radius of the sun derived from observations of the 1976 and 1979 eclipses by the International Occultation Timing Association are also presented.

The numerical study of the motion of the closest natural satellite, the Moon, provides a means to examine the general concept of a numerical theory, as opposed to a simple ephemeris. Attempts to reconcile a discrepancy between our calculations and those of Oesterwinter and Cohen permit some conclusions on the documentation required for such a theory to be complete.

As I have already reported (Trans. IAU XVA, 9, 1973), the Working Group on Units and Time-scales was not able to reach any firm conclusions on whether the concepts of the astronomical unit and ephemeris time should be retained or replaced by the SI unit of length (metre) and atomic time. This disagreement was not unexpected as the membership was deliberately chosen to cover a wide spectrum of opinion. The following comments and suggestions represent a middle-of-the-road approach that is intended to meet the requirements of most astronomers and others who use the astronomical data. It has been suggested to me that this approach is not appropriate for use in those precise applications where relativistic concepts are necessary, and that therefore we should abandon completely the use of astronomical units of mass, length and time. There are, however, many applications where Newtonian concepts are perfectly adequate, and astronomical units are widely in use because of their general suitability and convenience. We should therefore continue to define a system of astronomical units, but should state quite clearly their relationships to SI units. An individual may use either system according to the circumstances, and standard conversion factors will be available for use by those who prefer the other system.

The realization of a conventional frame of reference in the time dimension, which will be called a time scale, requires the same phases as the reference frame in space: conception, definition, and realization.

The rotation of the Earth, when suitably averaged over its short-period fluctuations, provides us with a time scale known as Universal Time (UT). The orbital motion of the Earth around the fictitious mean Sun provides us — in principle at least — with a time scale known as Ephemeris Time (ET). Since the semi-major axis of the Earth’s orbit, and hence its period of revolution, are constant to a very high degree of approximation, the ET scale is uniform and represents an almost ideal clock.

Preliminary numerical integrations of the lunar motion indicate that defects in the lunar ephemeris, due to omissions in the revised Brown lunar theory, produce errors of the order of several hundred meters in the coordinates at certain times. Such errors are large enough to affect adversely analyses of data from spacecraft, as well as determination of ephemeris time. Distinct planetary periodicities seem to appear in the residuals.

The process of estimating the location of a spacecraft landed on the surface of Mars is investigated through the application of statistical estimation techniques to earth-based radio tracking data. The spacecraft location and the tracking geometry and schedule are consistent with Viking-type mission constraints. With mission control requirements in mind, the investigation is restricted to analysis of a short data arc (approximately 3 days). Statistics of the spacecraft location are obtained through analysis of (direct-link) tracking data for the landed spacecraft and through simultaneous analysis of tracking data for both a landed and an orbiting spacecraft. These estimates include the effects of model uncertainties in the ephemeris of Mars, tracking station locations, the Mars rotational period, the Mars gravity field, and the orientation of Mars axis of rotation. The most significant of these effects is shown to be due to the Mars ephemeris uncertainty. A dual spacecraft tracking technique is presented for substantially reducing these ephemeris effects.

Photographing the Moon against star-field backgrounds is recognized as a most useful technique for measuring the difference between universal and ephemeris times, determining various higher-order motions of the Earth and Moon, and investigating certain geodesic problems. Because simultaneous photographic observations of the Moon and stars might be effectively used with new reduction techniques developed by Kopal for determining lunar librations from star positions independent of reference to the lunar limb, Kopal recently requested that we investigate the feasibility of utilizing the 48-inch Palomar Schmidt as a moon-star camera. The Schmidt is rarely in use when the Moon is above the horizon and good supplementary use could be made of the instrument if it should prove adaptable for lunar work.

The timing of occultations of stars by the Moon provide data for the following studies: (a) Lunar theory — Constants and secular changes of its orbit. (b) Fundamental star systems — Systematic corrections to equinox and obliquity; individual star corrections. (c) Rotation of Earth — Comparison of atomic and ephemeris time scales.

The systems of units, co-ordinates and time-scales that are currently in use in dynamical astronomy are reviewed, and attention is drawn to the needs for simplification and clarification, and for explicit statements of the relationships between astronomical and SI units. It is concluded that ephemeris time, as it is currently defined, does not provide a satisfactory time scale for use in dynamical astronomy. It is recommended that the astronomical unit of time should be one day of 86400 SI seconds.

THERE have been many determinations of the acceleration of the Moon's mean longitude, mostly based on observations of occultations since 1680 and on records of ancient eclipses1–9. All these results have been expressed in Ephemeris Time, based on the annual apparent motion of the Sun about the Earth. Since 1955 Atomic Time came into use based on the period of oscillation of the caesium atom which is, by definition, constant. A new analysis of lunar occultations observed from 1955 to 1974 using Atomic Time, by Van Flandern (unpublished) gives a value for the acceleration of the Moon's mean longitude differing from other determinations which used the Ephemeris Time scale. His new results differ from earlier work10. The data reveal a difference between Ephemeris Time and Atomic Time of 25 s a century. Van Flandern suggests that the most probable explanation is a decrease in the gravitational constant, G, by 8 parts in 1011 per yr. Such a decrease would mean that the Earth is expanding somewhat and there is some geological evidence supporting this. We tried to check this conclusion using a method for determining the lengthening of the day verified by Wells11 in which the number of tiny lines of ridges on well preserved epitheca of corals in their annual growth increments are counted. We found no evidence for any expansion of the Earth in the past 5 × 108 yr.

En considerant les perturbations planetaires, on a calcule les elements orbitaux corriges de la comete ASHBROOK-JACKSON. On a utilise 196 observations relatives aux derniers deux passages du 1971 et 1978. Enfin on a calcule une ephemeride avec perturbations disponible sur demande. Unter Berucksichtigung der Planetenstorungen wurden die verbesserten Bahnelemente des Kometen ASHBROOK-JACKSON berechnet. Dazu wurden 196 Beobachtungen der letzten beiden Durchgange der Jahre 1971 und 1978 verwandt. Daruberhinaus wurde eine Ephemeride unter Berucksichtigung der Storungen berechnet, die auf Wunsch zur Verfugung steht.

A high-radiance, pulsed laser system with a transportable transmitting unit was used at Agassiz Station, Harvard College Observatory, Harvard, Massachusetts, to measure the transit times of 25-nanosecond, 10-joule, 530-nanometer pulses from the earth to the Apollo 15 retroreflector on the moon and back.

The results of B, V photometry of AO Cam are presented. Two equally good light-curve solutions, one with an occultation primary minimum and another with a transit primary, were calculated with the Wilson-Devinney code. In both cases the star barely fills its Roche lobe, and the mass ratio is large for this type of system. A revised ephemeris was derived from all available observations, and the period is found to have been roughly constant over the past four years.

Previously published tables of geocentric arrival times for 24 pulsars covering a 12 year span are extended here to 14.5 years. The list of pulsars is extended by nine, most of which were observed for about 4 years. Known positins of these new objects are confirmed, and limits on the proper motions are obtained. Large phase excursions in PSR 0525 + 21 are found. The orbital parameters of the binary pulsar 0820 + 02 are tentatively confirmed. Short-term timing noise in excess of that expected from receiver considerations alone is established. Variations in the timing residuals for the original 24 pulsars are analyzed for correlations with other observable parameters. Little significant correlation with changes in pulse shape or energy or with the drift correction is found on time scales of 500 pulses or longer.

New 6 cm observations of the binary radio, X-ray, and gamma-ray star LSI + 61 deg 303 obtained in August 1984 and September 1986 are presented. The data accumulated to date provide evidence for a strong modulation in the amplitude of the 26.496 day periodic radio outbursts. The modulation occurs on a time scale of 4 yr. Two possible explanations are considered: (1) variable beaming from a precessing relativistic jet and (2) variable accretion due to quasi-cyclic Be star envelope variations. 22 refs.

Since 1967, when the U.S. Navy Navigation System was released to the general public, the accuracy of geodetic and geodynamic satellite Doppler positioning using satellite Doppler has improved steadily. This improvement is due mainly to refinements in hardware, refraction, and orbital modeling. Point positioning, using a minimum of 30 passes and the U.S. Defense Mapping Agency (DMA) precise ephemeris, has reached submeter accuracy. Relative positioning among several simultaneously observing stations separated by distances up to 250 km and using a minimum of 30 passes has a typical accuracy below 0.5 m (1σ). Current hardware design and errors in modeling of delays in the wet portion of the troposphere limit the achievable accuracy in relative positioning at the 0.1- to 0.5-m (1σ) level, unless errors in receiver phase and tropospheric refraction delays are continuously measured (calibrated). Also, a crystal oscillator of lower short-term stability (≥ 5 × 10−12/100 s) increases the Doppler data noise and causes a positive correlation persisting over several minutes. Geodetic and geodynamic Doppler data reductions usually involve meticulous modeling for instrumental, atmospheric, and orbital errors as well as careful Doppler data editing. A short-arc orbit computation employed in such satellite Doppler reductions requires a gravitational potential expanded to at least degree and order 10 if the orbit shape accuracy is to be comparable to DMA precise ephemeris. Satellite Doppler positioning has had a significant impact on geodetic datum definition and the establishment of national and continental networks of unprecedented accuracy. Satellite Doppler methods, apart from providing one of the most accurate continuous methods of polar motion monitoring, have also been found useful in other geodynamical and ice motion studies. This review concentrates mainly on system performance, models, and computational methods.

W M Smart (revised by R M Green) London: Cambridge University Press 1977 pp xiii + 431 price £11.50 (cased), £5.50 (paperback) Smart's Spherical Astronomy has now appeared in its 6th edition since its first publication in 1931. The revision has been lightly handled with a new section on ephemeris time (itself to be phased out and replaced by international atomic time within a few years) and a few further examples added to the exercises which follow each chapter, being the only changes from the 5th edition that appeared to the reviewer.

Cassini, in his observations of Nova Vul in 1671, repeatedly used β Lyr for brightness comparison, apparently without even suspecting that it was a variable star. An attempt was made to correlate Cassini's "indirect" observations of β Lyr with modern ephemeris formulae in order to find out whether he could have overlooked a primary eclipse. None of the modern ephemeris formulae would allow a reliable extrapolation of minimum epochs back to 1671, but the coverage of the light curve by the unintended observations suggests perhaps a modest chance that the 17th-century observers missed the variable near its primary minimum.

New intermediate-band photometry of the late-giant eclipsing system RZ CNc is used to obtain photometric solutions, both with the Popper (1976) spectroscopic mass ratio and by allowing the mass ratio and gravity-darkening coefficients to vary. New y observations are combined with earlier V data of Lenouvel (1957) and Broglia and Conconi (1973) in one solution set. Additional solutions are obtained from the new observations. The mean photometric mass ratio is somewhat larger than Popper's spectroscopic values; the general indeterminacy of photometric solutions may explain this apparent discrepancy. Possible photometric effects of a mass-transferring stream are discussed, and it is concluded that such effects cannot account for the mass-ratio discrepancy. 26 refs.

A revised orbit and extended ephemeris are calculated for Leda, the thirteenth satellite of Jupiter, by means of numerical integration. Thirty-one observations between September 1974 and December 1977 satisfy the new orbit to 0.9 arcsec on the average.

Photoelectric V-filter observations of the variable star BW Vulpeculae made during the period from 1974 through 1978 are discussed. Consideration is given to the variation of the position and duration of the stillstand on the rising branch of the light curve near the time at which the star's velocity has its maximum value. A quadratic ephemeris relation is calculated on the basis of known maxima from 1937 to 1978, and it is pointed out that the relation implies a period increase of 2.24 sec/century. Linear expressions for the ephemeris relation are discussed, and it is concluded that stellar evolution theory appears to favor a quadratic ephemeris for BW Vul, although it is not possible to exclude the possibility of two sudden period increases during the past 40 years.

In correcting satellite doppler data for tropospheric effects, we have found that we can infer the precipitable water vapor (PWV) at the tracking site. The determination proceeds via a least squares fit of a refraction parameter, along with several others, to each 15-min pass of data. For its success the technique depends on having (1) an ephemeris for the satellite, (2) an analytic model for the refraction range effect that is good to a few centimeters, (3) doppler (range difference or cycle count) data with a noise level below 10 cm, and (4) a surface pressure/temperature measurement at the tracking site. The PWV is a byproduct of the computation necessary to correct the doppler data for tropospheric effects. We have tried for a number of years to reliably isolate the tropospheric refractive effect in the doppler shift measurement. It is only recently that we have succeeded in doing this. Our success is due to a formulation of the refraction integral that minimizes the necessity for explicit water vapor, temperature, and pressure profiles.

New UBV photometry of DN Cas indicates eclipse depths in V of and 0"'3 and an ephemeris for the primary of JD 2441388.571 + 2d310955 E. Since our new period is twice that of Hoffineister, DN Cas is no longer a curiosity in the period-spectrum diagram of EA variables. We discovered our comparison star HD 14817 = ADS 1833 AB to be variable, an eclipsing binary with an Algol-type light curve, eclipse depths in V of and , durations of Oe = and an ephemeris for the priiinary of JD 2441357.560 + 1d 4 E. Key words: UBV photometry - eclipsing binaries - variable stars