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1.
Nikolay Emelyanov 《Planetary and Space Science》2008,56(14):1785-1790
We suggest a new approach and develop an original method for deriving astrometric data from the photometry of mutual occultations and eclipses of planetary satellites. We decide to model not the relative apparent motion of one satellite with respect to another satellite but the deflection of the observed relative motion with respect to the theoretical motion implied by appropriate ephemerides.We have attempted to reduce the results of photometric observations of the Gallilean satellites during their mutual occultations and eclipses in 2002-2003. The data of observation for 319 light curves of 106 mutual events were received from the observers. The reliable 245 light curves were processed with our method. Eighty six apparent relative positions have been obtained.Systematic errors arise inevitably while deriving astrometric data. Most of them are due to factors that are unrelated to the methods for deriving astrometric data. The systematic errors are more likely due to incorrect excluding the effect of background on photometric counts. In the case of mutual occultations, the flux drop is determined to a considerable degree by the ratio of the mean albedos of the two satellites. Some mutual event observations revealed wrong adopted values of the mean albedos. 相似文献
2.
We analyze the possibility of determining the masses of outer planetary satellites from their mutual gravitational perturbations via ground-based observations. Such a technique has been applied in (Emelyanov, 2005b) to determine the mass of the Jovian satellite Himalia. In this paper, we use the least-squares method to compute the errors of satellite masses inferred from simulated observations. We analyze several of the most suitable variants of groups of outer satellites of planets with maximum mutual attraction. We found that the mass of the Satumian satellite Phoebe (S9) can be refined by continuing observations of the satellite S25 Mundilfari until 2027. We show that the masses of other known outer planetary satellites cannot be determined from ground-based observations. 相似文献
3.
Highly accurate astrometric positions obtained from eclipses and occultations of planetary satellites are reported. These measurements may be used to test existing ephemerides, to improve upon them, and to fit system constants such as satellite masses and planetary zonal harmonics. Eclipse and occultation photometry of 5 uranian satellite mutual events has resulted in precise astrometry for 3 of these moons. Relative satellite positions were determined with an uncertainty of less than 10 milli-arcseconds for 4 of the events. These observations plus two additional data from C. Miller and N.J. Chanover (private communication) indicate that predictions based on the SPICE [Acton, C.H., 1996. Planet. Space Sci. 44, 65-70] ephemeris URA083 and those from the LA06 ephemeris in a paper by Arlot et al. [Arlot, J.-E., Lainey, V., Thuillot, W., 2006. Astron. Astrophys. 456, 1173-1179] are significantly more accurate than predictions generated by Christou [Christou, A.A., 2005. Icarus 178, 171-178] using the GUST86 ephemeris in the along-track component of motion. The observations indicate that Ariel, Umbriel and Titania are lagging behind their predicted positions for all of the ephemerides, but by varying distances and significance levels. Analysis of data recorded by Hidas et al. [Hidas, M.G., Christou, A.A., Brown, T.M., 2008. Mon. Not. R. Astron. Soc. 384, L38-L40] suggests a similar lag for Oberon. Photometry recorded during the ingress portion of a saturnian eclipse of Iapetus on 2007 May 5 indicates that the middle of the event occurred at geocentric UTC 02:14:58. At that moment the center of the satellite disk facing the Sun was intersected by a solar-centered ray refracted at a minimum altitude of 240 km above the 1-bar pressure level in the planet's atmosphere. The uncertainty in the timings due to observational scatter was only 5 s which equates to 16 km of Iapetus motion, but other factors increased the overall uncertainty to 111 km or 16 milli-arcseconds at the distance of Saturn from the Sun. The astrometric result is fit very well by the SPICE ephemeris SAT288. 相似文献
4.
Astrometric satellite positions are derived from timings of their eclipses in the shadow of Jupiter. The 548 data points span 20 years and are accurate to about 0.006 arcsec for Io and Europa and about 0.015 arcsec or better for Ganymede and Callisto. The precision of the data set and its nearly continuous distribution in time allows measurement of regular oscillations with an accuracy of 0.001 arcsec. This level of sensitivity permits detailed evaluation of modern ephemerides and reveals anomalies at the 1.3 year period of the resonant perturbations between Io, Europa and Ganymede. The E5 ephemeris shows large errors at that period for all three satellites as well as other significant anomalies. The L1 ephemeris fits the observations much more closely than E5 but discrepancies for the resonant satellites are still apparent and the measured positions of Io are drifting away from the predictions. The JUP230 ephemeris fits the observations more accurately than L1 although there is still a measurable discordance between the predictions and observations for Europa at the resonance period. 相似文献
5.
C. Frederick Peters 《Celestial Mechanics and Dynamical Astronomy》1975,12(1):99-110
A general method is given for predicting eclipse events for natural planetary satellites suitable for use on a large scale digital computer. The precision is sufficient to process photometric eclipse observations to improve natural satellite ephemerides. Expected accuracy improvement for Saturn's satellites should be an order of magnitude or better. Predicted eclipse times of satellites by Saturn and the Rings are given for the next decade.Presented at IAU Colloquium No. 28, Ithaca, New York, August, 1974. 相似文献
6.
G. A. Kosmodamianskiy 《Astronomy Letters》2019,45(11):770-777
New versions of the ephemerides for the Galilean satellites of Jupiter (Io, Europa, Ganymede, and Callisto) constructed by numerically integrating the equations of motion of the satellites are presented. The satellite motionmodel takes into account the non-sphericity of Jupiter, the mutual perturbations of the satellites, and the perturbations from the Sun and major planets. The initial satellite motion parameters have been improved based on all the available series of ground-based optical observations spanning the interval 1891-2017, spacecraft observations, and radar observations. As a result, the coefficients of the expansion of the satellite coordinates and velocities in terms of Chebyshev polynomials in the interval 1891- 2025 have been obtained. The root-mean-square errors of the observations and the graphs of comparison of the constructed ephemerides both with the observations and with Lainey's numerical ephemerides are presented. The constructed ephemerides are publicly accessible. 相似文献
7.
An accurate technique has been developed for measuring planetocentric positions of Jupiter's satellites from Wide Field/Planetary Camera images. Our method of finding the centers of the satellites and planet is based upon established limb-fitting techniques, but we have adapted those techniques to astrometry. We compare our limb-fitting results with previously published work and discuss its errors. A model ellipse is generated from the physical ephemeris of the planet including its phase defect. Then the planet center coordinates are computed by fitting the model to the limb observations using the method of least squares. A satellite position is determined similarly, and its offset from the planet is calculated. A total of 76 positions of the galileans satellites, the small moon Amalthea, and the shadows of Io and Ganymede cast on Jupiter have been measured on 61 images. Comparison between the observational results and JPL satellite ephemerides demonstrates the validity of this new method of analysis. The accuracy of the galilean satellite measurements is estimated to be 0.04 arcsec in right ascension and in declination. 相似文献
8.
P. K. Seidelmann 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):1-12
Planetary and satellite theories have been historically and are presently intimately related to the available computing capabilities, the accuracy of observational data, and the requirements of the astronomical community. Thus, the development of computers made it possible to replace planetary and lunar general theories with numerical integrations, or special perturbation methods. In turn, the availability of inexpensive small computers and high-speed computers with inexpensive memory stimulated the requirement to change from numerical integration back to general theories, or representative ephemerides, where the ephemerides could be calculated for a given date rather than using a table look-up process. In parallel with this progression, the observational accuracy has improved such that general theories cannot presently achieve the accuracy of the observations, and, in turn, it appears that in some cases the models and methods of numerical integration also need to be improved for the accuracies of the observations. Planetary and lunar theories were originally developed to be able to predict phenomena, and provide what are now considered low accuracy ephemerides of the bodies. This proceeded to the requirement for high accuracy ephemerides, and the progression of accuracy improvement has led to the discoveries of the variable rotation of the Earth, several planets, and a satellite. By means of mapping techniques, it is now possible to integrate a model of the motion of the entire solar system back for the history of the solar system. The challenges for the future are: Can general planetary and lunar theories with an acceptable number of terms achieve the accuracies of observations? How can numerical integrations more accurately represent the true motions of the solar system? Can regularly available observations be improved in accuracy? What are the meanings and interpretations of stability and chaos with respect to the motions of the bodies of our solar system? There has been a parallel progress and development of problems in dealing with the motions of artificial satellites. The large number of bodies of various sizes in the limited space around the Earth, subject to the additional forces of drag, radiation pressure, and Earth zonal and tesseral forces, require more accurate theories, improved observational accuracies, and improved prediction capabilities, so that potential collisions may be avoided. This must be accomplished by efficient use of computer capabilities. 相似文献
9.
A model for computing the brightness of a satellite in the shadow of a planet is described, which takes into account the Sun–planet–satellite–sensor geometry, the satellite bi-directional reflectance function, and the refraction of sunlight in the planetary atmosphere. Synthetic light curves for eclipse ingress or egress of the five large satellites of Uranus are generated. The model luminosities can be fitted to photometric observations in order to calculate a precise distance between the centers of the satellite and the planet. Alternately, when the satellite ephemeris is accurately known the atmospheric state of the planet can be studied. 相似文献
10.
E. Myles Standish Jr. 《Celestial Mechanics and Dynamical Astronomy》1985,37(3):239-242
One may construct complete planetary and lunar ephemerides, referred to the equator and dynamical equinox of some epoch, strictly from ranging data alone. Such an ephemeris would be completely independent from any optical data and therefore independent of any stellar catalogue. By using such an ephemeris to then analyse optical observations, one could theoretically derive many of the pertinent features of the catalogue system to which the optical observations are referred. Such features include the equinox offset, equinox motion and systematic proper motion errors. In practice, the optical observations are used in the fitting process, but essentially the same determinations may be made.This paper presents estimates of the equinox offset and equinox motion of the FK4 as determined by the ephemeris fitting process and compares them with corresponding determinations by Fricke. No significant differences are found. Further, it is indicated how one may also estimate a value for precession and the value of the obliquity from the ephemerides. These' values are also compared with the presently adopted ones. 相似文献
11.
More than 70 new distant satellites of major planets have been discovered over the past five years. Until recently, the Jet Propulsion Laboratory (JPL) in the USA was the only institution that modeled the motion of these satellites based on observational data and computed their ephemerides. New independent computations are needed to ensure the reliability and to assess the accuracy of satellite ephemerides. In this paper, the results of our determination of orbital parameters for 73 new distant satellites of major planets based on all available observations are reported and the adopted model of perturbing forces acting on a satellite is described. The satellite motions are computed via numerical integration. A special program—an ephemeris server—is used to compute the ephemerides of satellites, which are freely available to any user on the Internet at http://lnfm1.sai.msu.ru/neb/nss/index.htm. The server offers ample choice in terms of the form and composition of the ephemerides produced. The paper gives examples of deviations of the theory from observations and comparisons of our results with JPL ephemerides. Standard deviations of observational results from the theory are equal to 0.3–0.5 for most of the satellites. A comparison of our models of the motion of satellites with those developed at JPL shows that deviations in topocentric coordinates do not exceed 0.01 over a six-year interval.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 2, 2005, pp. 128–140.Original Russian Text Copyright © 2005 by Emelyanov, Kanter. 相似文献
12.
《天文和天体物理学研究(英文版)》2016,(4)
Pulsar timing uses planetary ephemerides to convert the measured pulse arrival time at an observatory to the arrival time at the Solar System barycenter(SSB). Since these planetary ephemerides cannot be perfect, a method of detecting the associated errors based on a pulsar timing array is developed. By using observations made by an array of 18 millisecond pulsars from the Parkes Pulsar Timing Array, we estimated the vector uncertainty from the Earth to the SSB of JPL DE421, which reflects the offset of the ephemeris origin with respect to the ideal SSB, in different piecewise intervals of pulsar timing data, and found consistent results. To investigate the stability and reliability of our method, we divided all the pulsars into two groups. Both groups yield largely consistent results, and the uncertainty of the Earth-SSB vector is several hundred meters, which is consistent with the accuracy of JPL DE421. As an improvement in the observational accuracy, pulsar timing will be helpful to improve the solar system ephemeris in the future. 相似文献
13.
R. Vasundhara 《Planetary and Space Science》2008,56(14):1791-1796
Salient features of the analysis of the mutual event light curves of planetary satellites are presented. The need to carefully evaluate the flux contribution of the occulting/eclipsing satellite to the total flux is illustrated. Albedo variations on the satellites will produce signatures on the mutual event light curves. The partial events of the upcoming mutual event series of the uranian satellites can be modeled taking into account the albedo variations inferred from the maps of the southern regions imaged by Voyager 2 when only these regions are occulted/eclipsed. This will enable a robust determination of the astrometric parameters. The shape and asymmetry of the mutual event light curves along with the rotational light curves of the satellites obtained simultaneously during the planet's equinox crossing period can be utilized to obtain a coarse albedo map of the northern hemisphere of the satellites. These studies will also help in investigating possible changes in the known southern regions since the 1986 encounter of Voyager 2. 相似文献
14.
由于星际探测事业的发展,对土星卫星的定位精度要求愈来愈高,经典的分析法定轨方法已难以适应,在当今计算技术条件高度发展的背景下,本文给出了土星卫星的数值法定轨方案,采用了土星卫星运动的高精度力学模型,并运用１８７４－１９８９这１００多年间的观测资料,引用现代最小二乘估计,对土星卫生进行精密定轨。该方案可以在引用同样的力学模型的前提下,对土星各颗卫星进行定轨,亦可同时进行多颗卫星的定轨。相应的软件比较 相似文献
15.
V. Lainey 《Planetary and Space Science》2008,56(14):1766-1772
We have developed a new dynamical model of the main Uranian satellites, based on numerical integration and fitted to astrometric observations. Old observations, as well as modern and Voyager observations have been included. This model has provided ephemerides that have already been used for predicting the mutual events during the PHE-URA campaign. It is updated here to improve the prediction of these events. We also tried to assess the real accuracy of our ephemerides by checking the distance differences of the Uranian satellites, using simultaneously our former and new model. It appears that both solutions are very close to each other (within few tens of kilometers), and most probably accurate at the level of few hundred of kilometers. Using new available meridian observations of the Uranian satellites, we have checked the Uranian ephemeris accuracy using DE406. An error of more than 0.1 arcsec on the Uranian position is observed. 相似文献
16.
The satellite-borne GPS receivers dedicated to precise orbit determination are now being carried by more and more low earth orbit (LEO) satellites and the satellite-borne GPS has become one of the main means for the precise orbit determination of low earth orbit satellites. The accuracy of satellite-borne GPS precise orbit determination depends on the accuracies of the GPS ephemeris and the clock error. Based on the orbit determination function of SHORDEIII zero-difference dynamics and using the observational data obtained by the GRACE satellites for the week from 2005 August 1 to 7 as an example, three versions of GPS ephemerides (igs, igr and igu) are used to carry out orbit determination under the same conditions and to estimate the effect of the GPS ephemeris accuracy on the accuracy of orbit determination of low earth orbit satellites. Our calculated results show that the two ephemerides, igs and igr, are equivalent to each other in orbit determination accuracy (about 9.5 cm), while igu is slightly less accurate, at about 10.5 cm. The effect produced by the data of the high frequency GPS satellite clock error on the accuracy of orbit determination is 1–6 cm. 相似文献
17.
Apostolos A. Christou 《Icarus》2005,178(1):171-178
The upcoming crossing of the Sun and the Earth through the equatorial plane of the planet Uranus presents an opportunity to observe mutual eclipses and occultations of the uranian satellites. We present predictions for 321 such events from 2006 to 2010. 230 of these events are “nominal” i.e. they are predicted to occur based on the currently available ephemeris while a further 91 “grazing” events are allowable given the positional uncertainties of the satellites. Taking into account the statistical frequency of events that occur too close to the planet, during solar conjunction or are too “shallow” to observe, we conclude that about 150 events should be detectable from different longitudes around the world. We argue that a worldwide campaign of photometric observations of these events will yield, as in the case of the jovian and saturnian systems, high-precision astrometric information on the satellites toward improving their ephemerides as well as the system constants (satellite masses, uranian zonal harmonics, etc.). In addition, mathematical inversion of the lightcurves should permit, subject to the photometric quality and number of observed events, mapping of albedo variegations over the satellite hemispheres that were in darkness during the Voyager 2 encounter with the uranian system in 1985/1986. 相似文献
18.
We studied small perturbations acting on Galilean satellites. Most of them are still not computed in the analytical theories and could probably improve the ephemeris of these satellites which are outside the precision of the observations. We used a numerical method to test the effect of such perturbations. Here are reporting the main results we obtained. 相似文献
19.
N. V. Emelyanov 《Monthly notices of the Royal Astronomical Society》2009,394(2):1037-1044
The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events.
This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data.
We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites.
We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms 'O-C' residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17. 相似文献
This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data.
We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites.
We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms 'O-C' residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17. 相似文献
20.
N. V. Emel’yanov 《Solar System Research》2008,42(5):448-450
Noteworthy phenomena, viz., mutual occultations and eclipses in the system of Jupiter’s Galilean satellites and in the system of Saturn’s principal satellites, will occur in 2009. The relatively simple photometry of these phenomena makes it possible to obtain positional data at a higher accuracy than can be achieved in regular astrometric observations. The visibility conditions for the satellites are described here and observational recommendations are given. The ephemerides of these phenomena are available via the Internet from the MULTI-SAT ephemerides server at http:/www.sai.msu.ru/neb/nss/index.htm. 相似文献