In 1997 the Sun and the Earth passed through the equatorial plane of Jupiter and therefore through the orbital planes of its main satellites. During this period, mutual eclipses and occultations occurred and were observed. We investigate the precision of the catalogue to produce improved data for the development of dynamical models. Light curves of mutual eclipses and occultations were recorded by the observers of the international campaign PHEMU97 organized by the Institut de Mecanique Celeste, Paris, France. We made 275 observations of 148 mutual events from 42 sites. For each observation, information is given about the telescope, the receiver, the site and the observational conditions. This paper gathers together the data and gives a first estimate of the precision. The catalogue of these rare events represents a collection of improved accurate astrometric data useful for the development of dynamical models.

Ground-based and spacecraft photometry covering phase angles from 2° to 179° has been acquired in wavelength bands from blue to near infrared. An unexpected brightness surge is seen in the B and V bands when the disk of Venus is less than 2% illuminated. This excess luminosity appears to be the result of forward scattering from droplets of H2SO4 (sulfuric acid) in the high atmosphere of Venus. The fully sunlit brightness of Venus, adjusted to a distance of one AU from the Sun and observer, was found to be V=−4.38, and the corresponding geometric albedo is 67%. The phase integral is 1.35 and the resulting spherical albedo is 90%. Comparison between our data and photometry obtained over the past 50 years indicates a bias in the older photoelectric results, however atmospheric abundance variations suggest that brightness changes may have occurred too.

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.

CCD observations of Mercury were obtained with the large angle spectrometric coronograph (LASCO) on the solar and heliospheric observatory spacecraft, near superior and inferior solar conjunctions. Whole disk photometry was extracted from the orange and blue filter images and transformed to V magnitudes on the UBV system. The LASCO data were combined with ground-based, V-filter photometry acquired at larger elongation angles. The resulting photometric phase function covers the greatest span of angles to date and is the first wide-range function to be obtained since the era of visual observation. We analyzed the data using a polynomial fit and a Hapke function fit, and derived the following photometric results. Mercury's fully lit brightness, adjusted to a distance of 1.0 AU from the Sun and observer, was found to be V=−0.694(±0.030), which is more luminous than previously measured. The corresponding geometric albedo is 0.142(±0.005). The phase integral is 0.478(±0.005) and resulting spherical albedo is 0.068(±0.003). The upper limit of a possible rotational brightness variation is about 0.05 magnitude. Mercury's brightness surges by more than 40% between phase angles 10 and 2°, while the illuminated fraction of the disk increases by less than 1%. A set of coefficients for Hapke's function that fit most of the phase curve includes h=0.065±0.002 indicating that Mercury and the Moon have similar regolith compaction states and particle size distributions, and θ-bar=16°±1° implying a macroscopically smoother surface than the Moon. However, we found other solutions that fit the observations nearly as well with significantly smaller and larger values of h, and with values of θ-bar around 25°. The wide range for θ-bar is due to the inability of the model to fit the photometry obtained at large phase angles.

A thermal infrared imager for mapping the changing cloud cover over a ground‐based observing site has been developed. The two main components to our instrument are a 10 μm detector that produces a 120 × 120 pixel thermogram and a convex electroplated reflector, which is situated underneath the detector and in its field of view. The resulting image covers the sky from zenith down to about 10° elevation. Atmospheric transparency is distinguished by the difference between the sky temperature and the ambient air temperature at ground level. Clear sky is indicated by pixels that are more than 20°C cooler than ambient. The qualitative results “clear, haze, and cloud” have proved to be very reliable during 2 years of development and testing. This information will be very useful to observers taking photometric, photographic, and spectroscopic data at optical wavelengths. The instrument can distinguish between different degrees of cloud opacity as a result of a new and more sophisticated data‐processing algorithm. Advances in infrared technology including uncooled detectors and area imaging have also made our instrument easier to use, more versatile, and faster to acquire data than previous cloud imaging detectors.

CCD photometry of Jupiter's satellite Callisto in eclipse has been fitted to model light curves to determine polar radii of 67,168±50 km (north) and 67,106±62 km (south). These values are about 172 and 110 km, respectively, greater than that computed from Jupiter's equatorial dimension and its hydrostatic figure at the 0.5-mbar eclipse altitude. We attribute the excess radius to attenuation of light by the high haze layer of the polar atmosphere and set an upper limit of detectable haze at about 300 km above the 1-bar pressure level. Nonpolar eclipse results give radii that are in good agreement with the accepted size of Jupiter and do not indicate haze above the eclipse altitude.

A computer-automated radio system for monitoring meteor activity is described. The receiver is tuned to the frequency of a television video carrier whose transmitter is located beyond the horizon. The system registers only a weak signal except when the ion trail from a meteor reflects additional power to the receiver. A sudden power increase alerts the computer to a possible meteor. Our system employs a unique method for distinguishing between meteors and false alerts due to lightning and other noise. Using the receiver's audio output, a meteor echo is identified by increased audio signal autocorrelation, whereas electrical noise is recognized by a decreased correlation. The system has now accumulated more than a year of observations. The data show clearly the expected diurnal variation in meteor count rate, as well as most of the stronger meteor showers. We have also obtained evidence of some new showers. Analysis of the data from 1997 November 15-20 reveals Leonid meteor shower activity with a peak at November 17.5 (+/- 0.2) UT or solar longitude 235.degrees 3 (+/- 0.2). Leonid meteors are of current interest because the shower may be building toward a supermaximum or "meteor storm" in 1998 or 1999.

In this paper, all the light-curves obtained during the PHEMU91 campaign of observations of the mutual phenomena of the Galilean satellites are presented. These observations give accurate astrometric positions of major interest for dynamical studies of the motion of the Galilean satellites. The aim of this work is to give observational data directly usable for theoretical studies. We made 374 observations of 111 mutual events from 56 sites. The corresponding data are given in this paper(1). The accuracy of each observation has been deduced from a comparison with the theoretical predictions. For each observation, information is given about the telescope, the receptor, the site and the observational conditions.

A computer program for automation of the Meade LX-200 Schmidt-Cassegrain telescope is described. The code has been extensively tested and observations have been obtained. The telescope automation program is available in the C and Basic programming languages, along with complete documentation.

CCD photometric data for eclipses of Tethys, Dione, and Rhea are fit to model light curves that represent the geometry and radiometry of the events. Comparison of our midevent timings with modern ephemerides indicates that the predictions are typically accurate to about 300 km. We also present results from our model that allow eclipse and occultation photometry of Mimas through Phoebe to be used for precise astrometry of those satellites.

We examine spatial variability of attenuation in the Earth's atmosphere as a cause of asymmetrical eclipses and consequent acceleration of LAGEOS, i.e., the solar radiation pressure on LAGEOS due to the Earth's penumbra. Measurements of atmospheric attenuation derived from the satellite‐borne Stratospheric Aerosol and Gas Experiment after the eruption of Mount Pinatubo were used to simulate the largest expected aerosol content of the atmosphere. In our experiment one hemisphere was loaded with volcanic aerosols, while the other was not. The difference between attenuation in the two hemispheres sets a maximum reasonable limit to the size of eclipse asymmetry. This condition would accelerate LAGEOS only about 0.2 picometers per second squared (pm s−2 or 10−12 m s−2) and indicates that eclipse asymmetry can only account for about 40–50% of the remaining unmodeled residuals. This is slightly less than the penumbral acceleration found by Vokrouhlicky et al. (1994).

A comparison between visible light charge‐coupled device (CCD) photometry and model light curves for several Jovian satellite eclipses reveals that significant attenuating material was present in Jupiter's atmosphere up to about 300 km (relative to the 1‐bar pressure level) over the comet Shoemaker‐Levy 9 impact sites a month after the explosions occurred.

Astrometric positions for the Galilean satellites are derived from high-precision timings of their jovian eclipses observed with CCD cameras between 1990 to 1993, and the positions are compared to Lieske's E-3 ephemeris. The root-mean-square (rms) ephemeris residuals for Io and Callisto were only 80 and 89 km, respectively; the rms residuals for Europa and Ganymede were larger, 185 km and 142 km, with maximum residuals of 340 km and 244 km, respectively.

Models for the Galilean satellites have been used to determine the distribution of brightness on their surfaces. The results indicate that the distance between a satellite's photocenter and its center-of-figure can reach 209 km for Io, 221 km for Europa, 303 km for Ganymede, and 255 km for Callisto. Astrometry of the satellites can achieve much greater precision than this, so a correction for the photocentric offset should be applied. This paper presents tables of photocentric offsets for the Galilean satellites as functions of orbital longitude and solar phase angle. The estimated accuracy of these corrections is 32 km for Io, 45 km for Europa, 49 km for Ganymede, and 40 km for Callisto, but the latter two may be optimistic. The satellite ephemerides derived from astrometry are essential for interpreting observations of variable phenomena on Io, such as volcanic activity inferred from IR observations taken during occultations of the satellite. Accurate ephemerides are also critical to spacecraft navigation.

The light curve of a partial solar eclipse of Callisto caused by Jupiter's south pole was recorded on 6 December 1992. The observed data were fit to a set of model lightcurves in which luminosity is a function of the satellite's location in the penumbral shadow. The photometric solution was combined with Callisto ephemeris information to determine a radius for Jupiter's pole of 67,111 ± 76 km at 0.5 mbar atmospheric pressure. The corresponding polar flattening was found to be 6.35% ± 0.11%. The observed polar radius is 115 km less flat than the value implied by hydrostatic equilibrium.

Twelve eclipses and occultations of Io were recorded with a CCD camera during the mutual eclipse and occultation season of 1991. In 11 of these events Io was covered by Europa, and in the twelfth it was covered by Callisto. These observations give high quality astrometric information that should be useful in connection with infrared determinations of the locations of Io's volcanoes made by other investigators during the occultations. Differential astrometric positions were determined by fitting the photometry to a model light curve that is based on the photometric properties of the eclipsed or occulted satellite, as well as the apparent motion of the satellites during the event. The astrometric results agree with Lieske's E-3 ephemeris predictions at a 1 σ level of about 13 milliarcsec in orbital latitude. However, an 80-milliarsec longitude residual, seen in the Europa-Io events, is many times larger than the uncertainty. This mean longitude residual can be applied to the E-3 ephemeris in order to use it for Europa-Io events that were not observed photometrically but that need astrometric calibration. Evidence for the longitude residual in previous mutual event astrometry is briefly discussed.

Timings of nine Jovian eclipses of the Galilean satellites observed during 1990 and 1991 are compared to predictions from modern ephemerides and are shown to exhibit very little internal scatter. These data can be used to supplement astrometry from the mutual occultations and eclipses of the satellites that occurred during the same time period.

A model for the light curve of a Galilean satellite eclipsed by Jupiter's shadow is developed. This model allows center-of-figure information on the satellite's position to be derived from photometric eclipse data. The major features of the model are the satellite-Jupiter-Sun-Earth geometry, limb-darkening and albedo features of the satellite, and refraction of light in the Jovian atmosphere. Sample output from the model reveals that tens of seconds may elapse between the time of half-phase in the eclipse and that of half-luminosity of the satellite. The model fits eclipse photometry to less than 1% rms luminosity. Furthermore, much of the scatter in O − C (observed minus calculated) residuals, for eclipse times compared to modern ephemeris predictions, is reduced when the model is used to correct the times of half-luminosity to half-phase.