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1.
High spatial resolution 8–14 μm images of Venus were obtained on March 6, 1974. The planet was at a phase angle of 112° with the morning terminator in view. Our images confirm the existence of a previously mapped flux anomaly near the south pole and show evidence of other infrared features, presumably transient in nature. Flux differences of 2–7% were measured, corresponding to brightnes temperature variations of roughly 1–3°K. The images also confirm the difference between polar and equatorial limb darkening. Finally, we present evidence for a night-day asymmetry in the flux, with the brightness temperature greater by about 2°K on the sunlit side. 相似文献
2.
Disk scans of Saturn at 10 and 20 μm were obtained when the Saturnicentric solar declination (B′) was ?11°.8. The scans show little change from scans obtained when B′ was ?16°.3, and this could result from the long radiative time constant of the Saturnian atmosphere. The observations at 20 μm, in the H2 continuum, show positively that the temperature inversion at the south pole has a higher temperature than at any other point on the disk. In addition, the 12.1- and 20-μm scans indicate that the temperature of the inversion region is higher at the equator compared to the temperate zone. The data also suggest that enhanced 20-μm emission is correlated with the strength of the ultraviolet absorption. 相似文献
3.
We present Monte Carlo simulations for the polarization of light reflected from planetary atmospheres. We investigate dependencies of intensity and polarization on three main parameters: single scattering albedo, optical depth of a scattering layer, and albedo of a Lambert surface underneath. The main scattering process considered is Rayleigh scattering, but isotropic scattering and enhanced forward scattering on haze particles are also investigated. We discuss disk integrated results for all phase angles and radial profiles of the limb polarization at opposition. These results are useful to interpret available limb polarization measurements of solar system planets and to predict the polarization of extra-solar planets as a preparation for VLT/SPHERE. Most favorable for a detection are planets with an optically thick Rayleigh-scattering layer. The limb polarization of Uranus and Neptune is especially sensitive to the vertically stratified methane mixing ratio. From limb polarization measurements constraints on the polarization at large phase angles can be set. 相似文献
4.
Isophotes of the luminance distribution over the disk of Venus at several phase angles and in several wavelengths are constructed by means of isodensitometry of high-quality photographic negatives of Venus. Twenty-three plates were selected from more than 2000 original negatives available at the IAU Planetary Photographs Center of Meudon Observatory. Six isophote maps were made from a series of yellow light images (λ = 5850Å), corresponding to phase angles from 22° to 129°. Special attention was paid to the rare occurrences of distinct features in yellow light. A sequence of isophote maps was taken in six wavelengths from λ = 5850 to 3250Å. The ultraviolet cloud markings appear as changes in the isophote configurations for different wavelengths. Variations of contrast with wavelengths are deduced. Dark features, almost invisible at 4500Å, reach a contrast of 25% at 3500Å which then no longer increases toward ultraviolet. The polar bright clouds give contrasts of 40% to 60% in ultraviolet. A series of images taken in ultraviolet at 3500Åshows configurations characteristic of observations at short wavelengths for both the waxing and the waning crescent.In Parts II and III of this series of papers, the isophote maps will be compared with theoretical curves computed from the theory of multiple-order scattering by aerosol particles. 相似文献
5.
Cloud motions were obtained from a number of images acquired in reflected solar ultraviolet light during spring and fall of 1979 from the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) to determine the zonal mean circulation of the atmosphere of Venus at the cloud top level. The meridional profile of the zonal component of motion is somewhat different from that previously obtained from Mariner 10 and preliminary Pioneer Venus observations, although the equatorial magnitude is about the same (?94 m/sec). The mean meridional motion is toward the south pole south of about 5° south latitude, and toward the north pole north of this latitude, with peak mean magnitudes of about 7 m/sec polewards of 20° north and 40° south latitudes in the respective hemispheres. From the few measurements obtained at higher latitudes the magnitude of the mean meridional component appears to decrease although it is still directed toward the respective poles. Due to the evolution of the cloud patterns over the duration of the images from which the cloud velocities are obtained, the uncertainties in the mean zonal and meridional components may be as large as 5–10 and 2–4 m/sec, respectively. Preliminary estimates of meridional momentum transport show that the mean circulation dominates the eddy circulation transport completely, in agreement with the estimates obtained from Mariner 10 data, although the uncertainties in both the mean and eddy circulation transports are large. The momentum transports are polewards and their peak magnitudes occur at latitudes between 20° and 40° in both the hemispheres. 相似文献
6.
Four-color photographic photometry of Saturn for the 1977–1979 apparitions has been analyzed to determine the dependence of ring brightness on wavelength, solar phase angle, ring particle orbital phase angle (azimuthal effect), declination of the Earth relative to the ring plane (tilt angle), and radial distance from Saturn. Azimuthal brightness variations up to ±20% relative to the ansae are clearly apparent for the maximum of ring A, but are not detectable for ring B or the outer portion of ring A. The shape of the intensity (I) versus orbital phase angle (θ) curve varies with ring tilt (B) and probably with wavelength, and shows 180° symmetry. As characterized by its slope near the ansae, this curve suggests that the azimuthal effect increases as B decreases from 26 to ≈11°. The phase curves l(α) for the ansae show very little dependence on ring tilt (26° > B > 6°), on wavelength, or on radial distance from Saturn; possibly the curves are somewhat steeper at the smallest tilt angles and for ring A relative to ring B. The radial profile of both rings becomes flatter with decreasing tilt angle and with decreasing wavelength. The latter effect is a natural result of the classical, many-particle-thick ring model. 相似文献
7.
Edwin S. Barker 《Icarus》1975,25(2):268-281
The Venus water vapor line at 8197.71 Å has been monitored at several positions on the disk of Venus and at phase angles between 21° and 162°. Variations in the abundance have been found with spatial location, phase angle and time. During the 1972–1974 period, the total two-way absorption has varied from less than 1 to 77 μm of water vapor. The dependence on phase angle indicates 20 to 50 μm over the disk between 30° and 110° and small, but detectable amounts present during the rest of the observations. The spatial distribution with respect to the intensity equator is uniform with no location on the disk having systematically a higher or lower abundance. Comparisons made between the water vapor abundandances and the CO2 abundances determined from near-simultaneous observations of CO2 bands at the same positions on the disk of Venus show no correlation for the majority of the samples. 相似文献
8.
The existence of limb brightening at the equator of the quiet Sun at 3.1 cm is derived from a statistical analysis of scans of the solar disk taken during 1968.A ratio of 0.7% is found between the flux emitted by the equatorial limb enhancements and that of a disk of uniform brightness temperature. 相似文献
9.
Spectropolarimetric observations from 5000 to 8000 Å have been obtained for comets P/Austin (1982g) and P/Churyumov-Gerasimenko (1982f). The observations were spaced over phase angles of 50–125° for comet Austin and 10–40° for comet Churyumov-Gerasimenko. The use of spectropolarimetry allowed an evaluation of continuum polarization without molecular line contamination. Especially for comet Churyumov-Gerasimenko, the curve of polarization versus phase angle resembles curves for asteroids, where the polarization is negative (electric vector maximum parallel to the scattering plane) for phase angles less than 20° and the most negative polarization is from ?1 to ?2%. The negative polarization at backscattering angles may be due to multiple scattering in agglomerated grains, as assumed for asteroids, or to Mie scattering by small dielectric particles. If multiple scattering is important in comet dust, polarization measurements may imply a low albedo, less than 0.08. The polarization of comet Austin remained steady during a large change in the dust production rate. Both comets increased continuum flux by a factor of 2 near perihelion. The continuum of comet Churyumov-Gerasimenko had the shape of the solar spectrum with derivations less than 5%. The equivalent width of spectral features of C2, NH2, and O varied as r?2. 相似文献
10.
J. Veverka 《Icarus》1973,18(4):657-660
The disk-integrated polarization of Titan has been measured at phase angles ranging from 0°.4 to 6°.l. The observed polarization is positive throughout this interval. This fact, when combined with published photometric data, suggests a model in which an optically thin Rayleigh atmosphere overlies an opaque cloud deck. 相似文献
11.
The preliminary measurements by Pioneer 11 of the limb darkening and polarization of Titan at red and blue wavelenghts (M. G. Tomasko, 1980,J. Geophys. Res., 85, 5937–5942) are refined and the measurements of the brightness of the integrated disk at phase angles from 22 to 96° are reduced. At 28° phase, Titan's reflectivity in blue light at southern latitudes is as much as 25% greater than that at northern latitudes, comparable to the values observed by Voyager 1 (L. A. Sromovsky et al., 1981,Nature (London), 292, 698–702). In red light the reflectivity is constant to within a few percent for latitudes between 40°S and 60°N. Titan's phase coefficient between 22 and 96° phase angle averages about 0.014 magnitudes/degree in both colors—a value considerably greater than that observed at smaller phase from the Earth. Comparisons of the data with vertically homogeneous multiple-scattering models indicate that the single-scattering phase functions of the aerosols in both colors are rather flat at scattering angles between 80 and 150° with a small peak at larger scattering (i.e., small phase) angles. The models indicate that the phase integral, q, for Titan in both red and blue light is about 1.66 ± 0.1. Together with Younkin's value for the bolometric geometric albedo scaled to a radius of 2825 km, this implies an effective temperature in equilibrium with sunlight of 84 ± 2°K, in agreement with recent thermal measurements. The single-scattering polarizations produced by the particles at 90° scattering angle are quite large, >85% in blue light and >95% in red. A vertically homogeneous model in which the particles are assumed to scatter as spheres cannot simultaneously match the polarization observations in both colors for any refractive index. However, the observed polarizations are most sensitive to the particle properties near optical depth in each color, and so models based on single scattering by spheres can be successful over a range of refractive indices if the size of the particles increases with depth and if the cross section of the particles increases sufficiently rapidly with decreasing wavelenght. For example, with nr = 1.70, the polarization (and the photometry) are reproduced reasonably well in both colors when the area-weighted average radous of the particles, α, is given by α = (0.117 μm)(τred/0.5)0.217. While this model does not reproduce the large increase in brightness from 129 to 160° phase observed by Voyager 1, the observed increase is determined by the properties of the particles in the top few hundredths of an optical depth. Thus the addition of a very thin layer of forward-scattering aerosols on top of the above model offers one way of satisfying both the Pioneer 11 and Voyager 1 observations. Of course, other models, using bimodal size distributions or scattering by nonspherical particles, may also be capable of reproducing these data. 相似文献
12.
Kiyoshi Kawabata 《Earth, Moon, and Planets》1981,24(3):291-318
Three major geometric factors which are likely to influence theoretical interpretation of planetary polarization measurements, viz., observer—planet distance, horizontal inhomogeneity of planetary disk, and deviation from a spherical body, are investigated.The distance effect is examined for regional as well as global polarizations. For convenience of analysis, the expressions for zenith and azimuth angles of incident and emergent light appropriate for a snap-shot observation are derived as explicit functions of distance between observer and planet. Sample computations for Venus indicate that regional polarization near the planetary limb is significantly affected by the observer's distance. This effect should be particularly noticeable when an observation is made at a phase angle around which the single scattering polarization of atmospheric scattering agents exhibits a steep variation. The global polarization at large phase angles (measured at disk-center) is gradually moved toward smaller phase angles, as the observer approaches the planet. Any narrow polarization features such as rainbow and glory at small phase angles are heavily smoothed out.The effects of horizontal inhomogeneity are investigated with a planetary disk having highly polarizing regions at high latitudes. Comparison of theoretical global polarization computed for such a disk with the Pioneer Venus OCPP measurements shows a possible change in cloud-haze stratification approximately at 50° latitude, consistent with other imaging observations. An approximate analytical representation of residual polarization at zero phase angle is then derived to compare to the numerical results for Venus. An attempt is also made to explain the relatively large magnitude of residual polarization observed on Jupiter.Finally, to study the effects of nonsphericity of planetary body, the global polarizations are computed for a spheroidal planet. The global polarization tends to increase as the planet's oblateness increases. However, for Jupiter and Saturn, such effect may be of secondary importance. 相似文献
13.
This paper presents the results of polarization observations of asteroid 554 Peraga obtained with the UBVRI polarimeter using
the 1.25 m telescope of the Crimean Astrophysical Observatory down to phase angles of 3.1°–16.6° from October to November
2006. The asteroid’s polarization phase curve is shown to have a negative branch with the parameters P
min = −1.7% and αmin = 8.4°, which is typical of C-type asteroids. However, these data contradict the results of Zellner and Gradie (1976) obtained
in March 1975 that the reflected light from the asteroid’s surface is positively polarized, ≈1% at phase angles of 8°–10°.
Since the asteroid’s ecliptic longitudes differ by 160°-145° for the two observation periods, we discuss the possibility that
the two sets of observations refer to the asteroid’s two hemispheres with different polarimetric properties. 相似文献
14.
The polarization of Pluto has been measured for a range of solar phase angles from 0.8 to 1.8°. A mean linear polarization of 0.29 ± 0.01% (error of the mean) was found. No dependence of both the amount of polarization and position angles with rotational phase or solar phase angle could be detected. The positional angles of polarization agree with calculated position angles of the defect of illumination and are therefore parallel to the scattering plane. The observed polarization cannot be explained as resulting purely from a surface material which is similar to asteroidal surfaces. A hypothesis of polarization from a thin atmosphere, in addition to the surface polarization, is advanced. 相似文献
15.
We have statistically studied the 344 Coronal Mass Ejections (CMEs) associated with flares and DH-type-II radio bursts (1??C?14 MHz) during 1997??C?2008. We found that only 3?% of the total CMEs (344) compared to the general population CMEs (13208) drives DH-type-II radio bursts (Gopalswamy in Solar Eruptions and Energetic Particles, AGU Geophys. Monogr. 165, 207, 2006). Out of 344 events we have selected 236 events for further analysis. We divided the events into two groups: i) disk events (within 45° from the disk center) and ii) limb events (beyond 45° but within 90° from the disk center). We find that the average CME speed of the limb events (1370?km?s?1) is three times, while for the disk events (1055?km?s?1) it is two times the average speed of the general population CMEs (433?km?s?1). The average widths of the limb events (129°) and disk events (116°) are two times greater than the average width of the general population CMEs (58°). We found a better correlation between the CME speed and width (correlation coefficient R=0.56) for the limb events than that of the disk events (R=0.47). The shock speed of the CMEs associated with DH-type-II radio bursts is found by applying Leblanc, Dulk, and Bougeret??s (Solar Phys. 183, 165, 1998) electron density model; the disk events are found to have an average speed of 1190 km?s?1 and that of the limb events is 1275 km?s?1. From this study we compare the CME properties between limb and disk events. The properties like CME speed, width, shock speed, and correlation between CME speed and width are found to be higher for limb events than disk events. The results in disk events are subject to projection effects, and this study stresses the importance of these effects. 相似文献
16.
The apparent angles of more than 5000 quiet region spicules situated at various position angles around the Sun's limb have been measured on off-band H filtergrams taken during the years 1972–1975. The counts were made exclusively in projection on the disk, within 5–25° of the limb. The tendency of the average spicule to lean towards or away from the pole is small at most, and at no latitude exceeds 8°. The spread in angles is 30–35°. 相似文献
17.
UBV pinhole scans of the Saturn disk have been made with a photoelectric area-scanning photometer. Limb profiles, spaced parallel to the equator, were obtained over the entire southern hemisphere of the planet. Saturn was found to exhibit strong limb brightening in the ultraviolet, moderate limb brightening at blue wavelengths, and strong limb darkening in the visual region of the spectrum. Latitudinal variations in the disk profiles were found. In general, the degree of limb brightening decreases towards the polar region. Pronounced asymmetry is apparent in the disk profiles in each color. The sunward limb is significantly brighter than the opposite limb. This asymmetry depends on phase angle; approaching zero at opposition, it reaches a maximum near quadrature. Our observations are interpreted using an elementary radiative transfer model. The Saturn atmosphere is approximated by a finite homogeneous layer of isotropically scattering particles overlying a Lambert scattering haze or cloud layer. The reflectivity of the haze or clouds is a strongly dependent function of wavelength. Our best-fitting model consists of a clear H2 layer of column density ～31 km-am above the haze or clouds; the maximum permitted H2 column density is ～46 km-am. The H2 column density above the equatorial region appears to be less than at temperate latitudes. The phase-dependent asymmetry in the disk profiles is a natural consequence of the scattering geometry. Our results are consistent with current knowledge of the Saturn atmosphere. 相似文献
18.
Fourteen photometric lightcurves of 433 Eros were made at the Astronomical Observatory of Torino during the 1974–75 close passage. The absolute magnitude of the primary maximum (10m78), the phase coefficient (0.023 mag/degree), the synodic and sidereal period of rotation (0d.21956 and 0d.21959, respectively) and the ecliptic coordinates of the pole (λ = 17°, β = 10°) were deduced. 相似文献
19.
Thirty well-exposed photographic plates showing the spectrum of the carbon-dioxide band at 8689 Å in the atmosphere of Venus were obtained during 1968 and 1969. All spectra were obtained at a dispersion of 2 Å/mm for Venus phase angles varying from 10° to 126°. We find rotational temperatures ranging from 236 to 274 K. The average value of the rotational temperature is 246 ± 1 K (one standard deviation); for our 1967 observations, the rotational temperatures ranged from 222 to 248 K, with an average value of 238 ± 4 K. The variation of the equivalent width of the 8689 Å band, with Venus phase angle, was very similar for the two sets of observations (53 plates). The temporal variations, of approximately 30% were comparable with the phase variations over this limited range of phase angle. 相似文献
20.
A. V. Morozhenko 《Kinematics and Physics of Celestial Bodies》2010,26(1):36-38
We propose a modification of the method of polarimetric measurements of the twilight sky, traditionally performed in a zenith
direction, to study physical properties of the stratospheric aerosol (at altitudes higher than 30 km). The measurements carried
out in zenith directions as a rule limit phase angles by values of 80–100°. We suggest setting up the declination of the telescope
equal to the declination of the sun and measuring the polarization degree of the twilight sky at different values of the right
ascension. It will allow us not only to enhance the range of the phase angles but also to plan observations in a way to obtain
data on the phase dependence of the polarization degree of the light scattered by atmospheric layers at different altitudes. 相似文献