Polarimetry of the twilight sky and stratospheric aerosol

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.     

Imaginary part of the refractive index of aerosol in latitudinal belts of Jupiter’s disc

The values of the imaginary part of the refractive index n _i of aerosol in bright (EZ, NTrZ, and STrZ) and dark (NTB, NEB, SEB, and STB) latitudinal bands of Jupiter’s disc have been determined. They are averaged over the effective depth where the intensity of radiation diffusely reflected by the planet is formed. These values turned out to be lower in the zones than in the belts: specifically, 0.00017–0.00041 vs. 0.00063–0.00098, 0.00019–0.00041 vs. 0.00065–0.00097, 0.00017–0.00041 vs. 0.00070–0.00112, and 0.00019–0.00044 vs. 0.00069–0.00111 at λ = 605, 631, 714, and 742 nm, respectively. These results probably indicate the difference in the vertical stratification of the nature of cloud layers, as well as in the sizes of aerosol particles (they are larger in the belts).     

On the accuracy of indirect methods for estimating the sizes of asteroids

We have shown that the least reliable data source for estimating the albedo of asteroids is the maximal value of the degree of negative polarization. To increase the accuracy of the method that uses the data on the slope of the positive branch of polarization, the values of the approximating coefficient should be selected in accordance with a specified type of asteroids. The similar situation is in the shadow method, where the value of the phase integral q should be selected in accordance with each of the types. Moreover, the estimates obtained by both methods will be more reliable if the phase dependences of brightness that are characteristic of a specified type of asteroids, including the range of the opposition effect, are used in transforming from A(0) to A(α). The modeling performed with the Irvine-Yanovitskii modification of the shadow model of Hapke showed that the values of the phase coefficient β (10° ≤ α ≤ 20°) and q are, respectively, in the ranges of 0.016–0.030 and 0.6–1.0 for the E-type asteroids, 0.026–0.033 and 0.42–0.52 for the M-type asteroids, and 0.031–0.039 and 0.42–0.52 for the C-type asteroids.     

On the intensity of helium and hydrogen lines in quiescent prominences with filamentary structure

Diffuse penetration of ionizing radiation into prominences with filamentary structure is considered. The equations of radiative transfer, ionization balance and steady state of the triplet system of the helium atom (with 27 levels and continuum) are solved for a chosen model of prominence. The calculated intensity ratios of helium and hydrogen lines for prominences of various brightness are compared with observations. Parameters of filamentary structure of prominences which are in a good agreement with observations are given.     

Coherent scattering effects in the polarizing properties of the Galilean satellites of Jupiter

Attention is drawn to the fact that not quite reliable data on the position of the polarization plane were used in study [Rosenbush, V.K. et al., Astrophys. J., 1997, vol. 487, no. 1, pp. 402–414] for the comparison of calculated and observed peaks in the polarization of the Galilean satellites of Jupiter near opposition. We propose the hypothesis that this polarization peak is formed by light interference on microcracks aligned in a required way rather than on closely-spaced particles.     

The application of the brewster angle data for the lunar surface mapping by the real part of the refractive index

To map the lunar surface in terms of mineralogy, we suggest to use the data on variations of the real part of the refractive index obtained from the measurements of Brewster’s angle in the far ultraviolet spectral range. Such data can be acquired with an ultraviolet polarimeter onboard a spacecraft launched into a circumlunar polar orbit.