On peculiarities of the H and K Ca ii lines of quiescent prominences

A study of the metallic lines in bright quiescent prominences indicates that the optical thickness in the K line of Ca ii may reach values as high as 10³. This is about 10 times larger than the optical thickness in the H line and may explain some peculiarities of the H and K lines in solar prominences.     

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.     

Corrected spectral dependence of the imaginary part of the refractive index of aerosol in Jupiter’s atmosphere in the short-wavelength spectral range

To correctly determine the relative contribution of aerosol to the scattering properties of a gas–aerosol medium in the continuum, we propose a method that allows more reliable values of the imaginary part of the refractive index n _i to be obtained for Jupiter’s atmosphere in the short-wavelength spectral range. We considered the measurement data on the spectral values of the geometric albedo of Jupiter acquired in 1993 and used the model of homogeneous spherical aerosol particles. The obtained values of n _i are 0.00378, 0.00309, 0.00254, 0.00175, 0.00123, 0.00084, 0.00064, 0.00045, 0.00031, 0.00033, 0.00013, and 0.00008 at wavelengths λ = 320, 350, 375, 400, 420, 450, 470, 500, 520, 550, 606, and 631 nm, respectively.     

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.