New Criterion for Lunar Crescent Visibility

A new criterion for lunar crescent visibility has been established using 737 observations, almost half of them obtained by the Islamic Crescent Observation Project (ICOP). This criterion is based on two variables, viz. the topocentric arc of vision and the topocentric crescent width. The new model is able to predict the visibility of the lunar crescent both for naked eye and optically aided observations. From the database we found a Danjon limit of 6.4 degrees. Vice-President of “Crescents, Calendars and Mawaqeet Committee” of AUASS.     

Neutron stars in the bimetric scalar—tensor theory of gravitation. II. solutions with a variable scalar field

Solutions of the equations of the bimetric scalar—tensor theory of gravitation with a variable scalar field are found for configurations of superdense matter with different versions of the equation of state. The possible existence of static superdense and supermassive configurations is established for all of the versions of the equation of state of superdense matter used. Translated from Astrofizika, Vol. 41, No. 1, pp. 131–135, January-March, 1998.     

Study of magnetic field,rock magnetization and lunar electrical conductivity in the Bay Le Monnier

The data of three-times repeated magnetic survey of the section of Lunokhod-2 route 1.5 km long are analyzed. The linear size of the regions of magnetic field anomalies disclosed is 200–300 m. The results of magnetic survey near the tectonic break of Straight Rille and near the south rim of crater Le Monnier were used for estimation of rock magnetization in situ. It is shown that mare basalts in south-east region of crater Le Monnier have oblique magnetization (at the angle ç30° to horizon). The magnitude of magnetization is × 5 × 10^–5 G cm g^–1. The south-east slope of the crater Le Monnier is magnetized roughly vertically, the upper limit of magnetization of the rocks of the rim is ç 1 × 10^–5 G cm³ g^–1. The results of an analysis of 160 magnetic field variations recorded by Lunokhod-2 indicate that the horizontal components of variations have nearly linear polarization. The principal axes of hodographs stretch in the direction north-west-south-east. Such a polarization of variations may be due to an increase of the thickness of the upper isolated layer under Mare Serenitatis.     

On the calculation of spurious velocity signal produced by atmospheric differential extinction in whole-disk oscillation measurements

The systematic diurnal signal drift in full-disk solar oscillation measurements has been calculated taking into account differential rotation, the inclination of the rotational axis of the Sun with respect to the picture plane, the limb-darkening function and a realistic estimation of the sky transparency, slightly variable during the day. An illustration of this method on the Kumbel (U.S.S.R.) IRIS data is presented and discussed.     

Relative deformations of selenodetic nets of coordinates

One of the main problems of selenodesy consists of the construction of a net of basic reference points on the surface of the Moon. At present there exist many catalogues containing the coordinates of selected objects on the Moon. These catalogues differ by the presence of both systematic and accidental errors.The investigations concerning the comparison of catalogues and the elucidation of their systematic differences are of very recent date. Various methods of interpretation of the systematic differences between catalogues have been proposed. Without an attempt to encompass the whole problem in what follows, we shall describe one method for comparative study of catalogues based on the theory of the deformation of continuous media.     

A nonlinear tensor field and the second metric tensor

In our preceding paper {see [L. Sh. Grigorian and S. Gottlöber, Astrofizika (in press)]} we investigated a self-gravitating system consisting of a scalar field and a linear tensor field _ik= _ki with minimal coupling and with allowance for the action of vacuum polarization effects. In the present paper we investigate the case of a nonlinear tensor field _ik. The action S ⁽⁾ of the field _ik is determined by the difference R_ik — _ik, where R_ik is the space-time Ricci tensor and Rik is the analogous quantity constructed using the metric _ik=g_ik+_ik induced by _ik ( is a free parameter). Here S ⁽⁾ coincides with the previously known expression for the action of a linear field _ik. Equations of motion are derived for _ik in curved space-time. The energy-momentum metric tensor, determining the contribution of _ik to the gravitational field equations, is calculated.Translated from Astrofizika, Vol. 39, No. 1, pp. 135–144, January-March, 1996.     

On the rotation of rigid Venus

According to A.A. Khentov Venus' rotation is in the quasi-stationary state as a result of the balance interaction of the solar tidal torque with the aerodynamical torque of the rotating Venus' atmosphere. In case of the nonconservative forces are negligible and the solar attraction is the stabilizing factor, the rotation of the rigid Venus may be assumed as the first approximation. The theory of the rotation of the rigid Venus in the coordinates,, had been constructed. It have been found that Venus rotates almost uniformly and the libration harmonics are negligible.     

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