Radiative decay behind strong M.H.D. shocks

The effect of radiation up on the state of gas behind strong M.H.D. shock front has been studied. The jump conditions for flow variables across the shock boundary have been obtained and temperature decay behind the shock front is determined for a optically-thin brehmsstrahlung radiation plasma. It has been found that, for a shock within strong magnetic field, the temperature decay is much quicker.     

Self-similar flows behind M.H.D. shock waves

In this paper a self-similar motion in a medium of infinite electrical conductivity has been investigated in spherical symmetry under the influence of an idealized magnetic field and a comparison has been made of the state of flow variables with and without magnetic field.     

Sunspot turning-points and aurorae since A.D. 1510

Dates of solar maxima and minima extending back to c. 1610 were estimated by Wolf and Wolfer at Zürich (Waldmeier, 1961) in the nineteenth century, and those back to c. 1710 have been generally accepted. Slight modifications have already been suggested by the author (Schove, 1967) for the seventeenth century, although, in that century, even the existence of the eleven-year cycle has been questioned (Eddy, 1976). In the course of any sunspot cycle we find a pattern of the aurorae in place and time characteristic of sunspot cycles of the particular amplitude-class. These patterns since c. 1710 can be linked to the precise dates of the Zürich turning-points by a set of empirical rules. A sunspot rule is based on the Gnevyshev gap, the gap in large sunspots near the smoothed maximum. These rules are here applied to the period c. 1510–1710 to give improved determination of earlier turning-points, and approximately confirm the dates given for the seventeenth century by Wolfer and for most of the later sixteenth century by Link (1978). Some turning-points for the fifteenth century and revised sunspot numbers for the period 1700–48 are also given.     

Carte de la Lune de J. D. Cassini

Sans résuméPresented at the IAU-COSPAR Julius Schmidt Symposium on 100 Years of Lunar Mapping held at Lagonissi, Greece, 25–27 May, 1978.     

An intensified C.C.D. camera for telescope guidance

This paper deals with the study and the fabrication of an intensified C.C.D. camera for guiding telescopes or for searching fields containing faint stars. It describes the sensor of the camera (by connecting the Thomson C.C.D. and the RTC image intensifier) and its three working modes. The first is the direct exploitation of the video signal sent to the TV monitor, in conformity with the C.C.I.R. standard (the N.T.S.C. standard is also available). However, the study of stability and sensitivity of the intensifier lead us to create a second working mode necessary for the correct detection of faint objects (by an averaging filter improving the signal to noise ratio). The last mode is the integration by the C.C.D. itself: it allows a maximum of three-seconds integration time (therefore the detection of fainter objects), with the help of a thermoelectric cooling system. Moreover, the tests made on the 1.52 meter telescope of the O.A.N. (Calar-Alto, Spain) have been successful and confirm the capabilities of this camera to replace the intensified TV tube cameras, like the super-isocon camera.     

Evidence for a sunspot in A.D. 939 in an Arabian Source

It is the purpose of this paper to present evidence concerning the appearance of a sunspot in A.D. 939 observed by Arabs from the Iberian Peninsula. The sunspot record appears in the Arab source known as al-Muqtabis V.