The chromospheric h and k emission cores of the G dwarfs and subdwarfs Beta Hyi (14), Zeta Tuc (5), Delta Pav (5), and Tau Cet (5) have been monitored over a period of four years using the IUE satellite long wavelength camera. A detailed statistical examination of the data has shown that no variation in h and k fluxes of less than 15 percent could

Some considerations about the zodiacal light brightness integral from the stand point of the theory of integral equations are made. It is shown that for observation directions confined to a plane perpendicular to the ecliptic and passing through the Sun, the Z.L. brightness integral can be formally considered as a first kind integral equation of

Over the past two decades NASA spacecraft missions obtained photographs permitting accurate size measurements of the planets and moons, and their surface features. Planetary global views are displayed at the same scale, in each picture to allow visual size comparisons. Additionally, special geographical features on some of the planets are compared

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The authors discuss two aspects related to the radial dependence of spatial density of interplanetary dust. First, they ask which spatial distribution the dust source should have to lead to the observed relative spatial distribution. Sources limited to a shell at several AU heliocentric distance are found to be inadequate, while extended (0.1 AU ≤

An analysis of 28 contiguous days of whole disk observations of the solar surface by means of optical resonant scattering in the K 769.9 nm line, taken at the Teide Observatory at Izana during July-August 1980, have thus far yielded two significant facts. Firstly when the results of an iterative sine-wave fitting procedure are considered in the