Although the QSO PKS 2128 - 123 appears as highly variable in the I band, with Delta-I of up to 1.69 mag, it is a moderate amplitude variable object in the other bands of the present UBVRI observations. Excluding these I fluxes, the average continuum is well fitted by a power law when the Balmer continuum contribution, which enters the V band, has

This publication is a collection of pictorial comparisons of prominent physiographic features found on Mars and Earth, consisting of equal-scale side-by-side pairs or cartographic overlays. Martian features compared with terrestrial ones include Valles Marineris, the Tharsis bulge, Olympus Mons, the Hellas and Argyre basins, areas of catastrophic

Contents: The classical scheme for gas phase reactions. Charge transfer at low energies. Electron abundances in dense clouds. Some problems in interstellar S chemistry. Gas versus grain: the case of HCN and HNC. Remarks.

The derivation of electron abundances in dense clouds of interstellar gas and related problems are briefly discussed. Charge transfer at low energies is briefly reviewed, and the methods of deuterium fractionation and of the (HCO(+))/(CO) ratio for determining electron abundances are summarized. The formation of molecules in the gas phase versus

Papers on stellar spectral line formation theory are presented. The general topics considered include: frequency redistribution problems in line formation theory, methods in line radiative transfer, and observational and theoretical aspects of spectral line formation in astrophysical and laboratory environments. Some individual subjects discussed

Over the past two decades NASA spacecraft have visited many of the planets and moons of the solar system. During these missions many detailed photographs were taken. This publication utilizes some of the best of the photos to show size comparisons - to scale - of these planets and moons.