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.

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Middle and far infrared studies of the irregular galaxy M 82 and of Seyfert galaxies are presented. M 82 was observed spectrophotometrically from 8 to 13 microns at 6 different positions selected across its 10 microns emitting region. A model is proposed which explains satisfactorily most of the observed properties of M 82 from X-ray to radio