A summary is presented of the physical considerations governing line formation in molecular clouds with kinetic temperatures in the range from 5 to 100 K and hydrogen number densities in the range from 100 to one million per cubic centimeter. An exposition of the classical Sobolev formulation due to Goldreich and Kwan (1973) is followed by results

This publication is a compilation of photographic and cartographic comparisons of large, well-known geographical features on planets and moons in the solar system. Included are structures caused by impacts, volcanism, tectonics, and other natural forces. Each feature is discussed individually and then those of similar origin are compared at the

The decay of a sunspot region was studied using high resolution white-light pictures. The photometric and geometric parameters of a light-bridge showing granular structure were determined. No difference is found comparing it with the quiet photosphere.

High resolution white-light pictures of sunspot penumbrae are presented. These include pictures showing details of their filamentary structure and some instances of the birth of a penumbra. The observations are discussed in the framework of current penumbra theories.

Using a radically new suite of data extraction routines, IUEARM, high resolution IUE spectra of six F and G stars, taken at regular intervals since 1978 are analysed. The salient features of the new routines are: reduction of interorder scattering via two-dimensional deconvolution of the echelle spectrograph image plane, with high frequency

Attention is given to problems which arise when an attempt is made to use observational material to clarify the mechanisms responsible for the heating of the chromosphere in a late-type star, in order to derive a clearer physical view of the nature of a chromosphere, its relation to the underlying photosphere, and the overlying corona. Problems