This paper presents new methods for knowledge extraction and visualization, applied to datasets selected from the astronomical literature. One of the objectives is to detect correlations between concepts extracted from the documents. Concepts are generally meta-information which may be defined a priori, or may be extracted from the document contents and are organised along domain ontologies or concept hierarchies. The study illustrated in the paper uses a data collection of about 10,000 articles extracted from the NASA ADS, corresponding to all publications for which at least one author is a French astronomer, for the years 1996 to 2000. The study presents new approaches for visualizing relationships between institutes, co-authorships, scientific domains, astronomical object types, etc.