Historical studies are the most obvious archival activity.
The major issues to consider for historical studies are ease of access to data, and the ability to perform cross-instrument calibration. An activity related to historical studies is the use of archival data as part of a justification to propose the use of a new telescope. Theoretical follow-up is the need to test new models against existing data. In many cases, the interpretation of a phenomenon can take many years, with theoreticians repeatedly building models and testing them against the data. The major issue for theoretical studies then is that the theoretician does not have a detailed of the instrument characteristics or analysis techniques.