They come for a well-defined scientific purpose which may be to collaborate with a specific individual, to access unique data, or to use specialized facilities. Visits vary from a few days to several weeks or months, and in some cases up to a year. Stipend support varies with the length of the visit and the amount of support being provided by the visitor's home institution, or by fellowship such as a Guggenheim, NATO, etc. An overview of the Observatory and its facilities can be found here. Application to the program is made by directly contacting a member of the research staff to request support.
Awards are dependent upon availability of funding.