The Rossi X-ray Timing Explorer (RXTE) Index table was created for the purpose of providing a concise and easily accessible tracking of RXTE observations, both those already completed and those still scheduled to be done. Each entry in this table corresponds to a specific proposal/target combination or `complete observation', in contrast to the RXTE Master table in which each entry corresponds to a specific proposal/target/ObsID combination or `observing segment'. A complete observation can consist of many (in some cases dozens) observing segments. This is a service provided by NASA HEASARC .
The ZWCLUSTERS database is based upon the Catalogue of Zwicky Clusters of Galaxies. The Zwicky clusters were identified by F. Zwicky in 560 POSS fields. They are rich clusters, each having at least 50 members within 3 magnitudes of the brightest member. This is a service provided by NASA HEASARC .
