The search for massive energy usage by an extremely advanced civilization.
The UC Berkeley Infrared Excess Search (DYSON) attempts to identify excess thermal infrared radiation emitted from highly advanced civilizations by searching the IRAS and 2MASS catalogs and performing follow-up observations on likely candidates with the SETI@home , Serendip V, and Optical SETI databases. Pictured at right is a cut-away diagram of an idealized Dyson surface.
The initial dataset consists of 1000 stars with ages determined by Ca II absorption to be >1 gigayear to reduce the likelihood of an associated protoplanetary disk.
Infrared excess was determined via the K- indicator. The K band is thought to be quite insensitive to stellar atmosphere fluctuations, and hence provides a stable benchmark for color excess.
33 IR excess candidates were found and subsequently searched for anomalous radio emission nanosecond-scale optical pulses. No convincing signals were found. New searches for IR excess candidates will use survey data from the Spitzer Space Telescope, and soon the Wide-field Infrared Survey Explorer.
For more information on the search for IR excess, check out this excellent article put together by the Planetary Society.