(1990s/2000s radio survey aimed at gravitational lensing)
The Cosmic Lens All-sky Survey (CLASS)
was a 1990s/2000s radioastronomical survey to
discover and characterize galaxy-massgravitational lensing
amongst over ten thousand promising radio sources.
Very Large Array (VLA) radio images of the sources were produced,
after which about a hundred and fifty of the most promising were
followed up using MERLIN, the VLBA, HST, and Keck.
Twenty two such gravitational lenses were discovered.